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 typic ally considered to impact only electrostatic energy. In this work, the impact of aqueous electrolytes on van der Waals and Lewis acid/base p otential energies was quantified using both hydrophobic and hydrophili c substrates. Increases in ionic strength beyond 0.001 M resulted in c omparable increases in solid-water interfacial energy in polytetrafluo roethylene (PTFE) and organically coated sodium montmorillonite system s. The change in water/PTFE interfacial energy, as determined by conta ct 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 s alt concentration, were greater with increasing substrate hydrophilici ty. Although the systems studied in this work were disparate in nature , they all appeared to exhibit similar trends in interfacial surface e nergy as a function of ionic strength. Similarity in the results may s uggest that aqueous electrolytes may modify the solvent structure with in the interfacial region. (C) 1998 Academic Press.