INTERCALATION OF TETRAALKYLAMMONIUM CATIONS INTO SMECTITES AND ITS APPLICATION TO INTERNAL SURFACE-AREA MEASUREMENTS

Monolayer to bilayer (MTB) and bilayer to pseudotrimolecular (BTP) tra nsitions were observed for smectites exchanged with symmetrical tetraa lkylammonium cations of increasing sizes: +NR4, where R = (CH2)nCH3, w ith 0 less-than-or-equal-to n less-than-or-equal-to 7. In the case of SWy-1, SHCa-1 and SWa-1, the variation in layer spacing observed from intercalation of tetramethylammonium up to tetraoctylammonium cations showed a behavior characteristic of smectites with homogeneously distr ibuted interlayer cations. In the case of STx-1, the change in interla yer spacing with the increase of the alkyl chain length was characteri stic of a very high charge heterogeneity. Higher charge smectites (SAz -1 and SCa-3, CEC > 1.20 mmol/g) were found to have decreasing cation exchange with increasing cation size, resulting in a ''leveling off'' of the interlayer spacing toward larger cations. The MTB and BTP trans itions were used lo determine the internal surface area of various sme ctites. The proposed method was found to be a quicker and simpler alte rnative to the polar liquid sorption method for this measurement, but was ineffective for high-charge smectites (CEC > 1.20 mmol/g).