8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P9.34Tue 611:23-14:00Reverse osmosis in non-equilibrium simulations withactive solute particlesThomas Lion 1 and Rosalind Allen 11 SUPA, School of Physics and Astronomy University of Edinburgh, MAYFIELD ROAD,EH9 3JZ, EDINBURGH, United KingdomOsmosis is a fundamental and important process, responsible for physical and biological phenomenaranging from water desalination to the flow of sap in plants. In the classic osmosis experiment,in which two solutions of differing concentration are separated by a semi-permeable membrane,an initial imbalance in the solvent chemical potentials causes solvent to flow from low to highsolute concentration. This leads to the well-known osmotic pressure difference at equilibrium. Wepresent Molecular Dynamics(MD) simulations of a non-equilibrium version of this experiment,in which the solute particles are active. This is achieved by maintaining the solute particles at ahigher temperature than the surrounding solvent. We show that an interesting and counter-intuitivephenomenon can occur in this case: the active solute particles can drive reverse osmosis, in whichthe solvent is driven out of the more concentrated solution. We analyse the physical basis of thisfinding using a modified version of the Virial relation. Our results could have interesting implicationsfor the likely osmotic behaviour of suspensions of active particles such as motile bacteria orcolloidal “swimmers”.34