BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a process for preparing

fluorinated, inorganic hollow nanospheres, more particularly to a process for preparing fluorinated, inorganic hollow nanospheres using water-based silica precursors and their use in coating compositions.

Description of the Related Art

Nanospheres are submicroscopic colloidal systems composed of a solid or liquid core surrounded by a thin polymer or inorganic shell. This solid or liquid core is removed to form hollow nanospheres. Such core- shell systems may be prepared from micro or miniemulsions via

polymerization reaction at the interface of the droplets, the so-called interfacial polymerization reaction. Interfacial polymerization occurs at the interface of two immiscible phases, for example, oil and water, and a thin shell is formed. In the formation of the shell, the monomers are in either oil or water phase to participate in the reaction. Typically, for the

preparation of core-shell nanocapsules via interfacial polymerization, an microemulsion or miniemulsion is first prepared, either water in oil or oil in water, wherein in the former nanocapsules with an aqueous core suspended in oil are formed and in the latter nanocapsules with an oily core suspended in water are formed. Existing processes for the

preparation of fluorinated inorganic hollow particle dispersions often involve using polymer spheres as hard template or produce hollow particles of unwanted large-size aggregation in addition to hollow particles.

A need exists for a process for preparing fluorinated inorganic hollow particle dispersions via an interfacial miniemulsion sol-gel reaction without using a hard polymer template. SUMMARY OF THE DISCLOSURE

In a first aspect, the disclosure provides a process for preparing a fluorinated silica hollow nanosphere comprising:

(a) providing a mixture comprising water, at least one non-reactive solvent; at least one fluorosilane having a general formula

R _f (CH ₂ ) _m SiR _x (OR') _y or R _f (CH ₂ ) _m -A-C(O)-NH-(CH ₂ ) _n SiR _x (OR') _y where, Rf is a linear or branched perfluoroalkyi group containing 1 -10 carbon atoms, m = 1 -5, n = 1 -5, R is a linear or branched alkyl group containing 1 -12 carbon atoms, R' is a linear or branched alkyl group containing 1 -4 carbon atoms, x = 0-2, y = 1 -3 x + y = 3, A = O or NH; at least one water based silica precursor solution; and at least one surfactant;

(b) shearing the components of the mixture from (a) with high shear energy at an energy density of at least 10^6 J/m^3 to form a mini- emulsion; and

(c) initiating a one-step sol-gel reaction forming fluorinated hollow silica nanospheres having a particle size of less than about 400nm.

By non- reactive solvent we mean that the solvent does not substantially react, more typically does not react, with any of the other components added to the reaction.

DETAILED DESCRIPTION OF THE DISCLOSURE

In this disclosure "comprising" is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Additionally, the term "comprising" is intended to include examples encompassed by the terms "consisting essentially of and "consisting of." Similarly, the term "consisting essentially of is intended to include examples encompassed by the term "consisting of."

In this disclosure, when an amount, concentration, or other value or parameter is given as either a range, typical range, or a list of upper typical values and lower typical values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or typical value and any lower range limit or typical value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the disclosure be limited to the specific values recited when defining a range.

In this disclosure, terms in the singular and the singular forms "a," "an," and "the," for example, include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to "fluorinated silica hollow nanosphere", "the fluorinated silica hollow nanosphere", or "a fluorinated silica hollow nanosphere" also includes a plurality of fluorinated silica hollow nanospheres

The disclosure relates to a process for preparing an inorganic hollow particle dispersion using fluorosilanes and water-based silica precursors. These fluorinated inorganic hollow particle dispersions are useful as hiding or opacifying agents in coating and molding compositions. They also provide easy-clean property in coatings. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

The dispersion has a solids concentration of at least about 2 wt% solids, more typically about 2 wt% to about 10 wt%, still more typically about 2 wt% to about 5 wt%,

These nanospheres have a particle size of less than about 400nm, more typically about 5 nm to about 400 nm, still more typically about 50 nm to about 300 nm, and most typically about 100 nm to about 250 nm.

