Impact of aqueous electrolytes on interfacial energy

The effects of aqueous electrolytes on particle-particle interactions in aqueous media are not completely understood. Electrolytes are typically considered to impact only electrostatic energy. In this work, the impact of aqueous electrolytes on van der Waals and Lewis acid/base potential energies was quantified using both hydrophobic and hydrophilic substrates. Increases in ionic strength beyond 0.001 M resulted in comparable increases in solid-water interfacial energy in polytetrafluoroethylene (PTFE) and organically coated sodium montmorillonite systems. The change in water/PTFE interfacial energy, as determined by contact angle measurements, was greater than that predicted by screening of the nondispersion component of the Hamaker constant using the Mahanty and Ninham model. Increases in interfacial energy, as a function of salt concentration, were greater with increasing substrate hydrophilicity. Although the systems studied in this work were disparate in nature, they all appeared to exhibit similar trends in interfacial surface energy as a function of ionic strength. Similarity in the results may suggest that aqueous electrolytes may modify the solvent structure within the interfacial region. (C) 1998 Academic Press.