• journal_title：Clays and Clay Minerals
• Contributor：Yusuke Imai ; Satoshi Nishimura ; Yoshinari Inukai ; Hiroshi Tateyama
• Publisher：Clay Minerals Society
• Date：2003-
• Format：text/html
• Language：en
• Identifier：10.1346/CCMN.2003.0510205
• journal_abbrev：Clays and Clay Minerals
• issn：0009-8604
• volume：51
• issue：2
• firstpage：162
• section：Articles

The organoclay quasicrystals formed by exchange reactions of fluoromagnesian smectite (FMS) and two kinds of cationic surfactants were investigated by X-ray diffraction (XRD) of both aqueous suspensions and dried powders. ζ potential measurements were also carried out. The two cationic surfactants employed in this study, dodecyltriphenylphosphonium bromide (C₁₂PBr) and dodecyltrimethylammonium bromide (C₁₂NBr), have the same alkyl chain length but different head group structures. In aqueous suspensions of C₁₂N/FMS, regular stacking with a basal spacing of 2.28 nm was observed within the range 0.4 to 1.0 of the cation exchange capacity (CEC) of the C₁₂N/FMS ratios. The basal spacing was constant in this range. The most intense diffraction for the C₁₂N/FMS suspension was observed at 0.6 CEC, and a further increase in the C₁₂N/FMS ratio resulted in a decline of the diffraction intensity and a slight increase in the peak width. On the other hand, in C₁₂P/FMS suspensions with the surfactant/FMS ratios <0.6 CEC, only weak, broad XRD peaks were observed. With higher C₁₂P/FMS ratios (0.8 and 1.0 CEC), strong diffraction peaks appeared with a basal spacing of 3.20 nm. The differencein the observed basal spacings of C₁₂N/FMS and C₁₂P/FMS tactoids was ~0.9 nm, which did not agree with the difference in the estimated height of the two surfactants (~0.1 nm). These differences of the tactoid structures between C₁₂N/FMS and C₁₂P/FMS suspensions could be explained in terms of the difference in the adsorption manner of the surfactants on the silicate surface and in the size of the surfactant head groups.