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Title:
A SEPARATION DEVICE AND A METHOD FOR SEPARATING A LIQUID-LIQUID MIXTURE
Document Type and Number:
WIPO Patent Application WO/2018/176086
Kind Code:
A1
Abstract:
A separation device for use in separating a liquid-liquid mixture, and methods for preparing a separation device and using said separation device for separating a liquid-liquid mixture are disclosed. The separation device comprises a porous substrate and a coating formed on at least one surface of the porous substrate, wherein the coating comprises a plurality of polyelectrolyte layers of opposite charge formed on the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement, and a plurality of nano-fibrillated species collectively formed as a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers.

Inventors:
WANG DAYANG (AU)
HUANG SHU (AU)
Application Number:
PCT/AU2018/050276
Publication Date:
October 04, 2018
Filing Date:
March 23, 2018
Export Citation:
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Assignee:
UNIV RMIT (AU)
International Classes:
B01D17/02; B01D39/04; B01D39/16; B01D39/18; C02F1/40
Foreign References:
US20160361674A12016-12-15
US20160059167A12016-03-03
US20160136554A12016-05-19
Other References:
ROHRBACH, K. ET AL.: "A cellulose based hydrophilic, oleophobic hydrated filter for water/oil separation", CHEM. COMMUN., vol. 50, 2014, pages 13296 - 13299, XP055552080
HOMONOFF, E. ET AL.: "Nanofibrillated Cellulose Fibers: Where Size Matters in Opening New Markets to Nanofiber Usage", 25 June 2008 (2008-06-25), Retrieved from the Internet [retrieved on 20171109]
CARPENTER, A. ET AL.: "Cellulose Nanomaterials in Water Treatment Technologies", ENVIRON SCI. TECHNOL., vol. 49, no. 9, 5 May 2015 (2015-05-05), pages 5277 - 5287, XP055279657
Attorney, Agent or Firm:
PHILLIPS ORMONDE FITZPATRICK (AU)
Download PDF:
Claims:
CLAIMS

The claims defining the invention are as follows:

1 . A separation device comprising a porous substrate and a coating formed on at least one surface of the porous substrate, wherein the coating comprises a plurality of polyelectrolyte layers of opposite charge formed on the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement, and a plurality of nano-fibrillated species collectively formed as a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers.

2. A separation device according to claim 1 , wherein each of the plurality of nano- fibrillated species is formed from a polysaccharide source.

3. A separation device according to claim 1 , wherein each of the plurality of nano- fibrillated species is formed from a cellulosic source.

4. A separation device according to claim 1 , wherein each of the plurality of nano- fibrillated species is formed from a cellulosic source selected from the group consisting of cellulose nanofibrils (CNFs), cellulose nanofibers, bacterial nanocellulose, nanocrystalline cellulose (NCC) and nanofibril cellulose whiskers.

5. A separation device according to claim 1 , wherein each of the plurality of nano- fibrillated species comprises a structurally rigid backbone and a plurality of hydrophilic side groups extending outwardly therefrom.

6. A separation device according to claim 5, wherein each of the plurality of hydrophilic side groups is selected from the group consisting of: hydroxyl functionalised groups, carboxyl acid functionalised groups, amine functionalised groups, sulfonamido functionalised groups, sulfonic acid functionalised groups, sulfonate functionalised groups, phosphate functionalised groups and phosphonic acid functionalised groups.

7. A separation device according to claim 1 , wherein the plurality of alternating polyelectrolyte layers comprises alternating layers of positively-charged polydiallyldimethylammonium chloride (PDDA) and negatively-charged poly(styrene sulfonate) (PSS), and wherein the outermost polyelectrolyte layer is a positively- charged polydiallyldimethylammonium chloride (PDDA) layer.

8. A separation device according to claim 1 , wherein the at least one coated surface of the porous substrate has a water contact angle in air (Qw/a) that falls within a range of between about 5° and about 25°.

9. A separation device according to claim 1 , wherein the at least one coated surface of the porous substrate has an oil contact angle in air (θ0 3) that falls within a range of between about 0° and about 5°.

10. A separation device according to claim 1 , wherein the at least one coated surface of the porous substrate has a water contact angle in oil (6w/o) that falls within a range of between about 5° and about 30°.

1 1 . A separation device according to claim 1 , wherein the coating has a thickness that falls within a range of about 5 nm to about 100 nm.

12. A separation device according to claim 1 , wherein the porous substrate comprises a plurality of pores with an average pore size that falls within a range of about 50 nm to about 100 μιη.

13. A separation device according to claim 1 , wherein the porous substrate has a thickness that falls within a range of about 9 μιη to about 10 cm.

14. A separation device according to claim 1 , wherein the porous substrate is selected from the group consisting of a screen, a mesh, a paper, a woven cloth, a nonwoven cloth, fibres, a molecular sieve, a sponge and a foam.

15. A separation device according to claim 1 , wherein the porous substrate is constructed from a metal selected from the group consisting of iron, steel, titanium, aluminium, nickel, copper and alloys of any of these metals.

16. A separation device according to claim 1 , wherein the porous substrate is constructed from a polymer selected from the group consisting of polytetrafluoroethylene (Teflon), polyethylene, polypropylene (PP), polydimethylsiloxane (PDMS), polystyrene (PS), poly(ether sulfone), polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polysulfone, polyamide, polyurethane, poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), poly(ethylene terephthalate) (PET), and poly(4-methyl-1 -pentene) (PMP).

17. A separation device according to claim 1 , wherein the porous substrate is constructed from a ceramic selected from the group consisting of a SiC/AI2O3 ceramic and an AI2O3/S1O2 ceramic.

18. A method for producing a separation device, comprising the steps of:

- preparing a porous substrate;

- applying a coating to at last one surface of said porous substrate by:

- applying successive solutions of at least two polyelectrolytes of opposite charge to the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement to form a plurality of alternating polyelectrolyte layers thereon; and

- applying a solution comprising a plurality of nano-fibrillated species to the plurality of alternating polyelectrolyte layers, wherein the plurality of nano-fibrillated species collectively form a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers.

19. A method according to claim 18, wherein the plurality of alternating polyelectrolyte layers comprise alternating layers of positively-charged and negatively-charged polyelectrolytes and wherein the outermost polyelectrolyte layer is a positively-charged polyelectrolyte layer.

20. A method according to claim 19, wherein the positively-charged polyelectrolyte is selected from the group consisting of: polyethylenimine (PEI, linear), polyethylenimine (PEI, branched), polydiallyldimethylammonium chloride (PDDA) and polyallylamine hydrochloride (PAH).

21 . A method according to claim 19, wherein the negatively-charged polyelectrolyte is selected from the group consisting of: polyacrylic acid (PAA), poly(styrene sulfonate) (PSS), poly(vinylphosphonic acid) (PVPA) and poly(vinylsulfonic acid) (PVSA).

22. A method according to claim 19, wherein the plurality of alternating polyelectrolyte layers comprises alternating layers of positively-charged polydiallyldimethylammonium chloride (PDDA) and negatively-charged poly(styrene sulfonate) (PSS), and wherein the outermost polyelectrolyte layer is a positively- charged polydiallyldimethylammonium chloride (PDDA) layer.

23. A method of separating a liquid-liquid mixture, comprising the step of:

- contacting a liquid-liquid mixture with at least one surface of a porous separation device modified with a coating comprising a plurality of polyelectrolyte layers of opposite charge formed on the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement, and a plurality of nano-fibrillated species collectively formed as a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers, wherein the liquid-liquid mixture comprises an aqueous medium as a first component and at least a second component that is partially or substantially immiscible with the first component, and wherein the contacting facilitates passage and separation of at least a portion of the first component through the porous separation device, and causes a continuous water layer to form at the least one surface of the porous separation device that precludes passage of the second component through the porous separation device.

24. A method according to claim 23, wherein the step of contacting occurs when the porous separation device is in a dry state.

25. A method according to claim 23, wherein the step of contacting occurs when the porous separation device is in a dry state or a wetted state.

26. A method according to claim 23, wherein the step of contacting occurs by passing the liquid-liquid mixture through the porous separation device under gravity in ambient temperature and pressure conditions.

27. A method according to claim 23, wherein the step of contacting occurs by immersing the porous separation device below an interface formed between the first component and the second component of the liquid-liquid mixture under ambient temperature and pressure conditions.

28. A method according to claim 23, wherein the first component is water and the second component is a liquid selected from the group consisting of crude oil, canola oil, engine oil, petroleum, diesel, fats, vegetable oils, fish oils, animal oils, n-butanol, n-pentanol, hexane, n-hexadecane, chloroform and toluene.

Description:
A SEPARATION DEVICE AND A METHOD FOR SEPARATING A

LIQUID-LIQUID MIXTURE

TECHNICAL FIELD

[0001] The present invention relates to a separation device for use in separating a liquid-liquid mixture, and methods for preparing a separation device and using said separation device for separating a liquid-liquid mixture.

[0002] The invention has been developed primarily for use in separating immiscible or at least partially immiscible liquids, and in particular, for use in separating mixtures of oil and water and will be described hereinafter with reference to this application.

[0003] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge in Australia or any other country as at the priority date of any one of the claims of this specification.

BACKGROUND OF THE INVENTION

[0004] Incidents of oil spills, particularly in large bodies of water, are known to cause untold damage to marine life that, in many cases, can last for several years.

[0005] Currently, two conventional technologies are used to remediate oil spills in marine environments. The first technology employs the use of separation tanks in which the oil and water are allowed to phase separate by gravity. However, this method is time consuming, inefficient and not suitable for separation of large volumes.

[0006] The second technology employs the use of oil/water separation membranes, which can be divided into two types: (super)hydrophobic/(super)oleophilic membranes, and

(super)hydrophilic/(super)oleophobic membranes.

[0007] The (super)hydrophobic/(super)oleophilic membranes are configured to selectively permit oil to pass through. However, as the density of oil is lower than that of water, water naturally settles below the oil. Therefore, oil-water separation through hydrophobic membranes of this type often requires high energy input to push oil through the membranes. The considerable cost associated with using hydrophobic/oleophilic membranes, therefore renders these membranes unsuitable for oil spill remediation, particularly when required for remediating large bodies of water.

[0008] The (super)hydrophilic/(super)oleophobic membranes on the other hand, are capable of completely repelling oil in a water-wetted state (i.e., underwater superoleophobicity) and thus selectively allow water to penetrate the membrane by gravity while retaining the oil on the membrane. That said, these (super)hydrophilic/(super)oleophobic membranes can only be used in a water-wetted state because they are easily contaminated by oil when they are in a dry state due to the intrinsic high surface energy associated with these membranes. Such oil contamination is difficult to remove once adsorbed, because of the strong adhesion of oil, which leads to a loss of the oil/water separation functionality associated with these (super)hydrophilic/(super)oleophobic membranes. And, since oil tends to float on water on account of it having a lower density than water, this makes the use of (super)hydrophilic/(super)oleophobic membranes for the purpose of oil spill remediation impractical.

[0009] Recently, zwitterionic phosphorylcholine coatings have demonstrated stable hydrophilicity both in air and oil because of the super-strong water affinity at the zwitterionic phosphorylcholine/water interface resulting in excellent self-cleaning performance. In this respect, meshes with zwitterionic phosphorylcholine coatings can not only separate oil from oil/water mixtures in a water-wetted state, but they can also be used to separate oil from oil/water mixtures in a dry state. Although the use of zwitterionic phosphorylcholine coatings for such membranes is promising, the synthesis of these coatings is complicated.

[0010] The present invention seeks to provide a separation device for use in separating a liquid-liquid mixture, and methods for preparing a separation device and using said separation device for separating a liquid-liquid mixture, which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.

SUMMARY OF THE INVENTION

[0011] According to a first aspect of the present invention, there is provided a separation device comprising a porous substrate and a coating formed on at least one surface of the porous substrate, wherein the coating comprises a plurality of polyelectrolyte layers of opposite charge formed on the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement, and a plurality of nano-fibrillated species collectively formed as a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers.

[0012] In one embodiment, the plurality of nano-fibrillated species is formed from a polysaccharide source.

[0013] In one embodiment, the plurality of nano-fibrillated species is formed from a cellulosic source.

[0014] In one embodiment, the plurality of nano-fibrillated species is formed from a cellulosic source selected from the group consisting of cellulose nanofibrils (CNFs), cellulose nanofibers, bacterial nanocellulose, nanocrystalline cellulose (NCC) and nanofibril cellulose nanowhiskers.

