Abstract:

Entropy, information, and order are important concepts in many fields, relevant for materials to machines, for biology to economics. Entropy is typically associated with disorder; yet, the counterintuitive notion that particles with no interactions other than excluded volume might self-assemble from a fluid phase into an ordered crystal has been known since the mid-20th century. First predicted for rods, and then spheres, the ordering of hard shapes by nothing more than crowding is now well established. In recent years, surprising discoveries of entropically ordered colloidal crystals of extraordinary structural complexity have been predicted by computer simulation and observed in the laboratory. Colloidal quasicrystals, clathrate structures, and structures with large and complex unit cells typically associated with metal alloys, can all self-assemble from a disordered phase of identical particles due solely to entropy maximization. These findings demonstrate that entropy alone can produce order and complexity beyond that previously imagined. They also suggest that, in situations where other interactions are present, the role of entropy in producing order may be underestimated. We present the latest discoveries for entropic systems of identical particles, including a Bergman-like phase with a 432-particle unit cell, and fluid-fluid transitions preceding crystallization that are reminiscent of liquid-liquid phase separation in water, proteins, and even within cells. To understand these phenomena, and in loose analogy with traditional chemical bonds that produce order in atomic and molecular substances, we introduce the notion of the entropic bond.

Biography:

Sharon C. Glotzer is the John W. Cahn Distinguished University Professor of Engineering and the Stuart W. Churchill Collegiate Professor of Chemical Engineering and Professor of Materials Science and Engineering at the University of Michigan, Ann Arbor, and also holds faculty appointments in Physics, Applied Physics, and Macromolecular Science and Engineering. Since July 2017 she is the Anthony C. Lembke Department Chair of Chemical Engineering at the University of Michigan. Her current research on computational assembly science and engineering aims toward predictive materials design of colloidal and soft matter. Using computation, geometrical concepts, and statistical mechanics, her research group seeks to understand complex behavior emerging from simple rules and forces, and use that knowledge to design new materials. Glotzer's group also develops and disseminates powerful open-source software including the particle simulation toolkit, HOOMD-blue, which allows for fast molecular simulation of materials on graphics processors, the signac framework for data and workflow management, and several analysis and visualization tools.