Glass Dynamics Facilitated or Hindered by Interfaces, Chain Connectivity, and Other Factors

Enhanced molecular mobility near the free surface is crucial for advancing organic electronic devices, yet understanding the substrate's impact on the surface glass transition temperature(T_g^surf )as film thickness decreases remains limited.This study explores how polymer films possessing attractive,neutral, and unfavorable polymer-substrate  interactions affect T_g^surf. Results show that neutral interactions have no effect, while attractive or unfavorable interactions can increase or decrease T_g^surf  by up to around 37 ℃. The onset thickness for this change is smaller for attractive interactions(up to 37nm) than for unfavorable interactions (>100nm), supporting the observed broadening of the surface  glass transition with attractive interactions. We surmise that segment exchange  between surface and substrate regions introduces disparate dynamic components at the surface. Therefore, attractive  interactions causing a sharper change in  T_g^surf with film thickness lead to a broader surface glass transition.