Neutrons Experiments A Contrast Variation Story

Significant breakthroughs have been obtained by the collaborative group between Saclay (L. Brillouin Laboratory) and Strasbourg (C. Sadron Institute) for determining the chain conformation in the polymer bulk state [9]. These scientists were then able to confirm the assumption by Flory that the chains should be described by a Gaussian statistics under 

Similarly, the chain trajectory in thermoreversible gel of isotactic polystyrene (IPS) has been determined. Zimm plots can be obtained (Fig. 4.3) that, after the usual proper extrapolation both to C = 0 and g = 0, have given values of radii of gyration Rg about twice larger than its value in the polymer bulk state [49]. 

Clearly, only neutrons could provide one with such a result, which gave the key for understanding why iPS forms a gel in some solvents rather than the usual chain-folded crystals. 

Similar results [51] were obtained with syndiotactic polystyrene (sPS) solutions prior to gelation (Fig. 4.5). A persistence length of about / = 9 nm was derived from a fit with Yamakawa pseudoanalytical approach. The broader -range explored with respect to iPS experiments allowed one to fit the departure from linearity with Equation 4.22, which yielded a cross-section radius, % = 0.62 0.1 nm, and a mass per unit length, = 530g/nmmol, values consistent with 

Some systems that are partially labeled may show differing scattering curves whether deuterated or hydrogenous solvents, or a mixture of them are used. A typical example is given by a polyelectrolyte/surfactant complex (Fig. 4.7). 

---