Surface Dynamics of Polymer Glasses with Varying Chain Lengths

The surface dynamics of polymer glasses are complex due to strong coupling between the long-chain molecular structure and the surface mobility gradient. Herein, we investigated the surface relaxation of polymer glasses with varying chain lengths using an interfacial wetting-induced rheological (WIR) method. We identified rapid, Rouse-like motion on a short time scale, with activation energies independent of chain length, and slow, chain-dependent dynamics on a long time scale, with activation energies that increased with increasing chain length before attaining an asymptotic value. We attribute the former to the relaxation of the top strands of surface chains embedded in the surface mobility gradient and the latter to the relaxation of entire chains, which do not occur until the deepest segments of the surface chains are released. The findings of the study provide new insights into the hierarchical relaxation of interfacial polymers.