Revisiting the effect of substrate surface on the Tg of polymer films

Many T_g measurements obtained in the recent ten years have shown that substrate effect may not always be explained by using the conventional picture – that is, it is simply accountable by the polymer-substrate interaction energy, ꝩ_s, alone. In fact, two of our earlier results revealed the same. ^{9, 10} Just before this issue of substrate effect became widespread, we discovered that polystyrene polymer forms an irreversibly adsorbed layer on silicon after extensive annealing at temperatures above T_g,bulk. ¹¹ This finding was surprising because the polymer-substrate interaction energy, ꝩ_s, of this system is small, and no measurement at the time suggested that polymer-substrate interaction plays a role in the T_g-confinement effect in this system. However, increasing evidence suggests that the adsorbed layer plays a key role in how a substrate surface affects the T_g of polymer films. By collaborating with Prof. Xinping Wang’s group in Zhejiang University of Science and Technology, we will investigate the fundamental underpinnings of how an adsorbed layer affects the T_g-confinement effect of polymer films.