Using Phase Field Models to Simulate the Full Chemohydrodynamics of Passive and Active Colloids*

Colloidal particles can migrate in a solution in response to a solute concentration field, a phenomenon known as diffusiophoresis. Chemically active colloids can modify the concentration field of its surrounding, thus harvesting energy from the environment to self-propel or to change the trajectory of neighboring colloids. To date, the most efficient methods to simulate these active systems rely on Green's functions of the Laplace and Stokes operators that are only valid in the steady and dilute limits. However, many active systems of interest display interesting feedback behavior in dense and unsteady systems. We have recently developed a method using phase field models that performs full chemohydrodynamics simulations of such dense and unsteady systems and incorporates colloidal particles as highly viscous fluid phases. We demonstrate the feasibility of this approach by simulating diffusiophoresis of colloidal particles and comparing to known theoretical results. We also demonstrate the capacity of the method to simulate self-diffusiophoresis by adding asymmetric chemical reactions to colloidal systems. Finally, we explore the computational and phenomenological limits of the method by simulating multi-particle phoretic motion coupled to complex concentration fields.