mediate distances. Unfortunately, the DLVO SS modeling ap-The effects of aqueous electrolytes on particle-particle interacproach has often proved inadequate in explaining particletions in aqueous media are not completely understood. Electrolytes particle interactions in polar media (3-5). It has been susare typically considered to impact only electrostatic energy. In this pected for many years (6-11) that components of surface work, the impact of aqueous electrolytes on van der Waals and tension, such as those related to solvent hydrogen bonding Lewis acid/base potential energies was quantified using both hycapabilities must also be considered. Van Oss and co-workdrophobic and hydrophilic substrates. Increases in ionic strength ers (12) have developed an extended DLVO model beyond 0.001 M resulted in comparable increases in solid-water (DLVO EX ) which accommodates polar components of surinterfacial energy in polytetrafluoroethylene (PTFE) and organiface tension for both liquids and solids. These Lewis acid/ cally coated sodium montmorillonite systems. The change in water/PTFE interfacial energy, as determined by contact angle mea-base (AB) interactions may be of quantitative significance surements, was greater than that predicted by screening of the in systems with electron donor/acceptor potentials. nondispersion component of the Hamaker constant using the Ma-Investigations into the effects of salt on the interfacial hanty and Ninham model. Increases in interfacial energy, as a properties of water have been conducted for over a century function of salt concentration, were greater with increasing sub-(13). Within the framework of the DLVO SS colloid stability strate hydrophilicity. Although the systems studied in this work model, an increase in electrolyte concentration is often correwere disparate in nature, they all appeared to exhibit similar trends lated with a concomitant reduction in the extent of the elecin interfacial surface energy as a function of ionic strength. Simitrostatic force. This typically results in increased attraction larity in the results may suggest that aqueous electrolytes may between two similar surfaces. However, cases have been modify the solvent structure within the interfacial region. α§ 1998 reported in the literature which do not conform to this frame-Academic Press work. For example, Yotsumoto and Yoon (14) reported a Key Words: contact angle; DLVO; electrolyte; Hamaker constant; Lewis acid/base interactions; surface tension; van der Waals redispersion of rutile colloids, above a specific salt conceninteractions.
tration, which resulted in an increase in suspension turbidity. Similarly, Craig et al. (15) observed that the stability of air bubbles increased with increases in aqueous electrolyte concentration. Moreover, the presence of an indifferent elec-