Technique of labelled molecules

The technique of labelled molecules13 provides the possibility of determining the structure functions H (q) and H (q) of the solute for any concentration. We shall use the more explicit notation 

The method consists in measuring the apparent structure function associated with different labelled solute fractions. Let pD be the mass concentration of the labelled chains. For a solvent that occults the non-labelled molecules, the 

Incidentally, we note that for neutral polymer solutions, the form function can also be determined in a simpler way, by choosing the solvent composition so as to get zero average contrast (C, b + C2 bj = 0). 

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This situation changed not long ago polymer solutions with overlap have aroused new interest. The use of neutron scattering and the technique of labelled molecules has contributed to this change. Furthermore, a decisive step was taken when it became obvious that experiments on solutions with overlap are easily interpretable in terms of the concentration p and of the basic quantities Rg and A2 (which are defined for p - 0). In other words, it is necessary to account for swelling effects, which remain important... 

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