Polar and dispersive surface tension components of water-guanidinium chloride (Gdmcl) binary mixtures

Abstract

Interfacial interaction of water with guanidinium chloride (GdmCl) is crucial to understanding protein solubility and denaturing mechanism. However, molecularly resolved parameters such as polar and dispersive surface energy components of water-GdmCl mixtures remain unknown. Here, we developed a method to determine water-GdmCl mixture surface tension and its components using four different substrates including polydimethylsiloxane (PDMS), silicone, polyethylene, and polystyrene. Results show all six combinations, PDMS-silicone, PDMS-polystyrene, PDMS-polyethylene, silicone-polyethylene, silicone-polystyrene, and polyethylene-polystyrene can estimate similar trend of total surface tension, polar and dispersive components with respect to salt concentration changes. Silicone-polyethylene pairs yield the most accurate surface tension compared to others because silicone and polyethylene have large distinctive surface energy differences. Results show that polar components increase from 51 mJ/m2 to 64 mJ/m2 when salt concentration increases; dispersive components decrease from 21 mJ/m2 to 15 mJ/m2 when salt concentration increases. Total surface tension increases from 72.8 mJ/m2 to 78.1 mJ/m2 when GdmCl increases from 0% to 40 wt%. The results of this study can elucidate molecular interaction between water and GdmCl.