A stepwise mechanism for intercalating hydrophobic organics into multilayered clay nanostructures

Abstract

Intercalating organics into cationic clays generally occurs by ionic exchange. For a number of hydrophobic polyetheramines with a backbone of poly(oxypropylene) (POP), we observed that monoamines with a methyl terminus intercalated into montmorillonite (MMT) clay in two distinct steps. Remarkably, the monoamine with a molecular weight of 2000 g mol⁻¹ widened the basal spacing of the layered clay up to 74 Å; the space expanded further to 84 Å, 96 Å, and 100 Å by a mechanism that was different from conventional ionic exchange. The organoclays that we examined were amphiphilic, dispersing in organic media and in water. Kinetic studies indicated that the first stage of intercalation occurred after a critical concentration of monoamine, while the second stage had no critical concentration. The methyl terminus of the POP-amine also appears to drive the aggregation of organics into the layered clay. Our findings show the potential for synthesizing new organoclay nanostructures that can encapsulate large molecules in natural clay.