[0015] In one embodiment, the plurality of nano-fibrillated species comprises a structurally rigid backbone and a plurality of hydrophilic side groups extending outwardly therefrom.

[0016] In one embodiment, each of the plurality of hydrophilic side groups is selected from the group consisting of: hydroxyl functionalised groups, carboxyl acid functionalised groups, amine functionalised groups, sulfonamido functionalised groups, sulfonic acid functionalised groups, sulfonate functionalised groups, phosphate functionalised groups and phosphonic acid functionalised groups.

[0017] Suitably, the plurality of alternating polyelectrolyte layers comprises alternating layers of positively-charged polydiallyldimethylammonium chloride (PDDA) and negatively-charged poly(styrene sulfonate) (PSS), and wherein the outermost polyelectrolyte layer is a positively-charged polydiallyldimethylammonium chloride (PDDA) layer.

[0018] Suitably, the at least one coated surface of the porous substrate has a water contact angle in air (6 w/a ) that falls within a range of between about 5° and about 25°. [0019] Suitably, the at least one coated surface of the porous substrate has an oil contact angle in air (θ 0 3 ) that falls within a range of between about 0° and about 5°.

[0020] Suitably, the at least one coated surface of the porous substrate has a water contact angle in oil (6 w/o ) that falls within a range of between about 5° and about 30°.

[0021] Suitably, the coating has a thickness that falls within a range of about 5 nm to about 100 nm.

[0022] Suitably, the porous substrate comprises a plurality of pores with an average pore size that falls within a range of about 50 nm to about 100 μιη.

[0023] Suitably, the porous substrate has a thickness that falls within a range of about 9 μιη to about 10 cm.

[0024] In one embodiment, the porous substrate is selected from the group consisting of a screen, a mesh, a paper, a woven cloth, a nonwoven cloth, fibres, a molecular sieve, a sponge and foam.

[0025] In one embodiment, the porous substrate is constructed from a metal selected from the group consisting of iron, steel, titanium, aluminium, nickel, copper and alloys of any of these metals.

[0026] In one embodiment, the porous substrate is constructed from a polymer selected from the group consisting of polytetrafluoroethylene (Teflon), polyethylene, polypropylene (PP), polydimethylsiloxane (PDMS), polystyrene (PS), poly(ether sulfone), polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polysulfone, polyamide, polyurethane, poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), poly(ethylene terephthalate) (PET), and poly(4-methyl-1 -pentene) (PMP).

[0027] In one embodiment, the porous substrate is constructed from a ceramic selected from the group consisting of a S1C/AI2O3 ceramic and an AI2O3/S1O2 ceramic.

[0028] According to a second aspect of the present invention, there is provided a method for producing a separation device, comprising the steps of:

[0029] preparing a porous substrate;

[0030] applying a coating to at least one surface of said porous substrate by: [0031] applying successive solutions of at least two polyelectrolytes of opposite charge to the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement to form a plurality of alternating polyelectrolyte layers thereon; and

[0032] applying a solution comprising a plurality of nano-fibrillated species to the plurality of alternating polyelectrolyte layers, wherein the plurality of nano-fibrillated species collectively form a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers.

[0033] In one embodiment, the plurality of alternating polyelectrolyte layers comprises alternating layers of positively-charged polyelectrolytes and negatively- charged polyelectrolytes and wherein the outermost polyelectrolyte layer is a positively-charged polyelectrolytes layer.

[0034] Suitably, the positively-charged polyelectrolytes layers are selected from the group consisting of polyethylenimine (PEI, linear), polyethylenimine (PEI, branched), polydiallyldimethylammonium chloride (PDDA) and polyallylamine hydrochloride (PAH)

[0035] Suitably, the negatively-charged polyelectrolytes are selected from the group consisting of: polyacrylic acid (PAA), poly(styrene sulfonate) (PSS), poly(vinylphosphonic acid) (PVPA) and poly(vinylsulfonic acid) (PVSA).

[0036] In one embodiment, the plurality of alternating polyelectrolyte layers comprise alternating layers of positively-charged polydiallyldimethylammonium chloride (PDDA) and negatively-charged poly(styrene sulfonate) (PSS), and wherein the outermost polyelectrolyte layer is a positively-charged polydiallyldimethylammonium chloride (PDDA) layer.

[0037] According to a third aspect of the present invention, there is provided a method of separating a liquid-liquid mixture, comprising the step of:

[0038] contacting a liquid-liquid mixture with at least one surface of a porous separation device that has been modified with a coating comprising a plurality of polyelectrolyte layers of opposite charge formed on the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement, and a plurality of nano-fibrillated species collectively formed as a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers,

[0039] wherein the liquid-liquid mixture comprises an aqueous medium as a first component and at least a second component that is partially or substantially immiscible with the first component, and

[0040] wherein the contacting facilitates passage and separation of at least a portion of the first component through the porous separation device, and causes a continuous water layer to form at the at least one surface of the porous separation device that precludes passage of the second component through the porous separation device.

[0041] In one embodiment, the step of contacting occurs when the porous separation device is in a dry state.

[0042] In one embodiment, the step of contacting occurs when the porous separation device is in a dry state or a wetted state.

[0043] In one embodiment, the step of contacting occurs by passing the liquid- liquid mixture through the porous separation device under gravity in ambient temperature and pressure conditions.

[0044] In one embodiment, the step of contacting occurs by immersing the porous separation device below an interface formed between the first component and the second component of the liquid-liquid mixture under ambient temperature and pressure conditions.

[0045] In one embodiment, the first component is water and the second component is a liquid selected from the group consisting of crude oil, canola oil, engine oil, petroleum, diesel, fats, vegetable oils, fish oils, animal oils, n-butanol, n- pentanol, hexane, n-hexadecane, chloroform and toluene.

[0046] Other aspects of the invention are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Notwithstanding any other forms which may fall within the scope of the present invention, preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: [0048] Fig. 1 shows a schematic representation of a method for depositing polyelectrolyte multilayers according to an alternate layer by layer (LbL) arrangement using polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS), in which a positively-charged polydiallyldimethylammonium chloride (PDDA) layer forms the outermost layer of the (PDDA/PSS) 4 5 multilayered system;

[0049] Fig. 2 shows a schematic representation of a dipping process for preparing a (PDDA/PSS) 4 .5/CNF multilayered system, in which a plurality of cellulose nanofibrils (CNFs) collectively form a capping layer adsorbed to the outermost PDDA layer of the (PDDA/PSS) 4 5 multilayered system;

[0050] Fig. 3 shows a plot of mass density ^g/cm 2 ) of CNFs adsorbed to the outermost PDDA layer versus NaCI concentration (mM) for the (PDDA/PSS) 4 5 /CNF multilayered system, achieved during dipping of the (PDDA/PSS) 4 5 multilayered system into an aqueous solution of CNFs across a range of NaCI concentrations;

[0051] Fig. 4(a) shows a schematic representation of a method for preparing a (PDDA/PSS) 4 5 /PAA multilayered system, in which a polyacrylic acid (PAA) layer forms the outermost layer;

[0052] Fig. 4(b) shows a schematic illustration of the orientational configuration of uncompensated carboxyl groups on (PDDA/PSS) 45 /PAA and (PDDA/PSS) 4 5 /CNF multilayered systems in response to a change in the surrounding environment;

[0053] Fig. 5 shows (a) a plot of water contact angle in air (6 w/a (°); squares), water contact in oil (6 w /o (°); circles), and theoretical values (e c w / 0 ; triangles) taken on a surface of a series of (PDDA/PSS) 4 .s/CNF multilayered systems, each prepared in an aqueous solution of CNFs at a particular NaCI concentration (mM), (b) a plot of water contact angle in air (6 w/a (°); squares), water contact in oil (6 w/0 (°); circles), and theoretical values {Q° w / 0 ; triangles) taken on a surface of a (PDDA/PSS) 4 multilayered system (PSS), a (PDDA/PSS) 4 . 5 /PAA multilayered system (PAA), and a (PDDA/PSS) 4 5 /CNF multilayered system (CNF) across a range of pH values; (c) photographs of a canola oil droplet on a surface of a (PDDA/PSS) 4 .s/CNF multilayered system (in water), and (d) an AFM image of the surface of the same (PDDA/PSS) 4 . 5 /CNF multilayered system in (c);

[0054] Fig. 6 shows a comparison of grazing angle reflectance FTIR spectra (in water, oil (hexadecane) and air) taken at an angle of 85° to the surface of: (a) a (PDDA/PSS) 4 5 /CNF multilayered system, and (b) a (PDDA/PSS) 4 5 /PAA multilayered system, (in which both multilayered systems are formed on a gold coated silicon substrate);

[0055] Fig. 7 shows time-lapse photographs taken of a 30 μΙ_ canola oil droplet on a surface of: (a) a (PDDA/PSS) 4 5 /CNF multilayered system (pH=neutral), (b) a (PDDA/PSS) 4 , multilayered system (pH=neutral), (c) a (PDDA/PSS) 4 5 /PAA multilayered system (pH=neutral), and (d) a (PDDA/PSS) 4 .s/CNF multilayered system (pH=1 );

[0056] Fig. 8 shows time lapse photographs taken when a biphasic mixture composed of canola oil (stained red with Sudan Red 7B) and water is: (a) filtered through a dry steel mesh coated with (PDDA/PSS) 4 .s/CNF multilayers, (b) re-filtered through the same CNF-coated steel mesh of (a), and (c) filtered through a steel mesh coated with (PDDA/PSS) 4 .s/CNF multilayers that have been pre-wetted by water;

[0057] Fig. 9 shows time lapse photographs taken when a biphasic mixture composed of canola oil (stained red with Sudan Red 7B) and water is filtered through: (a) a dry steel mesh coated with (PDDA/PSS) 4 5 /PAA multilayers, and (b) a steel mesh coated with (PDDA/PSS) 4 .s/PAA multilayers that have been pre-wetted with water;

[0058] Fig. 10 shows photographs of a simulation of an oil-spill remediation process using: (a) a (PDDA/PSS) 4 coated mesh (left-hand tube) and a (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube), and (b) a (PDDA/PSS) 4 5 /PAA coated mesh (left-hand tube) and a (PDDA/PSS) 4 . 5 /CNF coated mesh (right-hand tube), when immersed in a solution comprising a mixture of canola oil (upper layer; stained with Sudan Red 7B) and water (lower layer);

[0059] Fig. 11 shows time-lapse photographs taken of a 30 μΙ_ high viscosity engine oil (brown coloration) droplet on a surface of a (PDDA/PSS) 4 .s/CNF multilayered system in (a) water, and (b) 0.5M NaCI aqueous solution, and (c) photographs showing a simulation of an oil-spill remediation method using a (PDDA/PSS) 4 5 /PAA coated mesh (left-hand tube) and a (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube) when immersed in a solution comprising a mixture of high viscosity engine oil (upper layer) of a generally brown coloration and 0.5 M NaCI aqueous solution (1 .03g/ml_) (lower layer); [0060] Fig. 12 shows photographs of (a) an n-pentanol droplet and (b) an n- butanol droplet on a surface of a (PDDA/PSS) 4 5 /CNF multilayered system (in water), and plots of oil contact angle in water (0 o/w O) versus time (minutes) for (c) an n- pentanol droplet and (d) an n-butanol droplet, each formed on a surface of a (PDDA/PSS) 4 multilayered system (in water), (all multilayered systems formed on a silicon substrate);

[0061] Fig. 13 shows time-lapse photographs taken of: (a) a 30 μΙ_ n-pentanol droplet on a surface of a (PDDA/PSS) 4 . 5 /CNF multilayered system, (b) a 30 μΙ_ n- butanol droplet on a surface of a (PDDA/PSS) 4 5 /CNF multilayered system, (c) a 30 μΙ_ n-pentanol droplet on a surface of (c) a (PDDA/PSS) 4 multilayered system, and (d) a 30 μΙ_ n-butanol droplet on a surface of a (PDDA/PSS) 4 multilayered system, after immersion in water, (in which each multilayered system is formed on a silicon substrate and each droplet is stained with Nile Red); and

[0062] Fig. 14 shows photographs of a simulation of an oil-spill remediation process using a (PDDA/PSS) 4 coated mesh (left-hand tube) and a (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube) when immersed in a solution comprising: (a) a mixture of n-pentanol (upper layer; stained with Nile Red) and water (lower layer), and (b) a mixture of n-butanol (upper layer; stained with Nile Red) and water (lower layer).

