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Title:
LAYER BY LAYER SUPERHYDROPHOBIC FLUOROPOLYMER COATED METAL SUBSTRATE FOR DROPWISE CONDENSATION
Document Type and Number:
WIPO Patent Application WO/2019/090356
Kind Code:
A1
Abstract:
A substrate surface includes a hierarchal structure on the substrate surface, the hierarchal structure includes layers of liquid fluorocarbon polymer and/or hydrofluorocarbon polymer and particles of a fluorocarbon polymer and/or hydrofluorocarbon polymer. The multi-layer structure compromises a nano-textured and/ or a micro-textured structured of a fluorocarbon polymer and/or a hydrofluorocarbon polymer coating on the substrate surface. The liquid layer of the fluorocarbon polymer and/or hydrofluorocarbon polymer is embedded between the substrate surface and the upper particle layer. The multi-layer structured fluorocarbon polymer and/or a hydrofluorocarbon polymer coating a substrate acts a biomimetic of the lotus leaf effect.

Inventors:
ISMAIL, Tareq Isam (P.O. Box 2026, Huntsville, Texas, 77341, US)
WOOD, Stephen Lathrop (P.O. Box 2026, Austin, Texas, 77341, US)
SHENKER, Jonathon (P.O. Box 2026, Huntsville, Texas, 77341, US)
Application Number:
US2018/059492
Publication Date:
May 09, 2019
Filing Date:
November 06, 2018
Export Citation:
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Assignee:
SAM HOUSTON STATE UNIVERSITY (P.O. Box 2026, Huntsville, Texas, 77341, US)
International Classes:
H05K7/20; B05D5/08; B32B27/16; C08L27/18; H01L21/02
Attorney, Agent or Firm:
DELUCA, Mark R (Meyertons, Hood Kivlin, Kowert & Goetzel, P.C.,P.O. Box 39, Austin Texas, 78767-0398, US)
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Claims:
WHAT IS CLAIMED IS:

1. An article for enhanced heat transfer, and/or reducing adhesion of liquids, and/or mitigation of nucleation of unwanted particles thereupon, the article comprising a substrate and a hierarchal structure coating on the substrate.

2. The article of claim 1, wherein the substrate comprises a metal selected from the group consisting of aluminum, brass, copper, gold, molybdenum, nickel, silver, steel, stainless steel, titanium, and an alloy formed from two or more of the metals thereof.

3. The article of claim 1, wherein the substrate comprises a polymer selected from the group consisting of acrylate polymer, chlorinated rubber, expanded polytetrafluoroethylene, fluoropolymer, high density polyethylene, polyethylene, low density polyethylene, polyacrylonitrile, polyamide resin, polyanhydride, polyester, polyethylene terephthalate, polyisoprene, polymethylmethacrylate, polyorthoester, polyphenazine, polypropylene, polyurethane, polyvinylchloride, polytetrafluoroethylene, polyvinylidene fluoride, synthetic rubber, and vinyl resin.

4. The article of claim 1, wherein the substrate comprises a semiconductor comprising: elements found in Group 14 of the periodic table selected from the group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl); a binary compound composed of two elements, one element found in Group 13 of the periodic table and one element found in group 15 of the periodic table, or one element found in Group 12 of the periodic table and one element found in Group 16 of the periodic table, or one element found in group 14 of the periodic table and one element found in group 16 of the periodic table, or between two different group 14 elements; or organic semiconductors.

5. The article of claim 1, wherein the substrate comprises a rare earth element selected from the group consisting of cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y).

6. The article of any one of claims 1-5, wherein the hierarchal structure coating comprises a fluoropolymer.

7. The article of claim 6, wherein the fluoropolymer is selected from the group consisting of ethylene tetrafluoroethylene copolymer (ETFE), ethylene chlorotrifluoroethylene copolymer (ECTFE), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), Polychlorotrifluoroethylene (PCTFE or PTFCE), and perfluoroalkoxy alkanes (PFA).

8. The article of any one of the preceding claims, wherein the hierarchal structure coating comprises a copolymer of two or more monomer species.

9. The article of any one of the preceding claims, wherein the hierarchal structure coating has a texture comprising micro- and/or nano-scale features, wherein the micro- and/or nanoscale features are selected from the group consisting of bumps, grooves, pores, posts, and protrusions.

10. The article of any one of the preceding claims, wherein the hierarchal structure coating has a texture comprising micro- and/or nano-scale features that are patterned and/or unpatterned.

11. The article of any one of the preceding claims, wherein the substrate is textured and wherein the hierarchal structure coating conforms to the textured substrate surface.

12. The article of claim 11, wherein the substrate is textured with micro- and/or nano- scale surface textures selected from the group consisting of bumps, grooves, pores, posts, and/ or protrusions.

13. The article of claim 11, wherein the substrate is textured with micro- and/or nano- scale surface textures.

14. The article of claim 11, wherein the substrate is textured with micro- and/or nano- scale surface textures that are patterned.

15. The article of any one of the preceding claims, wherein the hierarchal structure coating has a crystalline or semi-crystalline surface formed via annealing.

16. The article of any one of the preceding claims, wherein the article is a condenser, and wherein dropwise condensation is promoted on the top of the surface of the hierarchal structure coating to enhance heat transfer to substrate.

17. The article of any one of the preceding claims, wherein the article is a Thermal Interface Material.

18. The article of any one of the preceding claims, wherein the article is performed to retrofit an existing component of a system, wherein the system is selected from the group consisting of a boiler, a condenser, a desalination plant, a radiator, a power plant, an ocean thermal energy conversion (OTEC) plant, and nuclear power plant cooling towers, by forming a hierarchal structure coating upon a surface of the existing component.

19. The article of any one of the preceding claims, wherein the hierarchal structure coating provides dropwise condensation and shedding of a low surface tension liquid.

20. The article of claim 19, wherein the low surface tension liquid is a refrigerant or water.

21. A method for manufacturing a surface for promoting dropwise condensation and/or shedding of a liquid, the method comprising providing a substrate; and coating the substrate with a hierarchal structure coating as described in any one of claims 1-20.

22. A method of forming a fluorinated polymer coating on a substrate surface comprising: applying a liquid first fluoropolymer to substrate surface to form a first coating on the substrate surface; applying particles of a second fluoropolymer to the first coating; heating the coated metal surface to produce the fluorinated polymer coating.

23. The method of claim 22, wherein the coated metal surface is heated at a temperature, and for a time, sufficient to form a hierarchal structure on the metal surface comprising particles of the first fluoropolymers embedded in a film of the second fluoropolymer.

24. The method of any one of claims 22-23, wherein the first and/or the second fluoropolymer(s) are a fluorocarbon polymer and/or a hydrofluorocarbon polymer.

25. The method of any one of claims 22-24, wherein the first fluoropolymer is ethylene tetrafluoroethylene copolymer.

26. The method of any one of claims 22-24, wherein the first fluoropolymer is selected from the group consisting of ethylene tetrafluoroethylene, ethylene chlorotrifluoroethylene, polytetrafluoroethylene, fluorinated ethylene propylene, Polychlorotrifluoroethylene, and perfluoroalkoxy alkanes.

27. The method of any one of claims 22-26, wherein the second fluoropolymer is ethylene tetrafluoroethylene copolymer.

28. The method of any one of claims 22-26, wherein the second fluoropolymer is selected from the group consisting of ethylene tetrafluoroethylene, ethylene chlorotrifluoroethylene, polytetrafluoroethylene, fluorinated ethylene propylene, Polychlorotrifluoroethylene, and perfluoroalkoxy alkanes.

