Hydrophobic Interaction at More Realistic Distances

In Section 8.5, we devised a measure of the HI at some distance R a (a being the solute diameter) which was found useful for a systematic comparison of various solvents. In Section 8.8, we discussed the case jR = 0. In both cases, it was argued that since our primary interest is the solvent rather than the solute, we can study the problem of HI at any convenient distance for which we get a connection with experimental quantities. 

In this section, we turn to a more practical question What is the strength of the HI at contact, or approximately contact, distance for a pair of solute particles After all, one should eventually return to the original problem of HI between real solute molecules approaching each other to a distance of cr at most. 

We outline here two possible routes for obtaining such information. The full answer to the question is contained in the study of the function gssW [or equivalently yssi )] topic which will be mentioned in Section 8.12. 

In Section 2.6, we also saw that the function y(i ) is a monotonically decreasing function of R in the range 0 cr. We write here the form 

Right and left scales correspond to curves b and a, respectively. 

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