Method for making surfactant-templated thin films

Abstract

An evaporation-induced self-assembly method to prepare a porous, surfactant-templated, thin film by mixing a silica sol, a solvent, a surfactant, and an interstitial compound, evaporating a portion of the solvent to form a liquid, crystalline thin film mesophase material, and then removal of the surfactant template. Coating onto a substrate produces a thin film with the interstitial compound either covalently bonded to the internal surfaces of the ordered or disordered mesostructure framework or physically entrapped within the ordered or disordered mesostructured framework. Particles can be formed by aerosol processing or spray drying rather than coating onto a substrate. The selection of the interstitial compound provides a means for developing thin films for applications including membranes, sensors, low dielectric constant films, photonic materials and optical hosts.

1. An evaporation-induced self-assembly method to prepare a liquid, crystalline film mesophase material, comprising:
 mixing a precursor sol, a solvent, a surfactant, and an interstitial compound to prepare a silica  sol, wherein said surfactant is at a concentration less than the critical micelle concentration; and  
 evaporating a portion of the solvent from said silica  sol to form a liquid, crystalline, film mesophase material.  
 
     
     
       2. The method of  claim 1  further comprising the step of heating said liquid, crystalline, film mesophase material to form a surfactant-templated film. 
     
     
       3. The method of  claim 2  wherein the step of heating removes a portion of said surfactant. 
     
     
       4. The method of  claim 3  wherein the surfactant-templated film has pores of diameter of approximately less than 200 Å. 
     
     
       5. The method of  claim 3  wherein the surfactant-templated film has a surface area greater than approximately 100 cm 2 /cm 2  film surface. 
     
     
       6. The method of  claim 1  wherein the interstitial compound is physically entrapped within said liquid, crystalline, thin  film mesophase material. 
     
     
       7. The method of  claim 1  wherein the precursor sol is selected from the group consisting of tetraethylorthosilicate  tetramethylorthosilicate, tetraethylorthosilicate, titanium butoxide, titanium iso-propoxide, zirconium n-butoxide, aluminum iso-propoxide,  and aluminum iso-propoxide. 
     
     
       8. The method of  claim 1  wherein the interstitial compound is selected from the group consisting of organoalkoxysilanes, proteins, dyes, and metal-containing compounds. 
     
     
       9. The method of  claim 8  wherein the interstitial compound is selected from the group consisting of tridecafluoro-1,1,2,2,-tetrahydrooctyltriethoxysilane, mercaptopropyltrimethoxylsilane, rhodamine B, cytochrome c, and 3-(2,4-dinitrophenylamino)propyl(triethoxy) silane. 
     
     
       10. The method of  claim 2  wherein the surfactant-templated film is an ordered material with at least two x-ray diffraction peaks in the range 2θ=0.5-10°. 
     
     
       11. The method of  claim 2  wherein the surfactant-templated film is a disordered material with one x-ray diffraction peak in the range 2θ=0.5-7°. 
     
     
       12. The method of  claim 2  wherein the surfactant-templated film is exposed to ammonia vapor to promote condensation. 
     
     
       13. The method of  claim 1  wherein the surfactant is selected from the group consisting of sulfates, sulfonates, phosphates, carboxylic acids, alkylammonium salts, gemini surfactants, cetylethylpiperidinium salts, dialkyldimethylammonium, primary amines, poly (oxyethylene) oxides, octaethylene glycol monodecyl ether, octaethylene glycol monohexadecyl ether and block copolymers. 
     
     
       14. The method of  claim 1  wherein the solvent is selected from the group consisting of an alcohol, formamide, and tetrahydrofuran. 
     
     
       15. The method of  claim 1  wherein the step of  evaporating a portion of the solvent is performed by a method selected from the group consisting of spin-coating, spray-coating, dip-coating, and aerosol processing. 
     
     
       16. The method of  claim 15  wherein the silica  sol is coated onto a substrate by a method selected from the group consisting of spin-coating, spray-coating, and dip-coating. 
     
     
       17. The method of  claim 16  wherein said substrate is selected from the group consisting of a crystal silicon wafer and a piezoelectric crystalline quartz substrate. 
     
     
       18. The method of  claim 1  wherein the interstitial compound is selected from the group consisting of a hydrophobic molecule, an oligomer, and a polymer. 
     
     
       19. An evaporation-induced self-assembly method to prepare a porous, surfactant-templated film, comprising:
 mixing tetraethylorthosilicate, alcohol, water, an acid, a surfactant, and tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane, wherein said surfactant is at a concentration less than the critical micelle concentration, to form a homogeneous mixture;  
 coating a substrate with said homogeneous mixture, said coating inducing evaporation of a portion of the solvent to produce a liquid, crystalline film mesophase material; and  
 heating said liquid, crystalline film mesophase material to decompose said surfactant, forming a porous, surfactant-templated film.  
 
     
     
       20. The method of  claim 19  wherein the surfactant is cetyltrimethylammonium bromide. 
     
     
       21. The method of  claim 20  wherein the molar ratios of tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane:tetraethylorthosilicate:alcohol:water: cetyltrimethylammonium bromide are 0.15:0.85:21.8:5.1:0.0053.