Emergent Behaviors of Dense Active Suspensions Under Shear

Non-Technical Abstract The flow of dense suspensions comprised of microscopic particles in solution is important to a variety of industrial processes ranging from 3D printing to polishing of semiconductor components. This project seeks to develop a new knob for manipulating the flow of such materials. In particular, it is proposed that particle activity, i.e. using electric fields to inject energy in the form of particle rotations or other motions at the single particle level, can be developed into a novel knob for manipulating the properties of flowing suspensions. The work capitalizes on a novel combination experimental, simulation, and theory techniques developed by the PIs to map out the range of behaviors that activity in flowing suspensions can induce and determine the underlying organization of the suspended particles that drives these changes to the flow. In addition to these technological impacts, a number of education and outreach activities are proposed including science communication workshops, participation in research experience for undergraduate summer activities, and various outreach activities to the broader public. Technical Abstract Active matter has become a major branch of statistical mechanics where energy, rather than being conserved, is pumped into the system at the particle level. One of the great anticipated potentials of synthetic active materials is the ability to tune their macroscopic bulk properties through control of the microscopic interactions governing their constituents. To date, however, most active systems have been limited in their manufacturing scalability making it difficult to investigate bulk properties. This project capitalizes on the development of new Quincke rotor active systems that enable the investigation of the effect of activity on the bulk rheological properties of suspensions. The proposed work focuses on the effects of activity in the dense 3D regime since this is the regime where particles couple most strongly with one another and with the flow. In particular, it aims to determine how activity alters the rheological properties of suspensions including shear thickening and jamming transitions. Specifically, it is proposed to use experiments, simulations, and theory to determine: 1) how activity alters the shear behavior (e.g. thickening) of dense suspensions; 2) how the active particle interactions affect formation of mesoscale load bearing structures, and 3) how the force networks driving these behaviors are organized spatially. These investigations will provide a new knob, activity, for tuning the rheological behaviors of suspensions, an important material system for processes ranging from 3D printing, to polishing in semiconductor processes. In addition to these technological impacts, a number of education and outreach activities are proposed including science communication workshops, participation in research experience for undergraduate activities, and various outreach activities. 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.