29. The method of any one of claims 22-28, wherein applying a liquid of the first fluoropolymer to substrate surface comprises spray coating the metal surface.

30. The method of any one of claims 22-28, wherein applying a liquid of the first fluoropolymer to substrate surface comprises spray coating, dip coating, or flow coating the metal surface.

31. The method of any one of claims 22-30, wherein applying a powder of the second fluoropolymer to substrate surface comprises electrostatic powder spray coating.

32. The method of any one of claims 22-30, wherein applying a powder of the second fluoropolymer to substrate surface comprises electrostatic powder spray coating, or fluidized bed.

33. The method of any one of claims 22-30, wherein applying a powder of the second fluoropolymer to substrate surface comprises one topcoating.

34. The method of any one of claims 22-30, wherein applying a powder of the second fluoropolymer to substrate surface comprises multiple topcoating.

35. The method of any one of claims 22-30, wherein applying a powder of the second fluoropolymer to substrate surface comprises a middle coating and one topcoating.

36. The method of any one of claims 22-30, wherein applying a powder of the second fluoropolymer to substrate surface comprises middle coating and multiple topcoating.

37. The method of any one of claims 22-36, wherein applying middle coat to substrate is a liquid of the first fluoropolymer.

38. The method of any one of claims 22-36, wherein applying middle coat to substrate is a powder of the second fluoropolymer

39. The method of any one of claims 22-39, wherein the substrate surface is a tubular conduit, and wherein the coating is applied to the outer surface of the tubular conduit.

40. The method of any one of claims 22-39, wherein the substrate surface wherein the article is a component of a condenser that comes into contact with a condensing liquid.

41. The method of claim 40, wherein the component comprises including but not limited to aircraft, boiler, consumer electronic device, cookware, fin, electronic component, industrial machinery, pipe, pipeline, solar panel, satellite station, network dish, vessel, turbine, windshield, or medical equipment thereof.

42. The method of claim 41, wherein the liquid comprises including but not limited to aqueous based, water based thereof.

43. The method of claim 22, wherein the particles comprises including but not limited to powder thereof.

44. A coated substrate surface made by the method of any one of claims 22-43.

45. A coated substrate comprising: hierarchal structure on the substrate surface, the hierarchal structure comprising particles of a first fluoropolymer embedded in a film of a second fluoropolymer.

46. A method of producing purified water, comprising, obtaining a coated substrate as described in claim 44 or 45; passing a cooled fluid through a substrate tubular conduit; contacting the metal tubular conduit with air having a water content of at least about 10%, collecting water that condenses on the substrate tubular conduit.

47. The method of claim 46, wherein the air has a temperature that is greater than the temperature of the fluid passing through the metal tubular conduit.

48. The article of any one of the preceding claims, wherein the hierarchal structure coating has an exposed substrate surface with low hysteresis contact angle, where the hysteresis contact angle is defined as the difference between the receding contact angle and advancing contact angle for liquid droplet, for liquid water droplet, wherein the hysteresis contact angle is no greater 30°, no greater 25°, no greater 20°, no greater 15°, no greater 10°, no greater 9°, no greater 8°, no greater 7°, no greater 6°, no greater 5°, no greater 4°, no greater 3°, no greater 2°, or no greater 1°.

49. The article of any one of the preceding claims, wherein hierarchal structure coating has an exposed substrate surface with a high receding contact angle for a liquid water droplet wherein the high receding contact angle is no less than 130°, no less than 135°, no less than 140°, no less than 145°, no less than 150°, no less than 155°, no less than 160°, no less than 165°, or no less than 170°.

50. The article of any one of the preceding claims, wherein hierarchal structure coating has an exposed substrate surface with high advancing contact angle for liquid water droplet including but not limited to no less than 130°, no less than 135°, no less than 140°, no less than 145°, no less than 150°, no less than 155°, no less than 160°, no less than 165°, or no less than 170°.

Description:
TITLE: LAYER BY LAYER SUPERHYDROPHOBIC FLUOROPOLYMER COATED METAL SUBSTRATE FOR DROPWISE CONDENSATION

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to fluorinated carbon coatings.

2. Description of the Relevant Art

Condensation of water to produce purified water, suitable for drinking and other uses, is a well-known process. Condensation processes, however, can be cost prohibitive due to low condensation efficiencies of condensers, and the high energy cost for continually producing a coolant fluid. It is therefore desirable to improve the efficiency of a condenser in order to reduce the production costs for the generation of purified water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood the present invention is not limited to particular devices or methods, which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification and the appended claims, the singular forms "a", "an", and "the" include singular and plural referents unless the content clearly dictates otherwise. Furthermore, the word "may" is used throughout this application in a permissive sense (i.e., having the potential to, being able to), not in a mandatory sense (i.e., must). The term "include," and derivations thereof, mean "including, but not limited to." The term "coupled" means directly or indirectly connected.

List of Abbreviations and Frequently Used terms

Ultraphobic, known as Ultrahydrophobic / Ultralyophobic: Means "super repellant". Hydrophilic: Means "Loves Water".

Hydrophobe: Means "Hate Water".

Lipophilic: Means "fat lover".

Filmwise condensation: In film condensation which is known as (filmwise condensation) vapor latent energy is released, heat transfers to the surface, condensate forms, where drops form quickly and coalesce to produce a continuous wet thin layer of liquid that forms over the condensing surface.

Dropwise condensation: In drop condensation which is known as (dropwise condensation), if the condensation rate is low due the presence of non-condensable gas, the liquid does not wet the surface wall of the condenser or the condensing surface is non-wetting surface, condensation will form as droplets from the vapor at particular nucleation sites on solid surfaces; the drops remain separate during growth. Hydrophilic surfaces: are surfaces that like water where the droplet creates a contact angle larger than 0° and less than 90°, (0° <θ< 90°) with condensing surface.

Hydrophobic surfaces: are surfaces that hate water where the droplet creates an angle greater than 90°, (90°<θ<150°) with condensing surface.

Super-hydrophobic: Is very hydrophobic where the droplet creates an angle greater than 150°,(θ>150°) with condensing surface.

Wetting: If a droplet is added on substrate and the surface energy of the substrate changes upon the addition of the droplet, the substrate is said to be "wetting" Once a liquid is in contact with a solid surface.

Adhesion: Dissimilar particles or surfaces cling to one another. Adhesion is the force of attraction between two unlike molecules.

Cohesion: Similar particles or surfaces cling to one another. Cohesion is the force of attraction between like molecules.

Capillary: Is water molecules move up the fiber walls and spanning the space of the tunnel that are pulled along.

Contact angle: is the angle measured where a liquid-vapor interface meets a solid surface. Ideal solid surface: A solid surface that is chemically homogenous, flat, smooth, and has a zero contact angle hysteresis is said to have ideal solid surface.

Contact angle hysteresis: is equal the difference between the advancing and receding angles.

Complete spreading: Is also known as complete wetting, when S > 0, where the liquid wets the surface completely.

Partial spreading: Is also known as partial wetting, when S < 0, where the liquid wets a smaller portion of the surface.

Dynamic wetting: Is the motion of a phase boundary which involves the advancing and receding of contact angles.

