Structure analysis of montmorillonite intercalated with cetylpyridinium and cetyltrimethylammonium: Molecular simulations and XRD analysis

Abstract

Molecular mechanics and molecular dynamics simulations combined with X-ray powder diffraction were used in srtucture investigation of montmorillonite intercalated with cetylpyridinium(CP) and cetyltrimetylammonium (CTA) cations. Molecular modeling revealed the interlayer strusture and differences in intercalation behavior of CP and CTA cations in montmorillonite. The experimental and calculated values of basal spacing were in good agreement for both intercalates: in the case of CP-montmorillonite d(exp) = 20.59 A, d(calc) = 20,60A

for CTA montmorillonite d(exp) = 18,00 A, d(calc) = 18,10 A. CTA-montmorillonite exhibits significantly higher total sublimation energy and higher host-guest interation energy than the CP montmorillonite. The main difference between both intercalates is in charge distribution on the host layers and guest species. The charge transfet from the guest species to the host layer is higher in CTA-montmorillonite than in CP - montmorillonite, and consequently the charge polarization between the host and guest layers is much higher in CTA-montmorillonite\This leads to the much stronger host-guest electrostatic interaction in the case of the CTA-montmorillonite.