Estimating Advancing and Receding Contact Angles for Pure and Mixed Liquids on Smooth Solid Surfaces using PCP-SAFT Equation of State

Abstract

Contact angle is an important measure of wetting in systems involving liquid-solid interfaces. This study focuses on estimating advancing and receding contact angles of pure and mixed liquids on smooth solid surfaces using perturbed-chain polar statistical associating fluid theory equation of state (PCP-SAFT EoS). For the receding contact angle, we propose a model in which the surface energy of solid containing a liquid film is approximated by the geometrical average of surface energies of the pure solid and liquid. The PCP-SAFT model is used to calculate the ratio of dispersion-to-total surface energy for diverse pure and mixed liquids. The results are validated against 104 experimental data points for advancing and receding contact angles, showing an average absolute relative deviation (AARD) of 7.4% for advancing angles and 10.6% for receding angles. In the contact angle models, there is an α-parameter in power term which is 0.75 and 0.5 for the advancing and receding contact angles, respectively. To assess the reliability of this α-parameter, we varied it and optimized it using experimental data. The optimized power term was found to be 0.74 for advancing and 0.48 for receding contact angle, and the AARD values slightly reduced to 7.2% and 10.5%, respectively. The optimized model parameter values are remarkably close to those based on the model assumptions (0.75 for advancing and 0.5 for receding), which validates the assumed values. The contact angle model combined with the PCP-SAFT framework allowed to accurately predict the advancing and receding contact angles of binary mixtures.