Fabrication of honeycomb polyvinyl butyral film under humidity provided by super saturated salt solutions

We introduce a novel method for making breath figure arrays (BFAs) on polyvinyl butyral (PVB) films under humidity by putting the dip coated samples inside a chamber filled with supersaturated salt solutions. With the increase in humidity or retention time, multiple porous films with bigger pore sizes and wider size distributions are generally obtained, resulting from the coalescence of the following-up water drops. The presence of nitrogen flow accelerates the evaporation of solvents and vapor, thus increases the elastic interaction among water droplets such that films with smaller pores can be obtained. Compared to PVB/ethyl acetate solution, it is easier to obtain a film with regular honeycomb pattern by using PVB/chloroform solution. Its lower boiling point makes it evaporate faster to increase temperature gradient between film surface and the atmosphere; while its higher density makes it provide stronger support to maintain the shape of water droplets. In this study, the solubility of polymer in solvents is initially proposed to explain the BFAs formation. Higher mobility of polymer chains in a good solvent increases chances of its polar groups to interact with water droplets, thus increases the possibility of regular arrangements of water droplets on the film. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012