Adhesion of plasma-polymerized hexamethyldisiloxane films on polytetrafluoroethylene films.

Abstract

Plasma-polymerized hexamethyldisiloxane (PPHMDS) was deposited on polytetrafluoroethylene (PTFE) films by changing the conditions for the plasma pre-treatment of PTFE surface prior to PPHMDS coating. The adhesion strength measured by the direct pull method increased from about 30 kg/cm2 for the untreated films to about 80 kg/cm2 for the treated ones in Ar and N2 plasmas for 10 minutes. In the case of O2 plasma treatment, the adhesion strength increased to about 70 kg/cm2 by 1 minute treatment, but then decreased rapidly to the value lower than that of the untreated surface. The fracture of PPHMDS/PTFE system took place cohesively in the PTFE films except for the substrate films treated in O2 plasma for about more than 5 minutes. The increase in adhesion strength is due to the sputtering of the surface layers of PTFE films which otherwise might produce weak boundary layers at the interface, while the rapid decrease, in the case of O2 plasma treated PTFE films, is due to the lowering of cohesive force of the surface layers caused by the scission of the polymer chain by atomic oxygen in plasma.