Thermal and Mechanical Effects in the Spreading of a Liquid Film Due to a Change in the Apparent Finite Contact Angle

A new physical model for the spreading dynamics of fluids with an apparent finite contact angle on solid substrates is presented. The model is based on the premise that both interfacial intermolecular forces and temperature control change-of-phase heat transfer and (therefore) motion in the moving contact line region. Classical change-of-phase kinetics and interfacial concepts like the Kelvin–Clapeyron, Young–Dupre, and augmented Young–Laplace equations are used to compare the effects of stress (change in apparent dynamic contact angle) and temperature (superheat). Explicit equations are obtained for the velocity, heat flux, and superheat in the contact line region as a function of the change in the apparent contact angle. Comparisons with experimental data demonstrate that the resulting interfacial model of evaporation/condensation not only describes the “apparently isothermal” contact line movement in these systems at 20°C but also describes the substrate superheat at the critical heat flux.