2012 Volume 45 Issue 8 Pages 622-629
The effects of mixed solvent on polymer film morphologies formed from droplets of solution dried on a substrate with circular hydrophilic surfaces patterned on a hydrophobic surface were investigated. Several solvent mixtures were used, with polystyrene as a solute at various concentrations. Droplets formed a thin film after shrinking on the hydrophobic surface to the boundary between the two surfaces. The results from the chosen binary solvent pair combination showed that ring films tend to shift to flat films at each mixing ratio as the initial solute concentration increases. Marangoni flow arising from the concentration profiles of the solvents and solute was discussed. However, no evidence was found for Marangoni effects changing the experimental film morphologies when considering the effect of solute. Instead, the viscosity and contact angle at self-pinning was found to affect film morphology.
