(623g) Influence of Cap Weight on the Motion of a Janus Particle Very Near a Wall

Colloidal particles dispersed in a liquid interact via surface forces, which will have a profound impact on the microstructure, properties, and ultimate performance of the material. Understanding these surface interactions and subsequently predicting dynamic particle behavior are important to the design of colloidal particles in real applications. This talk will summarize our work on determining the influence of gravitational and electrostatic torque on the dynamics of a Janus particle. Brownian dynamics simulations were conducted for Janus particles very near a boundary, where near-wall hydrodynamics plays a significant role. Torque was systematically varied for a Janus particle with a cap of non-matching density and an asymmetry in zeta potential. Further variations for the simulation included hemisphere zeta potential (-5 mV and -50 mV), particle diameter (1 mm – 6 mm), cap coating material (gold and titanium) and thickness (0 – 40 nm). Results from these simulations showed rotational torque due to the mismatch in density quenches rotational diffusion, while electrostatic torque arising from a mismatch in zeta potential had a minor impact. The severity of quenching depended strongly on the coating thickness and particle diameter. Our findings demonstrate the role of Janus particle cap properties on the rotational dynamics of the particle, which is an important characteristic relevant to a variety of experimental systems.