(7hn) Spherically Confined Colloidal Suspensions of Hydrodynamically Interacting Particles: A Model for Intracellular Transport

We study the diffusion in and rheology of hydrodynamically interacting colloids confined by a spherical cavity via dynamic simulation, as a model of intracellular and other confined biophysical transport. The modeling of transport and rheology in such confined inhomogeneous soft materials requires an accurate description of the microscopic forces driving particle motion, such as entropic and hydrodynamic forces, and of particle interactions with nearby boundaries. Previous models of such micro-confined transport behavior had been limited primarily to a single particle inside a spherical cavity. Although attempts had been made to extend such models to more than one confined particle, none had yet successfully accounted for the effects of hydrodynamics, owing to the difficulties of modeling many-body long-ranged interactions. To accurately model spherically confined suspensions, we derived new far-field mobility functions and, together with the appropriate near-field resistance functions, implemented them in a Stokesian-dynamics like approach. The method fully accounts for all many-body far-field interactions and near-field interactions both between the particles themselves and between particles and the enclosing cavity. Utilizing our newly developed method, we study short- and long- time self-diffusion at equilibrium, with a focus on the dependence of the former on particle positions relative to the cavity, and of both on volume fraction and size ratio. We find the cavity exerts qualitative changes in transport behavior, such as a position dependent and anisotropic short-time self-diffusivity and anisotropic long-time transport behavior. Such qualitative changes suggest that careful interpretation of experimental measurements in 3D confined suspensions requires accounting for such confinement induced behaviors. To elucidate the effects of confinement on inter-particle hydrodynamic interactions, we utilize our method to determine the concentrated mobility of particles in the spherically confined domain. We find that confinement induces qualitative changes in the functional dependence of particle entrainment with inter-particle separation. For widely separated particles, the functional dependence on inter-particle separation can be predicted via a Green’s function, we discuss how this behavior can be utilized to develop a more accurate framework for two-point microrheology measurements near confining boundaries.

Teaching Interests:

My primary teaching interests are in topics related to fluid mechanics, transport phenomena, soft matter physics and mathematical methods at both the undergraduate and graduate level. In teaching, I am interested in instilling in students the need to understand these subjects from first principles, and in clearly communicating both the subject matter and its importance in practical applications.