Loss and recovery of hydrophobicity and surface energy of HTV silicone rubber

Abstract

The loss of surface hydrophobicity of high temperature vulcanized (HTV) silicone rubber (SIR) due to immersion in saline solutions (0.005 to 100 mS/cm) has been studied as a function of immersion time (0 to 576 h) and temperature (0 to 98/spl deg/C). The subsequent recovery of the hydrophobicity in air is determined also. The loss and recovery of the hydrophobicity is correlated with the absorption of water during immersion and its subsequent desorption in air. The hydrophobicity is determined by measuring the static contact angle /spl theta/ between the tangent to a droplet of distilled water and the horizontal HTV-SIR surface. The surface energies /spl gamma//sub S/, /spl gamma//sub SD/ and /spl gamma//sub SH/ of HTV-SIR, the energy of adhesion W/sub SL/ and the surface tension /spl gamma//sub SL/ of water to HTV-SIR were determined as a function of time of immersion (loss of hydrophobicity), the time of recovery of hydrophobicity and the contact angle of water. For virgin HTV-SIR at 24.5/spl plusmn/3.5/spl deg/C the surface energies were determined to be /spl gamma//sub S/=31.6 mJ/m/sup 2/, /spl gamma//sub SD/=28.5 mJ/m/sup 2/, /spl gamma//sub SH/=3.1 mJ/m/sup 2/, W/sub SL/=61.4 mJ/m/sup 2/ and /spl gamma//sub SL/=43.0 J/m/sup 2/. These values are in reasonable agreement with the literature.