DETAILED DESCRIPTION

[0063] It is to be understood that the following description is for the purpose of describing particular embodiments only and is not intended to be limiting with respect to the above description.

[0064] Wettability is a fundamental characteristic of a solid surface. Surfaces that can form ionic or hydrogen bonds with water molecules are categorized as hydrophilic. Hydrophilic surfaces have many practical applications, such as anti- fogging, anti-oil-fouling, and self-cleaning. However, the water-wettability of a hydrophilic surface is unstable because the surface structure changes according to the surrounding environment. The core reason for this is that the hydrophilic groups of such surfaces tend to reconstruct/reorient upon contact with, for example, an oil, which leads to a lower surface free energy. For example, a surface comprising charged polyelectrolytes is easily wetted by water. Upon contact with oil, however, the ionic groups of the polyelectrolytes become oriented inwards while the hydrophobic moieties and backbone of the polyelectrolytes are oriented outwards, thus resulting in a significant increase of hydrophobicity.

[0065] From a molecular perspective, the hydrophilic stability of a surface depends on not only the properties of the associated hydrophilic groups (for example, charged groups, carboxyl groups, hydroxyl groups and the like), but also on the structural stability of the molecules. The design of a stable hydrophilic surface requires optimization of these two important physical characteristics. However, such a surface is difficult to achieve in terms of a system comprising conventional polyelectrolytes.

[0066] The present invention is herein, predicated on the finding of a separation device for use in separating liquid-liquid mixtures of immiscible or at least partially immiscible liquids, that has a surface that is not only both hydrophilic and oleophobic towards liquid components such as oils in a water-wetted state, but is also self- cleaning in the dry state.

[0067] Separation Device

[0068] In its simplest form, the separation device (not shown) comprises a porous substrate, and a coating formed on at least one surface of said porous substrate that renders the surface hydrophilic in both air and water. The surface of the porous substrate referred to here is that which the liquid-liquid mixture first contacts during the process of separating the immiscible or partially immiscible liquids of the liquid- liquid mixture. For instance, in a gravity-driven separation process, in which the liquid- liquid mixture is added to a separation apparatus (not shown) such as a tube or cylinder equipped with the porous separation device, the surface of first contact is the upper surface of the porous substrate.

[0069] However, in a preferred form, both the upper and lower surfaces of the porous substrate are ideally modified with the coating. In this respect, the separation device can be used not only in a gravity-driven separation process as described above, it can also be used in an immersion- or skimming-type process, whereby the separation apparatus is immersed into the liquid-liquid mixture such that the separation device part of the apparatus is located below the interface between the immiscible or partially immiscible liquids to allow all of the liquid components of the mixture to contact the lower surface of the porous substrate. [0070] Porous Substrate

[0071] The porous substrate may be selected from any one of a number of suitable materials provided with pores that are appropriately sized for separation of liquid-liquid mixtures. Indeed, it will be appreciated by those skilled in the relevant art that the thickness of the porous substrate and the size of the pores will have some bearing on the efficiency of the separation process.

[0072] In one or more embodiments, the porous substrate may be constructed from a material selected form the group consisting of polymers, metals, and ceramics.

[0073] In a preferred form, good results have been obtained for this particular application when the porous substrate is a steel mesh, preferably a stainless steel mesh.

[0074] As will be demonstrated in the various embodiments below, good results can be obtained when the steel mesh has a thickness that falls within a range of about 9 μιη to about 10 cm, and a plurality of pores that have an average pore size that falls within a range of about 50 nm to about 100 μιη.

[0075] Coating

[0076] It was unexpectedly found that the surface of the steel mesh can achieve the desired hydrophilic and oleophobic behaviour toward a non-aqueous liquid component of a liquid-liquid mixture in a wetted state by virtue of applying a coating that comprises at an outermost layer, a plurality of nano- and/or micro-fibrillated species or fibres that have a structurally rigid backbone and a plurality of hydrophilic side groups extending outwardly from the backbone.

[0077] Specifically, it is demonstrated, as will be described below, that good results can be accomplished when the outermost or capping layer of the coating formed on the surface of the steel mesh is a nano- and/or micro-fibrillated cellulosic material such as nanocellulose, or more specifically, cellulose nanofibers (CNFs).

[0078] Cellulose nanofibrils (CNFs), which have attracted increasing attention as high-performance and sustainable bio-based nanomaterials, are typically composed of nano-sized cellulose fibrils with a high aspect ratio (length to width ratio). Typical fibril widths are 5-20 nanometers with a wide range of lengths, typically several micrometers. The fibrils are isolated from any cellulose containing source including wood-based fibers (pulp fibers) through high-pressure, high temperature and high velocity impact homogenization, grinding or microfluidization.

[0079] It was unexpectedly found that CNFs have two distinct advantages as a hydrophilic material over other commonly used surface modifying agents for the purposes of the present invention. Firstly, CNFs have a rigid skeleton or backbone, which arises from the highly crystalline structure of the nanofibrils. Such rigid CNFs make these nanofibrils more structurally stable than other surface modifying agents, such as polyelectrolytes. Secondly, the hydrophilic groups, such as the carboxyl groups and hydroxyl groups that are directly bonded to the crystalized surface of the CNFs, do not re-orient inwards toward the rigid backbone of the CNFs when the CNFs are exposed to a non-aqueous liquid component such as oil in a water-wetted state.

[0080] It will be appreciated by persons skilled in the relevant art that a plurality of CNFs may be applied to the surface of the steel mesh via any one of a number of methods to achieve a porous separation device with an outermost or capping layer of CNFs.

[0081] Fabrication

[0082] In a preferred embodiment, the inventors have found that one of the simplest methods by which to form a layer of CNFs at the surface of the steel mesh is to employ a layer by layer (LbL) deposition process, in which successive solutions of two oppositely charged polyelectrolytes are first deposited onto a freshly cleaned and negatively-charged surface of the steel mesh in alternate fashion to form a multilayered arrangement of alternating polyelectrolyte layers formed through electrostatic coupling.

[0083] The inventors have found that the positively-charged polyelectrolyte polydiallyldimethylammonium chloride (PDDA) and the negatively-charged polyelectrolyte poly(styrene sulfonate) (PSS) can be successively applied to the surface of the steel mesh to produce a plurality of alternating polyelectrolyte layers of PDDA and PSS denoted as (PDDA/PSS) n , where "if represents the number of bilayers.

[0084] Figure 1 shows a schematic representation of the layer by layer (LbL) deposition process employed by the inventors for depositing alternate layers of polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS) onto the surface of a substrate, with a positively-charged polydiallyldimethylammonium chloride (PDDA) layer forming both the first layer and the outermost layer of the plurality of alternating polyelectrolyte layers. The modified substrate was then washed to remove any residual polyelectrolyte before employing the next step of the process.

[0085] As shown in Figure 2, the modified substrate was dipped into a solution of CNFs to electrostatically couple a plurality of CNFs to the outermost PDDA layer of the plurality of alternating polyelectrolyte layers to form a multilayered system with a capping layer of CNFs. Again, residual CNFs not electrostatically coupled to the outermost PDDA layer were removed by washing.

[0086] The inventors have found that at least one layer of the positively-charged PDDA (0.5 bilayer) must be deposited on the surface of a porous substrate in order to bind CNFs electrostatically. Moreover, the inventors have observed that there is no limit on the number of bilayers which can be used. Although, the more bilayers that are used will increase the time for LbL deposition.

[0087] The inventors have obtained good results when alternating layers of PDDA (5 layers) and PSS (4 layers) are electrostatically deposited onto the surface of a porous substrate to form a (PDDA/PSS) bilayer arrangement (4.5 bilayers). The corresponding multilayered system when capped with a layer of CNFs on the outermost PDDA layer is denoted hereinafter as (PDDA/PSS) 4 5 /CNF.

[0088] Quartz Crystal Microbalance Studies

[0089] Certain parameters such as ionic strength, pH, charge density and the like are known to influence the LbL deposition process with respect to certain polyelectrolytes. Therefore, in order to study the effect of NaCI concentration on the amount of CNFs that can be adsorbed to the outermost polyelectrolyte layer of the (PDDA/PSS) 4 .5/CNF multilayered system, a quartz crystal microbalance (QCM) with dissipation monitoring (QCM-D) was used to characterize the LbL deposition process of the CNF capping layer.

[0090] Figure 3 shows a plot of mass density (pg/cm 2 ) versus NaCI concentration for use in determining the amount of CNFs adsorbed onto the outermost PDDA layer of the (PDDA/PSS) 4 .5/CNF multilayered system. As shown in this figure, when the (PDDA/PSS) 4 .5 modified substrate was dipped into an aqueous solution of CNFs at 0 mM NaCI concentration, the mass density of CNFs adsorbed to the outermost PDDA layer was found to be 1.08 pg/cm 2 . The mass density of CNFs was observed to increase as the NaCI concentration increased, reaching a peak value of 4.28 pg/cm 2 at a NaCI concentration of 50 mM. However, when the NaCI concentration in the aqueous solution of CNFs was increased to 100 mM, the mass density of CNFs adsorbed to the outermost PDDA layer was observed to fall to 2.27 pg/cm 2 .

[0091] In an LbL deposition of multilayers, increasing ionic strength can screen not only the electrostatic attraction between oppositely-charged chains from neighbouring layers but also the electrostatic repulsion between groups with like charges on the same chain. The former is unfavourable for the multilayer growth due to the decrease of attraction between PDDA and the CNFs. In contrast, the latter would give rise to a more compact conformation of the CNFs on the (PDDA/PSS) 4 .5/CNF surface and thus would favour the CNF deposition process by increasing the extent of surface charge overcompensation. This result demonstrates that the optimized ionic strength for adsorbing CNFs to the outermost PDDA layer of the (PDDA/PSS) 4 5 modified substrate occurs at a NaCI concentration of 50 mM.

[0092] As indicated earlier in the description, while it is envisaged that the porous substrate (that is the steel mesh) may simply be modified on just one surface of the steel mesh, that being the upper surface, the preferred approach is to modify both the upper and lower surfaces of the steel mesh so that the resulting porous separation device may be employed in both a gravity-driven separation process and an immersion- or skimming-type process.

[0093] The inventors have determined that the thickness of the coating on each surface of the steel mesh in the (PDDA/PSS) 4 5 /CNF multilayered system falls within a range of about 5 nm to about 100 nm.

[0094] In order to gauge the suitability of the as-formed (PDDA/PSS) 4 5 /CNF multilayered system as a porous separation device for use in separating liquid-liquid mixtures of immiscible liquids, the inventors have prepared additional multilayered systems for comparative purposes.

[0095] Figure 4(a) shows a schematic representation of the method employed by the inventors to fabricate a second multilayered system in which the same substrate modified with (PDDA/PSS) 4 .5 bilayers was dipped into a solution of polyacrylic acid (PAA) to electrostatically couple a PAA layer to the outermost PDDA layer, so as to form a PAA capping layer. The corresponding multilayered system is denoted hereinafter as (PDDA/PSS) 4 5 /PAA.

[0096] The (PDDA/PSS) 4 5 /PAA multilayered system provides a means by which to study and compare the effects a surrounding environment may have on the capping layers of the (PDDA/PSS) 4 5 /CNF and (PDDA/PSS) 4 5 /PAA multilayered systems.

[0097] For instance, Figure 4(b) shows a schematic representation of the orientational configuration of uncompensated carboxyl groups on the (PDDA/PSS) 4 5 /PAA and (PDDA/PSS) 45 /CNF multilayered systems in air and in water.

[0098] As shown in the bottom part of Figure 4(b), the carboxyl groups associated with the capping layers of the respective (PDDA/PSS) 4 .s/PAA and (PDDA/PSS) 4 .5/CNF multilayered systems remain at the surface when the two multilayered systems are exposed to water.

[0099] However, as shown in the top part of Figure 4(b), when the carboxyl groups of the PAA capping layer at the surface of the (PDDA/PSS) 4 5 /PAA multilayered system are exposed to, for example, a droplet of oil in air, the carboxyl groups re-orient away from the surface to expose the hydrophobic backbone of PAA. In direct contrast, the carboxyl groups of the CNF capping layer at the (PDDA/PSS) 4 .5/CNF surface remain exposed, thereby maintaining a hydrophilic surface.

