Probing Glass Transitions in Thin and Ultrathin Polystyrene Films by Stick–Slip Behavior during Dynamic Wetting of Liquid Droplets on Their Surfaces

Abstract

A novel method was developed to detect the glass transition of thin and ultrathin polystyrene (PS) films by correlating the relationships between the temperature-dependent viscoelasticity of the PS films and stick–slip behavior on their surfaces during dynamic wetting of glycerol or oligo-poly(ethylene glycol) droplets. The peak temperature (Tjm) obtained from the jumping angle–film temperature curve, in which the jumping angle Δθ was employed to scale the stick–slip behavior, was nearly identical to the corresponding Tg (or Tα) of the PS film. This was confirmed by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The change of the measured Tjm with film thickness and substrate chemistry (SiO2–Si and H–Si) further confirmed that the developed method is very sensitive for detecting the dynamics of ultrathin polymer films.