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DIVISION S-2—"PARTICLE INTERACTIONS IN COLLOIDAL SYSTEMS"

Small-Angle X-Ray Scattering Study of the Quasi-Crystal Structure of Montmorillonite-CTAB in Suspension

^a Dept. of Chemistry and Biochemistry, South Dakota State Univ., Brookings, SD 57007-0896
^b Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831

* Corresponding author (james_rice{at}sdstate.edu)

The quasi-crystals of hexadecyltrimethylammonium (CTA⁺)-montmorillonite formed in suspension were investigated by small-angle x-ray scattering (SAXS). The d-spacing of the quasi-crystals increased from 17.1 to 21.7 Å, corresponding to an increasing surfactant loading from 20 to 250% of the clay's cation exchange capacity (CEC). One-dimensional grating theory was used to describe the scattering in the Porod region so that the number of clay layers and crystal size were obtained. The quasi-crystal reaches maximum size at a surfactant loading equal to the clay's CEC. The scattering peaks in the Porod region are due solely to quasi-crystals. Small-angle x-ray scattering avoids intermediate peaks resulting from the artificial interstratification of free and complexed layers in conventional x-ray diffraction analysis.

Abbreviations: CEC, cation exchange capacity • CMC, critical micelle concentration • CTA⁺, hexadecyltrimethylammonium • CTAB, hexadecyltrimethylammonium bromide • SAXS, small-angle x-ray scattering