(409f) Brownian Dynamics of a Spherical Janus Particle Near a Boundary As a Tool to Investigate TIRM

Authors: 
Rashidi, A., Cleveland State University
Wirth, C. L., Cleveland State University
Colloidal particles dispersed in a liquid interact via surface forces to form microstructure that may have a profound impact on the mechanics and rheology of that liquid. Total Internal Reflection Microscopy (TIRM) has been used for decades to measure very weak ~kT scale colloidal interactions, including electrostatic double layer repulsion, van der Waals attraction, steric repulsion, depletion attraction, hydrodynamic friction, and even the Casimir force, between a sphere and flat plate. Unfortunately, one major restriction currently imposed by TIRM is that the particle needs to be chemically uniform and geometrically spherical. In response to this need, we are currently developing the theoretical and experimental tools to conduct TIRM of anisotropic particles. This talk will summarize our efforts to use Brownian Dynamics simulations to conduct in silico TIRM of a Janus sphere very near a boundary. We systematically altered a variety of system and experimental parameters, including the zeta potential of each half of the Janus sphere, sampling rate, measurement duration, and salt concentration, to test the impact and optimize conditions. We simulated the position and rotational trajectories near a boundary and subsequently calculated potential energy landscapes for the Janus particles. Results show that the Janus sphere will sample a potential energy landscape with a transition region at the location of the boundary between the two Janus halves, which depends on the relative zeta potential magnitude. Additionally, simulations show that an experiment may require more than 106 observations to obtain a suitable potential energy landscape. These results demonstrated the utility of Brownian dynamics simulations as a tool to probe TIRM for anisotropic particles.