Pure solvent structure function and compressibility

For pure solvent, the situation is especially simple in this case, we have only one concentration C0, one fugacity f and one structure function H()0 (q) (zero is the solvent index). 

there exists a relation between ff00 (8) and the compressibility. In fact, (9.3.15), (9.3.24), and (9.3.34) take the simple form 

When a radiation is scattered by density fluctuations, the scattered intensity is directly proportional to the structure function (see Chapter 7). Thus in the zero angle limit, the scattered intensity is proportional to the compressibility. 

This relation will be generalized in the following sections and we shall find another important relation between the structure function and the osmotic pressure. 

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