(432f) Macrotransport of Chemotactic and Diffusiophoretic Species: Characterizing Species Spreading, Size, and Diffusivity

The transport of chemotactic microorganisms shares the same “log-sensing” response with diffusiophoretic colloid motion, despite their distinct physico-chemical and biological origins. In this work, we employ a recent macrotransport theory to analyze the advective-diffusive transport of a chemotactic or diffusiophoretic colloidal species (colloids) in a uniform circular channel under a pressure-driven flow. Chemotactic/diffusiophoretic colloid motion is caused by a transient solute gradient and is competing with hydrodynamic dispersion due to the pressure-driven flow. We derive an exact solution for the chemotactic/diffusiophoretic colloid macrotransport. The exact solution enables an efficient quantification of the large parameter space in colloid chemotaxis/diffusiophoresis. We reveal that by competing with chemotaxis/diffusiophoresis hydrodynamic dispersion can increase or mitigate the overall colloid spreading. We generalize the exact solution to decaying colloids, e.g. death of microorganisms, and show that the evolution of colloid spreading is not altered by colloid decay. To capture a hallmark of chemotaxis that log-sensing occurs only over a finite range of solute concentration, we extend our analysis by adopting a more biologically realistic model that prescribes a hybrid logarithmic and linear dependence of the chemotactic velocity on the solute concentration. Utilizing numerical simulations, we present new regimes of colloid sub-diffusion and super-diffusion, matching qualitatively with experiments. Lastly, we propose a new technique to measure the size and diffusivity of chemotactic/diffusiophoretic colloids using hydrodynamic dispersion. Our findings will enable new analytical and modeling tools for characterizing chemotactic/diffusiophoretic colloids as well as designing their transport under hydrodynamic flows. These are central to understanding biological processes such as intracellular protein localization and biofilm formation; and devising applications including drug delivery, enhanced oil recovery, and bioremediation of aquifers.