Brownian Interactions in Colloid-Polymer Mixtures

Department of Mechanical Engineering

University of Connecticut

Predicting transport properties and interactions of colloidal particles in complex or polymer fluids is important for advancing manufacturing and storage of food, pharmaceutical, and chemical products. One of the interesting behaviors in colloid polymer mixtures is the macromolecular crowding, that is influence of the surrounding polymers or other crowding agents on the diffusivity or association of the nano-particles. In submicron scale, both of the colloidal particles and polymer chains are influenced by thermal fluctuation in aqueous solutions. The polymer molecules continuously sample their environment and to avoid loss of configurational entropy close to the surface of the particles, polymers tends to be away from the particle surface and a depletion zone forms around particle, which also alters the mobility of particles. The focus of this work is on microscopic dynamics of colloidal motion, specifically the stochastic and correlated motion of pair and many particles in nonadsorbing polymer solutions. On the fluid flow aspect a boundary integral model has been developed to compute the pair additive mobility tenser. The hydrodynamic mobility is connected to the thermal fluctuation through the fluctuation dissipation theory so the Brownian random force applied to the colloids can be realized in the diffusive regime. The effect of the depletants on the auto- and cross correlation of pair interactions are investigated in details.