ABSTRACT CTS-9809053 Somasundaran, P. Columbia U. Surface modification of solids plays a vital role in many traditional and emerging industrial processes dependent upon interfacial phenomena such as adhesion, wetting, lubrication, electrodeposition, catalysis and aggregation/dispersion. Chemical modification by adsorption offers an excellent means to control interfacial behavior of colloidal systems. Past work on adsorption of surfactants and polymers on solid minerals has shown that interactions among these species leading to aggregation can have marked effects on interfacial behavior1. Using a multipronged approach combining traditional techniques of adsorption, wettability and lubrication with advanced spectroscopic techniques of fluorescence, electron spin resonance and resonance Raman, we have proposed ionic surfactants to adsorb individually at low concentrations and in clusters at high concentrations (hemimicelles, admicelles, solloids)2,3. Importantly, reorientation of adsorbed species has been proposed to occur under high concentrations. Such reorientation and reconformation can have drastic effects, for example, in wettability and adhesion inorganics) are introduced into the system. While fluorescence and electron. Reconformation can also occur when additives (surfactants, polymers and spin resonance techniques have yielded information on such microproperties as polarity, viscosity and aggregation number of the clusters on solids, direct investigation on a molecular scale in the concentration range where surface aggregates evolve has not yet been done. Studies conducted in the past have been carried out in the higher concentration ranges above critical micelle concentration4,5. A promising innovation allowing such investigation is the development of scanning probe microscopy (SPM). SPM is a generic name and at present it includes scanning tunneling microscopy and atomic force microscopy. Other SPM techniques under development are scanning ion, magnetic f orce, photon scanning and thermal profiler microscopy6. The three dimensional topography-mapping capabilities of SPM techniques at extremely high resolution (atomic scale) in vacuum, air, or liquid environments are unparalleled. The interaction force measurements in colloidal systems are important both from a theoretical and practical point of view. The interaction force between the SPM tip and the sample can yield information which so far has not been obtainable for dispersed systems. The proposed acquisition of the atomic force microscope will enable us to directly probe the adsorbed layer in-situ and changes in its structure due to chemical and hydrodynamic factors. This will markedly increase our investigative capability since the use of atomic force microscope concurrently with other techniques will enable us to develop an understanding of interfacial processes on a nanoscale. Such information also leads to engineering capability to manipulate and control modification of surfaces by adsorption for optimum effect.
