Tunable hydrodynamics and restricted motions: probing dynamics and the mechanisms of self-organization in soft matter

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The relationship between microscopic structure and interactions, and macroscopic behaviour is central to almost all fields of science. In the colloidal domain, which is common to soft and biological materials, several length- and time-scales coexist and complex structures emerge from simple building blocks due to both pairwise electrostatic interactions and many-body hydrodynamic interactions. We will use soft materials - colloidal suspensions, surfactants, proteins - to construct nano- and micro-scale model systems with which to address fundamental questions in condensed matter physics. How coherent structures form is an important question: How do crystals grow? When does crystallization get arrested? In driven systems, incoherent structures such as clusters and clouds can also form. We will control entropic excluded volume interactions via packing fraction, and tune long-range electrostatic and hydrodynamic interactions. In doing so, we aim to better understand underlying mechanisms: how coherent and incoherent structures form, and eventually, how to approach the complexity of living organisms. We use optical microscopies to study structure formation on the micrometer scale and nuclear magnetic resonance to study dynamics of nanoscale structures. Rheology measures stresses and strains in materials and is used to characterize macroscopic properties. Our strategy, which has been very fruitful thus far, is to create systems where the governing interactions can be controlled and varied via an external field. Coherent micro-scale crystalline structures can be easily controlled with external forces, and can be used to make novel kinds of field responsive (or smart) materials. Making functional materials can be a very satisfying end point for a study of fundamental processes, as it can really test the degree to which we understand the basic physics. In other cases, however, where the discovery of a new material is serendipitous, and underlying mechanisms are unclear, application of a materials science approach can yield interesting new fundamental problems in condensed matter physics. This research program is designed to accommodate both eventualities.