| Research Abstract |
x-ray scattering and ultramicrosopic studies were carried out for dilute solutions of various ionic species such as proteins, polynucleotide, ionic detergent micelles, and synthetic macroions in solutions. When the concentration of macroions and the molecular weight were reasonably high, when the concentration of coexisting salt is sufficiently low, and when the solute was electrically charged, the scattering curve gave a single peak for ionic macroion systems. Mixing of two molecular-weight samples of synthetic macroions gave a new peak at a position different from those of the mother fraction before mixing. This indicated that the scattering peak was caused by intermolecularly ordered arrangement of the macroions. The Bragg spacing was found smaller than the average intermacroion spacing when the macroions were charged, indicating the localized ordering due to intermacroionic attraction. Theoretical consideration showed that the arrangement involved so large paracrystalline distortion that higher-order peaks were indiscernible. The ultramicroscopic study furnished a most direct evidence of the particle ordering. At low concentrations, localized ordered regions were observed to coexist with disordered ones, confirming the presence of interparticle attraction. The thermal motion of the particles in the ordered regions and the free motion of disordered particles were analyzed. The Fourier transform of the micrographs was carried out to obtain the scattering patterns. The attraction was demonstrated theoretically to be due to counterions between the macroions, in contradiction to the widely accepted point of view.
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