A kinetic non-equilibrium effect: Occurs when a rapid movement of contact line happens at a high speed that a complete wetting cannot be achieved.

Homogeneous wetting: Is when the liquid fills in the rough grooves of a surface.

Heterogeneous wetting: Is when the surface is composed of two types of patches.

Surface energy: Is known as "interface energy," and is used to quantify the disruption of intermolecular bonds that occur when a surface is created and is defined as the excess of energy at the surface of the material when it is compared to the bulk of the material.

Surface tension: Is identified as a force per unit length. For liquids the surface energy density and surface tension are identical.

Gibbs isotherm: Describes the phenomenon when two liquids are mixed and their molecules are dissolved and the surface tension of their mixture is different than the pure liquid values.

Surface tension: Is the resistance of a liquid surface to an external force. Fully wettable: Is when the contact angle is 0°, the liquid will spread out into a micro-thin layer over the surface. This surface is called "fully wettable" by the liquid. Pull-off force: The tensile load at separation is known as pull-off force.

London dispersion forces: Is the random shift in charges due to constant movement of electrons within the non-polar molecule. Electrostatic gun (corona gun): The most popular form of applying powder coating to metal objects is to spray the powder with the use of electrostatic gun (corona gun).

Tribo gun: Uses triboelectric friction to charge the powder. The tribo uses mechanical application of charge to the powder particles by means of friction as these partials are deflected and forced to rub against Teflon tubing inside the barrel of the gun.

Fluidized bed: Technique used to apply powder coating on substrate, where the part to be coated is heated and dipped into aerated powder-filled bed. Electrostatic fluidized bed coating: Is similar to fluidized bed dib coating except for the electrostatic charging medium paced inside the bed which charges the powder partials as the fluidizing air lifts it up.

Electrocoat dip (electrodeposition): Unlike manual spray of metal parts with anti- corrosion, in electrocoat dip process, metal parts are dipped into a tank with electro charged primer in it.

In one embodiment, a method of forming a fluorinated coating on a metal surface includes applying a liquid first fluoropolymer to the metal surface to form a first coating on the metal surface. As used herein a fluoropolymer is a polymer that is composed of at least carbon and fluorine. A fluoropolymer may also include other elements such as hydrogen, oxygen, nitrogen and other halogens. Specific types of fluoropolymers include fluorocarbon polymers and hydrofluorocarbon polymers. Fluorocarbon polymers, as used herein, are polymers that are only composed of carbon and fluorine. Hydrofluorocarbon polymers, as used herein, are polymers that are only composed of carbon, fluorine, and hydrogen. Specific examples of fluoropolymers include, but are not limited to:

polytetrafluoroethylene (PTFE);

ethylene tetrafluoroethylene copolymer (ETFE);

ethylene chlorotrifluoroethylene copolymer (ECTFE);

fluorinated ethylene propylene (FEP); F-C-F

I

F

perfluoroalkoxy alkanes (PFA)

Polychlorotrifluoroethylene (PCTFE or PTFCE)

In some embodiments, the first and/or the second fluoropolymer(s) are a fluorocarbon polymer and/or a hydrofluorocarbon polymer. The first and the second fluoropolymers may be the same polymer. In a preferred embodiment, the first and second fluoropolymers are ethylene tetrafluoroethylene copolymer. When the first and second fluoropolymers are the same polymer, the liquid first fluoropolymer may be a polymer that has a molecular weight and/or a level of crosslinking that is less than the polymer used to form the particles of the second fluoropolymer. The liquid first fluoropolymer will, generally, be a liquid at or proximate to room temperature (25 °C).

In some embodiments the first and second fluoropolymers are different polymers. In a preferred embodiment, the liquid first fluoropolymer is an ethylene tetrafluoroethylene copolymer, while the second fluoropolymer is selected from the group consisting of ethylene chlorotrifluoroethylene, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, and perfluoroalkoxy alkanes.

The metal surface may be any metal (either a pure metal or an alloy) that can benefit from having a hydrophobic coating. In a specific embodiment, the metal surface is part of a condenser for a liquid (e.g., water) condensation system. In a preferred embodiment, the metal is copper. The metal surface may be flat or curved, depending on the application. For condenser systems the metal surface (e.g., copper) may be the exterior of a tubular conduit (a pipe) that forms the condenser of the condensation system.

In one embodiment, the liquid first fluoropolymer is applied using a spray coating process. It should be understood, however, that while a spray coating process is described herein, other methods (e.g., dip coating, deposition, etc.) could also be used to produce the initial coating. In a spray coating process, the liquid fluoropolymer is applied as a neat liquid or may be dissolved in a suitable solvent (e.g., water) and sprayed onto the metal surface. When a solvent is used, the metal surface may be heated to accelerate evaporation of the solvent. In some embodiments, the neat liquid first fluoropolymer may be heated to reduce the viscosity of the polymer. To complete the formation of the first coating the sprayed on layer may be further dried by applying a heat (e.g., using infrared light) to the coating to remove all of the solvent. Examples of spray coating systems may be found in European Patent No. 894 541; PCT Publication No. WO 02/14065; and U.S. Patent Nos.: 5, 160,791; 5,230,961; 5,223,343; 5, 168,107; 5, 168,013; and 7,462,667, all of which are incorporated herein by reference.

In an embodiment, particles of a second fluoropolymer are applied to the first coating. The applied particles become embedded in the liquid first coating to form a coated metal surface. Any commercially available powder coating equipment can be used to apply the particles of the second fluoropolymer. There are many different types of equipment that can be used to apply powder fluoropolymer coatings. Fluoropolymer powder coatings may be applied as a free- flowing dry powder and does not need a solvent to keep the binder parts and filler parts in a liquid suspension form. Fluoropolymer powder coatings are applied electrostatically with a fluidized bed or spray gun. Because fluoropolymer powder permits a wide range of application voltages, voltage application and techniques are dependent on the equipment are used for such application. By subsequent curing under heat, the fluoropolymer powder coating forms a skin. A coated part may become too insulated after electrostatically applying one or two coats of a fluoropolymer powder. When this condition occurs the part may be sprayed hot (hot flocked) as it comes out of the oven after being cured. Some examples of methods of coating substrates are set forth in more detail below.

Fluoropolymer coating can produce thicker coatings than conventional liquid coatings without running or sagging. Because powder coating does not have a liquid carrier, when compared to liquid coating, fluoropolymer powder coating produces almost no appearance differences between horizontally coated surfaces and vertically coated surfaces. Fluoropolymer powder coating process emits few volatile organic compounds; due to no carrier fluid to evaporate away. Different colored fluoropolymer powders could be mixed together before curing allowing for color blending and bleed special effects in one single layer.

It is easier to apply thick powder coatings than thin powder coatings, as the thickness of the powder coating is reduced an orange peeled texture is obtained due to the glass transition temperature (Tg) and the practical size of fluoropolymer powder. After applying a first coating of the second fluorinated carbon particles on the substrate, the substrate becomes somewhat electrically insulated. Subsequent coats of the particles are poorly attracted, resulting in less coating of the substrate with each application of particles. To improve coating of the substrate with the second fluoropolymer particles, the metal substrate is heated and, shortly after the part is removed from the heat source, the particles of the second fluorinated polymer are applied to the heated substrate. This method is generally known as hot flocking. The hot flocking method may be combined with the electrostatic application. Depending on the mass of the part, and its temperature and its ability to hold heat, the coating thickness will vary. Generally a thicker film may be obtained by spraying a hot part than spraying a cold part. To decrease pit formation on the surface of the part, it may be necessary to decrease the application voltage after the first coat of particles.

