Novel Dynamics in Complex Fluids: From Phonons to the Drying Process

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****Technical Abstract****This experimental program explores fundamental properties of complex fluids. Complex fluids are materials such as particle suspensions, emulsions, oil-water interfaces, polymer & surfactant solutions, liquid crystals, and mixtures thereof. A unifying feature of the proposed experiments is their focus on dynamics in complex fluids. One set of experiments will measure the vibrational properties of colloidal crystals with defects and in colloidal glasses & gels, with an eye towards elucidating connections between localized vibrations and internal rearrangements within these materials, especially in the absence of external stresses. A second set of experiments will investigate the effects associated with particle shape and interfacial interactions in drying colloidal drops. This work builds on the recent discovery that the geometric shape of suspended particles can be used to eliminate the famous coffee ring effect; we will carry out experiments to understand the nature of the novel elastic membranes that arise in these systems, i.e., via adsorption and interaction of the particles on the air-water surface. Soft materials find applications in the paint, food science, & cosmetics industries, in practical control of fluid rheologies & microfluidics, in cell biology, in high-tech problems such as photonics, printing & lithography, biochemical sensing, and in design of composites. Knowledge gained will enhance our ability to manipulate micro-/nano-particles and macromolecules in solution, providing insight for practical problems listed above. The program trains PhD students and post-docs in the science of soft materials and the technology of optical microscopy & micromanipulation; these students and post-docs, in turn, will leave Penn and strengthen the technological infrastructure of our nation.****Non-Technical Abstract****Complex fluids are materials such as colloidal suspensions, emulsions, oil-water interfaces, polymer & surfactant solutions, liquid crystals, and mixtures thereof. These soft materials find applications in the paint, food science, & cosmetics industries, in practical control of fluid rheologies & microfluidics, in cell biology, in high-tech problems such as photonics, printing & lithography, biochemical sensing, and in design of composites. The complex fluid research elucidates a wide-range of phenomena: probing vibrations in glasses, exploring the origin of internal rearrangements in glasses, and investigating the role of particle shape and interface deformation in affecting drying processes. Knowledge gained in these studies will enhance our ability to manipulate macromolecules in solution, providing insight for the many of the practical problems listed above. Technology developed as part of this research has led to the formation of two start-up nanotechnology companies and to a major collaboration with a larger chemical company. The program also teaches a new generation of PhD/post-doctoral scientists and engineers about soft materials and optical microscopy & micromanipulation; after finishing work here, these students and post-docs strengthen the technological and economic infrastructure of our nation.