Wetting by polymer solutions

Very small droplets of polystyrene dissolved in toluene were placed on a glass slide and studied under a goniometer microscope. The drops were allowed to spread and dry and their extent of spreading is plotted as a variation of the concentration of the polymer in the solution. It was observed that drops of polystyrene in a volatile solvent such as toluene, spread to some extent and then gets dried up thus preventing the contact line from moving further. When liquid PDMS in non-volatile solvent, HMDS, and in volatile solvent, toluene, was used, the droplets continued to spread. One conclusion among others, is that even if the droplet dries but leaves behind a mobile contact line then the solution spreads out, on the other hand if the droplet dries and the contact line loses its mobility, the spreading automatically comes to a stop.