SHORT-RANGE AND LONG-RANGE FORCES IN COLLOIDAL AND MACROSCOPIC SYSTEMS

The concept of interfacial interactions was revised through the employment of Lifshitz theory of forces acting across condensed phases.;The combination of Wenzel's theory of the effect of surface roughness on contact angles, Good's theory of contact angle hysteresis and the aforementioned revisions to interfacial interaction theory has resulted in the development of an advanced method of analyzing contact angle data on low energy polymers. The model was tested on smooth and artificially roughened Teflon-FEP and satisfactory results were obtained.;The analysis of contact angle data on smooth polar solids revealed some interesting features of the long-range ((gamma)('LL)) and short-range ((gamma)('SR)) components of the surface energy of polar solids: (gamma)('LL) of a material is an invariant quantity, whereas (gamma)('SR) is not! An explanation of this phenomenon was presented in terms of the Drago-Fowkes acid-base interaction theory.;During the course of the above investigation, a new three-phase effect was observed, i.e., certain liquids formed stable thick films between two dissimilar condensed phases. This phenomenon has been explained by using Lifshitz theory of electrodynamic interactions with a special emphasis on the retardation effect.;These studies revealed that the pairwise additivity theories of interfacial interactions break down seriously for condensed phases and especially for hydrogen bonding liquids. As a result, it has been proposed that a large portion of the high surface tension of hydrogen bonding liquids should be attributed to specific short-range interactions; also, the long-range (London-Lifshitz) and specific interactions should be treated separately because of their different distance dependence.;As a consequence of the aforementioned studies, a quantitative theory of the negative adsorption of non-electrolytes has been developed, viz., the negative adsorption of sucrose at the air/water interface. The theoretical treatment employed a Lifshitz theory of forces in conjunction with Gibbs' thermodynamics of interfacial distances. Calculations yielded a quantitative prediction of the increase in surface tension of water as a function of solute concentration, which agreed very well with experimental observations.