Self-assembly of organic molecules on montmorillonite

Smectite clays have been modified via ion exchange reactions with organic onium ions for five decades and are of industrial importance in diverse industries including oil well drilling, paint, grease, ink, cosmetics, environmental clean-up, polymer nanocomposites and pharmaceuticals. Over the past decade, a substantial amount of research has been conducted on other methods of organic modification of smectite clays. One method that has seen increased attention is surface treatment via ion–dipole bonding of organic molecules, oligomers or polymers to the exchangeable cation on the clay surface. Utilizing this method, a unique self-assembly of certain organic molecules has been discovered in which the molecules form rigid posts around each cation on the surface. This paper reports a parametric study coupled with molecular modeling of a series of three different families of ion–dipole bonding molecules. The bonding trends and controlling factors in the self-assembly of these molecules are described in detail. In general, it appears that the head group of the molecule is one of the principal factors controlling self-assembly but the chain length of the alkyl group also plays a role.