Mixed equilibrium/nonequilibrium effects govern surface mobility in polymer glasses.

ABSTRACT: Using angle-resolved X-ray photoelectron spectroscopy, sum-frequency generation vibrational spectroscopy, contact angle measurements, and molecular dynamics simulations, we verify that the glass transition temperature (T_g) of polymer glass is lower near the free surface. However, the experimental T_g-gradients showed a linear variation with depth (z) from the free surface, while the simulated equilibrium T_g-gradients exhibited a double exponential z-dependence. In typical simulations, T_g is determined based on the relaxation time of the system reaching a prescribed threshold value at equilibrium. Conversely, the experiments determined T_g by observing the unfreezing of molecular mobility d

SUBMITTER: Xu J 

PROVIDER: S-EPMC11474049 | biostudies-literature | 2024 Oct

REPOSITORIES: biostudies-literature