MCE Ph.D. Thesis Seminar

Chemically active particles may swim by self-diffusiophoresis in a concentration gradient of chemical solutes they created themselves by patterned surface catalytic reactions. Those particles also achieve particle-particle interaction by diffusiophoresis from the same solute concentration field, which can be attractive or repulsive. This 'field-driven' nature of the system makes its dynamics different from a thermodynamic system, and is analyzed with a new simulation method. Simulations show that attractive active particles exhibit the coexistence of dense and dilute regions, but is different from a liquid-gas phase equilibrium. To explain the dynamics, a continuum mechanics theory is developed with the minimal Active Brownian Particles (ABP) model. The surface force is found to be the swim stress, which can be anisotropic. The body force includes the average swim force as an internal contribution and an 'activity-gradient' force contribution. Further, behaviors of active matter at the sub-continuum scale are also analyzed. The continuum mechanics theory is applied to chemically active particles, and the system dynamics is explained well. The clustering process is explained with a linear stability analysis, and the steady state is explained with a sedimentation-like mechanical force balance.