(552f) 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. New fabrication techniques developed over the past decade have enabled a wider range of anisotropic colloidal particles to be utilized in experiments and applications. One specific type of anisotropic colloid is a Janus particle, which consists of a base particle with a cap of a different material. The work presented in this talk seeks to determine the influence of gravitational and electrostatic torque on the dynamics of a Janus particle. These torques were systematically varied for a Janus particle with a cap of non-matching density and an asymmetry in zeta potential. Brownian dynamics simulations of a Janus particle very near a wall were conducted with systematically varied 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 show rotational torque due to the mismatch in density quenches the rotational diffusion and shifts the caped side of the particle to the lower angles, while electrostatic torque arising from a mismatch in zeta potential has a minor impact. The severity of quenching depends strongly on the coating thickness, cap material density and particle diameter. Initial experimental efforts for measuring quenching will also be summarized. 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.