97 research outputs found
Generalized Langevin equations for a driven tracer in dense soft colloids: construction and applications
We describe a tracer in a bath of soft Brownian colloids by a particle
coupled to the density field of the other bath particles. From the Dean
equation, we derive an exact equation for the evolution of the whole system,
and show that the density field evolution can be linearized in the limit of a
dense bath. This linearized Dean equation with a tracer taken apart is
validated by the reproduction of previous results on the mean-field liquid
structure and transport properties. Then, the tracer is submitted to an
external force and we compute the density profile around it, its mobility and
its diffusion coefficient. Our results exhibit effects such as bias enhanced
diffusion that are very similar to those observed in the opposite limit of a
hard core lattice gas, indicating the robustness of these effects. Our
predictions are successfully tested against molecular dynamics simulations.Comment: 21 pages, 7 figure
Molecular diffusion between walls with adsorption and desorption
The time dependency of the diffusion coefficient of particles in porous media
is an efficient probe of their geometry. The analysis of this quantity,
measured e.g. by nuclear magnetic resonance (PGSE-NMR), can provide rich
information pertaining to porosity, pore size distribution, permeability and
surface-to-volume ratio of porous materials. Nevertheless, in numerous if not
all practical situations, transport is confined by walls where adsorption and
desorption processes may occur. In this article, we derive explicitly the
expression of the time-dependent diffusion coefficient between two confining
walls in the presence of adsorption and desorption. We show that they strongly
modify the time-dependency of the diffusion coefficient, even in this simple
geometry. We finally propose several applications, from sorption rates
measurements to the use as a reference for numerical implementations for more
complex geometries.Comment: 4 pages, 2 figures, 1 supplementary material of 3 page
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