  Based on our recent study on physical origin of hydrophobic effects, this is
applied to investigate the dependence of hydrophobic interactions on the solute
size. As two same hydrophobic solutes are dissolved into water, the hydration
free energy is determined, and the critical radius (Rc) is calculated to be 3.2
Angstrom. With reference to the Rc, the dissolved behaviors can be divided into
initial and hydrophobic solvation processes. These can be demonstrated by the
molecular dynamics simulations on C60-C60 fullerenes in water, and CH4-CH4
molecules in water. In the association of C60 fullerenes in water, with
decreasing the separation between C60 fullerenes, hydrophobic interactions can
be divided into H1w and H2s hydrophobic processes, respectively. In addition,
it can be derived that maximizing hydrogen bonding provides the driving force
in the association of hydrophobic solutes in water.
