Dynamic wetting of soluble polymer surfaces

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Understanding the wetting process, and thus the contact line dynamics, of solvents spontaneously spreading on polymer surfaces is essential in various technical applications, from printing to painting, to coating, to food science or to aerosol drug delivery. The dependence of the wetting speed on the surface energy or wettability of the surface is described by a power law in the case of simple liquids and surfaces. What is not yet understood is if this holds also for more complex systems, e.g. liquids or solvents in contact with polymer surfaces. Furthermore, if the liquid spreading on the polymer surface is a solvent for the polymer, it will diffuse into the polymer causing swelling, and on larger time scales it will eventually dissolve the polymer.The goal of the present project is to shed light on the complex interplay between the processes of wetting, swelling, solvation, and evaporation occurring at a polymer surface when a drop of solvent spreads over it.Well-defined polymer/solvent systems will be characterized experimentally and by molecular dynamics simulations: toluene drops on surfaces of polystyrene with different molecular weight and surface microstructure. High speed camera measurements of the spreading process and of the imprints left from the solvent after evaporation will be compared to atomistic and coarse-grained simulations.