From Colloidal Diffusiophoresis to Bacterial Chemotaxis in Complex Environments

Chemical gradients are ubiquitous in porous and confined environments, from soils and subsurface flows to tissues and biofilms, where they drive phoretic motion of passive colloids and emulsions and guide the chemotaxis of motile bacteria. Most previous studies treat these responses in simple, static, one-dimensional gradients and quiescent fluids, leaving open whether such weak, gradient-driven motions matter in the presence of flow and geometric disorder. In this talk, I will show how microfluidic experiments, theory, and simulations reveal that diffusiophoresis of colloids and emulsions, and chemotaxis of bacteria, can strongly reorganize transport in porous and heterogeneous environments: biasing particles across streamlines, modulating dispersion and retention, and reshaping microbial colonization patterns. In particular, I will demonstrate how chemical gradients can either amplify or suppress the influence of geometric disorder by steering particles and cells between slow and fast pathways. Together, these results suggest a unified framework for chemically guided transport in complex media, with implications for contaminant spreading, filtration, and microbial ecology.