Rediscovering Silicones: The Anomalous Water Permeability of Hydrophobic PDMS Suggests Nanostructure and Applications in Water Purification and Anti-Icing

Cross-linked polydimethylsiloxane (PDMS) is simultaneously water-repellent and highly permeable to water vapor. Unfilled and silica-free cross-linked PDMS films of variable thickness (8-160 mu m) are prepared and their water vapor transmission rates and permeability values are determined. Vapor transmission rate increases as membrane thickness decreased from 160 to 15 mu m, but does not increase further when the film thickness is decreased to 8 mu m. Rate-limiting sorption is implicated as the cause of this effect and substantiated by a surface modification to enhance adsorption rate. Water vapor does not macroscopically condense on films thin enough to operate in this kinetic regime, and vapor transmission rates as high as 60% of the transmission rates through air are measured. A mechanism for water permeation is offered based on those proposed for nanoscopically confined water in carbon nanotubes and aquaporins.

Automated summary

Cross-linked polydimethylsiloxane (PDMS) is water-repellent and highly permeable to water vapor. The vapor transmission rate increases as the membrane thickness decreases, but does not further increase when the film thickness is decreased to a certain level. The mechanism for water permeation is based on proposals for nanoscopically confined water in carbon nanotubes and aquaporins.