Fluoropolymers may be given an electrostatic charge which will help attract the particles to a grounded metal part. To provide a good electrostatic attraction without repulsion a maximum voltage charge may be employed. The voltage used usually varies with specific equipment use, but is generally in the range of 20-30 kV. Adjusting air pressure delivery will help produce a powder cloud that does not blow past the part.

Electrostatic gun The most popular form of applying powder coating to metal objects is to spray the powder with the use of electrostatic gun (corona gun). The gun exposes the powder to positive electrostatic charge, the powder is sprayed towards a grounded metal part mechanically or by compressed air, and the powder is accelerated toward the metal part by powerful electrostatic charge. The electrostatic gun (corona gun) uses a strong electric field between the ionized tip inside the gun and the part to be sprayed. The powder particles gain a negative charge as they pass through the ionized field. The particles repel each other as mist because of the similar charge they carry. These particles as they discharge out of the gun, they follows the field lines to the part to be coated, coating all sides of the part. The thickness of the coat is reliant on the amount of voltage is applied. Because there is no electric field inside the part, the inside of the part is not coated. This phenomena is called the Faraday cage effect. Electrostatic coating equipment uses a wide variety of spray nozzles which depends on the shape of the work piece to be coated and the thickness of the coat. Once the spray coat is done, the coated part will be heated, the powder melts into a uniform film, and the coated part is coaled to allow for the coat to harden. Preheating the metal part before spray coating it can help achieve a uniform finish but also can cause problems by excess powder.

Tribo gun

Another method is to use a tribo gun, which uses triboelectric friction to charge the powder. The tribo uses mechanical application of charge to the powder particles by means of friction as these partials are deflected and forced to rub against Teflon tubing inside the barrel of the gun. The charged powder partials once is released from the gun, adhere to the grounded surface of the part. Since there is no external electric field for the traveling particles to follow, this method becomes very useful when need is arisen to coat the inside area of the part. Tribo gun requires different powder formulas than the one used for corona gun. The tribo gun does not have problems associated with back ionization and the Faraday cage affects that corona gun encounter.

Fluidized bed

Fluidized bed is another technique is used to apply powder coating on substrate, where the part to be coated is heated and dipped into aerated powder-filled bed. Then the powder gets hot, starts to melt, and sticks to the substrate. Finally, the part is heated to finish cure the part. This method is preferred when a thickness of coating more than 300 m is needed. Electrostatic fluidized bed coating

Electrostatic fluidized bed coating is much similar to fluidized bed dib coating except for the electrostatic charging medium paced inside the bed which charges the powder partials as the fluidizing air lifts it up. The charged powder partials form a cloud and move in an upward direction above the fluid bed. As the grounded substrate move in a downward direction inside the cloud of charged powder particles, the particles get attracted to the substrate and attached to its surface. Also the substrate to be coated is not preheated before gets dipped in the electrostatic fluidized bed and much less powder depth is used as it is for fluidized bed dipping.

Electrocoat dip (electrodeposition)

Unlike manual spray of metal parts with anti-corrosion, in the electrocoat dip process, metal parts are dipped into a tank with electro charged primer in it. An electric current is used to apply a primer to a conductive substrate. Then the part gets dipped into an electrocoat dip tank. An electrical charge is applied to the primer powder. The powder is then gets attached to the conductive substrate. The part then moves to the rinse tank. Finally the part is moved to the oven to be cured. Electrocoat dipping is fully automated and is minimizes powder waste (no pollution), reduces parts weight, coat parts uniformly, coat complex-shaped pars.

After application of the particles to the second fluoropolymer, the polymer is cured by heating the coated metal surface to produce the fluorinated polymer coating. The coated metal surface is heated at a temperature, and for a time, sufficient to form a hierarchal structure on the metal surface comprising particles of the first fluoropolymers embedded in a film of the second fluoropolymer.

Before applying fluoropolymer liquids and solids, the choice of substrates and surface preparation of these substrates should be considered. Substrates which have thermal and dimensional stability at bake temperature can be coated with fluoropolymer coatings. These substrates should be free of excessive roughness at joints and welds, excessive pits or porosity, and sharp corners and edges before treated with fluoropolymers. In a preferred application of this invention, copper is used as the substrate. Copper is thermally stable under a bake temperature, thus it can be coated with fluoropolymers.

Poor adhesion of fluoropolymers to copper results from the poor adhesion of copper to the copper oxide that is formed when copper is baked in the air at high temperatures. It is known that between room temperature and 100°C, copper forms a thin Cu 2 0 layer; and when the temperature reaches about 150°C a complex oxide is formed Cu 3 0 2 ; and when the temperature gets in the range between 200-300°C CuO forms. When CuO begins to form, significant oxidation occurs. Copper should be cooled to below 150°C to insure only a protective thin film has formed. For copper substrates it was found that curing copper metal at 280°C for 10 - 15 minutes will be sufficient enough to coat a copper substrate with a fluoropolymer without copper oxide formation.

Fluoropolymer should not be applied until the substrates are cleaned. Precaution must be taken to remove all residues from the cleaning process when using chemical washes or solvent cleaning and degreasing. It is also recommended to physically remove dirt, paint, mill scale, rust, or any foreign species that industrial chemical washes or solvent cleaning and degreasing could not remove. Gloves should be used to handle metal after metal cleaning to avoid fingerprint and/or residual oil contamination which may show up as a stain on the finish.

It is beneficial to preheat the metal substrates to the required bake temperature before applying the fluoropolymer. This helps to eliminate any traces of oil contaminants from substrates especially when the metal is made of cast and somewhat porous. Preheating has its advantages when the substrate is ferrous metal, whereas it is temporarily passivate the surface against rusting and the blue oxide formed increases the adhesion of the acid primers. The advantages of preheating are not existent in the case of aluminum and stainless steel and preheating the metal substrate step can be omitted where clean metal is involved. Preheating copper and brass in air should be avoided because the resulting oxide has poor adhesion to the metal substrate. To reduce oxide from forming on copper surface a formic acid rinse should be used.

The most common method to obtain good adhesion of fluoropolymer coatings is via grit blasting. In order to retain the protective oxide formed on ferrous metal, grit blasting should always precede preheating. The order of operating preheating and grit blasting is of less importance for other clean substrates. Profiling a surface in excess of 100 microinches (2.5 microns) is recommended and profiling a surface in the range of 200-250 microinches (5.1-6.5 microns) is frequently employed. Aluminum oxide grits range from #40 to #80 at air pressures ranging from 80 to 100 psi (5.8 to 7.3 kg/cm2) at the gun, are commonly used on hard substrates. Air pressures ranging from 80 to 100 psi (5.8 to 7.3 kg/cm2) or below are commonly used on aluminum and brass substrate. Air pressure of excess of 100 psi (7.3 kg/cm2) may be used on stainless steel. Chilled iron grit has found considerable use in blasting metal substrates because of its high density and sharp particle shape. This grit, which is recommended for centrifugal abraders, is approximately twice that of aluminum oxide because its density.

Sand is not recommended to be used to rough a substrate because it is considered too smooth, uniform, and short-lived yet glass beads are compatible to aluminum oxide grits and have produced the same surface roughness. Micro-inches or root mean square (RMS) by means of a profilometer are common measuring units for grit blast profiles. Also eddy-current thickness gauge is used as a rough estimate of profile of nonferromagnetic metal.

