(440g) Hydrodynamic Coupling to the Electrical Response of Fluid Suspensions of Non-Brownian Conducting Particles

We describe the electrical response of conducting non-Brownian suspensions to start-up shear. These observations are made in a rheo-dielectric device that tracks the transient and steady electrical response of complex fluids to well-defined deformations. We show using dc-conductivity measurements a shear-rate dependent conductivity that increases both with the shear intensity and the particle volume fraction. The conductivity increases instantaneously upon flow start-up and returns instantaneously and reversibly to the quiescent value upon flow cessation. For volume fractions exceeding 30 vol% microspheres, the ratio of the conductivity under flow to that in the quiescent state can exceed a factor of 10⁵. We further examine the origin of this increase using impedance spectroscopy. These measurements reveal a dielectric relaxation feature that is associated with the pair hopping rate of electrons between particles within the suspensions. By fitting this dielectric response, a characteristic hopping time can be extracted that is linear with shear rate. These results agree quantitatively with a simple scaling model that approximates the pair-hopping rate as proportional to the collision frequency of particles within the suspension. This result confirms that the hydrodynamic force imposed by simple shear couples to the interparticle charge transfer rate. In this way, the electrical response is directly linked to the displacement rate of the fluid. These observations help to reconcile emerging experimental evidence for the role of particle mobility in determining electrical transport in colloidal fluids and suspensions and could prove a basis for new mechano-electric sensing modalities as well as improved electrochemical storage technologies.