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 µm) are prepared and their water vapor transmission rates and permeability values are determined. Vapor transm...

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Bibliographic Details
Published in:Macromolecular rapid communications. 2021-03, Vol.42 (5), p.e2000682-n/a
Main Authors: Bian, Pei, Wang, Yan, McCarthy, Thomas J.
Format: Article
Language:English
Subjects:
anti‐fogging
anti‐icing
aquaporin
Aquaporins
Carbon nanotubes
Film thickness
Hydrophobicity
Membrane permeability
membranes
Nanotechnology
Nanotubes
Permeability
Polydimethylsiloxane
Silica
Silicon dioxide
Silicone resins
Silicones
Thin films
Variable thickness
water permeation
Water purification
Water treatment
Water vapor
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Summary: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 µm) 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 µm, but does not increase further when the film thickness is decreased to 8 µm. 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. Polydimethylsiloxane films are water‐repellent yet highly permeable to water vapor. Water vapor transmission rates increase as membrane thickness decreases to ≈15 µm, but does not increase further below this value. A mechanism for the anomalous water permeation rates is offered based on those proposed for nanoscopically confined water in carbon nanotubes and aquaporins.
ISSN:1022-1336
1521-3927
DOI:10.1002/marc.202000682