[00100] As indicated earlier in the description, the ability of the (PDDA/PSS) 4 5 /CNF multilayered system to maintain a hydrophilic surface in the dry state (such as in air), confers a desirable self-cleaning behaviour, whereby residual oil contamination on the surface may simply be washed away using water.

[00101] The inventors also fabricated a third multilayered system using the layer by layer (LbL) deposition process to deposit alternate layers of polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS) onto the surface of a substrate to form a system with only 4 bilayers and no capping layer. The corresponding multilayered system is denoted hereinafter as (PDDA/PSS) 4 . Characterization

The following section provides a comparison of certain properties of the as-formed (PDDA/PSS) 4 . 5 /CNF, (PDDA/PSS) 4 5 /PAA and (PDDA/PSS) 4 multilayered systems, with reference to the relevant figures.

[00102] Contact Angle Measurements

[00103] Water wettability of a solid surface is typically characterized by water contact angle. According to Young's equation, the water contact angle of a solid surface in air (6 w /a), the water contact angle in oil (6 w /o) , and the oil contact angle in air (θο a) can be correlated with each other by:

[00104] COS6 w /o = (Yw/a COS6 w /a - Yo/a COS6 0 /a) / Yw/o (1 )

[00105] According to equation (1 ), the theoretical value of e c w 0 can be calculated from the values of e w a and θ 0 3 . For a stable hydrophilic surface, it should maintain hydrophilic stability in air, oil, and water. In terms of contact angle, an experimental θνν/ο value should agree with the theoretically calculated 6 c w /o value.

[00106] To evaluate the hydrophilic stability of the (PDDA/PSS) 4 5 /CNF multilayered system, the inventors investigated the water wettability of the (PDDA/PSS) 4 5 /CNF surface under various conditions.

[00107] Figure 5(a) shows a plot of 6 w /a (squares), 6 w /o (circles), and 6 c w /o (triangles), all angles measured in (°), taken on the surface of a series of (PDDA/PSS) 4 5 /CNF multilayered systems, each prepared in an aqueous solution of CNFs at a particular NaCI concentration (0 imM, 12.5 imM, 25 imM, 50 imM, 75mM and 100 mM).

[00108] When a droplet (2 μΙ) of water was applied to the surface of the (PDDA/PSS) 4 5 /CNF multilayered system under ambient conditions, the (PDDA/PSS) 4 .5/CNF surface prepared at a NaCI concentration of 0 mM was observed to be readily wetted, as confirmed by a water contact angle in air (6 w/a ) reading of 20.7°. The excellent wettability of this particular (PDDA/PSS) 4 5 /CNF surface is a result of the effective hydration of the surface carboxyl and hydroxyl groups of the deposited CNFs.

[00109] As the NaCI concentration of the aqueous solutions of CNFs was increased to 12.5, and 25 mM, respectively, the water wettability of the corresponding (PDDA/PSS) 4 5 /CNF surface formed was observed to improve, as confirmed by the concomitant decrease in the e w a values to 19.8° and 17.6°, respectively.

[00110] The e w a reading for the (PDDA/PSS) 4 5 /CNF multilayered system reached its lowest value of 16.5° for the (PDDA/PSS) 4 .s/CNF surface prepared in an aqueous solution of CNFs at a NaCI concentration at 50 imM.

[00111] The inventors observed however, that the e w a reading increased for (PDDA/PSS) 4 .5/CNF surfaces prepared in aqueous solutions of CNFs at higher NaCI concentrations. For instance, a (PDDA/PSS) 4 .s/CNF surface prepared at a NaCI concentration of 100 imM yielded an e w a reading of 22.3°.

[00112] While not wishing to be bound by any one particular theory, the inventors believe that the reason for the observed decrease in the e w/a reading for the (PDDA/PSS) 4 5 /CNF multilayered system prepared in an aqueous solution of CNFs at a NaCI concentration of 50 imM is due to the mass of CNFs deposited on the surface of the substrate being greater than for all the other (PDDA/PSS) 4 .s/CNF multilayered systems prepared in this study. It is considered that the higher mass of deposited CNFs associated with this particular (PDDA/PSS) 4 5 /CNF multilayered system equates to more densely packed CNF monolayers.

[00113] When the same experiment was conducted in hexadecane (not shown), the inventors observed that the water wettability of the (PDDA/PSS) 4 5 /CNF surface yielded very similar results to that conducted in water.

[00114] For instance, as shown in Figure 5(a), when a water droplet (2 μΙ) was applied to the surface of each of the (PDDA/PSS) 4 .s/CNF multilayered systems prepared in aqueous solutions of CNFs with NaCI concentrations at 0 imM, 12.5 imM and 25 imM, the obtained water contact angle in oil (6 w/0 ) readings were 30.8°, 27.2° and 25.1 °, respectively. These readings reveal a very similar decrease to that observed for the corresponding water contact angle measurements in air (e w/a ; squares).

[00115] The inventors found that the corresponding theoretical values (6 c w /o) calculated according to equation (1 ) for (PDDA/PSS) 4 5 /CNF multilayered systems prepared in aqueous solutions of CNFs with NaCI concentrations at 0 imM, 12.5 imM and 25 imM are 25.9°, 24.6° and 22.7°, respectively. The actual 6 w /o readings obtained are, respectively, 4.9°, 2.6° and 2.4° larger than the theoretical values. [001 1 6] Interestingly, when the concentration of NaCI in the water droplet was increased to 100 imM, the (PDDA/PSS) 4 . 5 /CNF surface exhibited a e w0 reading of 34.0°, suggesting that the same phenomenon observed for water droplets in air, also occurs for water droplets in hexadecane.

[001 17] By the same token, the water contact angle in oil (6 w/0 ) reading for a water droplet on the (PDDA/PSS) 4 5 /CNF surface also reached its lowest value of 20.2° when the PDDA/PSS) 4 .s/CNF multilayered system was prepared in an aqueous solution of CNFs at a NaCI concentration at 50 imM. This reading is nearly equal to the theoretical (6 c w/0 ) value of 20°, indicating that the (PDDA/PSS) 4 . 5 /CNF surface behaves as a stable hydrophilic surface in hexadecane.

[001 18] In essence, the inventors have surprisingly found that the (PDDA/PSS) 4 5 /CNF multilayered system prepared at optimized NaCI concentrations displays a stable hydrophilic surface in both air and hexadecane.

[001 19] In stark contrast, neither the (PDDA/PSS) 4 multilayered system nor the (PDDA/PSS) 4 5 /PAA multilayered system was observed to display a stable hydrophilic surface in air or hexadecane under the same conditions.

[001 20] For instance, the surface of the (PDDA/PSS) 4 multilayered system was found to be easily wetted by water, as confirmed by a 6 w /a reading of 37.0° (pH=6), as shown in Figure 5(b). This good water wetting of the (PDDA/PSS) 4 surface suggests an effective hydration of the anionic sulfonate (SO 3 " ) moieties of the PSS capping layer at the (PDDA/PSS) 4 surface. However, when the (PDDA/PSS) 4 multilayered system was immersed into hexadecane, the inventors observed that the (PDDA/PSS) 4 surface was poorly wetted by water, as confirmed by a e w0 reading of 95.0°, as shown in Figure 5(b) .

[001 21 ] According to equation (1 ) , the theoretical value (6 c w /o) calculated for the (PDDA/PSS) 4 surface is 50.0°, which is significantly smaller than the corresponding θνν/ο reading (95.0°) observed above, suggesting that the (PDDA/PSS) 4 surface is a highly unstable hydrophilic surface.

[001 22] Whilst not wishing to be bound by any one particular theory, the inventors believe that this poor water wetting of the surface of the (PDDA/PSS) 4 multilayered system is due to the hydrophobic phenyl (Ph) moieties of PSS at the (PDDA/PSS) 4 surface re-orienting inwardly to adopt a configuration that is approximately parallel to the surface plane, which not only reduces the surface charge density it also increases the hydrophobic area at the (PDDA/PSS) 4 surface.

[00123] Similarly, in the case of the (PDDA/PSS) 4 5 /PAA multilayered system, the (PDDA/PSS) 4 5 /PAA surface displayed a 6 w /a reading of 32.0° (pH=6) for a water droplet, as shown in Figure 5(b), suggesting an effective hydration of the surface carboxyl groups of the PAA chains of the capping layer. However, when the same measurement was conducted in hexadecane, the e w / 0 reading was observed to increase to 55.3°, as shown in Figure 5(b).

[00124] According to equation (1 ), the theoretical value (6 c w/0 ) calculated for the (PDDA/PSS) 4 5 /PAA surface is 45.0°, which is 10.3° smaller than that of the actual θνν/ο reading (55.3°).

[00125] Again, whilst not wishing to be bound by any one particular theory, the inventors believe that this poor water wetting of the (PDDA/PSS) 4 .s/PAA surface is due to the hydrophilic carboxyl groups of the PAA chains in the capping layer reorienting inwards toward the hydrophobic carbon-carbon backbone of the polymer on contact with the canola oil, thereby increasing the hydrophobic area at the (PDDA/PSS) 4 /PAA surface.

[00126] In summary, the results demonstrate that the (PDDA/PSS) 4 5 /CNF multilayered system prepared under optimized NaCI concentrations exhibits a stable hydrophilic surface in air, water and hexadecane.

[00127] Oil Wetting Behaviour Study in Water

[00128] To investigate the self-cleaning behaviour of the (PDDA/PSS) 4 5 /CNF multilayered system, the inventors conducted an oil wetting behaviour study in water of the (PDDA/PSS) 4 5 /CNF surface in water using canola oil as a model oil.

[00129] Figure 5(c) shows photographs highlighting the underwater superoleophobicity behaviour of a pendent droplet of canola oil (2 μΙ) on the (PDDA/PSS) 4 .5/CNF surface (under water). Specifically, the first and second photographs show that as the (PDDA/PSS) 4 .s/CNF surface moves closer to the pendant droplet, the canola oil droplet deforms due to the pressure applied by the (PDDA/PSS) 4 . 5 /CNF surface, and produces an oil contact angle in water (θ 0 νν ) reading of around 165°. As shown in the third photograph, when the (PDDA/PSS) 4 5 /CNF surface is retracted away from the pendant droplet, the canola oil droplet comes away cleanly from the surface leaving no obvious oil residue.

[00130] In summary, the inventors have successfully demonstrated that the surface of the (PDDA/PSS) 4 .5/CNF multilayered system exhibits excellent underwater superoleophobicity behaviour, and thus a desirable self-cleaning behaviour.

[00131] Atomic Force Microscopy Study

[00132] As is well-known, the wettability of a surface is mainly governed by two factors; the chemical composition at the surface and its roughness. Therefore, in order to better understand the factors determining the wettability characteristics of the surface of the (PDDA/PSS) 4 5 /CNF multilayer system, the inventors have conducted an atomic force microscopy (AFM) study of the (PDDA/PSS) 4 .s/CNF surface to understand whether surface roughness is an influencing factor.

[00133] As shown in Figure 5(d), the AFM study (in air) revealed that the surface of the (PDDA/PSS) 4 5 /CNF multilayer system has a root-mean-square (RMS) roughness of 2.3 nm, which implies that the contribution of surface roughness to the excellent wettability characteristics observed for the (PDDA/PSS) 4 5 /CNF surface will be negligible. In this respect, the extraordinary underwater superoleophobicity behaviour associated with the (PDDA/PSS) 4 .s/CNF surface can be largely attributed to the strong hydration of the carboxyl and hydroxyl groups of the CNFs of the capping layer.

[00134] Grazing Angle Reflectance FTIR Study

[00135] To further understand the mechanism behind the observed wettability characteristics of the surface of the (PDDA/PSS) 4 5 /CNF multilayer system, the surface molecular structures of the (PDDA/PSS) 45 /CNF and (PDDA/PSS) 4 5 /PAA multilayered systems were examined by grazing angle reflectance FTIR spectroscopy.

