Cross-Linking Nanometer-Sized Reactive Spherosilicates to Synthesize Tuneable Hydrophobic POSiSil Foams Suitable for Applications as Sensors

Thin hydrophobic polyoligosiloxysilicone (POSiSil) films were synthesized on silicon wafer substrates by spin coating reactive nanometer-sized spherosilicate solutions. Surface roughness was spontaneously induced due to the generation of HCl gas bubbles during the coating procedure, involving the cross-linking and solidification of spherosilicates. Variations in the coating solution and/or relative humidity during the curing phase allowed for a degree of precision in controlling this roughness, thereby impacting parameters such as the porosity and the static contact angle of water on the surface. The introduction of Pluronic 123 into the coating solution, followed by a calcination step after curing, was employed to further augment the surface roughness and porosity. Coatings characterized by uniform foam-like morphologies were synthesized, exhibiting static water contact angles as elevated as 135°. These hydrophobic POSiSil thin films with thicknesses in the nanometer scale have minimal interaction with water, as evidenced by wetting experiments conducted during the ellipsometry. The films also demonstrate the high chemical and thermal stability with no change in the morphology or static contact angle with water. The presence of significant surface area, resulting from the foam-like matrix, coupled with its innate hydrophobic properties and a relatively simple and easily attainable synthesis process, bestows upon the POSiSil coatings considerable potential across a broad spectrum of applications. One noteworthy application includes their use in the detection of volatile organic compounds.