A Pratt-Chandler theory

The eelebrated Pratt-Chandler (PC) theory is usually the starting point of any diseussion on the hydrophobie effeet. This theory ean be regarded as an application of the Weeks-Chandler-Andersen (WCA) perturbative theory of liquids to the solvation of one and a pair of non-polar solute moleeules. While Stillinger discussed the ehemieal potential involved in ereating a hard-sphere cavity in water using the scaled partiele theory, the Pratt-Chandler theory used an integral equation deserip-tion and showed how to properly discuss the effect within a general statistieal mechanical theory. 

We discussed in section 15.8 the essential ingredient of the PC theory. In particular, we discussed how Eq. (15.13) can be used to obtain the chemical potential of a non-polar solute in water. This expression requires the solute-solvent 

In order to investigate both the water structure in the vicinity of a non-polar solute (hydrophobie hydration) and the eorrelation between two solute molecules in water (pair hydrophobieity), one caleulates the change in local density of water molecules at r due to the introduetion of a solute molecule at the origin. According to the linear response theory, the response (that is, the change) of the densities is dependent on the structure of water in the absenee of the disturbance. As a result, the equations for solute-pair eorrelations become dependent on the water-water correlation functions for pure water. 

The PC theory uses integral equations of the liquid state to obtain the pair correlation fiinetions associated with spherical non-polar solutes in water. It 

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