Pyrolyzed polysiloxane membranes with tailorable hydrophobicity, porosity and high specific surface area

Abstract

Polysiloxane precursors with either only methyl moieties or methyl and phenyl groups are used for the preparation of graded structures with adjustable hydrophobicity, macroporosity and specific BET surface area. We demonstrate how the membrane properties can be controlled by adjusting the precursor ratio, the applied pyrolysis temperature as well as the sieving fraction of the precursor powder. The surface characteristics are evaluated by contact angle measurements and compared with data from vapor sorption experiments. Water contact angles can be adjusted from about 100° to 140° depending on the precursor type used during pyrolysis at 630°C, while featuring a high specific BET surface area from 419 to 534m2/g. The contact angles can be decreased to values between about 80 and 100° by pyrolysis at 700°C. Graded membranes are synthesized by using different precursor ratios and applying a one-step pyrolysis process. The macroporosity is controlled by the sieving fraction of the precursor powder. The obtained graded membranes have a high potential for a variety of applications in separation processes.