[00136] Figure 6 shows a comparison of grazing angle reflectance FTIR spectra (in water, hexadecane (i.e. oil) and air) taken at an angle of 85° to the surface of: (a) the (PDDA/PSS) 4 5 /CNF multilayered system, and (b) the (PDDA/PSS) 4 5 /PAA multilayered system, each prepared on gold-coated silicon substrates. [00137] As shown in Figure 6(a), the FTIR spectrum of the (PDDA/PSS) 4 5 /CNF surface shows a distinct absorbance peak at 1730 cm "1 , which is ascribed to the vC=O stretching of the carboxyl groups of the CNFs in the capping layer. Interestingly, the intensity of the vC=O stretching band remains largely the same irrespective of whether the (PDDA/PSS) 4 5 /CNF surface is measured in air, water or hexadecane. This result implies that the carboxyl groups of the CNFs in the capping layer are stable in all three environments.

[00138] By contrast, the FTIR spectrum of the (PDDA/PSS) 4 5 /PAA surface shown in Figure 6(b) reveals that the intensity of the absorbance peak at 1730 cm "1 , ascribed to the vC=O stretching of the carboxyl groups on the PAA chains in the capping layer, is noticeably weaker in air and in hexadecane, as compared to the intensity of this same peak in water. Whilst not wishing to be bound by any one particular theory, the inventors believe that this observed weakening of the vC=O peak intensity in hexadecane indicates that the carboxyl groups of the PAA chains have re-oriented inwards to the surface plane on exposure to the hexadecane, thereby causing the charge density associated with these carboxyl groups on the surface to be lowered, thus resulting in a noticeable reduction in surface hydration effectiveness. As a result, a less effective water wetting behaviour was observed for the (PDDA/PSS) 4 5 /PAA multilayered system in both hexadecane and air, as shown in Figure 6(b). A similar behaviour is also observed for other oils, most notably canola oil.

[00139] Oil Dewettinq Dynamics Study

[00140] Encouraged by this superior water binding capability observed for the CNFs in the capping layer on the (PDDA/PSS) 4 5 /CNF surface, the inventors turned their attention to explore the dynamic dewetting behaviour of oil on the (PDDA/PSS) 4 .5/CNF surface at the oil-solid interface in water. Here, the inventors employed the use of canola oil (viscosity of 57 mPa » s at 25 °C) as a model oil stained with Sudan Red 7B for ease of visualisation.

[00141] Figure 7 shows time-lapse photographs taken of a 30 μΙ_ canola oil droplet (stained red with Sudan Red 7B) that has been applied to the surfaces of each of the (PDDA/PSS) 4 5 /CNF multilayered system (see Figures 7(a) and 7(d), the (PDDA/PSS) 4 , multilayered system (see Figure 7(b)), and the (PDDA/PSS) 4 5 /PAA multilayered system (see Figure 7(c)), all in their respective dry states, and then subsequently immersed into water.

[00142] As shown in Figure 7(a), when the canola oil-fouled (PDDA/PSS) 4 5 /CNF surface was immersed into water, the canola oil droplet, which partially wetted the (PDDA/PSS) 4 5 /CNF surface, as confirmed by its layer-like appearance on the surface, underwent spontaneous dewetting, resulting in the formation of a single droplet, which then subsequently detached from the (PDDA/PSS) 4 .s/CNF surface in around 4 seconds. This spontaneous detachment of the canola oil droplet in water is further evidence of the underwater superoleophobicity behaviour of the (PDDA/PSS) 4 5 /CNF surface observed earlier, which as described above, translates into a desirable self- cleaning property.

[00143] By contrast, and as shown in (see Figure 7(b)), when the canola oil-fouled (PDDA/PSS) 4 surface was immersed into water, the canola oil droplet, which partially wetted the (PDDA/PSS) 4 surface in the dry state, as confirmed by its layer-like appearance on the surface, underwent a slower dewetting process in water (around 20 seconds) compared to that observed for the canola oil-fouled (PDDA/PSS) 4 5 /CNF surface. This slower dewetting resulted in the formation of a hemispherical-shaped droplet that remained pinned to the (PDDA/PSS) 4 surface with a contact angle of ca. 90°.

[00144] For the (PDDA/PSS) 4 5 /PAA surface, the similarly partially wetted canola oil droplet on the (PDDA/PSS) 4 .s/PAA surface in the dry state, underwent a much slower dewetting process (around 60 seconds) when immersed in water, resulting in the formation of a single droplet on the (PDDA/PSS) 45 /PAA surface, which as shown in Figure 7(c), remained pinned to the (PDDA/PSS) 45 /PAA surface. Similarly, when the same experiment was performed in a 0.5 M NaCI aqueous solution (results not shown), the canola oil droplet also failed to detach from the (PDDA/PSS) 4 5 /PAA surface, which suggests that the increased density of the water has little effect on the dewetting process for the (PDDA/PSS) 4 5 /PAA surface.

[00145] This failure of the canola oil droplet to detach from the surfaces of both the (PDDA/PSS) 4 multilayered system and the (PDDA/PSS) 4 5 /PAA multilayered system suggests that the hydration of these PAA and PSS surfaces is less effective. Rather, PAA and PSS surfaces are expected to achieve effective hydration only when all the surface carboxyl and sulfonate moieties orient themselves outwards with respect to the PAA and PSS surface plane. Any inward orientation of hydrophilic groups which is induced upon exposure to oil or air will significantly reduce the surface hydration effectiveness.

[00146] To investigate the effects of pH on the oil dewetting behaviour of the (PDDA/PSS) 4 5 /CNF surface, and taking into account the pKa value (4.0) of the carboxylic groups on the surface of the CNFs, the inventors prepared acidic water (pH =1 ) and alkaline water (pH=1 1 ) by addition of 0.1 M HCI and 0.1 M NaOH, respectively, to Milli-Q water, and subsequently immersed the canola oil-fouled (PDDA/PSS) 4 . 5 /CNF surface into said solutions.

[00147] As shown in Figure 7(d), when the canola oil-fouled (PDDA/PSS) 4 5 /CNF surface was immersed into acidic water (pH=1 ), the canola oil droplet underwent a slow dewetting process (around 40 seconds), resulting in the formation of a single droplet that remained pinned to the (PDDA/PSS) 4 . 5 /CNF surface.

[00148] By contrast, when the canola oil-fouled (PDDA/PSS) 4 5 /CNF surface was immersed into alkaline water (pH=1 1 ), (results not shown), the canola oil droplet underwent a spontaneous dewetting process, resulting in the rapid formation of a single droplet, which subsequently detached from the (PDDA/PSS) 4 .s/CNF surface. The speed by which the canola oil droplet was observed to detach from the surface of the (PDDA/PSS) 4 5 /CNF multilayered system in alkaline water (pH=1 1 ) was approximately two times faster than that observed in Milli-Q grade water (pH=6.2).

[00149] The inventors surmise that the faster detachment of the canola oil droplet from the (PDDA/PSS) 4 .s/CNF surface in alkaline water (pH=1 1 ) is evidence that the ionized carboxyl groups at the surface of the CNFs play a more important role than the non-ionized carboxyl groups.

[00150] Indeed, whilst not wishing to be bound by any one particular theory, the inventors postulate that since the dominant interaction between the carboxyl groups of the CNFs in the capping layer at the (PDDA/PSS) 4 5 /CNF surface and the water molecules in water (at pH>4) involves electrostatic-induced ion dipole interactions, which are much stronger interactions than the hydrogen-bonding interactions that occur between the carboxyl groups and the water molecules in acidic water (pH=1 ), the canola oil droplet will detach from the surface of the (PDDA/PSS) 4 5 /CNF multilayered system more readily in alkaline water than in either neutral or acidic water.

[00151] Method of Separating Liquid-Liquid Mixtures of Immiscible Liquids

[00152] As a result of the desirable wetting and dewetting characteristics observed for the (PDDA/PSS) 45 /CNF multilayered system, the following investigates the suitability of the (PDDA/PSS) 4 5 /CNF multilayered system for use as a porous separation device for application in an oil spill remediation process to separate oil from water.

[00153] To simulate a practical oil-spill remediation process, the inventors have devised an experimental set up in which standard 50 imL conical polypropylene centrifuge tubes were modified as follows to simulate a separation apparatus equipped with a porous separation device.

[00154] Firstly, the conical end portion of the centrifuge tube (distal to the neck of said centrifuge tube) is removed to provide an open-ended tube. Secondly, a substantial portion of the central portion of the blue screw cap is removed and substituted with a steel mesh with pore sizes of approximately 25 μιη in diameter. The steel mesh has been pre-coated on the upper and lower surfaces thereof with a corresponding one of the three multilayered systems [(PDDA/PSS) 4 .s/CNF, (PDDA/PSS) 4 or (PDDA/PSS) 4 5 /PAA]. The modified screw cap is then applied to the neck of the centrifuge tube by screw-threaded engagement. The resulting modified centrifuge tube is then inverted and clamped in a frame for immersing within a test solution comprising a phase-separated liquid-liquid mixture of oil (upper layer) and water (lower layer).

[00155] Canola Oil/Water

[00156] As shown in the series of time lapse photographs in Figure 8(a), the dry steel mesh coated with (PDDA/PSS) 4 5 /CNF multilayers is able to separate canola oil from water via filtration. However, a small amount of the canola oil is observed in the filtered water (180s photograph far right upper row). This is because when the canola oil/water mixture is poured through the mesh (1 s photograph left upper row), the dry mesh is first wetted by the upper oil phase and a small amount of oil trapped within the mesh pores is pushed through the mesh along with the water flow (3s photograph right upper row). The thin oil film floating on top of the filtered water can be removed via filtration through the mesh once more (Figure 8(b)).

[00157] As shown in Figure 8(c), the pre-wetted CNF-coated mesh enables effective oil/water separation with no oil leaking into the filtered water at the initial stage of filtration.

[00158] For comparative purposes, in the series of time lapse photographs shown in Figure 9(a), both canola oil and water are observed to filter through the dry steel mesh coated with (PDDA/PSS) 4 .s/PAA multilayers. In fact, water selectively filters through the PAA-coated steel mesh only when the PAA-coated steel mesh has been pre-wetted by water, as shown in Figure 9(b).

[00159] Figure 10(a) shows photographs of the experimental set up devised by the inventors to simulate an oil-spill remediation process. As shown, two modified centrifuge tubes, one with a screw cap modified to bear a (PDDA/PSS) 4 coated mesh (left-hand tube), and the other with a screw cap modified to bear a (PDDA/PSS) 4 . 5 /CNF coated mesh (right-hand tube).

[00160] According to a first step of a method to separate a mixture of immiscible liquids, the two modified centrifuge tubes are immersed into a phase separated mixture of canola oil (upper layer; stained red by Sudan Red 7B) and water (lower layer) under ambient conditions so that the PDDA/PSS) 4 5 /CNF coated mesh (right- hand tube) and the (PDDA/PSS) 4 coated mesh (left-hand tube) are located below the oil/water interface. This causes the liquid-liquid mixture of oil and water to contact the surface of the (PDDA/PSS) 4 .s/CNF coated mesh, and for comparative purposes, the surface of the (PDDA/PSS) 4 coated mesh.

[00161] After immersion in water for 1 minute, the two modified centrifuge tubes are removed from the liquid-liquid mixture to reveal that the centrifuge tube fitted with the (PDDA/PSS) 4 .5/CNF coated mesh (right-hand tube) is part-filled with canola oil (as determined visually by the red colouration of the canola oil), while the other centrifuge tube fitted with the (PDDA/PSS) 4 coated mesh (left-hand tube) contains nothing.

[00162] More specifically, in the case of the (PDDA/PSS) 4 5 /CNF-coated mesh (right-hand tube), as the (PDDA/PSS) 4 5 /CNF-coated mesh passes through the phase separated liquid-liquid mixture of canola oil and water, any canola oil that may wet the upper or lower surface of the (PDDA/PSS) 4 .5/CNF-coated mesh is simply displaced by the water as the modified centrifuge tube is lowered further into the phase-separated liquid-liquid mixture towards the water phase. This lack of resistance to oil contamination and the propensity of the CNFs in the capping layer of the (PDDA/PSS) 4 .5/CNF surface to maintain a stable hydrophilic surface in oil and water facilitate passage of the canola oil and water through the (PDDA/PSS) 4 5 /CNF-coated mesh into the volume of the modified centrifuge tube to form a corresponding phase- separated mixture of canola oil (upper layer) and water (lower layer) therewithin. When the modified centrifuge tube is slowly withdrawn from the liquid-liquid mixture, the water within the volume of the modified centrifuge tube passes back through the (PDDA/PSS) 4 5 /CNF-coated mesh into the water phase within the original liquid-liquid mixture. As it does so, the CNFs on the upper surface of the (PDDA/PSS) 4 . 5 /CNF- coated mesh adsorb some of the water molecules to form a continuous water layer at the upper surface of the (PDDA/PSS) 4 .5/CNF-coated mesh. The water-oil interfacial tension between the newly formed continuous water layer and the canola oil within the volume of the modified centrifuge tube creates a barrier to support the canola oil within the volume of the modified centrifuge tube and to thus prevent it from flowing back through the (PDDA/PSS) 4 .5/CNF-coated mesh when the modified centrifuge tube is withdrawn, that is, lifted out from the original liquid-liquid mixture. As a consequence of this, the inventors have unexpectedly found that it is possible to selectively separate canola oil from a liquid-liquid mixture of oil and water using a (PDDA/PSS) 4 5 /CNF-coated mesh.

