Simultaneous determination of surface energy and roughness of dense membranes by a modified contact angle method

This paper proposes a facile method to simultaneously determine surface energy and roughness parameters of dense membranes based on contact angles measured with multiple standard polar/nonpolar liquids. This method involves a combined solution of the Young-Dupre equation and Wenzel equation that jointly describe the relationships among surface energy, roughness and contact angle. Using this method, the Lifshitz-van der Waals and Lewis acid/base components of surface energy as well as the surface roughness (reflected by surface area difference) of a nanofiltration membrane (NF90) and a reverse osmosis membrane (ESPA1) were determined in one step, and were compared with those determined using conventional contact angle methods and atomic force microscopic roughness measurement. The reliability of the new method was investigated via error transmission analysis, sensitivity analysis and Monte Carlo simulation. The influence of surface roughness on energy determination could be amplified given surfaces with higher hydrophilicity. This method may be applicable to solid polymeric materials with Wenzel-type surfaces allowing for contact angle measurement.