Chemotactic Phase Separation in Size-Asymmetric Microcompartments

Chemotactic motion in active colloids is not driven by chemistry alone, as the surrounding fluid plays a crucial role in their collective behavior. Yet most models omit the near-field “lubrication” forces that arise when two particles approach and a thin layer of fluid is squeezed between them; these forces strongly influence how clusters form and reorganize. We present a Stokesian Dynamics framework that couples a self-consistent chemical model, with enzyme uptake dictated via Michaelis–Menten kinetics, to a many-body hydrodynamic solver that explicitly resolves near-contact lubrication as well as long-range interactions. Benchmarks against analytical and finite-element solutions validate the chemical field used for chemotaxis and capture gradient flattening near the surface of an active particle. 

Using this framework, we investigate chemotactic phase separation in mixtures of enzymatically active bacterial microcompartments with different sizes. The coupling between size-dependent chemotactic response and hydrodynamic interactions leads to spatial segregation and clustering dynamics. This approach provides a computational platform for studying how hydrodynamics and chemical signaling jointly control organization in bacterial microcompartment systems and related active colloidal suspensions.