(483e) Macrotransport of Replicating Species in Chemically Compressible Flows

Diffusiophoresis (DP) and chemotaxis (CT) have fundamentally different origins: DP refers to the deterministic motion of a larger (living or non-living) species induced by the concentration gradient of a smaller chemical species via electrokinetic interactions, whereas CT refers to an analogous deterministic motion but generated by the biological response of the larger, living species, which is capable of replication. Spanning across the organic and inorganic regimes, DP and CT underlie a wide array of applications from enhanced oil recovery to guided drug delivery and are principle mechanisms for microorganisms seeking favorable environments for survival. Unifying DP and CT is the compressible, deterministic flow of the larger species (referred to as colloids in the following) owing to the spatially varying chemical concentration (referred to as solute). In this talk, we present a novel framework which models a higher order DP and/or CT process of self-replicating colloids under the influence of an external flow via a one-dimensional macrotransport equation. We predict that two new transport phenomena ensue from the competition between the external flow, the chemically compressible flow induced by solute gradients, and the replicability of the colloids. First, dispersion reduces spreading of colloids. Such a non-intuitive phenomenon is a consequence of a strong external flow smearing out the solute gradient, hampering super-diffusion of colloids at long times, thus reducing spreading of colloids compared to a DP/CT process in the absence of an external flow. Second, self-replicating colloids whose reproductivity/death rate varies spatially will impact their own spreading profiles in the same manner as a compressible flow. In closing, we discuss how the present model could be employed to address the ongoing challenge of measuring the chemotactic sensitivity of microorganisms. We also discuss the arrested spreading and super-diffusion phenomena predicted recently in the context of DP and CT.