[00163] By contrast, in the case of the (PDDA/PSS) 4 coated mesh (left-hand tube), the inventors believe that as the (PDDA/PSS) 4 coated mesh passes through the phase separated liquid-liquid mixture of canola oil and water, the presence of the canola oil causes the SO 3 2" moieties in the PSS chains located at the surface to reorient inwards away from the lower surface, resulting in a less hydrophilic surface. The substantial oil wetting of the lower surface of the (PDDA/PSS) 4 coated mesh that occurs as a result, causes the lower surface of the (PDDA/PSS) 4 coated mesh to become contaminated by the canola oil. Any canola oil that may pass through the (PDDA/PSS) 4 coated mesh is also expected to contaminate the upper surface of the (PDDA/PSS) 4 coated mesh in the same manner. Thus, as the modified centrifuge tube is lowered further into the liquid-liquid mixture towards the water phase, this oil contamination precludes some or all the water from passing through the (PDDA/PSS) 4 coated mesh, and certainly precludes the formation of a continuous water layer being formed at the upper surface of the (PDDA/PSS) 4 coated mesh. In this respect, any canola oil that may have passed through the (PDDA/PSS) 4 coated mesh into the volume of the centrifuge will not be prevented from passing back through the (PDDA/PSS) 4 coated mesh into the original liquid-liquid mixture.

[00164] Figure 10(b) shows photographs showing a second simulation of an oil- spill remediation process in which the centrifuge tube fitted with the (PDDA/PSS) 4 .5/CNF coated mesh (right-hand tube) is compared with a second centrifuge tube, which has been fitted with a screw cap modified to bear a (PDDA/PSS) 4 5 /PAA coated mesh (left-hand tube).

[00165] After immersion in water for 1 minute, the two modified centrifuge tubes were removed from the liquid-liquid mixture to reveal that again, the centrifuge tube fitted with the (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube) is part-filled with canola oil (as determined visually by the red colouration of the canola oil), while the second modified centrifuge tube fitted with the (PDDA/PSS) 4 .s/PAA coated mesh (left- hand tube) comprises nothing.

[00166] In much the same manner as that observed for the (PDDA/PSS) 4 coated mesh, the inventors believe that as the (PDDA/PSS) 4 .s/PAA coated mesh passes through the upper layer of canola oil, the presence of the canola oil causes the carboxyl groups in the PAA chains of the capping layer to re-orient inwards away from the lower surface, resulting in a less hydrophilic surface. The substantial oil wetting of the lower surface of the (PDDA/PSS) 4 coated mesh that occurs as a result, causes the lower surface of the (PDDA/PSS) 4 coated mesh to become contaminated by the canola oil. Any canola oil that may pass through the (PDDA/PSS) 4 5 /PAA coated mesh is also expected to contaminate the upper surface of the (PDDA/PSS) 4 5 /PAA coated mesh in the same manner. This oil contamination of the (PDDA/PSS) 4 .s/PAA coated mesh is not completely displaced by the water as the modified centrifuge tube is lowered further into the liquid-liquid mixture towards the water phase. As such, at least some water is allowed to pass through the (PDDA/PSS) 4 5 /PAA coated mesh into the volume of the modified centrifuge tube. However, since the canola oil contaminants cannot be fully removed from the surfaces of the (PDDA/PSS) 4 5 /PAA coated mesh, this residual canola oil precludes a continuous water layer from being formed at the upper surface of the (PDDA/PSS) 4 .s/PAA coated mesh. Consequently, any canola oil that may have passed through the (PDDA/PSS) 4 5 /PAA coated mesh into the volume of the centrifuge tube, will simply flow back through the (PDDA/PSS) 4 5 /PAA coated mesh into the original liquid-liquid mixture.

[00167] Other Liquid-Liquid Mixtures

[00168] To determine the applicability of the (PDDA/PSS) 4 5 /CNF coated mesh as a porous separation device for use in separating other liquid-liquid mixtures, the inventors have investigated a series of other liquids that are partially or substantially immiscible with water.

[00169] Viscous Liquids

[00170] Oil spill contamination, particularly at sea, will invariably involve oils of a considerably higher viscosity to that of canola oil. The following study investigates the separation capability of the (PDDA/PSS) 4 .s/CNF multilayered system with respect to a high viscosity engine oil (208.89 mPa.s at 20°C).

[00171] Figure 11 shows a series of time lapse photographs taken of a 30 μί droplet of high viscosity engine oil (brown) that has been applied to the surface of the (PDDA/PSS) 4 5 /CNF multilayered system in the dry state, and then subsequently immersed in: (a) water, and (b) a 0.5 M NaCI aqueous solution (1 .03g/mL).

[00172] As shown in Figure 11 (a), the inventors observed that when the engine-oil fouled (PDDA/PSS) 4 .5/CNF surface was immersed into water, the engine oil droplet, which partially wetted the (PDDA/PSS) 4 5 /CNF surface, as confirmed by its layer-like appearance on the surface, underwent gradual dewetting to form a single droplet within a matter of around 60 seconds. Although, unlike in the case of canola oil (see Figure 7(a)) described above, the inventors observed that the engine oil droplet remained pinned to the (PDDA/PSS) 4 5 /CNF surface without detachment.

[00173] As shown in Figure 11 (b), when the same experiment was conducted in 0.5M NaCI solution (1 .03g/mL), the engine oil droplet was also observed to undergo gradual dewetting from the (PDDA/PSS) 4 5 /CNF surface, but this time, the single droplet formed was observed to detach from the (PDDA/PSS) 4 .s/CNF surface in a time of approximately 45 seconds.

[00174] For comparison, a 2M NaCI aqueous solution was gradually added to the water in Figure 11 (a). This caused the engine oil droplet pinned on the (PDDA/PSS) 4 .5/CNF surface to detach from the surface when the concentration of NaCI aqueous solution reached 0.5M (results not shown). Without wishing to be bound by any one particular theory, the inventors believe that the failure of the engine oil droplet to detach from the (PDDA/PSS) 4 .s/CNF surface in water is related to the high density of the engine oil (0.86g/ml_).

[00175] By contrast, when a 30 μΙ_ droplet of the same high viscosity engine oil was applied to the surfaces of the (PDDA/PSS) 4 5 /PAA and (PDDA/PSS) 4 multilayered systems (results not shown), the engine oil droplet, which wetted the corresponding (PDDA/PSS) 4 5 /PAA and (PDDA/PSS) 4 surfaces, showed only negligible dewetting behaviour and failed to detach from these surfaces.

[00176] Based on the observations above, and without wishing to be bound by any one particular theory, the inventors believe that oils with high viscosity, such as engine oil, adhere strongly to hydrophilic surfaces because the oil droplet has a high resistance to shrinkage. In principle, a liquid with high viscosity has a high resistance to shrinkage and thus, a lower propensity for detaching from a surface.

[00177] Encouraged by the desirable dewetting characteristics observed for the (PDDA/PSS) 4 5 /CNF multilayered system with respect to high viscosity engine oil in 0.5M NaCI aqueous solution (1 .03g/ml_), the inventors employed the same experimental set up described above to simulate an oil spill remediation process to separate high viscosity engine oil from 0.5M NaCI aqueous solution (1 .03g/ml_), as a substitute for seawater.

[00178] As shown in Figure 11 (c), two centrifuge tubes, one fitted with a screw cap modified with a (PDDA/PSS) 4 .5/PAA coated mesh (left-hand tube), and the other fitted with a screw cap modified with a (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube), were immersed into a solution comprising a phase separated liquid-liquid mixture of the high viscosity engine oil (upper layer; brown) and 0.5M NaCI aqueous solution (1 .03g/ml_) (lower layer) under ambient conditions, so that the PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube) and the (PDDA/PSS) 4 . 5 /PAA coated mesh (left-hand tube) are located below the oil/water interface. This causes the liquid-liquid mixture of oil and 0.5M NaCI aqueous solution to contact the surfaces of the (PDDA/PSS) 4 5 /CNF coated mesh, and for comparative purposes, the surfaces of the (PDDA/PSS) 4 . 5 /PAA coated mesh. [00179] After immersion in water for 1 minute, the two modified centrifuge tubes were withdrawn from the solution to reveal that the modified centrifuge tube fitted with the (PDDA/PSS) 4 .5/CNF coated mesh (right-hand tube) is part-filled with engine oil (as determined visually from the brown colouration of the oil), while the other modified centrifuge tube fitted with the (PDDA/PSS) 4 5 /PAA coated mesh (left-hand tube) comprises nothing.

[00180] Similar to the observations made with respect to the corresponding experiments performed in canola oil described above (see Figure 10(b)), the inventors observed that the (PDDA/PSS) 4 5 /CNF coated mesh is able to maintain a stable hydrophilic surface in the presence of the engine oil, thereby facilitating the clean passage of engine oil and 0.5M NaCI aqueous solution through the (PDDA/PSS) 4 .5/CNF-coated mesh into the volume of the modified centrifuge tube to form a corresponding phase-separated mixture therewithin. Similarly, as the modified centrifuge tube is slowly withdrawn from the liquid-liquid mixture, the CNFs on the upper surface of the (PDDA/PSS) 4 5 /CNF-coated mesh adsorb some of the water molecules of the 0.5M NaCI aqueous solution to form a continuous water layer at the upper surface of the (PDDA/PSS) 4 .5/CNF-coated mesh, and that the resulting water- oil interfacial tension between the newly formed continuous water layer and the engine oil within the volume of the modified centrifuge tube creates a barrier to support the engine oil within the volume of the modified centrifuge tube and to thus prevent it from flowing back through the (PDDA/PSS) 4 .5/CNF-coated mesh.

[00181] The inventors observed a similar outcome when this same experiment was conducted with an engine oil/water (deionized) biphasic mixture. It is worth noting that the immersion time for (PDDA/PSS) 4 5 /CNF coated mesh in water is longer, around 2.5 minutes.

[00182] Whilst not wishing to be bound by any one particular theory, the inventors believe that the higher density associated with seawater, as compared to deionized water, is effective in promoting the detachment of engine oil from the surface of the (PDDA/PSS) 4 5 /CNF coated mesh, which enables a continuous water layer to be formed at the upper surface of the (PDDA/PSS) 4 5 /CNF coated mesh in a shorter timeframe than if performed in water only.

[00183] By contrast, the modified centrifuge fitted with the (PDDA/PSS) 4 5 /PAA coated mesh (left-hand tube) failed to achieve the same outcome, presumably on account of the failure to create the necessary continuous water layer at the upper surface of the (PDDA/PSS) 4 5 /PAA coated mesh to be able to support any engine oil that may have passed through the (PDDA/PSS) 4 .s/PAA coated mesh into the volume of modified centrifuge tube. The inventors observed a similar outcome when this same experiment was conducted with the (PDDA/PSS) 4 coated mesh (results not shown).

[00184] In summary, the inventors have demonstrated that the (PDDA/PSS) 4 5 /CNF coated mesh could find application as a porous separation device for use in separating oil from seawater.

[00185] Polar Liquids

[00186] In general terms, liquids that are at least weakly polar can be partially dissolved in water under ambient conditions. For instance, if one assumes that the polarity of water is 1 , the polarity of liquids such as n-pentanol and n-butanol is 0.568, and 0.586, respectively, and the corresponding solubility of these liquids in water is 22 g L "1 and 73 g L "1 , respectively.

[00187] The following study investigates the use of the (PDDA/PSS) 4 5 /CNF multilayered system with respect to separating liquid-liquid mixtures of (i) n-butanol and water, and (ii) n-pentanol and water, in order to ascertain whether the higher polarity of n-butanol and n-pentanol, as compared to that of canola oil (non-polar) and engine oil (non-polar), and the subsequent partial solubility of these liquids in water, will have any bearing on the separation capability of the (PDDA/PSS) 4 .s/CNF multilayered system.

