Study of a Commercial SiO2 Sol and Gel by Small Angle X-ray Scattering: Effect of Sample Thickness and Interpretation by Means of Smoluchowski Scheme

Yingnian Xu1, Pang L. Hiew1, Matthew Akira Klippenstein1 and Yoshikata Koga2, †
1 Department of Chemistry, The University of British Columbia, Vancouver, B. C., Canada V6T 1Z1
2 Center for Ceramics Research, Research Laboratory of Engineering Materials, Tokyo Institute of Technology Nagatsuta, Midori-ku, Yokohama, 227 Japan
Permanent address: Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, B.C., Canada V6T 1Z1.

Abstract: Ludox HS SiO2 sols at high concentrations show a peak in small angle x-ray scattering (SAXS) reminiscent to a “structure.” The appearance of such a peak was found to depend crucially on the thickness of the sample cell used for SAXS measurements. The thinner the cell used, the more prominent the peak. When the thickness was larger than 2 mm, it was no longer observable. When sols were treated with activated charcoal powders (in order to remove a surfactant) the peak became less prominent.

For the cases where clear features for structure were absent (thick sample regime), the Smoluchowski scheme was utilized to study the nature of sols. Namely, the distribution of the Smoluchowski species were estimated by numerically calculating the size distribution of particles directly from SAXS data. The distribution was found basically bimodal, and the main distribution peak, particularly for dilute sols (less than 5 wt%), was consistent with primary particles of SiO2. The second distribution peak was strongly dependent on the concentration of SiO2 particles. The observed trend was that the higher the concentration of SiO2 particles, the more prominent the second distribution peak and the locus of the maximum tended to move toward a smaller value in diameter. This behavior of the second distribution peak of the Smoluchowski species is no doubt a manifestation of the interparticle correlation. The observation of such behavior may provide a convenient means to characterize sols with interparticle correlation. This method was also applied for characterizing gels formed when the pH values were altered.

Key Words: Dependence of Sample Thickness • Ludox HS SiO2 • SAXS • Smoluchowski Scheme • Structure in sol

Clays and Clay Minerals; April 1996 v. 44; no. 2; p. 197-213; DOI: 10.1346/CCMN.1996.0440205
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)