This award will support collaborative research between Dr. John Brady, California Institute of Technology, and Dr. George Bossis, Laboratoire de Physique de la Matiere Condensee, University of Nice, France. The objective of this research is to study the transport properties of fractal aggregates and polymers by dynamic simulation. The past several years has seen an increased interest in the transport properties of condensed matter in the form of colloids, ceramics and polymers. Part of this interest arises from the practical uses of such substances, motivated by the potential to design and manufacture materials with novel and desired properties. A large part of the recent theoretical activity in these research areas has been sparked by the recognition that collodial aggregates and polymers have an important geometrical feature in common--they are fractals. A fractal is an object that is not space filling; the mass does not grow as the radius cubed, but rather to some other power called the fractal dimension. Fractals also possess a dilational symmetry; that is, the object looks the same at least statistically, regardless of the magnification used. These two aspects, particularly the dilational symmetry, have allowed researchers to make simple and far reaching predictions about polymer structure and properties. The transport properties of polymers and collodial aggregates depend on the basic fractal microstructure, and an understanding of the relationship between structure and property will aid in predicting and controlling the manufacture of these microstructured materials. In this project, the investigators will use a general molecular-dynamics-like method which they have developed together, called Stokesian dynamics, with the aim of providing a computational bridge betwen analytical theories and laboratory experiments. A major focus of the work will be to assess the importance of hydrodynamic interactions and the restrictions imposed by the preaveraging assumption on aggregate and polymeric behavior. This project will benefit from the specific expertise of Dr. Bossis in statistical mechanics and Dr. Brady's background in fluid mechanics.
