Entropic transport in a crowded medium.

To know how liquid matter moves through a crowded medium due to the action of a force constitutes currently a problem of great practical importance, present in cases as diverse as the transport of particles through a cell membrane and through a particulate porous medium. To calculate the mass flow through the system, we present an approach that emulates the texture of the medium by using entropic barriers that the particles must overcome in order to move. The model reproduces the scaling behavior of the velocity with the force found in many systems in order to show how the scaling exponent depends on the micro-structure of the medium. Our model offers a new perspective that is able to characterize the flow of matter through the medium and may be useful in studies of nano-fluids, oil recovery, soil drainage, tissue engineering, and drug delivery.