SURFACE FORCES BETWEEN PLASMA POLYMER-FILMS

The surface properties of two different plasma polymer coatings were i nvestigated by means of ESCA, wetting studies, and surface force measu rements. The plasma polymer films formed from hexamethyl-disiloxane (H MDSO) monomers were found to be very smooth. This made it possible to measure the attractive van der Waals interaction between HMDSO-coated surfaces in air. When the HMDSO-coated surfaces were immersed in water , they initially appeared strongly hydrophobic with an advancing and r eceding contact angle of 109-degrees and 98-degrees, respectively. Nev ertheless, no long range ''hydrophobic'' interaction was observed. The HMDSO coating became slightly more hydrophilic when kept in an aqueou s phase for a prolonged time, indicating migration/reorientation of po lar groups to the surface. Surface force measurements in water clearly demonstrated the appearance of electrostatic charges and extending po lymer tails as a result of a prolonged exposure to water. Plasma polym er coatings Of C2F4 or C2F6 deposited on top of a plasma polymer of CH 4 were also studied. The forces between such a polymer and a glass sur face are on the first approach in air characteristic of a van der Waal s force. However, the attraction increases as the surfaces are brought together repeatedly. The increase in the long range attraction is a r esult of contact electrification due to electron transfer from glass t o the fluorocarbon surface. It was found that in aqueous environment t he C2F4 plasma polymer surface is significantly less smooth and less s table than the HMDSO plasma polymer surface.