Poly(dimethylsiloxane), PDMS, is by far the most important silicone material and is used, as a neat liquid (oil), crosslinked solid (elastomer), or component of a more complex system, in an extremely wide array of applications and technologies. The interactions that PDMS-based materials have with water vary as well - in interesting ways that are not seen with other materials and that are counter-intuitive to most scientists who have been trained in modern materials science and chemistry curricula. PDMS is "hydrophobic" and PDMS-based materials are used to impart water repellency to solids in multiple applications. PDMS oil, however, spreads on water as a molecular layer (Langmuir monolayer) that can be compressed and transferred to solid substrates. Surprising to most is that cross-linked PDMS materials exhibit extremely high water permeability. This high permeability is the basis of moisture-cured RTV silicones, but is also apparently inconsistent with its hydrophobic, water-repellent nature.<br/> <br/>Quantitative data on both water repellency and water permeability of model silicone systems will be discussed. In particular, we will discuss the mechanism of water vapor transport in silicone membranes and how the thickness and surface chemistry of the membranes affect permeation. We will also discuss water contact angle hysteresis and how the molecular weight of the silicone can affect water repellency.<br/>

Rediscovering silicones: Water repellency and water permeability

253rd National Meeting (2017)

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