Surface modification of conventional polymers by depositing plasma polymers of trimethylsilane and of trimethylsilane plus O-2 II. Dynamic wetting properties

The dynamic wetting properties of TMS (trimethylsilane) and TMS + O-2 plasm a-deposited films on ten low energy conventional polymers were investigated using the Wilhelmy balance method. Plasma deposition resulted in wetting p roperties that were independent of the underlying polymer substrate for the majority of polymers studied. TMS plasma modification resulted in virtuall y the same degree of hydrophobicity with an average cosine of the dynamic a dvancing contact angle from the first immersion, cos theta(D,a,1) = -0.381 (theta(D,a,1) = 112 +/- 3.6), for eight of the ten polymers. RIPE and UHMWP E were slightly more hydrophobic after TMS plasma treatment with an average cos theta(D,a,1) = -0.785 (theta(D,a,1) = 141 +/- 4.2). TMS + O-2 plasma m odification resulted in high wettability of all polymers with an average co s theta(D,a,1) = 0.654 (theta(D,a,1) = 49.2 +/- 11.7). Dynamic hysteresis, mainly a result of the change in meniscus shape during immersion and emersi on, and intrinsic hysteresis, due to the extent of surface configuration ch ange, were both found to vary according to the size of the polymer plate. I n general, dynamic hysteresis can be quite large for more hydrophobic TMS t reated polymers and considerably smaller for highly hydrophilic TMS + O-2 t reated polymers. The extent of intrinsic hysteresis of only TMS treated pol ymers was found to be independent of the underlying polymers within the tim e-scale of wetting. TMS + O-2 plasma treatment resulted in wide variations in intrinsic hysteresis probably due to substrate specific etching of oxyge n plasma species. The wettability of the untreated and TMS and TMS + O-2 tr eated polymers, indicated by the static "advancing" contact angles from the sessile droplet method and dynamic "advancing" and "receding" contact angl es from the Wilhelmy balance method, were found to conform well to the corr elation, cos theta(S) = (cos theta(D,a,1) + cos theta(D,r,1))/2. (C) 1999 A cademic Press.