The concept of effective depletion forces between two fixed big colloidal particles in a bath of small particles is generalized to a non-equilibrium situation where the bath of small Brownian particles is flowing around the big particles with a prescribed velocity. In striking contrast to the equilibrium case, the non-equilibrium forces violate Newton's third law, are non-conservative and strongly anisotropic, featuring both strong attractive and repulsive domains.
@article{arxiv.cond-mat/0306069,
title = {Depletion forces in non-equilibrium},
author = {J. Dzubiella and H. Lowen and C. N. Likos},
journal= {arXiv preprint arXiv:cond-mat/0306069},
year = {2009}
}