Superhydrophobilization of SiO2 surface with two alkylsilanes for an application in oil/water separation

This study reported a novel approach to superhydrophobilize silica (SiO2) surface by silanizing with two alkylsilanes including non-polar short hydrocarbon chains of chlorotrimethylsilane (CTMS) followed by long hydrocarbon chains of octadecyltrichlorosilane (OTS). The silanization of CTMS prior to OTS affected the increase in the density of short and long alkyl chains throughout SiO2 surface resulting in the surface with low surface energy and high degree of hierarchical micro-nanoscale roughness which were responsible for the superhydrophobicity. The oil/water separation filters prepared by coating cotton fabric with the CTMS- and OTS-modified SiO2/polystyrene (PS) composite using a weight ratio of the modified SiO2:PS at 2:1 possessed the highest water contact angles of 156 degrees +/- 1 degrees. The superhydrophobic/superoleophilic filters showed excellent water repellent, oil/water separation efficiency, and reusability. The results obtained in this study suggest that salinizing the two different structure alkylsilanes, CTMS followed by OTS, can provide synergetic benefit in improving the superhydrophobicity by enhancing the density of alkyl chains on SiO2 surface. This alternative strategy can be extensively applied for development of other superhydrophobic materials.