[00188] Figure 12(a) shows photographs highlighting the underwater superoleophobicity behaviour of a pendant droplet of n-pentanol (2 μΙ) when applied to the surface of the (PDDA/PSS) 4 .s/CNF multilayered system (in water). Specifically, the first three photographs show that as the (PDDA/PSS) 4 .s/CNF surface moves closer to the pendant droplet, the n-pentanol droplet deforms due to the pressure applied by the (PDDA/PSS) 4 .s/CNF surface, and produces an oil contact angle in water (θ 0 νν ) reading of around 165°. As shown in the last photograph, when the (PDDA/PSS) 4 5 /CNF surface is retracted away from the pendant droplet, the n- pentanol droplet comes away cleanly from the surface leaving no obvious oil residue. [00189] Figure 12(b) shows photographs highlighting similar underwater superoleophobicity behaviour in respect of an n-butanol droplet (2 μΙ) when applied to the (PDDA/PSS) 4 .5/CNF surface (in water). Similarly, the n-butanol droplet deforms due to the pressure applied by the (PDDA/PSS) 4 .s/CNF surface, and produces an oil contact angle in water (θ 0 νν ) reading of around 1 65°.

[00190] Exploring the self-cleaning behaviour of the (PDDA/PSS) 4 5 /CNF surface further, the inventors tested a number of additional liquids including n-hexadecane, hexane, toluene and chloroform. In each case, the corresponding pendant droplet was observed to produce an initial oil contact angle in water (θ 0 νν ) reading of around 165° or greater, and when the (PDDA/PSS) 4 5 /CNF surface was retracted away from the pendant droplet, the (PDDA/PSS) 4 .s/CNF surface showed no obvious signs of contamination.

[00191] By contrast, the (PDDA/PSS) 4 surface did not show the same underwater superoleophobicity behaviour. For instance, Figure 12(c) shows a plot of oil contact angle in water (θ 0 νν ) (°) versus time (in minutes) for a pendant droplet of n-pentanol (2 μΙ) when applied to the (PDDA/PSS) 4 surface (in water). Here, the (PDDA/PSS) 4 surface exhibits an initial e 0w reading of 149° which then gradually decreases to 68° over a period of around 60 minutes. Similarly, Figure 12(d) shows a plot of oil contact angle in water (θ 0 νν ) (°) versus time (in minutes) for a pendant droplet of n-butanol (2 μΙ) when applied to the (PDDA/PSS) 4 surface in water. In this instance, the droplet of n-butanol initially exhibits a e 0w reading above 150° which then decreases to 129° over a period of around 10 minutes. In both cases, the inventors observed that the n- butanol and n-pentanol droplets remained stably adhered to the (PDDA/PSS) 4 surface even when the (PDDA/PSS) 4 surface was retracted away from the droplet. Only after a prolonged period of time was it observed that the n-butanol and n- pentanol droplets had become completely dissolved in water.

[00192] Figure 13(a) shows a series of time-lapse photographs taken of a 30 μΙ_ n- pentanol droplet (stained with Nile Red) that has been applied to the (PDDA/PSS) 4 5 /CNF surface in the dry state, and then subsequently immersed into water. Here, the inventors observed that when the n-pentanol fouled (PDDA/PSS) 4 .5/CNF surface was immersed into water, the n-pentanol droplet underwent spontaneous dewetting, resulting in the formation of a single droplet that subsequently detached from the (PDDA/PSS) 4 5 /CNF surface within a matter of around 166 milliseconds.

[00193] Figure 13(b) shows a similar series of time-lapse photographs taken of a 30 μΙ_ n-butanol droplet (stained with Nile Red) that has also been applied to the (PDDA/PSS) 4 5 /CNF surface in the dry state, and then subsequently immersed into water. Here again, the n-butanol droplet underwent spontaneous dewetting and detached from the (PDDA/PSS) 4 .s/CNF surface in practically the same amount of time as that observed for the n-pentanol droplet.

[00194] For comparative purposes, the inventors conducted a similar study using to investigate the dewetting behaviour of n-butanol and n-pentanol on the surface of the (PDDA/PSS) 4 multilayered system.

[00195] For instance, Figure 13(c) shows a series of time-lapse photographs taken of a 30 μΙ_ n-pentanol droplet (stained with Nile Red) on the surface of the (PDDA/PSS) 4 multilayered system (formed on a silicon substrate), after immersion in water, while Figure 13(d) shows a corresponding series of time-lapse photographs taken of a 30 μΙ_ n-butanol droplet (stained with Nile Red) on the surface of the (PDDA/PSS) 4 multilayered system, after immersion in water. In both cases, the droplets spontaneously dewetted and became detached from the (PDDA/PSS) 4 surface in a similar timeframe (200 ms for n-pentanol and 300 ms for n-butanol) to that observed for these same liquids on the (PDDA/PSS) 4 5 /CNF surface above (see Figure 13(a) and Figure 13(b)) .

[00196] Encouraged by the desirable dewetting characteristics observed for the (PDDA/PSS) 4 . 5 /CNF and (PDDA/PSS) 4 multilayered systems with respect to n- butanol and n-pentanol, the inventors employed the same experimental set up described above to simulate an oil spill remediation process in an attempt to separate these liquids from water.

[00197] Figure 14(a) shows photographs showing the simulated oil-spill remediation process using a (PDDA/PSS) 4 coated mesh (left-hand tube) and a (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube) when immersed in a phase separated liquid-liquid mixture of n-pentanol (upper layer; stained with Nile Red) and water (lower layer). While Figure 14(b) shows photographs showing the same (PDDA/PSS) 4 coated mesh (left-hand tube) and (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube), this time immersed in a phase separated Iiquid-liquid mixture of n- butanol (upper layer; stained with Nile Red) and water (lower layer).

[00198] As shown in both Figure 14(a) and Figure 14(b), the presence of n- pentanol and n-butanol, respectively, within the volume of the corresponding centrifuge tube fitted with the (PDDA/PSS) 4 . 5 /CNF coated mesh (right-hand tube) suggests that the surfaces of the (PDDA/PSS) 4 5 /CNF coated mesh are not contaminated by either n-pentanol or n-butanol, and that the interracial tension between a continuous water layer formed at the upper surface of the (PDDA/PSS) 4 5 /CNF coated mesh and the liquid (n-pentanol or n-butanol) is sufficiently strong to support the liquid (n-pentanol or n-butanol) within the volume of the modified centrifuge tube and to thus prevent it from flowing back through the (PDDA/PSS) 4 5 /CNF-coated mesh.

[00199] It is interesting to note that the amount of n-pentanol supported within the volume of the modified centrifuge tube fitted with the (PDDA/PSS) 4 .s/CNF coated mesh (right-hand tube) in Figure 14(a) is greater than the amount of n-butanol supported within the volume of the modified centrifuge tube fitted with the (PDDA/PSS) 4 5 /CNF coated mesh (right-hand tube) in Figure 14(b). Whilst not wishing to be bound to any one particular theory, the inventors believe that the smaller volume of n-butanol is due to the weaker interfacial tension that occurs between n-butanol and the continuous water layer, as compared to that which occurs between n-pentanol and the continuous water layer.

[00200] In the case of the (PDDA/PSS) 4 coated-mesh, the inventors observed that in both cases, water was able to pass through the (PDDA/PSS) 4 coated-mesh when the modified centrifuge tube (left-hand tube) was immersed into the phase separated Iiquid-liquid mixture below the liquid/water interface because of the excellent dewetting behaviour of n-pentanol and n-butanol in water observed above. As such, the corresponding liquid (of n-pentanol and n-butanol) and water were able to pass through the (PDDA/PSS) 4 -coated mesh into the volume of the modified centrifuge tube to form a corresponding phase-separated mixture therewithin, and the subsequent formation of a continuous water layer at the upper surface of the (PDDA/PSS) 4 -coated mesh. However, when the modified centrifuge tube (left-hand tube) was slowly withdrawn from the Iiquid-liquid mixture, the liquid (n-pentanol and n- butanol) within the volume of the corresponding modified centrifuge tube (left-hand tube) gradually wetted the upper surface of the (PDDA/PSS) 4 -coated mesh thereby causing the continuous water layer to break and the liquid (n-pentanol and n-butanol) to flow out of the (PDDA/PSS) 4 coated-mesh.

[00201] Additionally, the inventors observed in a separate study (result not shown) that that if the polarity of the liquid was increased beyond that of n-butanol (0.586), then the interfacial tension between the polar liquid and water became negligible, such that attempts to create a continuous water layer at the upper surface of the (PDDA/PSS) 4 .5/CNF coated mesh for the purpose of separating the polar liquid from water using the separation method as described herein is unlikely to succeed.

CONCLUSIONS

[00202] In summary, the inventors have successfully fabricated a multilayered system via a simple layer-by-layer (LbL) deposition of alternating polydiallyldimethylammonium chloride (PDDA) and poly(styrene sulfonate) (PSS), together with an outermost or capping layer that comprises a plurality of nano- and/or micro-fibrillated species in the form of nanocellulose or cellulosic nanofibrils (CNFs). The density of CNFs present at the surface of this (PDDA/PSS) 4 5 /CNF multilayered system confers a very stable hydrophilic surface (in air and in oil) on account of the structural rigidity of the CNFs, and the resistance of the hydroxyl and carboxyl groups associated with the CNFs, from re-orientating inwards away from the (PDDA/PSS) 4 5 /CNF surface when exposed to a hydrophobic liquid such as an oil.

[00203] By virtue of the preferred arrangements described herein, a person of ordinary skill in the relevant art would recognise that by applying the coating to both the upper and lower surfaces of the porous substrate, the resultant separation device can be used not only in a gravity-driven separation process, it can also be used in an immersion- or skimming-type process, whereby the separation apparatus is immersed into the liquid-liquid mixture such that the separation device part of the apparatus is located below the interface between the immiscible or partially immiscible liquids to allow all of the liquid components of the mixture to contact the lower surface of the porous substrate.

[00204] Encouraged by the underwater superoleophobicity and dewetting behaviours observed for this PDDA/PSS) 4 .s/CNF multilayered system, the inventors have successfully coated the surfaces of a steel mesh with this PDDA/PSS) 4 .s/CNF multilayered to realise a porous separation device that can be used for the purposes of separating mixtures of partially or immiscible liquids such as oil and water.

[00205] Based on these findings, the resulting (PDDA/PSS) 4 5 /CNF-coated mesh is expected to find wide application in the clean-up remediation of oil spills both in freshwater and at sea.

EXPERIMENTAL SECTION

[00206] Reagents and Materials

[00207] PDDA ( /v 100 000), PSS ( /v 70 000), PAA {Mw 100 000), n- hexadecane, n-butanol, n-pentanol, Sudan Red 7B, Nile Red, 2,2,6,6,-tetramethyl-1 - piperidinyloxy radical (TEMPO) were purchased form Sigma-Aldrich. H 2 O 2 (30%) and H 2 SO 4 (98%) NaCI, HCI (37%), NaCIO, NaOH, acetone, isopropanol, ethanol, chloroform and cyclohexane were purchased from Chem-Supply, Australia. All the chemicals were used as received without further purification. Stainless steel meshes with apertures of 25 pm were purchased from Sefar Pty Ltd, Australia. Silicon wafers were supplied by Mitsubishi Silicon (USA).

[00208] Preparation of cellulose nanofibrils

[00209] Wood pulp was first modified through a TEMPO-mediated oxidation reaction. Typically, 1 g wood pulp fibres were washed thoroughly with deionized water, and then suspended in 100g water with vigorous stirring for 24 hours. Afterwards, 100 mg NaBr and 16 mg TEMPO were dissolved into the pulp suspension. 1 1 .16 g NaCIO (10 %) was added dropwise to the suspension. With the addition of 0.1 M NaOH solution, the pH of the suspension was maintained at a constant value of 10. The reaction stopped when all NaCIO was consumed. The obtained pulp fibres suspension was then dialysed against deionized water for 4 days. The carboxylate content of the oxidized pulp fibres was 1 .6 mmol g ~1 , as determined by conductometric titration. The carboxylated pulp fibres were stocked at 4 °C and kept in water suspension with a solid content of 1 .0 wt%.

