Intercalation of alkylammonium cations into expandable fluorine mica and its application for the evaluation of heterogeneous charge distribution

The interstratified layer nano-hybrids between n-alkylammonium and fluorine mica are prepared by ion-exchanging the interlayer Na+ ions in the synthetic fluorine mica, Na0.66Mg2.68(Si3.98Al0.02)O10.02F1.96, with n-alkylammonium cations, CH3(CH2)(n - 1)NH3+ (C-n; n = 6, 8, 10, 12, 14, 16, and 18). According to the X-ray diffraction profiles of nano-hybrids and their computer simulation results, their interstratified structural features could be clearly distinguished depending upon the number of carbon atoms in the alkyl chain (C-n). The C-6-C-8 and C-14-C-16 derivatives exhibit normal intercalation phases with the basal spacings of similar to 13.8 Angstrom and similar to 18.0 Angstrom, indicating the parallel mono- and bilayer arrangements of the intercalants between silicate layers, respectively. On the other hand, the C-10-C-12 and C-18 hybrids show distinct superlattice lines in the X-ray diffraction patterns due to the interstratification between parallel monolayer-bilayer (d(001) = 31.6 Angstrom) and parallel bilayer-pseudotriple layer (d(001) = 39.6 Angstrom) of alkylammonium molecules, respectively, in the interlayer space of mica. The origin of such interstratification is found to be due to the charge heterogeneity of silicate interlayers in the Na+-fluorine mica; a high layer charge with 0.37 e(-)/Si4O10 and a low one with 0.28 e(-)/Si4O10 charge densities, respectively. The charge heterogeneity of silicate layers is also confirmed through the step-wise deintercalation of intercalants during their thermolysis under a nitrogen atmosphere.