Rational tuning of the viscosity of membrane solution for the preparation of sub-micron thick PDMS composite membrane for pervaporation of ethanol-water solution

The cost of polymer membranes significantly affects their industrial applications, which is inversely proportional to their thickness. Hence, to economically realize the industrial applications of polymer membranes, their thickness should be reduced. In this work, a facile and scalable coating method was used to fabricate thin pervaporation composite membranes. The viscosity of the membrane solution and the hydrodynamic diameter of the polymer coil in heptane were optimized. Polydimethylsiloxane/polytetrafluoroethylene composite membranes with thickness as low as 700 nm could be obtained. The composite membranes showed an amorphous structure with almost constant surface hydrophobicity, and a flux as high as 2.4 kg/(m²·h) can be obtained while the separation factor sustains 8.6 at 40 °C for the separation of 5 wt% ethanol-water solution. The effects of the feed pressure, feed temperature, and vapor permeation and substrates on their performance were investigated. Results showed that too low or too high viscosity of membrane solution is not suitable for the formation of the membrane without defects. This also indicated that the coating method developed in this study, using an optimum membrane solution viscosity, is an efficient approach for the large-scale fabrication of sub-micron-thick membranes.