Transitions between different motion regimes of the three-phase contact line during the pattern deposition of polymer from a volatile solution

Abstract

HypothesisThe interplay between different transport mechanisms during polymer deposition from a volatile solution determines the motion regime of the three-phase contact line, e.g. monotonous slip, stick-slip, and oscillatory wetting-dewetting regimes of motion, which define the morphology of the deposit. ExperimentTo investigate the transitions between the motion regimes of the contact line, we evaporate solutions of Poly-methyl-methacrylate (PMMA) and Poly-dimethyl-siloxane (PDMS) in toluene. The solutions are confined in a well-defined (micro-chamber) geometry, where we adjust the system temperature, initial polymer concentration and molecular mass, and precisely determine the rate of evaporation. FindingsWe show that transitions between particular motion regimes of the contact line are connected to two types of competition between physical mechanisms. A transport competition between polymer diffusion and convection determines the distribution of polymer in the volatile meniscus and hence of spatial variations in the surface energy of the solution. A competition between evaporative and surface energy stresses in the liquid meniscus determines the motion of the contact line. We report the temporal variations of the contact line position during each motion regime and give a phase diagram to quantify the physical parameters that are responsible to transitions between the different regimes.