Polyurethane-silica composite-based coating composition, polyurethane-silica composite film, and method of preparing the same

1. A method for preparing a polyurethane-silica composite film, comprising the steps of:

(a) preparing polystyrene particles;

(b) preparing silica-polystyrene particles by admixing the polystyrene particles with silica nanoparticles;

(c) preparing amphiphilic silica nanoparticles by subjecting the silica-polystyrene particles to a first surface treatment, removing the polystyrene particles, and then subjecting the remaining silica nanoparticles to a second surface treatment,

(d) preparing a coating composition by admixing the amphiphilic silica nanoparticles with polyurethane; and

(e) applying the coating composition to a surface of a substrate to form a coating layer, and curing the coating layer.

2. The method of claim 1 , further comprising, in step (a):

preparing a styrene fluid admixture by placing a styrene monomer and a solvent in a reactor, and stirring under a nitrogen atmosphere for a predetermined time; and

heating the styrene fluid admixture to a predetermined temperature, and

adding an initiator to the reactor and reacting the styrene fluid admixture with the initiator.

3. The method of claim 2 , wherein the solvent comprises one or more selected from the group consisting of water, ethanol, methanol, ethyl acetate, chloroform, and hexane.

4. The method of claim 2 , wherein the styrene fluid admixture is heated to a temperature of 60° C. to 70° C.

5. The method of claim 2 , further comprising adding a surfactant or a stabilizer to the styrene fluid admixture.

6. The method of claim 2 , wherein the initiator comprises 2,2′-azobis(2-methylpropionamidine)dihydrochloride.

7. The method of claim 1 , further comprising in the step (b),

preparing the silica-polystyrene particles by admixing and stirring a polystyrene solution comprising the polystyrene particles and a first silica solution comprising silica nanoparticles at a volume ratio of 1:1 for a predetermined time.

8. The method of claim 7 , further comprising, in the step (b), adding sodium chloride solution having a concentration of 0.1 mM to 10.0 mM to the admixture of the polystyrene solution and the first silica solution.

9. The method of claim 1 , further comprising, in the step (c):

subjecting the silica-polystyrene particles to a first surface treatment by adding the silica-polystyrene particles either to i) a first compound having a carboxyl group and an amine group or ii) a second compound having a carboxyl group and a fluorine functional group, and stirring;

adding the silica-polystyrene particles, after the first surface treatment, to tetrahydrofuran, and removing the polystyrene particles; and

subjecting the silica particles, which remain after removing of the polystyrene particles after the first surface treatment, to a second surface treatment by adding the silica particles to a compound, wherein the compound comprises the first compound or the second compound, which is not used in the first surface treatment, and stirring the silica particles and the compound.

10. The method of claim 9 , wherein the first compound comprises N-(tert-butoxycarbonyl)-β-alanine.

11. The method of claim 9 , wherein the second compound comprises perfluorooctanoic acid.

12. The method of claim 1 , further comprising, in the step (d):

preparing a second silica solution by dispersing the amphiphilic silica nanoparticles in tetrahydrofuran;

preparing a polyurethane solution comprising polyurethane and a curing agent; and

preparing the coating composition by admixing the polyurethane solution with the second silica solution.

13. The method of claim 1 , wherein the coating composition comprises the silica nanoparticles in an amount of 0.3 wt % to 10.7 wt % based on the total weight of the coating composition.

14. The method of claim 1 , wherein, in the step (e), the coating layer is cured at a temperature of 60° C. to 90° C.