Template synthesis of raspberry-like polystyrene/SiO2 composite microspheres and their application in wettability gradient surfaces

A method to fabricate wettability gradient surface with raspberry-like composite microspheres was described. The synthesis of composite microspheres was through the ethanol sol–gel processing of TEOS on carboxyl functionalized polystyrene (PS) template particles. The factors influencing the raspberry-like morphology and the deposition efficiency of SiO2 onto templates were discussed, including the surface carboxyl density, TEOS amount and water amount, and the optimal formulation of synthesis was given. The wettability gradient surface was built up by coating the suspension prepared on substrate and putting it in thermal gradient field for heat treatment. The resultant surface demonstrated wettability gradient from hydrophobic to superhydrophilic with the increasing of calcination temperature, which was because the physical topography of surface changed gradually from spike-type into pore-type and the main chemical compositions changed from polystyrene into SiO2.