THE STRUCTURE OF A FLUID CONFINED BY PERMEABLE WALLS

Osmosis has been studied using the methods of molecular dynamics and f or several different models of a semi-permeable barrier. One of these models has also been used in theoretical and Monte Carlo investigation s of the effect of such a barrier on the structure of a hard sphere fl uid (Marsh, P., Rickayzen, G., and Calleja, M., 1995, Molec. Phys., 84 , 799; Kim, S.-C., Calleja, M., and Rickayzen, G., 1995, J. Phys.: con dens. Matter, 7, 8053). Results presented in these papers showed that this problem also provides a sensitive test for the validity of variou s density functional theories. In order to bring the theory to bear on the problem of osmosis, this earlier study is extended to the hard co re Lennard-Jones fluid. At the same time a new sum rule for the densit y of a fluid in a periodic potential, which provides a useful check on the computations, is derived. It is again found that the agreement be tween the computed and the simulated density profiles is good except a t the centre of the barrier and when the bulk density and pressure are close to the critical.