The above methods only measure depth profile and by no means measure the coverage of the grit, sharpness of the peaks, or uniformity. It is only when the metal surface is viewed at flat grazing angle; a full coverage of the grit blast is obtained and is indicated by lack of gloss on the metal surface.

To avoid cuts, pits, and scratches, on the substrate surface it is preferred to avoid severe grit blasting, sanding, or wire brushing which could cause the finish to flow into the depressions and lead to mud cracking.

Even though grit blasting is the method of choice for metal treatment for the application of most fluoropolymer coatings, other surface roughening methods are used when best adhesion is not required such as directional grinding, wheel sanding, and wire brushing. Directional grinding, wheel sanding, and wire brushing reduce adhesion in the direction of the grind. For best adhesion, chemical etching gives smooth peaks, without the sharp "tooth". Also for best adhesion; rough, as-cast surfaces also are too smooth in microprofile. Rather than cleaning with any wet method such as chromic acid, hydrochloric acid, or sulfuric acid, it is much better to clean by grit blasting, sandpaper, steel wool, or No. 400 emery cloth. Caution must be used as etching reagents require immediate rinse to prevent salts from depositing on the surface which would lead to oxidizing or rusting problems that may require additional physical cleaning work with steel wool or No. 400 emery cloth in addition to rinsing and drying to remove the oxidation.

As a result of chemical treatment the surface of metal gets modified. These modified metal surfaces are called conversion coatings. Improving adhesion of finishes and maximizing corrosion resistance is the principle function of the conversion coatings, whereas the functionality depends upon the conversion coatings uniformity and the integrity of the coating, both before and after application of the final finish.

Because of the high temperature bake destroys the integrity of the conversion coating, PTFE finishes cannot be applied to conversion coatings especially when the substrate is steel. Micro crystal-line zinc phosphate is an effective conversion coating for steel substrates. For steel substrates, manganese phosphate has proven to be very effective conversion coating, especially in corrosive environments. But the use of iron phosphate on steel has been proven less effective conversion coating, especially when corrosion resistance is needed. Chromate conversion coatings are proven to be the best conversion coating for aluminum. Conversion coating may not work for all metal substrate and it should be applied on case to case basis as necessary.

Coatings should be applied immediately after grit blasting because steel and iron rust rapidly. A solvent rinse with VM&P naphtha or toluene containing 5% kerosene may be employed, where delay is expected, or under conditions of high humidity. A very thin film of kerosene remains to prevent rusting temporarily, when the volatile solvent evaporates. If the thin film of kerosene has been sitting for a long time, the kerosene film may collect dust and require solvent washing before the finish is applied. Phosphate or other metal cleaning treatments could cause poor adhesion of fluoropolymer coatings. Nonvolatile alkalis could promote poor adhesion to steel because it permeates the pores of the metal to the extent that a definite alkaline reaction to phenolphthalein can be obtained. If these problems arise it is recommended before applying the liquid fluoropolymer to neutralize the alkali by soaking the metal in a dilute solution of phosphoric or chromic acid followed by rinsing with water. Due to the presence of one or more contaminants such as fingerprints, forming lubricants, grease, or oils on the metal when the finish is applied, spotting or staining of the primers occasionally occurs. After grit blast, the metal may be preheated, rinsed, or solvent cleaned in a (10%) chromic acid solution for a few minutes to avoid such contaminations. It is recommended if present, rust spots should be removed before priming.

To obtain the best adhesion the metal substrate should be cleaned and roughened. Using a commercially available hot alkaline solution to clean is preferred method. Solvent degreasing is an alternative cleaning method, yet safety and health precaution should be taken into consideration when using such method, i.e. it is not recommended to solvent clean by hand. To improve performance of the final coating system, it is recommended that a high-temperature burn-off prior to grit blasting is employed. It is preferred that roughening is done by grit blasting with aluminum oxide. To create sharper peaks and valleys, it is recommended to use a new grit which will give the best profile when compared to old, rounded grit. For intended coating thicknesses above 750μπι (30 mil), the blast profile (surface roughness depth) should be at least 75-125μπι (3-5 mil). To achieve such a profile, a coarse grit (10-20 mesh) could be employed using 620-690kPa (90-100 psi) air pressure. A lower blast profile is more appropriate for thin films.

For the high-build systems, adherence to the recommended bake temperature is crucial to final performance. These coatings are formulated to have outstanding resistance to heat and to sagging in thick films. This is accomplished by changing the flowability of the molten material over time. At the begging, the molten ETFE flows well, as the time increases, the rate of flow decreases. A film with pinholes can result from insufficient dwell time in the molten state, which could be corrected by readjusting the process time and/or temperature accordingly and rebaking the part. Long exposure at maximum bake temperature will cause blistering, brown discoloration, and polymer sagging.

The final coated substrate may be used in a variety of applications. A particularly useful application is for condensation of water. In an embodiment, a method of producing purified water includes: obtaining a coated metal tubular conduit having a hierarchal structure on the metal surface as described above. A cooling fluid is then passed through the metal tubular conduit. The cooling fluid may be at or below room temperature (about 25 °C). In some embodiments, the cooling fluid may pass through a cooler to lower the temperature of the fluid before passing the fluid into the coated metal tubular conduit. The cooling fluid may be water or may be an organic fluid such as ethylene glycol, alcohols or mixtures of organic fluids with water. Moist air (e.g., air having a relative humidity of at least about 10%) is then brought into contact with the coated metal tubular conduit. When the moist air is contacted with the coated metal tubular conduit water in the moist air will begin to condense on the conduit and can be collected. Preferably the air is at a temperature that is greater than the temperature of the cooling fluid passing through the metal tubular conduit. The use of a hierarchal structure on the surface of the condensing element of a water collection system provides a significant increase over condensation of water on an uncoated surface.

EXAMPLES The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

ETFE was studies as a preferred substrate for coating a metal substrate. In a general process, a liquid ETFE primer was applied to the substrate, followed by the application of powdered ETFE to the primer coated substrate. Subsequent curing produced a hydrophilic coating on the substrate that can be used in a condensation reaction.

When it comes to adhesion, Teflon® ETFE (699N-129 Black or 532-6405 Green) is superior to most other fluoropolymers and it has been used without a primer in a variety of applications. However, the adhesive strength of the bond can be doubled by using Teflon® liquid primers.

The 699N-129 black liquid primer is formulated with adhesive resins having outstanding resistance to high temperatures that withstand thermal abuse from multiple bakes during topcoat application, thus making 699N-129 black Liquid Primer recommended for all coating systems.

