‘‘Ordered’’ structure in colloidal silica particle suspensions as studied by small-angle x-ray scattering

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Abstract
The distribution of colloidal silica particles in aqueous suspension was investigated by small-angle x-ray scattering. The scattering curves showed a broad but distinct peak and a shoulder corresponding to the second-order peak at low- and no-salt conditions, which suggests that the particles form more or less ordered arrays. The Guinier plot showed that the particles were nearly spherical (a radius of about 60 Å). From the scattering intensity I(q), the interparticle interference function S(q), which reflects the distribution of particles more correctly, was evaluated. S(q) also showed a broad peak and a shoulder. The peak position shifted to higher angles and became higher with increasing concentration. The peak intensity was lowered with increasing salt concentration. This suggests that the formation of the ordered structure is of electrostatic origin. The shape of the S(q) curve could be well reproduced by the scattering curve of the distorted face-centered-cubic or body-centered-cubic paracrystal calculated by our previous theory [H. Matsuoka, H. Tanaka, T. Hashimoto, and N. Ise, Phys. Rev. B 36, 1754 (1987)], and the degree of paracrystalline distortion of the structure was evaluated to be about 0.2.