CAREER: Mixing and Vorticity Dynamics in Active Fluid Systems

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This CAREER project will explore the mixing dynamics and kinematics of active fluid systems. Researchers and industrial practitioners often use microfluidic technology to process tiny quantities of fluids, which minimizes waster and enhances flexibility and efficiency. Microfluidic systems manipulate fluids at a very small scale, typically smaller than one millimeter. Progress in microfluidic technology is limited by the challenge of mixing at a small scale, because it is difficult to generate turbulence at in very small channels. Active fluids are fluids containing discrete entities that move under their own power and may be able to promote local mixing. Even in tiny spaces, active fluids can generates turbulence and promote micromixing. This research will explore the mixing process and vortex dynamics of active fluids, including the equations that describe the process, the effects of varying fluid activity and boundary conditions, and the effects of combining an active fluid with an inactive fluid. The resulting knowledge will stimulate development of new micromixing technologies that will increase production efficiency in the chemical engineering and pharmaceutical industries, enable products to be synthesized on demand, and reduce the need to store and transport hazardous or reactive chemicals. This project will also provide K-12 students with hands-on experiences in mixing dynamics through a contest mixing two different colors of dough and an online active matter simulation program. This project will also include an online teacher training module to help bring active matter concepts to US classrooms.Active turbulence has been characterized and modeled, but little is known about how active turbulence facilitates mixing. Several fundamental questions remain unanswered, such as, “What is the mixing efficiency of an active fluid system?” and “What parameters control the mixing efficiency of active fluid?” To address these questions and expand knowledge about active turbulence-induced mixing, the mixing process of microtubule-kinesin active fluid will be modeled by modifying established active nematohydrodynamic equations developed to characterize active turbulence. This project will extend the existing active nematohydrodynamic model to describe active fluid systems with inhomogeneous activity, a moving boundary, and multiple fluids. The expanded model, which will be validated with accompanying experiments, will guide the application of active fluid in science and industry and allow engineers to efficiently explore parameter space to optimize novel self- mixing systems, particularly at the micron scale. This project will connect two well-established fields— mixing and active fluid modelling —and thus extend established mixing theory to include active fluids and elucidate differences between how active and passive fluids mix.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.