Hyper-cross-linked thin polydimethylsiloxane films

Polydimethylsiloxane (PDMS) elastomers are widely used in many applications, such as in microfluidic devices or as membranes. These slightly cross-linked PDMS networks suffer from severe swelling upon contact with, especially non-polar, organic solvents, thereby drastically reducing the performance of the device. Here, we report on a new method to prepare ultra-thin, highly cross-linked PDMS films in a localized fashion by the interfacial polymerization of PDMS with polyhedral oligomeric silsesquioxane (POSS). The resulting thin poly(PDMS-POSSimide) films (150 nm) showed to have a drastic reduction in swelling upon contact with n-hexane vapor (15-fold decrease) and ethyl acetate vapor (5-fold decrease). These poly(PDMS-POSSimide) films showed an increase in swelling upon contact with ethanol vapor (up to a 4-fold increase) as compared to conventional PDMS. We attribute this increase in swelling to the enhanced affinity for polar solvents of these poly(PDMS-POSSimide) films due to the presence of positively charged ammonium groups. Despite the highest swelling in ethanol, the poly(PDMS-POSSimide) films are found to have extremely low ethanol permeances (