Temperature dependent soft wetting of polymer melts

Wetting studies on soft surfaces, though prolific, have been mostly limited to equilibrium cases at room temperature, often on crosslinked elastomers. In this work, we investigate the transient wetting characteristics of a polymer melt (poly n-butyl methacrylate) at temperatures much higher than its glass-transition. When a glycerol drop is placed on the polymer melt surface, an out-of-plane wetting ridge forms at the three-phase contact line. We use stylus profilometry to measure the height and the profile of the wetting ridge for different temperatures and times of contact between the drop and the melt. The wetting ridge growth rate is dependent on the system temperature and the time scale of the experiment. Using oscillatory rheology, scaling laws are developed to predict the time-dependent growth of the wetting ridge. We demonstrate that for a range of temperatures, both Rouse and reptation kinetics affect the rate of ridge growth over different timescales. Moreover, the shape profile of the wetting ridge is dictated by the time-dependent complex modulus, which is a departure from the constant shear modulus values often used for soft elastomers. However, the shape profile can be predicted by a simple consideration of the complex modulus within the context of current models.