Silicone elastomers are known for their relatively high hydrophobicity due to inherently low surface energy, and to the high mobility of the silicone chains.  The latter feature of silicones accounts for their 'surface reversion'.  Even if they are temporarily made hydrophilic by oxidative surface modification, or by grafting hydrophilic polymers, silicone surfaces soon return in air to their hydrophobic character.  Silicone superwetting surfactants (RO-(EO)n-link-siloxane) are used to disperse pesticides across leaves.  We have discovered that silicones are permanently rendered highly wettable (water contact angle < 10�) after the surface is grafted with superwetting chains.  The wettability of the surface is affected by the chain length of the ethylene oxide oligomer, and by the density of wetting groups on the surface.   Freshly prepared surfaces stored at ambient humidity achieve the low contact angle after a few seconds.  By contrast, after storing in air for a year, or after dehydrating the surface at 80 �C, it can take up to one minute for the wetting to occur.  Key elements of the wetting process thus appear to be the hydration of the PEG oligomers and appropriate choice of surface density of the wetting agents.  The origins of the wetting behavior will be discussed.

Permanently water wettable silicone elastomers

243rd National Meeting (2012)

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