Synergistic or Antagonistic Effects of Polymer/Surfactant Supramolecular Assembly on the Colloidal Depletion Force

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CBET - 1608003PI: Tilton, RobertWhen microscopic "colloidal" particles are suspended in a solution containing polymers, the polymers tend to be excluded from the gaps between particles. This exclusion gives rise to a force called the depletion force, which can draw particles together to form aggregates. Some industrial processes take advantage of the depletion force by promoting aggregation of contaminant particles to remove them from solution. However, the depletion force may be undesirable in other processes where ingredients must remain in solution, such as paint pigment particles or active agents in pharmaceuticals. Such liquid products must be formulated to prevent depletion-induced aggregation. When ionic surfactants are also present in the polymer solution, they can bind to the polymers and alter the depletion force in ways that are not completely understood. This project will examine various kinds of polymer/surfactant mixtures to better understand how polymer-surfactant binding influences the depletion force and the stability of the suspension. A colloidal probe atomic force microscope will be used to measure the depletion force in the polymer/surfactant mixtures. The results of the project will be useful to engineers who manufacture and process colloidal fluids, including paints, coatings, topical medications, and personal care products. The project will provide research opportunities for students at various academic levels, including middle school students who participate in the university's Physics Concepts Programs by designing experiments to examine the physical chemistry of liquid product formulations. This project will examine the role of polymer/surfactant complexation on depletion forces in colloidal suspensions. Colloidal forces in polymer/surfactant mixtures will be measured by colloidal probe atomic force microscopy. The project will reveal how complexation between ionic surfactants and either nonionic polymers or oppositely charged polyelectrolytes can amplify or suppress depletion forces. Experimental data will be interpreted in terms of a model that predicts depletion forces based on polymer/surfactant complex stoichiometry, charge and size. Results will be correlated with colloidal stability phase diagrams for a series of systems that represent canonical categories of polymer/surfactant association behavior. The outcomes of the project will benefit industrial practice where complexation is used in multicomponent liquid mixtures to produce novel material properties and products with diminished environmental impacts.