Surface Modification of Conventional Polymers by Depositing Plasma Polymers of Trimethylsilane and of Trimethylsilane + O2: II. Dynamic Wetting Properties

Abstract

The dynamic wetting properties of TMS (trimethylsilane) and TMS + O2plasma-deposited films on ten low energy conventional polymers were investigated using the Wilhelmy balance method. Plasma deposition resulted in wetting properties that were independent of the underlying polymer substrate for the majority of polymers studied. TMS plasma modification resulted in virtually the same degree of hydrophobicity with an average cosine of the dynamic advancing contact angle from the first immersion, cos θD,a,1= −0.381 (θD,a,1= 112 ± 3.6), for eight of the ten polymers. PTFE and UHMWPE were slightly more hydrophobic after TMS plasma treatment with an average cos θD,a,1= −0.785 (θD,a,1= 141 ± 4.2). TMS + O2plasma modification resulted in high wettability of all polymers with an average cos θD,a,1= 0.654 (θD,a,1= 49.2 ± 11.7). Dynamic hysteresis, mainly a result of the change in meniscus shape during immersion and emersion, and intrinsic hysteresis, due to the extent of surface configuration change, were both found to vary according to the size of the polymer plate. In general, dynamic hysteresis can be quite large for more hydrophobic TMS treated polymers and considerably smaller for highly hydrophilic TMS + O2treated polymers. The extent of intrinsic hysteresis of only TMS treated polymers was found to be independent of the underlying polymers within the time-scale of wetting. TMS + O2plasma treatment resulted in wide variations in intrinsic hysteresis probably due to substrate specific etching of oxygen plasma species. The wettability of the untreated and TMS and TMS + O2treated polymers, indicated by the static “advancing” contact angles from the sessile droplet method and dynamic “advancing” and “receding” contact angles from the Wilhelmy balance method, were found to conform well to the correlation, cos θS= (cos θD,a,1+ cos θD,r,1)/2.