The disclosure provides a process for preparing a fluorinated silica hollow nanosphere comprising:

(a) providing a mixture comprising water, at least one non-reactive solvent; at least one fluorosilane having a general formula

R _f (CH ₂ ) _m SiR _x (OR')y or R _f (CH ₂ ) _m -A-C(O)-NH-(CH ₂ ) _n SiR _x (OR') _y where, Rf is a linear or branched perfluoroalkyl group containing 1 -10 carbon atoms, m = 1 -5, n = 1 -5, R is a linear or branched alkyl group containing 1 -12 carbon atoms, R' is a linear or branched alkyl group containing 1 -4 carbon atoms, x = 0-2, y = 1 -3 x + y = 3, A = O or NH; at least one water based silica precursor solution; and at least one surfactant; (b) shearing the components of the mixture from (a) with high shear energy at an energy density of at least 10^6 J/m^3 to form a mini- emulsion; and

(c) initiating a one-step sol-gel reaction forming fluorinated hollow silica nanospheres having a particle size of less than about 400nm.

The non-reactive solvent may be an alkane, a hydrocarbon oil, aromatic hydrocarbon or halogenated hydrocarbon liquid, more typically alkane or hydrocarbon oil. The non-reactive solvent is typically present in the amount of about 65 wt% to about 99 wt%, based on the total weight of all components.

The fluorosilane has a general formula R _f (CH ₂ ) _m SiR _x (OR') _y or R _f (CH ₂ ) _m -A-C(O)-NH-(CH ₂ ) _n SiR _x (OR') _y wherein Rf is a linear or branched perfluoroalkyl group containing 1 -10 carbon atoms, m = 1 -5, n = 1 -5, R is a linear or branched alkyl group containing 1 -12 carbon atoms, R' is a linear or branched alkyl group containing 1 -4 carbon atoms, x = 0-2, y = 1 -3, x + y = 3, A = O or NH. The fluorosilane may be 1 H,1 H,2H,2H- Perfluoalkyltriethoxysilane, Dimethoxy-methyl(3,3,3-trifluoropropyl)silane, Trimethoxy(3,3,3-trifluoropropyl)silane, or 3,3,4,4,5,5,6,6,7,7,8,8,8- Tridecafluorooctyl [3-(triethoxysilyl)propyl]carbamate or

3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl [3-(triethoxysilyl)propyl]urea more typically 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane or

1 H,1 H,2H,2H-Perfluorodecyltriethoxysilane. The fluorosilanes above are commercially available from Sigma-Aldrich or can be prepared via the reaction of trial koxysilylalkylisocyante with fluorinated alcohols or fluorinated amines to provide corresponding carbamates, or ureas. The fluorsilane is typically present in the amount of about 1 wt% to about 50 wt%, based on the total weight of all silica precursors.

At least one surfactant is part of the mixture in step (a). Some suitable surfactants include cetyltrimethylammonium bromide (CTAB), Lauryltrimethylammonium bromide, dodecyltrimethylammonium bromide, octyltrimethylammonium bromide, sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), dioctylsulfosuccinate, or nonionic surfactants such as alkylphenol polyoxyethylene, polyoxyethylene glycol alkyl ethers, polyoxypropylene glycol alkyl ethers, octylphenol ethoxylates, or poloxamers, more typically CTAB or octylphenol ethoxylates. Some useful commercially available surfactants series include Triton X ^® manufactured by The Dow Chemical Company, Brij ^® manufactured by Croda International PLC, or Pluoronic ^® manufactured by BASF. The surfactant concentration is about 0.001 wt % to about 5 wt %, more typically about 0.1 wt% to about 2 wt%, based on the total weight of all components.

