Structure of guar in solutions of H2O and D2O:: An ultra-small-angle light-scattering study

We examine the structure of guar as a function of concentration in both H2O and D2O using several different scattering techniques. The range of scattering vectors spans 5 decades (143 cm(-1) < q < 10.3 x 10(6) cm(-1)), providing insight into the supramolecular and local, organization of the chains. This allows us to directly characterize the large-scale aggregate structure of the guar, which can be on the order of 100 mu m. The aggregates are most likely loosely interconnected with single chains and other aggregates, and the structure and organization are critical in determining solution viscoelastic properties. The solubility is poorer in D2O, as evidenced by larger aggregates, higher scattering intensities, a slightly higher fractal dimension, and a sublinear concentration dependence of the intensity. Aggregates were found in dilute neutral guar solutions as well as in cationic guar solutions (in H2O), whether screened or unscreened. The presence of aggregates at all concentrations for neutral and charged guar indicates the difficulty in determining a molecular weight of the guar molecule.