Melt adsorption of poly(tert-butyl methacrylate) and poly(ethyl methacrylate) on silica studied with chip nanocalorimetry

Abstract

Irreversible adsorption of polymer chains from a melt on a substrate surface can be strongly affected by interfacial interactions. In this study, we examined the adsorption of two polymers, poly(tert-butyl methacrylate) (PtBMA) and poly(ethyl methacrylate) (PEMA), on a silica surface at temperatures above their glass transition temperatures. The degree of adsorption γ(t) over time was evaluated with variations of storage heat capacity determined with alternating current chip nanocalorimetry (in-situ measurement of a buried interface). γ(t) revealed two-step profiles for both polymers. At the second stage of adsorption (regime II), the slope of a plot of γ(t) vs. log t increased as adsorption proceeded; this trend has not been reported for other polymers and may be characteristic of the present polymers. The trend observed in regime II suggested that the unadsorbed free chains near the interface became less mobile and were incorporated into the adsorbed layer via interactions with the tails of the chains directly attached to the substrate surface. The increasing slope in regime II was more prominent for PtBMA than for PEMA. In addition, a difference was observed for PtBMA and PEMA in the atomic force microscopy images of the exposed adsorption layer surfaces. We examined the adsorption behavior of poly(tert-butyl methacrylate) (PtBMA) and poly(ethyl methacrylate) (PEMA), on a silica surface. Time-evolution of the degree of adsorption γ(t) was evaluated with chip nanocalorimetry. γ(t) revealed a two-step profile for both polymers. At the second stage of adsorption, the slope of γ(t) vs. log t increased as adsorption proceeded; this trend has not been reported for other polymers so far. In addition, atomic force microscopy images of the adsorbed layers revealed corresponding evolutions of the morphologies.