  This work tests the statistical mechanical theory of hydrophobic
interactions, isolates consequences of excluded volume interactions, and
obtains B2 for those purposes. Cavity methods that are particularly appropriate
for study of hydrophobic interactions between atomic-size hard spheres in
liquid water are developed and applied to test aspects of the Pratt-Chandler
(PC) theory that have not been tested. Contact hydrophobic interactions between
Ar-size hard-spheres in water are significantly more attractive than predicted
by the PC theory. The corresponding results for the osmotic second virial
coefficient are attractive (B2 <0), and more attractive with increasing
temperature (Delta B2/Delta T < 0) in the temperature range 300K < T < 360K.
This information has not been available previously, but is essential for
development of the molecular-scale statistical mechanical theory of hydrophobic
interactions, particularly for better definition of the role of attractive
intermolecular interactions associated with the solutes.