[00210] A 0.1 % (w/v) slurry of modified cellulose fibres in water (50 imL) was agitated at 15000 rpm for 2 min using a blender-type homogenizer (Vita-Prep 3 model, Vita-Mix Corp., USA) at 4 °C. The gel thus obtained was then sonicated for 30 minutes using an ultrasonic homogenizer at 19.5 kHz and 300 W output power (7 mm probe tip diameter, US-300T, Nissei, Japan). After sonication, a transparent aqueous suspension of cellulose nanofibrils was obtained. By centrifuging at 8000 rpm for 30 minutes, unfibrillated and partly fibrillated fibres as precipitates could be discarded to leave the upper suspension for collection.

[00211] Fabrication of Multilayer Films on different substrates via LbL deposition

Silicon wafers were cleaned in Piranha solution (a 1 :3 (v/v) mixture of 30% H 2 O 2 and 98% H 2 SO 4 ) at 90 °C for 4 hours. Afterwards, the Si wafers were thoroughly rinsed with water and dried in a N 2 flow.

[00212] In a typical LbL deposition process, a freshly cleaned silicon wafer was immersed in a solution of PDDA for 20 min, rinsed for 1 min with Dl water, and gently dried under nitrogen flow for 2 min and subsequently immersed in PSS aqueous solution for 10 min, rinsed for 1 min, and dried in a stream of N 2 for a period of around 2 minutes. The cycle is then repeated as necessary to obtain the desired number of bilayers of (PDDA/PSS) n . In the polyelectrolyte aqueous solutions used for LbL deposition, the concentrations of PDDA and PSS were 1 .0 img/mL in 0.50 M NaCI aqueous solution.

[00213] After (PDDA/PSS) 4 multilayers were obtained, they were immersed in an aqueous solution of CNFs for 20 minutes, followed by a thorough rinse with Dl water and gentle drying in a N 2 stream. The resulting multilayers were denoted as (PDDA/PSS) 4 5 /CNF. In the CNF aqueous solutions used for the LbL deposition process, the concentrations of NaCI were varied from 0, 12.5, 25, 50, 75, to 100 imM.

[00214] For preparing (PDDA/PSS) 4 5 /PAA multilayers, the obtained (PDDA/PSS) 4 multilayers were immersed in 1 .0 img/mL PAA in 0.5 M NaCI aqueous solution for 20 minutes, followed by a thorough rinse with water and gentle drying in a N 2 stream. The resulting multilayers were denoted as (PDDA/PSS) 4 5 /PAA multilayers.

[00215] Following the identical protocol of LbL on silicon wafers, the (PDDA/PSS) 4 5 /CNF and (PDDA/PSS) 4 5 /PAA were also grown on gold-coated silicon wafer substrates. Specifically, gold-coated silicon wafer substrates were produced by using an electron-beam evaporator to deposit 2 nm of chromium as an adhesion promoter onto a cleaned silicon wafer, followed by depositing 200 nm of gold.

[00216] Prior to preparing coated meshes, stainless steel meshes were cleaned by successive sonication in acetone, isopropanol, ethanol and water. The cleaned stainless steel meshes were further treated by plasma to enhance the surface hydrophilicity. The freshly cleaned stainless steel meshes were coated with successive layers of PDDA and PSS, followed by capping with the appropriate layer (CNF or PAA) according to the above-described protocol to produce the corresponding (PDDA/PSS) 4 , (PDDA/PSS) 4 . 5 /CNF, or (PDDA/PSS) 4 5 /PAA multilayered system.

[00217] Characterization

[00218] Contact angle measurements were conducted with a Dataphysics OCA 20 contact angle system operated under ambient conditions using a 2 μΙ_ liquid droplet as an indicator. A colorimeter glass cell was used for the following contact angle measurements (θ 0 νν and e w 0 ) on solid surfaces. The contact angle measurements were reported an average of values measured at five different locations on the sample. Atomic force microscopy (AFM) experiments were carried out using a Dimension Icon AFM instrument obtained from Bruker and operated in a ScanAsyst mode using Si cantilevers.

[00219] Scanning electron microscopy (SEM) images were obtained on FEI Nova NanoSEM operated at 3 kV. The samples were directly observed without any gold coating. The grazing angle reflectance-Fourier transform infrared spectroscopy experiments were performed using a Nicolet Magna-IR 560 Fourier transform infrared spectrometer fitted with an 85° grazing angle reflectance accessory (SpectraTech) and an internal Mercury Cadmium Tellurite (MCT) detector. The MCT detector was cooled with liquid nitrogen before the experiments. The reflectance signal was averaged for 128 scans at 4 cm "1 resolution. LbL samples deposited on gold coated silicon wafers were used for analysis.

[00220] QCM-D studies were performed with a Q-Sense E4 system consisting of four flow modules that were configured to run in parallel. All throughout, standard QSX 301 crystals (Q-Sense) consisting of quartz with a thin evaporated gold electrode attached via a chromium adhesive were used. To remove any organic residues from the gold surface, the crystals were first cleaned with plasma, flushed with copious amounts of water, rinsed with ethanol, and dried in N 2 prior to being mounted in the measuring chamber. Before measurements, the QCM-D liquid chamber was stabilized at 23 °C. [00221 ] The LbL deposition of positively-charged PDDA and negatively-charged PSS layers onto cleaned quartz crystals was performed by passing, in alternating fashion, solutions of the positively-charged PDDA and negatively-charged PSS over the freshly cleaned surface of a silicon wafer at a flow rate of 100 pL/min.

All measurements were recorded at four different frequencies (5, 1 5, 25, 35 MHz). The QCM-D response, i.e. changes in both resonant frequency, Af, and the dissipation factor AD are sensitive to viscoelastic properties and density of any mass coupled to the mechanical oscillation of the quartz crystal. Adsorbed amount per unit surface area, Am, was calculated according to the Sauerbrey equation.

Afn

Am = —C

n

[00222] where C is a calibration constant for the crystal, n is the overtone, and Af \s related to frequency change. In this case, C = 0.177 mg/m 2 Hz and n = 3 were used.

Dissipation (D) is defined as the ratio between the energy dissipated and the stored energy during a single crystal oscillation.

EDissipated

2 Estored

[00223] where E D j SS j pated is the energy dissipated during on oscillation. E stored is the energy stored in the oscillation system.

Modeling based on linear viscoelastic theory was made using the QTools software from Q-Sense.

OTHER EMBODIMENTS

[00224] It will be appreciated by persons skilled in the relevant art however, that in other embodiments, that the porous substrate is not limited to a steel mesh as described above, but may be constructed from other materials. For example, the porous substrate may be constructed from a different metal, including but not limited to metals such as iron, titanium, aluminium, nickel, copper and alloys of any of these metals.

[00225] In another example, the porous substrate may be constructed from a polymer selected from the group consisting of polytetrafluoroethylene (Teflon), polyethylene, polypropylene (PP), polydimethylsiloxane (PDMS), polystyrene (PS), poly(ether sulfone), polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, polysulfone, polyamide, polyurethane, poly(tetrafluoroethylene-co- hexafluoropropylene) (FEP), poly(ethylene terephthalate) (PET), and poly(4-methyl-1 - pentene) (PMP).

[00226] In yet another example, the porous substrate may be constructed from a glass or ceramic. For instance, the ceramic may include, but is not limited to a SiC/AI 2 O 3 ceramic or an AI 2 O 3 /SiO 2 ceramic. In still yet another example, the porous substrate may even be constructed from a material selected from the group consisting of paper, textiles, woven or nonwoven cloth, fibres, meshes, molecular sieves, sponges and foams.

[00227] In other embodiments, it will be appreciated by those skilled in the relevant art that the choice of polyelectrolytes employed in the layer by layer (LbL) deposition process are not simply limited to the positively-charged polyelectrolyte polydiallyldimethylammonium chloride (PDDA) and the negatively-charged polyelectrolyte poly(styrene sulfonate) (PSS).

[00228] For instance, the positively-charged polyelectrolyte may be selected from any one of the following: polyethylenimine (PEI, linear), polyethylenimine (PEI, branched), polydiallyldimethylammonium chloride (PDDA) and polyallylamine hydrochloride (PAH).

[00229] Likewise, the negatively-charged polyelectrolyte may be selected from any one of the following: polyacrylic acid (PAA), poly(styrene sulfonate) (PSS), poly(vinylphosphonic acid) (PVPA) and poly(vinylsulfonic acid) (PVSA).

[00230] In other embodiments, it will be appreciated that the nano- and/or micro- fibrillated species is not limited to the cellulose nanofibers (CNFs) as described above, but may take the form of shorter fibres obtained from nanocellulose, including but not limited to nanocrystalline cellulose (NCC) nanoparticles (often referred to as CNC or nanowhiskers) which are shorter (100s to 1000 nanometers) than the CNFs obtained through the standard homogenization, microfluidization or grinding routes.

[00231] In other embodiments, it will be appreciated by those skilled in the relevant art that the choice of nano- and/or micro-fibrillated species is not limited to cellulose nanofibrils (CNFs) as described above, but that other nano- and/or micro-fibrillated species may be employed. For instance, the nano- and/or micro-fibrillated species from another polysaccharide source may be used, including but not limited to wood, wood pulp, cotton, hemp, flax, wheat straw, sugar beet, potato tuber, mulberry bark, ramie, algae, chitin, chitosan, bacterial cellulose, and tunicin.

[00232] In other embodiments, it will be appreciated by those skilled in the relevant art that the cellulose nanofibrils (CNFs) described above are not simply limited to comprising only the native hydroxyl and carboxyl groups hydrophilic side groups extending outwardly from the structurally rigid backbone. For example, these hydroxyl and carboxyl groups may be modified through appropriate chemistries to yield any one of a number of other different hydrophilic side group moieties, including but not limited to: amine functionalised groups, sulfonamido functionalised groups, sulfonic acid functionalised groups, sulfonate functionalised groups, phosphate functionalised groups and phosphonic acid functionalised groups.

DEFINITIONS

[00233] Whenever a range is given in the specification, for example, a temperature range, a time range, or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.

[00234] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

[00235] Throughout this application, the term "about' is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[00236] The indefinite articles "a" and "an," as used herein in the specification, unless clearly indicated to the contrary, should be understood to mean "at least one."

[00237] The phrase "and/or," as used herein in the specification, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising?' can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[00238] The phrase "hydrophobic surface" as used herein in the specification, should be understood to mean a surface with a water contact angle greater in air (9 w /a) than 90°, while the phrase "hydrophilic surface" as used herein in the specification, should be understood to mean a surface with a water contact angle in air (θνν a) smaller than 80°.

[00239] The phrase "oleophobic surface" as used herein in the specification, should be understood to mean a surface with an oil contact angle in air (θ 0/3 ) greater than 90°, while the phrase "oleophilic surface" refers to a surface with an oil contact angle in air (6 0 /a) smaller than 80°..

[00240] The term "mixture" as used herein in the specification, should be understood to encompass not only solutions having components (e.g., phases, moieties, solvents, solutes, molecules, and the like) that are homogenously mixed together, but also combinations of components or materials that are not necessarily evenly, homogeneously, or regularly distributed when combined (e.g., unevenly mixed combinations of components, separated layers of immiscible components, unevenly distributed suspensions, and the like).

[00241] The term " polyelectrolytes" as used herein in the specification, should be understand to encompass any polymer whose repeating units bear an electrolyte group. These electrolyte groups dissociate in aqueous solution, making the polymer charged. Based on the charged groups, polyelectrolytes are classified as polycations and polyanions.

[00242] The term "oil' as used herein in the specification, should be understood to encompass any liquids which are at least partially immiscible with water. Indeed, liquids with a broad range of viscosity (e.g. 2.5 - 208.9 mpa-s) and polarity (e.g. 0 - 0.586) may be utilized. Such liquids may include non-polar solvents (cyclohexane, benzene, hexane, octane, hexadecane), polar solvents (toluene, chlorobenzene, xylene, 1 ,2-dichloroethane, chloroform, diethyl ether, octanol, pentanol, butanol), and commonly used oils (crude oil, petroleum, refined or fractionated petroleum products, fats, vegetable oils, fish oils, and animal oils).

[00243] Spatially relative terms, such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the Figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the Figures.

[00244] While the invention has been described in conjunction with a limited number of embodiments, it will be appreciated by those skilled in the art that many alternatives, modifications and variations in light of the foregoing description are possible. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the invention as disclosed.

[00245] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.