699N-129 black liquid primer should be applied in a thin layer, barely hiding the blasted substrate when wet. The actual thickness of 699N-129 black liquid primer should vary depending on the depth of blast profile. For example; 699N-129 black liquid primer thickness of approximately 14μιη [0.5mil], will require a blast profile of 75μιη [3mil]. To prevent intercoat adhesion failure, excessive thickness should be avoided. After air drying, small white specs of

ETFE particles may be visible and 699N-129 black liquid primer should visibly appear to be slightly rough with a dull, mottled look, which is normal. Preheating substrates to 50°C (120°F) will minimize carbon steel from rusting, especially during humid weather or cool, damp, early morning start-ups. Also 699N- 129 Liquid Primer is equipped with antiflash-rust additives to prevent carbon steel substrates from rusting once it is coated. The first powder topcoat can be applied directly over wet, air-dried, or force-dried 66°C [150°F] primer. Avoid fully pre-baking the primer. Another particularly useful primer is Acquis Liquid Base primer, which is composed of ETFE polymer having a low glass transition state (below room temperature) allowing the neat polymer to act as a liquid at room temperature (about 25 °C)

For all thin-film applications 532-6210 Clear Ultrasmooth Topcoat Powders or 532-6200 White Ultrasmooth Topcoat Powder is used. These topcoats will provide glossier smoother films and have high melt flow value. For complete hiding when using 532-6200 White Ultrasmooth Topcoat Powder over 699N-129 Black Water-Based primer a minimum of ΙΟΟμιη (4mil) of 532- 6200 White Ultrasmooth Topcoat Powder should be used. Since the first coat electrically insulates the substrate of a metal part, a thin metal will not hold heat long enough to melt-fuse a second coat on the metal substrate. Thus it is going to be difficult to add a second electro- static application of a second coat on a thin-metal part. Therefore using triboelectric spray equipment would not produce a better coat. If a total film build thickness of 150-175 μπι (6-8 mil) is exceeded, blistering may occur with these thin film topcoats.)

For all high-build applications 532-6310 Clear High-Build Topcoat Powders, 532-6314 Green High-Build Topcoat Powders, 532-6118 Sparkling Beige High-Build Topcoat Powders, or 532-6410 Clear High-build Topcoat can be used, where the intended final film thickness exceeds 635μπι (25mil). These coatings have the ability to resist sagging and pulling away from sharp edges. For all general purpose CPI applications, 532-6314 Green High-Build Topcoat Powders is favored, due to its versatility to build thickness. For permeation resistant applications, 532- 6118 Sparkling Beige High-Build Topcoat Powders is specially formulated and provides tremendous benefit in comparison to 532-6310 Clear High-Build Topcoat Powders and 532-6314

Green High-Build Topcoat Powders. However due to risk of blistering at thicknesses above

750μιη (30mil), care must be taken when choosing 532-6118 Sparkling Beige High-Build

Topcoat Powders. Also 532-6118 Sparkling Beige High-Build Topcoat Powders adhesion is not as good as 532-6310 Clear High-Build Topcoat Powders and 532-6314 Green High-Build

Topcoat Powders adhesion. When using 532-6118 Sparkling Beige High-Build Topcoat

Powders, the part may be finished with a final coating of 532-6310 Clear High-Build Topcoat

Powders or for smoother final coating finish use 532-6210 Clear Ultrasmooth Topcoat Powders. It is recommended if using 699N-129 black liquid primer to apply the first topcoat powder electrostatically to a cold substrate and then place the part into a warm oven at approximately 300°F. The temperature should be stepped up to the recommended bake temperature once the temperature of the part reaches 300°F. To avoid heating the surface of the first coat too long, the cold part should not be loaded into an oven set at the final bake temperature, especially when the part is too thick or would take a long time to heat up. During hot flocking application the film build per coat is typically 75-250μπι (3-10mil). However, depending on the mass and size of the parts coated, hot flocking can yield highly variable builds per coat. The following combination of DuPont martial coatings on 12 inch copper pipes are used throughout the experimentations. 12 inch copper pipes were also used with no DuPont material coating for comparison.

Copper pipe with no DuPont coating

· Hand sanded with 400 grit copper pipe with no DuPont coating

• ETFE 699N-129 Aqueous primer on copper pipe

PTFE 850G-204 Aqueous One-Coat Green Primer on copper pipe

ETFE 699N-129 primer with ETFE 532G-6410 Super High-Build Clear Powder on copper pipe

· PTFE 850G-204 Aqueous One-Coat Green Primer with PTFE 851G-214 Aqueous Top- Coat Green Enamel on copper pipe

ETFE 532G-6405 Green Powder primer with ETFE 532G-6410 Super High-Build Clear Powder on copper pipe PFA 420G-703 Solvent primer with PFA 532G-5010 Powder Top-Coat Clear Powder on copper pipe

PFA 420G-703 Solvent primer with FEP 532G-8110 Powder Top-Coat Clear Powder on copper pipe

A condensation tower was built for studying the effect of the various coatings listed above on condensation rate and efficiency. FIGS. 1-4 depict various views of a condensation tower used in this study. The condensation tower is made of aluminum structural supports, transparent flexi glass and black flexi plastic.

FIG. 1 depicts a perspective view of the condensation tower. The condensation tower includes a lower section for holding the hot air source (for these experiments, a steamer) and a clear upper section that holds the condenser pipe. To keep the condenser pipe cool cooling reservoirs containing a cooled fluid (in this experiment, ice water) are coupled to the upper section via cooling fluid pipes (PVC pipes), see FIG. 2. The cooling reservoirs may include a pump for transferring cold fluids through the cooling fluid pipes, into the condenser pipe and into the opposing reservoir. The condenser's outside wall temperature is measured throughout the experiment to ensure the pipe's wall temperature stays at about 25°C. FIG. 3 shows a top down inside view of the condensation tower. Condenser is connected across the upper section of the condensation tower. A steamer is placed at the bottom of the condensation tower. Steamer includes a metal reservoir (e.g., a stainless steel bowl) coupled to a heat source (not shown). Water placed in the metal reservoir is heated to produce steam. The steamer is equipped with a temperature control valve that allows the steam to be kept at a temperature of between about 80 °C to about 85 °C.

FIG. 4 shows depicts a water collection device positioned below the condenser. The water collection device includes a grill and a water collection container. The grill is angled downward toward the water collection container. The grill does not affect the amount of steam that reaches the pipe since the steam rises and is exposed to the pipe's cold radiation. Condensation will occur at the surface of the pipe due to the temperature difference between the outside wall of the pipe and the hot steam.

Condensation on untreated copper pipe - control experiment #1 A length of untreated copper pipe was placed in the upper section of a condensation tower. Ice cooled water was used to keep the surface of the untreated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the copper pipe was measured to be 66 mL. The experiment was repeated twice and the amount of water collected was 67 mL in the second experiment and 63 mL in the third experiment. The average water collection was about 65 mL. Condensation on hand sanded (with 400 grit sandpaper) copper pipe - control experiment #2

An industrial copper pipe was hand sanded with 400 grit sandpaper, cleaned and placed in the upper section of a condensation tower. Ice cooled water was used to keep the surface of the sanded copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the sanded copper pipe was measured to be 25 mL. The experiment was repeated twice and the amount of water collected was 45 mL in the second experiment and 58 mL in the third experiment. The average water collection was about 43 mL. The differences in the amount of water gathered from each experiment is believed to be due to some powder/residue that was left behind on the pipe surface after sanding between the scratched surface lines, even after the pipe was cleaned. The powder acts as an insulator, reducing the amount of condensation. Each time the experiment was repeated, more power was removed from the surface of the pipe, leading to an increase in the amount of water gathered after each experiment.

Condensation on rough ETFE 699N-129 Water-Based Black coated copper pipe

A 1-inch diameter copper pipe was produced having a ETFE 699N-129 rough coat to give the copper pipe surface a rough appearance with nano-projections similar to the lotus leaf wax crystal without the microscopic bumps that are coated with a nanoscopic water-repellent coating (wax crystal). The ETFE 699N-129 coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with ETFE 699N-129 at 40 psi and dried under a heat light for 5 minutes.

