Impact of density fluctuations on solvent-induced interaction: A combined theoretical and simulation study

This study investigates solvent-induced interactions between two large particles immersed in a Lennard-Jones (LJ) solvent bath using molecular dynamics simulations and classical density functional theory. The LJ energy parameter between the large particles and the solvent particles is 1.439 times that of solvent–solvent interactions. The predictions of excess mean force align well under supercritical conditions with moderate or lower bulk solvent densities and moderate temperatures. However, deviations arise at high-density and high-temperature conditions, attributed to the reflective boundary conditions used in the theoretical calculations, which inadequately capture solid-like ordering effects. The study further explores the temperature dependence of the excess potential of mean force (PMF) at fixed reduced bulk densities ranging from 0.1 to 0.6 (in increments of 0.1). Within the gas density range, the excess PMF exhibits attractive behavior, with potential depths reaching up to 30 times the solvent particle LJ energy parameter as the gas density decreases and the temperature approaches saturation. Conversely, in the solvent liquid density range, the excess PMF remains repulsive, even near the saturation temperature. As the temperature increases, the excess PMF shifts upward, becoming less attractive or more repulsive, with the gas density range showing greater temperature sensitivity compared to the liquid density range. The substantial deepening of the potential well in the excess PMF leads to a significant increase in the critical temperature. Consequently, under a fixed system temperature, the working fluid operates in subcritical conditions. This behavior opens avenues for various phenomena, including wetting transition, enhanced adsorption and modified self-assembly, which can be exploited to achieve specific technical objectives.