Breath figure formation on polystyrene in ethanol–propanol binary mixture environment

Abstract

The self-assembly of water droplet patterns formed on a cold surface through the breath figure technique is ideally hexagonal. However in nature, the surfaces are not smooth which influences the self-assembled droplet pattern. The roughness of the substrate, the use of vapors other than water, the type of the polymer, and concentration of polymer used lead to a distortion in ideal patterns. Taking forward studies on the formation of breath figures by non-aqueous vapor environments, we report the formation of breath figures over polystyrene of molecular weights 35 K, 192 K, and 280 K with the binary mixture of ethanol and propanol (over the entire concentration range) as the condensing drops on smooth and grooved surfaces. Relatively ordered honeycomb patterns are observed on smooth while distorted patterns are observed on the grooved surfaces. The degree of order of breath figure patterns is characterized using Voronoi entropy. It is observed that the pore diameters increase both with the molecular weight and the weight percentage of the polymer. In addition, water contact angle measurements on the patterned surfaces show them to be hydrophobic with a Cassie-Baxter state of wetting.

Graphic abstract