Entropic diffusion in confined soft-matter and biological systems

Department of Condensed Matter Physics, Faculty of Physics, University of Barcelona - Diagonal 647, 08028 Barcelona, Spain and PoreLab, Department of Physics, Norwegian University of Science and Technology, NTNU - Trondheim, Norway

Received: 15 July 2019
Accepted: 16 July 2019

Abstract

To know how particles move in small cavities, micro-channels and in general in crowded media currently constitutes a challenge for the understanding of basic mechanisms governing the behaviour of small-scale soft-matter and biological systems. The presence of obstacles, constrictions and irregularities in the shape of these structures significantly alters their trajectories thus modifying their transport properties. An analysis of these properties based on the use of diffusion and stochastic equations faces the problem of solving these equations for very complex boundaries which may constitute a formidable task. Recent studies on transport through confined media have shown that this problem can be considerably simplified if one assimilates spatial restrictions to the entropic barriers which particles must surmount in order to proceed. A wide variety of situations can be studied in this way, including many that were thought to be beyond the reach of classical transport theories, such as diffusion through deformable channels, motion of ions at very small length scales and behaviour of confined active matter.