The ETFE 699N-129 coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the ETFE 699N- 129 coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the ETFE 699N-129 coated copper pipe was measured to be 96 mL. The experiment was repeated twice and the amount of water collected was 95 mL in the second experiment and 92 mL in the third experiment. The average water collection was about 94 mL. When the thickness of the ETFE 699N-129 water-base primer is increased slightly, the amount of water condensation on the copper pipe coated with ETFE 699N-129 increased from 95 ml to 120 ml of water. Condensation on rough PTFE 850G-204 Liquid Acid Green coated copper pipe

A 1-inch diameter copper pipe was produced having a PTFE 850G-204 Liquid Acid Green rough coat. The PTFE 850G-204 Liquid Acid Green coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PTFE 850G-204 Liquid Acid Green at 40 psi and annealed by heating to 750 °F for 10 minutes.

The PTFE 850G-204 coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the PTFE 850G- 204 coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PTFE 850G-204 coated copper pipe was measured to be 70 mL. The experiment was repeated twice and the amount of water collected was 72 mL in the second experiment and 71 mL in the third experiment. The average water collection was about 71 mL.

Condensation on copper pipe coated with ETFE 699N-129 top coated with super high-build clear ETFE 532G-6410 A 1-inch diameter copper pipe was produced having ETFE 699N-129 base (first) coat which is top coated with super high-build clear ETFE 532G-6410. The ETFE 699N/532G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with ETFE 699N-129 at 40 psi and cured under a heat light for 5 minutes. FIG. 8 is a photograph of the copper pipe after spray coating with ETFE 699N-129 and curing. The cured ETFE 699N-129 layer was spray coated with ETFE 532G-6410 at 40 psi and the pipe annealed by heating to 580 °F for 30 minutes. FIG. 9 is a photograph of the pipe after spray coating with the ETFE powder topcoat and annealing. In FIG. 10 the ETFE 699N/532G coated copper pipe has been placed in the condensation tower, but steam has not yet been introduced into the tower.

The ETFE 699N/532G coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the ETFE 699N/532G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. FIG. 1 1 is a photograph of the ETFE 699N/532G coated copper pipe with water droplets formed on the pipe from the stem in the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the ETFE 699N/532G coated copper pipe was measured to be 221 mL. The experiment was repeated twice and the amount of water collected was 223 mL in the second experiment and 215 mL in the third experiment. The average water collection was about 220 mL.

Condensation on copper pipe coated with ETFE 532G-6405 top coated with super high-build clear ETFE 532G-6410

A 1-inch diameter copper pipe was produced having ETFE 532G-6405 base (first) coat which is top coated with super high-build clear ETFE 532G-6410. The ETFE 532G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with ETFE 532G-6405 at 40 psi. The ETFE 532G- 6405 layer was spray coated ETFE 532G-6410 at 40 psi and the pipe annealed by heating to 580 °F for 30 minutes. The ETFE 532G coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the ETFE 532G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the ETFE 532G coated copper pipe was measured to be 91 mL. The experiment was repeated twice and the amount of water collected was 105 mL in the second experiment and 93 mL in the third experiment. The average water collection was about 96 mL.

Condensation on copper pipe coated with PTFE 850G-204 top coated with low coefficient of friction PTFE 851G-214

A 1-inch diameter copper pipe was produced having PTFE 850G-204 base (first) coat which is top coated with low coefficient of friction PTFE 851G-214. The PTFE 850G/851G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PTFE 850G-204 at 40 psi and annealed by heating to 550 °F for 3 minutes. The PTFE 850G-204 layer was spray coated with PTFE 851G- 214 at 40 psi and the pipe annealed by heating to 800 °F for 5 minutes. The PTFE 850G/851G coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the PTFE 850G/851G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PTFE 850G/851G coated copper pipe was measured to be 90 mL. The experiment was repeated twice and the amount of water collected was 85 mL in the second experiment and 88 mL in the third experiment. The average water collection was about 88 mL.

Condensation on copper pipe coated with PFA 420G-703 top coated with PFA 532G-5010

A 1-inch diameter copper pipe was produced having PFA 420G-703 base (first) coat which is top coated with PFA 532G-5010. The PFA 420G/532G coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PFA 420G-703 at 40 psi. The PFA 420G-703 layer was spray coated with PFA 532G-5010 at 40 psi and the pipe annealed by heating to 750 °F for 15 minutes. The PFA 420G/532G coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the PFA 420G/532G coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PFA 420G/532G coated copper pipe was measured to be 60 mL. The experiment was repeated twice and the amount of water collected was 65 mL in the second experiment and 64 mL in the third experiment. The average water collection was about 63 mL.

Condensation on copper pipe coated with PFA 420G-703 top coated with FEP 532G-8110

A 1-inch diameter copper pipe was produced having PFA 420G-703 base (first) coat which is top coated with FEP 532G-8110. The PFA/FEP coated copper pipe was prepared by initial cleaning of a 1 inch diameter copper pipe by heating at 750 °F for 60 minutes. The copper pipe was then grit blasted with medium grit sand at 40 psi. The grit blasted copper pipe was spray coated with PFA 420G-703 at 40 psi. The PFA 420G-703 layer was spray coated FEP 532G-8110 at 40 psi and the pipe annealed by heating to 750 °F for 20 minutes. The PFA/FEP coated copper pipe was handled with care by wearing gloves to prevent any contamination. Ice cooled water was used to keep the surface of the PFA/FEP coated copper pipe at about 25 °C. Steam at a temperature of about 85 °C was produced inside the condensation tower. After 120 minutes the experiment was stopped. The amount of water gathered from condensation on the PFA/FEP coated copper pipe was measured to be 73 mL. The experiment was repeated twice and the amount of water collected was 70 mL in the second experiment and 72 mL in the third experiment. The average water collection was about 72 mL.

Table 1 below summarizes the amount water collected by each type of pipe.

Pipe First reading Second reading Third reading

Copper 66 ml 60 ml 63 ml

400 grit sanded copper 25 ml 45 ml 58 ml

ETFE 699-129 aqueous primer 96 ml 95 ml 92 ml PTFE 850G-204 Acid primer 70 ml 72 ml 71 ml

ETFE 699-129/532G-6410 221 ml 223 ml 215 ml

ETFE 532G-6405/532G-6410 91 ml 105 ml 93 ml

PTFE 850G-204/851G-214 90 ml 85 ml 88 ml

Primer 420G-703/PFA532G-5010 60 ml 65 ml 64 ml

Primer 420G-703/FEP532G-8110 73 ml 70 ml 72 ml

TABLE 1

Discussion

Lotus Leaf Effect "Micro and Nano Structure of the Lotus leaf

A scanning electron microscope images reveal that the leaves of the Lotus leaf are very rough and covered in micro-lumps and bumps of protruding epidermal (outermost) cells, which in turn, are covered in wax crystals around one nanometer in diameter. A schematic diagram of a lotus leaf micro- and nano- structure is shown in FIG. 5. The wax crystals are hydrophobic (water hating) and so they repel water and keep water from getting into the valleys between the bumps. The bumps minimize the area of contact. FIG. 6 depicts wetting of four different surfaces. The combination of these micro- and nano-scale features allow the spherical water drops to roll off the lotus leaf, which is the key to the cleaning process.

