Comparison of mesoscopic solvation pressure at constant density and at constant chemical potential

The solvation pressures arising from the confinement of a fluid by surfaces are calculated under two different thermodynamic conditions, namely at constant density and at constant chemical potential, through mesoscopic scale simulations. We consider two types of fluids, a model monomeric solvent on the one hand, and a fluid composed of linear polymers dissolved in a monomeric solvent, on the other. For these systems our simulations show that the prediction of the solvation (or disjoining) pressure when the chemical potential is kept fixed is different from that obtained when the total density is fixed. We find however, that the same trend between both types of simulations can be obtained when the value of the fixed density is chosen as the average value of the density obtained at constant chemical potential.