Chemistry Weekly Seminar - Sheida Ahmadi

Title: Diffusion in highly confined channels: A transition state theory for hopping times

Brownian particles confined to narrow, quasi-one dimensional channels exhibit a dynamic transition from single file diffusion (SFD) to normal diffusion as the channel diameter reaches a passing threshold where the particles are able to hop past each other. In this crossover regime, molecular simulations have shown that the long time diffusion coefficient of the particles can be described in term of a hopping time, defined as the average time a particle performs SFD before escaping the cage formed by its neighbors. We use a two-particle small system isobaric-isothermal, n,p,T, ensemble to develop a Transition State Theory approach to calculating the hopping time for a confined hard disk fluid. The method is then used to explore how particle-particle and particle-wall interactions influence diffusion in narrow channels. Finally, we also begin to explore the possibility of using the SFD-normal diffusion crossover regime for the dynamic separation of mixtures.