Separation performance of alcohol-induced silk fibroin membranes with homogeneous and heterogeneous microstructures

Abstract

Biological membranes were prepared from silk fibroin (SF) to investigate the mechanism SF microstructure that induced by different alcohols (C1–C4OH). SF membranes which were induced by less carbon of alcohols had a more hydrophilic surface (∼44.4°) than that induced by multi-carbon alcohol (∼80.5°). Positron annihilation spectrum showed that treating SF membrane using highly polar methanol/water generates heterogeneous structures. The internal hydrophobic segment had more β-sheets and smaller free volume than the internal hydrophilic segments because the latter flipped over to the surface. Consequently, the methanol/water-induced SF membrane showed excellent isopropyl alcohol separation efficiency. The low polar butanol/water-induced SF membranes formed homogeneous structures with a more hydrophobic surface and a larger total free volume than the methanol/water-induced SF membranes. Therefore, the crystallinity of the SF membranes could be controlled through different alcohols/water treatment, where the homogeneous phase could transform into the heterogeneous phase.