Interactions and Assembly in Suspension

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

This experimental condensed matter physics project will explore the fundamental properties of complex fluids, which include colloidal suspensions, emulsions, polymer solutions, membranes, and mixtures thereof. These "soft" materials find applications in the paint, food science, and cosmetic industries, in the practical control of fluid rheologies, in cell biology, and in high-tech problems of photonics, lithography, and biochemical sensors and processors. This work addresses three basic issues in suspension science:(i) Microscopic interactions, (ii) Assembly, and (iii) New macroscopic model systems. Experiments are planned to: (1) Measure interactions in suspension produced by macromolecules, vesicles, and membranes, by subtle hydration effects, by polymer-induced steric interactions, and by dipolar or anisotropic background fluids; (2) Study the equilibrium assembly of colloidal crystals with templates that bias growth towards metastable states; and (3) Study the equilibrium phases of rods and plates at very high densities, and at very low densities (i.e. in the low-screening limit). (4) Develop methodologies to assemble colloidal crystal heterostructures. (5) Synthesize new suspension constituents that offer us the possibility to create new macroscopic model systems, for example macroscopic surfactants. Knowledge gained in these studies will improve our fundamental understanding about interactions and assembly in complex fluids, and should lead to new techniques for controlling assembly and for studying microscopic interactions in soft materials. Graduate students involved in the project receive training in fundamental cutting edge experimental techniques such as microscopy, optics, applied computation, and suspension science. This training will prepare students and associates for careers in industry, government or academe. This experimental condensed matter physics project investigates the properties of a range of complex fluids, examples of so-called "soft matter". Complex fluids include colloidal suspensions, emulsions, polymer solutions, membranes, liquid crystals and mixtures thereof. The structure and dynamics of soft materials are strongly influenced by disorder (entropy) and by relatively weak mechanical forces (as in thixotropy, catsup). These materials provide a fascinating testing ground for many-body statistical physics, and for investigations of phase transitions such as melting and solidification. Research on these substances is technology driven too. They are attractive starting materials in high-tech applications such as photonics, lithography, ceramics and biochemical sensing; particle additives also offer a means for practical control of fluid flow, improving the performances of conventional materials such as paints, motor oils, foods, and cosmetics. Finally, complex fluids experiments are increasingly stimulated by analogies from cell biology, in some cases providing critical insights about mechanisms that arise in crowded cellular environments. This research focuses on three basic issues: measurement of microscopic forces in suspension, the study of phase transitions and self-assembly, and the creation of exotic new macroscopic model systems. Students in this program receive rigorous training in optics, physics, and materials science that prepares them for careers in academe, industry, and government.