2004 Volume 37 Issue 5 Pages 657-661
A droplet of a colloidal suspension of 250 nm polystyrene latex particles was observed during evaporation from plates with different contact angles (20, 87 and 104°) and the behavior of the droplet was evaluated. When the edge of the droplet did not recede towards the center during the evaporation process, the particles were observed to aggregate at the edge of the droplet forming a ring-like deposit. This ring-like deposit had an opal color, and that is thought to be a result of its highly ordered array structure. The highly ordered structure was obtained when the droplet was deposited on a hydrophilic plate with a 20° contact angle. In addition, a highly ordered array was observed in the droplet upon evaporation on a hydrophobic plate with an 87° contact angle, when particles were dissolved in a solution with a high ionic strength. This observation was explained by the DLVO theory.