Specific behaviors of polymer solution droplets on surfaces due to solutal marangoni effect

Specific behaviors of polymer solution droplets evaporating on a lyophilic surface are reported. Polystyrene (solute) is dissolved in acetophenone, anisole and mesitylene (solvent). The single solvents and acetophenone/ mesitylene solvents are stationary during drying and form ring-like polymer films. On the other hand, mesitylene/ anisole droplets move around on the surface at low solute concentrations. This movement results from solutal Marangoni flow, whose direction is the opposite to the direction of the acetophenone/mesitylene solvents. The movement is almost inhibited at low temperatures. At low temperatures, the droplets comprise a core film surrounded by a ring structure. The morphology of the core film depends on the mixing ratio of the components of the solvent.