Method of chemical substitution

This method applies only to very dilute systems. A second sample is used (of the same size as the first one) in which the polymer molecules are replaced by equivalent sets of non-chemically-bound monomers. The system being dilute, the correlations between monomers can be neglected and, in this case, the coherent cross-section reads [see (6.4.33)] 

Method of chemical substitution. Sample 2 consists exclusively of non-deuterated polystyrene. It is assumed that the contribution of the protons to the scattering signal is completely incoherent. The intensity I2(q) is represented by crosses ( + ). 

---