Biological & Soft Matter Seminar: Uphill drift in the absence of current in single-file diffusion

Abstarct:

Single-file diffusion is a paradigmatic model for the transport of Brownian colloidal particles in narrow one-dimensional channels where the particles cannot cross each other. We study the effect of spatially varying potential and diffusivity on the dispersion of a tracer in such systems. 

We concentrate on a system where a different external uniform potential is present to the right and left of an origin. For example, this is the case when two channels meeting at the origin have different radii. In equilibrium, the chemical potential of the particles are equal, the density is thus lower in the region with the higher potential, and by definition there is no net particle current to either region. 

At the same time, we find that a single-file tracer particle initially located at the origin exhibits an average uphill drift toward the region of highest potential. This surprising effect is shown analytically by computing the first two moments of its displacement and also via numerical simulations.

A joint work with David S. Dean (University of Bordeaux).