Effect of surface polarity on wettability and friction coefficient of silicone rubber/poly(acrylic acid) hydrogel composite

Water absorption, surface energetic, and friction coefficient of filled silicone rubber composites containing different amounts of a superadsorbent hydrogel, poly(acrylic acid) (PAA), were investigated. Measurements were performed in two different time windows, 1 and 5 weeks, to study the effect of hydration time on surface polarity of the samples. It was shown that water absorption increased consistently with hydrogel content and that prolongation of hydration time led to a marked increase in surface tension and polarity. Friction, as measured by a solid-solid contact method in phosphate buffer saline, showed strong dependence on polarity of the composite surface. Results demonstrate that the surface of the composite continued to evolve after the bulk had reached equilibrium swelling and the surface tension reached that of PAA after 5 weeks of hydration time.