Thin Liquid Films - Structure and Stability

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The objective of this research is to examine, both experimentally and theoretically, the phenomenon of multilayered microstructuring or stratification in sub-micron thin liquid films produced by the use of surface active agents; further to explore its use as a probe for investigating long-range structural or interaction forces in colloidal dispersions. A unique feature of this continuing study lies in the development of a surface force balance for films with fluid interfaces for investigating the influence of microstructures on thin film stability. Using this new technique, both film thickness and capillary pressure are recorded simultaneously. The surface force balance in conjunction with the differential interference microscopy will be used to study films with curvature such as those existing between approaching small droplets or bubbles associated with emulsion and foam systems. Experiments using differential and common microinterferometic methods will be performed to obtain the contact angle and film tension and, thereby, the film interaction energy and the disjoining pressure attributable to the presence of micellar structure inside the film. Systems to be investigated will include both spherical and non- spherical micelles, mixed micelles (such as in mixtures of anionic and nonionic micellar solutions) and differently charged colloidal particles such as silica and latexes. This study will provide insights into the origin of structural disjoining pressure related to interfacial structuring in thin films which gives rise to an increased stability in colloidal dispersions.