Measurements of intrachain correlations

Measurements of intrachain correlations have been made by Matsushita et al.lB in order to determine experimentally how the swelling of a portion of chain varies with its position within the chain. 

Non-uniformity of swelling was predicted, by Yamakawa and later by des Cloizeaux. This effect appears in the expansion of the mean square distance, as a function of the interaction b (see Chapter 10, Section 7.2). The inhomogeneity effect is related to a fundamental property of swelling. Let us then give an experimental evaluation of this phenomenon. 

We are dealing here with distances greater than the persistence length /p ( 2 nm for polystyrene) related to a local rigidity of the chain. The experiment consists in the determination of gyration radii of chains or portions of chain having the same Brownian area S, but located in different places  

Matsushita et al. used three types of samples in order to determine the Rq associated with the different areas S mentioned above  

The solvent used in all cases is CS2, which is considered to be a fairly good solvent. The interaction b associated with polystyrene in CS2 is worth 0.97 nm 1 at 25°C [see (1,5.3.48) and Fig. 15.8, p. 000]. The experiment being carried out at 20 °C, we shall take the value b = 0.7 nm 1 for the interaction. In this case, the thermic correlation length has the value = 2.85 nm. We note that the latter is smaller than the end-to-end distance R of the sequences under consideration. (R y/Js — 10 nm) this point is not crucial, however. 

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