Organo-vermiculites: synthesis, structure and properties. Platelike nanoparticles with high aspect ratio

Abstract

Organo-vermiculites with large d-spacing, advantageous for the synthesis of polymer nanocomposites, were prepared by exchanging the mineral inorganic cations for quaternary alkylammonium ions. The interlayer Mg2+ of the pristine vermiculite was exchanged by Na+ in advance to enhance the exchange with the organic cations. The organophylization of the mineral was monitored by determining its exchange capacity as well as the organic surface coverage. Alkylammonium ions with different chain length and number of chains attached to the nitrogen atom were exchanged and the properties of the organo-vermiculites investigated by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Dioctadecyldimethylamonium–vermiculite showed a d-spacing as large as 3.9 nm. The alkylammonium ions self-assemble on the vermiculite surface, leading to an ordered two-dimensional lattice, in which the alkyl chains preferentially assume an all-trans conformation. On heating, conformational transformation of the alkyl chains gradually takes place resulting in a dynamically disordered phase. The transition from an ordered all-trans conformation to a dynamically disordered state manifests itself in IR-absorption and carbon resonance frequency shifts accompanied by an abrupt enthalpy change. The transition temperature and enthalpy depend on the alkyl chain length and packing density.