Surface microstructure evolution of polytetrafluoroethylene microporous materials by a casting–lyophilization–calcining (CLC) method

Abstract

This study aims at manipulating the surface microstructure of polytetrafluoroethylene (PTFE) microporous materials via a novel casting–lyophilization–calcining (CLC) process. In the CLC process, the emulsion consisting of polyvinylidene fluoride (PVDF), sodium dodecyl benzene sulfonate (SDBS) and distilled water was firstly poured onto the surface of the PTFE microporous materials and then the PTFE materials covered by the emulsion were sintered after removal of the distilled water by lyophilization. The results indicate that a compact thin PVDF layer can be easily constructed on the surface of the PTFE microporous materials by controlling the wetting state transition, which can be easily handled by regulating the SDBS concentration in the CLC process. The bubble point is enhanced owing to the compact PVDF layer on the surface, leading to a higher collection efficiency. In addition, the average pore size, porosity and thickness can be easily manipulated by controlling the SDBS concentration and PVDF mass fraction. Finally, the filtration mechanism changes from depth filtration to surface filtration, which brings about a higher air flux recovery. We hope such a novel process could be potentially useful in the surface microstructure regulation of polymer microporous materials with low surface energy.