ETFE 699N-129 represents a "nano structure" surface. This primer, when it is baked, turns to a rough surface similar to sand paper rough surface because of the water base. ETFE 699N-129 water-base primer has a slightly rough with a dull, mottled look, and with small white specs (ETFE projected particles) are visible, which gives the surface of the pipe the lotus leaf effect. The height of the projected partials is controlled by the thickness of the primer applied to the surface of the pipe. This primer was able to hold the water on the top of the projected partials for the whole experiment. Each water droplet was very small and suspended by a single asperity. The lotus leaf is covered with structural hierarchy called protuberances. Protuberances have the shape of hemispheroids (which will give the surface of the leaf hills and valleys). These hemispheroids are covered with wax crystalloids that point outward. ETFE 532G-6410 high build top coat finish is tough, seamless, and with pinholes that gives the surface hills and valleys. When a topcoat ETFE 532G-6410 was added on top of ETFE 699N-129 primer, the surface of the pipe started to mimic the surface of the lotus leaf. The lotus leaf is made of microscopic bumps that are coated with a nanoscopic water-repellent coating (wax). The bumps minimize the area of contact and the water-repellent coating keeps water from getting into the valleys between the bumps allowing the spherical water drops to roll off the lotus leaf. ETFE with aqueous (water-base) primer was a better water repellent than ETFE with powder primer. This has to do with water base surface acts as a sealer so water won't penetrate into the surface.

The model with smooth surface experienced minimal repellency of liquid droplets but the model with rough surface experienced higher liquid droplet repellency. This was shown when ETFE aqueous (water-based) primer rough surface was compared with projected particles (specs) against PTFE aqueous (acid-based) primer rough surface without projected particles. Furthermore, this was also shown when ETFE 699N-129 with high-build topcoat ETFE 532G- 6410, which give the surface of the copper pipe a tough and seamless with pinholes (hills and valleys effect), was compared to other DuPont topcoats. ETFE 699N-129 has shown more repellency than all DuPont primers and topcoats. ETFE 699N-129 with ETFE 532G-6410 topcoat also will create a pipe that is ultraphobic (supper repellent).

In the case of ETFE 699N-129 water-based primer and ETFE 699N-129 with high build top coat 532G-6410 (double structured) surfaces very few droplets became non-spherical and flattened while the majority of the droplets surrounding the non-spherical droplets stayed very spherical. But when these non-spherical droplets slid down the side of the pipe and new droplets are formed in their place they were spherical until the experiment was stopped. Water droplets, once in contact with a surface, have adhesion forces that result in the wetting of the surface. Depending on the structure of the surface and the fluid tension of the droplet either complete or incomplete wetting may occur. Dirt particle build up on the lotus leaf will change the minimum contact area of the water droplet and changes the surface tension. Water droplets are able to minimize their surface adhesion by achieving a spherical shape and when the water droplets roll across the surface of the lotus leaf contaminates are picked up keeping the surface of the leaf clean. This cleaning mechanism is due to the adhesion between the dirt particle and the droplet, which is higher than between the particle and the surface. Unfortunately this self-cleaning mechanism does not work with organic solvents. If the pipe is dirty, then the initial droplets did not have good adhesion with surface of the pipe and became deformed. When the initial droplets slide down the side of the pipe, they pick up dirt due to a higher adhesion between the dirt particle and the water drop than the dirt particle with the surface of the pipe. Once the dirt containing droplet was removed from the pipe surface the new droplets were spherical till the end of the experiment.

It was noticed that use of a direct steam flow onto the coated pipes caused the condensation on the pipe become unpredictable and exhibits a continuous change in the condensation from dropwise to filmwise then to dropwise and so on. To prevent turbulent steam flow over the pipe, it was found that positioning the water collector in the path of the steam rising from the bottom diverts the direction of rising steam around the pipe. The idea is to have a heat transfer to the pipe to create condensation through temperature difference.

Conclusions

It has been shown that ETFE that is an excellent ultraphobic surface. ETFE 699N-129 aqueous primer is unique due to the fact it is made of solid fluorocarbon and hydrocarbon at the same time.

The surface of the pipe coated with ETFE 699N-129 water-base primer has a slightly rough with a dull, mottled look, and with small white specs (ETFE particles) are visible, which gives the surface of the pipe projection like the wax crystals on the lotus leaf.

ETFE 532G-6410 high build top coat finish is tough, seamless, and with pinholes that gives the surface hills and valleys. Adding the topcoat ETFE 532G-6410 on the top of ETFE 699N-129 primer produced a coating that mimics the surface of the lotus leaf. · It is believed that the reason DuPont ETFE 699N-129 can be deposited on a copper substrate, while ETFE 532G-6405 is difficult to apply, has to do with the fact that ETFE 699N- 129 is in a liquid form, which makes it melt while baking instead of burning off. So ETFE 699N-129 aqueous (water-based) primer is the only ETFE primer could be applied directly to metal surface without having to use topcoat. The topcoat could be added later to ETFE 699N-129 aqueous (water-based) primer.

Dependence of Macroscopic Wetting is on Nanoscopic ETFE surface Textures. The model with smooth surface experienced minimal repellency of liquid droplets but the model with rough surface experienced higher liquid droplet repellency. ETFE 699N-129 has shown more repellency than all DuPont primers and topcoats and the only thing was better than ETFE 699N- 129 is ETFE 699N-129 with ETFE 532G-6410 topcoat. · Copper pipe coated with ETFE 699N-129 aqueous prime with secondary projections was found to be superior hydrophobic surface and excellent repellent. A copper pipe coated with ETFE 699N-129 aqueous primer was repelling more water than other coated copper pipes with Teflon primers and was repelling more water than copper pipes with smooth Teflon top coats. ETFE 699N-129 aqueous primer showed it superiority when was top coated with ETFE high built top coat with seamless and tough surface which gave the surface of the pipe hills and valleys. The copper pipe was repelling at least twice more water than copper pipe with ETFE 699N-129 aqueous primer alone.

Supper hydrophobic surface is not the best solution as it will make it very difficult for heat to flow to the surface of the pipe through a full sphere of liquid drop. Primer 420G-703 top coated with PFA 532G-5010 is an example of such surface where the amount of water accumulated was the least and the droplets on the surface of the pipe were supper hydrophobic.

It is also not good to have a hydrophilic surface because it will prevent heat to flow through the film to the pipe. So a droplet with large contact area with condensing surface will act as filmwise condensation when heat tries to flow through it. Copper pipe with no top coat is an example of such surface.

Large droplets are also not good to have because they tend to prevent heat transfer from making pass through them. Small droplets on hydrophobic surface will have better chance to let heat flow to pipes. Primer 699N-129 is an example of surface with small droplets hanging on the top of asperity. Droplets on top of nano-structure have more chance to let heat flow underneath the droplet to the surface of the pipe. Primer 699N-129 is an example of such surface.

Also droplets on top of micro-structure have more chance to let heat flow underneath the droplet to the surface of the pipe. ETFE 532G-6405 powder primer top coated with supper high- build clear ETFE 532G-6410 is an example of such surface.

The best surface to for heat flow is Ultraphobic surface where the surface has a double structure of both micro structure bumps (hills and valleys) and nano structure wax crystals (specs) sticking out of the micro structure where it will allow more heat to flow to the conducting surface. Heat will be able to flow from underneath the wax crystals and between the hills and valleys to the condensing surface continuously thus increasing heat flow under the droplet to the condensing pipe. * * *

Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.