Behavior of Plasma-Treated Elastomeric Polydimethylsiloxane Coatings in Aqueous Environment

Plasma treatment is a useful way of enhancing the wettability of polydimethylsiloxane (PDMS). The subsequent recovery of hydrophobicity in air once treatment is discontinued is well known, but less has been reported about the effect of the storage environment. Water storage is the most relevant, with some reports that this stops the hydrophobic recovery of plasma-treated Medical Grade PDMS elastomer. This is not our experience with a commercial industrial PDMS sealant that had been treated by a helium radio-frequency plasma and stored in pure water and in artificial sea water. Substantial hydrophobic recovery occurs on storage in these environments. The commercial sealant is likely to have more low molecular weight diffusible species and more pre-existing silanol groups than the Medical Grade material. Both of these factors could affect the recovery mechanism by diffusion of untreated polymer chains to the surface or reorientation of polar and non-polar groups in the surface region.