CAREER: Unveiling the Stability, Rheology, and Topology of Active Fluids

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This CAREER award involves emerging field of active fluids, which are a new class of liquid materials made up of densely packed suspensions of particles that can propel themselves by converting energy from locally available fuel into locomotion. Active fluids hold great potential for the development of new materials and products, but realizing this potential requires a quantitative understanding of the unusual material properties and transport mechanisms that these fluids exhibit, which can be much different than the properties of suspensions of inert particles. This project will combine theoretical analysis and numerical simulations to build a holistic computation framework for modeling, analysis, and control of active fluids in complex microfluidic environments. The project will provide undergraduate and graduate student training, create K-12 outreach opportunities, and support the development of a Virtual Reality package that will help interpret research results and enrich classroom teaching. The Virtual Reality package and demos will be available online to the general public, along with some of the open-source computation codes developed in the project, which will benefit both students and researchers in applied science and engineering.The physical properties of active fluids are fundamentally different from those of classical equilibrium systems. When suspended in a liquid, motile microparticles exert stresses on the ambient flows, which acts as a coupling medium for generating large-scale, unsteady collective dynamics. These concentrated systems often show common features, including ordering transition, fluctuating density, and force generation. The research in this project will take the next engineering step of learning how to manipulate active fluids by taking full advantage of their collective behaviors. The project consists of four research thrusts: (1) Develop a hybrid algorithm that combines penetration-free Stokesian dynamics particle simulations and coarse-grained active liquid crystal models; (2) Study the hydrodynamic instabilities and coherent flows; (3) Investigate non-equilibrium rheological properties and topological structures; and (4) Design active-liquid metamaterials for novel engineering applications. The hybrid algorithm will follow a bottom-up multiscale approach. The microscale discrete particle dynamics will be used to construct continuum kinetic models and new "polar" active liquid crystal models. The computational framework will permit researchers and practitioners to control active fluids by adjusting particle activity and interactions at the microscale, and by controlling and guiding constrained coherent flows at the macroscale. The numerical studies, together with supporting experimental verifications, will lead to quantitative understandings of the linkages between dynamics across scales, and possibly to new engineering devices for transporting fluids and particles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.