(6ai) Computer Simulations of Complex Fluids and Materials

Colloidal and polymeric systems and suspensions of elastic materials are often classified as "complex fluids" owing to the nonlinear relationship between the applied forces and resulting dynamics. This complexity arises from the wide range of time and length scales that govern their motion. The motion of such systems depend on a variety of different factors such as particle interactions and large scale collective motion related to structural relaxations. The simplest class of interactions are the direct inter-particle interactions such as electrostatic interactions and hard-sphere collisions which also exist in simple fluids. In addition to these, sub-micronsolute particles in a colloidal suspension are coupled in their motion through the fluid. This coupling is called "hydrodynamic interaction" and constitutes the focus of my work. These hydrodynamic interactions are long ranged and many-body, therefore they create a great deal of complexity for theoretical calculations as well as for traditional computational methods.

In my research, I investigate the dynamics of complex fluids with the lattice-Boltzmann method for fluid flow and a variety of mechanical models for suspended solid and deformable particles. Such an approach leads to the solution of Navier-Stokes equations on large time and length scales. The lattice-Boltzmann method is closely related to and is a descendent of the lattice-gas cellular automata; it has proven to be a computationally competitive, accurate, and flexible simulation method for complex fluids. In the lattice-Boltzmann method, hydrodynamic interactions, between solid objects, arise naturally as a result of local momentum conservation and exchange between solid and fluid phase. The flexibility is due to the ease of incorporating boundary conditions for a wide variety of different shapes of objects.

In this session, I will present the current research on both the method itself and applied problems in sorting of both polymer solutions and microcapsules. I will also discuss the future research ideas where this approach can make a significant impact.