The Pressure of Active Matter

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CBET 1437570Suspensions containing particles that can propel themselves through a liquid are interesting examples of a class of materials called active matter. The self-propelled particles, which are sometimes thought of as swimmers, can contribute to the properties of the suspension as a whole. This project will explore a novel concept called the swim pressure that can help characterize the state of such a suspension. The swim pressure is similar to the usual pressure that molecules in a gas exert on the walls of a container, but in this case the pressure is exerted by self-propelled particles that could be microorganisms, chemically reactive particles, or micro-motors moving through liquid. Preliminary data suggest that the swim pressure and its dependence on particle concentration can be used to predict changes in the suspension, including phase changes, deformation and motion, that cannot be predicted by other theories for active matter. The project will investigate the swim pressure and its utility in predicting suspension behavior by carrying out a series of numerical simulations. The results will be useful to scientists and engineers who process active matter suspensions in pharmaceutical, medicinal, food and similar industries.The micromechanical origin of spontaneous self-assembly in suspensions of self-propelled particles will be investigated by focusing on the swim pressure exerted by the particles. Numerical simulations based on Accelerated Stokesian Dynamics and other methods will be used to determine the variation of swim pressure with particle concentration, activity, etc., which can be used to formulate a nonequilibrium equation of state and pressure-volume phase diagrams for the suspension. Hydrodynamic interactions among the particles will be included in the computations. The swim pressure will then be correlated with detailed motions of the active particles that can lead to spontaneous formation of clusters, aggregates and other patterns, as well as the overall deformation and motion of the suspension.