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The present work provides a critical review of polymer crystallization studies using SALS; experimental methods, analysis techniques, observations and their relations with respect to other techniques are discussed. Furthermore, the fact that nucleation might be accompanied by large scale density fluctuations has been investigated for the flow-induced crystallization of iPB. SALS was applied to measure density and orientation fluctuations, whereas complementary results were obtained from optical microscopy. The observations from both crystallization and melting experiments seem to indicate that the detected density fluctuations result from the presence of weakly anisotropic structures, ratjer than being an indication of densification before the onset of crystallization. ispartof: Macromolecular materials and engineering vol:293 issue:4 pages:255-273 status: published

We discuss the coarsening of domains in bicontinuous structure of aqueous polymer mixtures, driven by hydrodynamic flow. Taking into account the bending energy as a contribution to the interfacial energy, we derive a general expression for the coarsening rate in these mixtures. Examining the limiting behavior of small and large length scales, we find two regimes. For small length scales, the size of the domains (¿) scales with time (t) as ¿ t1/3, while at large length scales, the domain size scales with time as ¿ t. The crossover between the two regimes occurs at a particular length scale, the critical radius Rc, which is dependent on the bending rigidity k, and the interfacial tension of a flat interface ¿0 (Rc = ). In the case of aqueous biopolymer mixtures, we predict this particular length scale to be in the micron range. This new general expression for the coarsening of domains in aqueous polymer mixtures can explain experimental results [Lorén et al. Macromolecules 2001, 34, 8117], which show the two regimes of coarsening with a crossover at 4 µm.

International audience; The evolution of the global orientation parameter for a series of aqueous hydroxypropylcellulose solutions both during and following the cessation of a steady-state shear Bow is reported. Time-resolved orientation measurements were made in situ through a novel X-ray rheometer coupled with a two-dimensional electronic X-ray camera, and using an intense X-ray source at the LURE synchrotron. After the cessation of flow, the global orientation decreases from the steady state orientation level to zero following shear flow at a low shear rate or to a small but finite value after flow at a high shear rate. The decrease of orientation with time shows different behaviour, dependent upon the previously applied shear rate.

The dynamic variation of optical birefringence during solution polycondensation of rigid rodlike molecules in a simple shear flow is obtained. At relatively high shear rates (413 s-1) and late stages of the polymerization the orientation of the molecules is found to be significant. Molecular orientation is important in such reactions since it increases the polymerization rate and alters the molecular weight distribution (Agarwal, U. S.; Khakhar, D. V. Nature 1992, 360, 53). The birefringence at different shear rates (gamma) over the course of the polymerization is found to depend only on gamma/D(r), where D(r) is the rotational diffusivity. The predictions of the theory of Marrucci and Grizzuti (J. Polym. Sci., Polym. Lett. Ed. 1983, 21, 83), however, show large deviations in comparison to the experimental birefringence measurements. The experiments are carried out using terephthaloyl chloride and p-phenylenediamine to produce poly(p-phenyleneterephthalamide) in a mixed solvent at low temperatures. A two-reactor system is used in which the second reactor is designed to give a uniform simple shear flow and to allow for measurement of birefringence during polymerization.