NSE Results from Stars in Dilute Solution

2 NSE Results from Stars in Dilute Solution Completely Labelled Stars 

The salient feature of the experimental results is the observation of a pronounced minimum in the Q(Q)/Q3 vs. z plot. It occurs at the same position, where the static structure factor in its Kratky representation exhibits its maximum. Furthermore, the reduced line width scales with the scaling variable z in the same way that the static structure factor does. Thus, the occurrence of the minimum is directly related to peculiarities of the star architecture. 

In the theory of liquids, such a phenomenon is well known under the term of de Gennes narrowing [152]. There the peak in S(Q) renormalizes the relaxation rate for density fluctuations Deff = D/S(Q). While in the liquid this is an effect involving different independent particles, here it occurs for the internal density fluctuations of one entity. 

A comparison with Burchard s first cumulant calculations shows qualitative agreement, in particular with respect to the position of the minimum. Quantitatively, however, important differences are obvious. Both the sharpness as well as the amplitude of the phenomenon are underestimated. These deviations may originate from an overestimation of the hydrodynamic interaction between segments. Since a star of high f internally compromises a semi-dilute solution, the back-flow field of solvent molecules will be partly screened [40,117]. Thus, the effects of hydrodynamic interaction, which in general eases the renormalization effects owing to S(Q) [152], are expected to be weaker than assumed in the cumulant calculations and thus the minimum should be more pronounced than calculated. Furthermore, since for Gaussian chains the relaxation rate decreases 

In another series of experiments [149] the correlation between structure and dynamics was investigated on dilute solutions of 12-arm PS star systems (Mw = 14.9 104 g/mol) in d-tetrahydrofurane, where either only one or all 12 arms were protonated (labelled). 

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