Physical Adsorption and Glass Transition of Thin Polystyrene Films at a Graphene Interface

Polymer adsorption at solid interfaces plays an important role in the dynamics of nanoscale polymer films. We investigated the influence of the interfacial chain adsorption on the glass transition temperature (T_g) and dewetting of polystyrene (PS) thin films on a graphene substrate that has strong interaction with PS. We found that the T_gs of PS films show a non-monotonic trend with increasing amount of polymer adsorption at the interface—first increasing and then decreasing, and this change in T_g is accompanied by a wetting-dewetting transition of the PS films. Film morphological analysis showed that the PS films dewet from the interfacially adsorbed layers rather than from the substrate, i.e., autophobic dewetting, indicating the presence of an unfavorable interaction between the adsorbed and free PS chains. We ascribed the repulsive interaction to the formation of a dense adsorbed layer on graphene due to the π-π interaction between PS and graphene, which prevents the non-adsorbed PS chain from penetrating into the adsorbed layer. This may lead to drops in T_g at high adsorption extent.