The water-based silica precursor is sodium silicate, potassium silicate, ammonium silicate or pre-formed silicic acid; more typically sodium silicate or potassium silicate; and still more typically sodium silicate. The concentration of water-based silica precursor is about 0.005 wt% to about 10 wt%, more typically about 0.005 wt% to about 5 wt%,; water to oil ratio is about 0.01 to about 0.55, more typically about 0.05 to about 0.25; and surfactant concentration is about 0.001 wt % to about 5 wt %, more typically about 0.1wt% to about 2 wt%, based on the total weight of all components. The water phase comprises water, water-based silica precursor and surfactant and the oil phase comprises at least one non- reactive solvent; and at least one fluorosilane having a general formula R _f (CH ₂ ) _m SiR _x (OR')y or R _f (CH ₂ ) _m -A-C(O)-NH-(CH ₂ ) _n SiR _x (OR') _y where, Rf is a linear or branched perfluoroalkyl group containing 1 -10 carbon atoms, m = 1 -5, n = 1 -5, R is a linear or branched alkyl group containing 1 -12 carbon atoms, R' is a linear or branched alkyl group containing 1 -4 carbon atoms, x = 0-2, y = 1 -3 x + y = 3, A = O or NH. It is important because the combination of silica precursor concentration, water to oil ratio and surfactant level determine the particle size, hollow or non-hollow particle structure, and allow high % solid hollow silica synthesis.

The mixture in step (a) may be prepared in any glass container or stainless steel reaction vessel and then sheared at an energy density of at least 10^6 J/m^3, more typically about 10^7 J/m^3 to about 5*10^8 J/m^3, to form a mini-emulsion. Some useful means for shearing include an ultrasonic disruptor, high speed blender, high pressure homogenizer, high shear disperser, membrane homogenizer or colloid mill, more typically an ultrasonic disruptor, high speed blender, or a high pressure homogenizer. Typically shearing occurs for a period of about 5 to about 120 minutes depending on amount of emulsion needed to be prepared and desired emulsion size range, more typically about 30 minutes to about 60 minutes. Typically, shearing is accomplished at room temperature.

Optionally, a defoamer may be needed to avoid foaming during

emulsifying. Some suitable defoamers include BASF's Foamaster®, Dow Corning® 71 and 74 Antifoams.

A sol gel reaction or process is a method used for

fabrication of solid metal oxides materials, especially the oxides of silicon and titanium, from small molecules. The process involves conversion of monomers (precursors) into a colloidal solution that later on turns into an integrated network (or gel) of particles or network polymers.

A one-step sol-gel reaction of this disclosure is initiated using the mini-emulsion formed in step (b), by holding it at room temperature or about 20 °C to about 90 °C with or without stirring for several hours to allow the silica precursors to diffuse to the oil/water interface, where they hydrolyze and condense to form a silica shell resulting in silica hollow particles having a particle size of less than about 400 nm being formed. The pH is typically adjusted between 4 and 10 prior for initiation of the one step sol gel process.

Typically the miniemulsion is held for several hours, more typically at least about 4 hours to form, in one step, a fluorinated hollow silica nanosphere having a particle size of less than about 400nm. The one- step sol-gel reaction may be initiated at room temperature, more typically about 20 °C to about 90 °C, and still more typically about 20 °C to about 70 °C. Heating may be accomplished using hot plate, heating mantle or any other heating method. pH adjustment in step (d) may be achieved using any reasonable choice of acid or base.

Applications:

These inorganic hollow particle dispersions are useful as hiding or opacifying agents in coating and molding compositions. They also provide water and oil repellency, easy to clean and or dirt-pickup resistance properties in coating and molding compositions. They are also useful as drug delivery systems in the pharmaceutical and medical industries; in food, personal care and cosmetics; and agriculture.

EXAMPLES

Example 1 :

A water/oil mixture which contains 250 g of kerosene, 5 g of 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane and 20 g of Triton X-45 ^® is first prepared and added to a water solution which contains 45 g of water, 3.7 g of CTAB,10 g of sodium silicate solution and 0.2 g of defoamer

(Foamaster® 1 1 1 , BASF). Miniemulsification is achieved by shearing the mixture for 30 minutes with a high speed blender at 9500 rpm. After forming a stable water-in-oil miniemulsion, the sol-gel reaction is initiated by adjusting the pH to about 6 by adding butyric acid and then letting the mixture sit overnight. The sodium silicate is expected to hydrolyze and condense to form a silica shell at the oil/water interface resulting in flunorinated silica hollow particles.