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 scatte ring vectors spans 5 decades (143 cm(-1) < q < 10.3 x 10(6) cm(-1)), provid ing 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 mos t likely loosely interconnected with single chains and other aggregates, an d the structure and organization are critical in determining solution visco elastic properties. The solubility is poorer in D2O, as evidenced by larger aggregates, higher scattering intensities, a slightly higher fractal dimen sion, and a sublinear concentration dependence of the intensity. Aggregates were found in dilute neutral guar solutions as well as in cationic guar so lutions (in H2O), whether screened or unscreened. The presence of aggregate s at all concentrations for neutral and charged guar indicates the difficul ty in determining a molecular weight of the guar molecule.