Effects of water salinity, electric stress and temperature on the hydrophobicity of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) is widely employed in electrical insulation systems, which demands a high stability against degradation due to the effects of salinity and oxidation in the presence of moisture. PTFE can be used at high temperatures up to 250/spl deg/C. In this paper a study on the loss of hydrophobicity of PTFE in the presence of moisture, different sailinities and temperatures is reported. The hydrophobicity is a property of the surface, which gives indication of the degree of resistance to the formation of a continuous film of water. The loss of hydrophobicity is due to the degradation of the material in wet and polluted conditions. PTFE specimens were immersed in saline solutions where the conductivity was varied from 5 /spl mu/S/cm to 100 mS/cm. The temperature of the solutions were 23/spl plusmn/2, 44/spl plusmn/2 and 73/spl plusmn/2/spl deg/C. The loss of hydrophobicity was measured by determining the contact angle of a droplet of distilled water on the PTFE surface. It was observed that the decrease in the contact angle depended on the combined stress of salinity, temperature and duration of immersion. The influence of a radio frequency (RF) discharge and dc stress on the loss of hydrophobicity was studied. The increase in the weight and the change in the surface roughness and their correlation with hydrophobicity of the specimens are also reported.