(70g) Simulations of Nonlinear Flows in Nonequilibrium Complex Liquids

Complex liquids, such as active biofluids and colloidal suspensions, are important for biophysical and other industrial applications. Here we focus on dense suspensions of semi flexible bioplomers, such as microtubule and actin filaments. When the biopolymer concentration is high, it exhibits nematic phase. And if motor protein clusters and adenosine triphosphate (ATP) are added to the suspension, biopolymers are able to slide on each other due to the action of motors - such collective motion leads to a spontaneous, cohesive flow in the system. The nature of such flows is not fully elucidated. Here we rely on a continuum hydrodynamic model of active nematics to characterize such nonequilibrium liquids. The model is realized via a hybrid lattice Boltzmann solver. We first validate the model by comparing it to benchmark problems of passive nematic liquid crystal flows and active nematics experiments. We then extend it to include unequal elasticities and local concentration variations. The model is able to describe actin-based active nematics with variable activity and elasticity. We further apply it to explain the ordered flow emerged from confinements and anisotropic boundaries. Based on the above results, we propose that active nematics can be the candidate for active microfluidic devices. Finally, we investigate the transient flows in dense suspensions. Discrete element method is used to simulate a suspension of bi-disperse non-Brownian spherical particles. As the system is subject to a sudden simple shear, dynamic jamming happens as there is a propagating wave moving with a constant speed. We focus on how the inter particle frictional force and the short-range repulsive force determine the formation of the front and its velocity. Our simulations provide detailed structures of the suspension at transient state and therefore helpful for elucidating the transient dynamics of dense suspensions.