Applicability of Cassie–Baxter equation for superhydrophobic fluoropolymer–silica composite films

Abstract

In this study, surface topographies and wettabilities of flat and composite rough films of perfluoro-styrene (TM/S) random copolymers with silica particles were investigated. The water and oil repellencies of flat TM/S copolymer and rough silica-TM/S composite surfaces were studied with varying perfluoro and silica contents. Increase in silica content resulted in an increase in water contact angle values; water contact angle values increased from 113° up to 170°, and the resultant surfaces were showing extremely superhydrophobic behavior depending on their silica contents. However a decrease in hexadecane contact angles from 61° to 25° depending on both silica %wt and perfluoro content of the TM/S copolymer was seen. Applicability of Cassie–Baxter equation was also investigated for TM/S copolymer films with silica particles. The results showed that Cassie–Baxter equation cannot be used for superhydrophobic surfaces, however, can be applied to oleophilic surfaces with caution. The oil repellencies of TM/S flat films in the terms of contact angle hysteresis was also compared with perfluoroethyl alkyl methacrylate–methyl methacrylate copolymer (TM/MMA) by using oil drops with varying surface tensions between 20.9mN/m and 26.9mN/m. The surface oleophobicities were changed according to the characteristics of the functional groups of MMA and S. The dependency of work of adhesion results of TM/S flat surfaces on wt.% of perfluoroalkyl content was also examined.