Estimating advancing and receding contact angles for pure and mixed liquids on smooth solid surfaces using the 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 a solid covered by a liquid film is approximated by the geometrical average of the surface energies of the 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 point contact angles, showing an average absolute relative deviation (AARD) of 7.4% for the advancing angle and 10.6% for the receding angle. The contact angle model uses an α-parameter, acting as a weighting factor for the solid and liquid effects on the work of adhesion. The model uses 0.75 and 0.5 for the advancing and receding contact angles, respectively. To assess the reliability of this α-parameter, we also optimized it using experimental data of contact angle. The optimized parameter 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 value of optimized model parameter are similar to those obtained based on the model assumptions, showing that the film surface energy is correctly represented by the geometrical average both in advancing and receding processes. The contact angle model combined with the PCP-SAFT framework also allowed to accurately predict the advancing and receding contact angles of binary liquid mixtures.