Fluid-mediated forces enhance colloidal diffusion in pulsatile, "dynamic" porous materials
ORAL
Abstract
We study the transport phenomena of colloidal particles embedded within a moving array of obstacles that mimics a dynamic, time-varying porous material. While colloidal transport in an array of stationary obstacles ("passive" porous media) has been well studied, we lack the fundamental understanding of colloidal diffusion in a nonequilibrium porous environment. We combine Taylor dispersion theory, Brownian dynamics simulations, and optical tweezer experiments to study the transport of tracer colloidal particles in an oscillating lattice of obstacles. We discover that the dispersion of tracer particles is a non-monotonic function of oscillation frequency and exhibits a maximum that exceeds the diffusivity in the absence of obstacles. By solving the Smoluchowski (convection-diffusion) equation using a generalized dispersion framework, we demonstrate that the enhanced transport of the tracers depends critically on both the direct interparticle interactions with the obstacles and the fluid-mediated, hydrodynamic interactions generated by the moving obstacles.
*This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-21-1-0287. S.G.N. acknowledges support from the National Institutes of Health (1T32GM141846). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. S.C.T. is supported by the Packard Fellowship in Science and Engineering. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. Use was made of computational facilities purchased with funds from the National Science Foundation (CNS-1725797) and administered by the Center for Scientific Computing (CSC). The CSC is supported by the California NanoSystems Institute and the Materials Research Science and Engineering Center (MRSEC; NSF DMR 2308708) at UC Santa Barbara.
