Escape Dynamics of Elliptical Brownian Particles from Cavities: Numerical Simulations

We numerically study the escape kinetics of an elliptical Brownian particle from two-dimensional cavities with various pore structures and geometries. We emphasize a scenario in which the pore size is smaller than the particle's largest diameter yet slightly larger than its shortest diameter. In this case, the particle must adopt a specific orientation to exit through the narrow pore. Our simulation results indicate that, in addition to the particle's aspect ratio and pore structure, its rotational dynamics play a crucial role in the escape kinetics. We observed that, for flattened pore tips, the mean first passage time as a function of rotational diffusion exhibits a minimum, akin to the phenomenon of resonant activation. In the limit of very slow rotational diffusion, the mean escape time is directly proportional to the rotational relaxation time, irrespective of the pore structure. On the other hand, in the fast rotational limit, the mean exit time is inversely proportional to the square root of the rotational relaxation time for flattened pore tips. Additionally, the divergence behavior of the mean exit time as the pore size tends to zero depends largely on the rotational dynamics, in addition to the pore structure. Beyond direct applications in microfluidic devices and nanotechnology, our simulation results may also help in understanding the diffusion of living or artificial micro/nano nonspherical objects, such as bacteria, viruses, and Janus rods, where rotational relaxation time plays a significant role.