Solvophobic interaction between hard spheres in a square-well fluid

Indirect interaction between hard spheres through solvent molecules is studied in a square-well fluid by a Monte Carlo method. The solvophobic interaction between hard spheres induced by the solvent-solvent interaction is repulsive in a close distance and attractive in the outer region. The solvophobic interaction extends to long distance at a medium density about half of the density of the usual liquid: while it has a local characteristic at the high density. The solvophobic interaction relies on the competition in the decrease of both the repulsive and the attractive indirect forces with the increase in the solvent-solvent interaction. The complicated fluid structure between the hard spheres is responsible for the larger decreasing rate of the repulsive force, which leads to the molecular association by the solvophobic interaction.