Self-assembly of a non-ionic surfactant onto a clay mineral for the preparation of hybrid layered materials

Abstract

The adsorption of the tri-ethylene glycol mono-n-decyl ether (C10E3) nonionic surfactant, characterized by its self-assembled lamellar phase above the critical micelle concentration (cmc), in a wide range of concentration, onto a layered clay mineral (montmorillonite) has been studied. C10E3 exhibits a high affinity for the montmorillonite (Mt) surface with an adsorption isotherm that differs strictly from previous studies on the adsorption of nonionic surfactants onto clay minerals for which a maximum of adsorption was reached below cmc. The self-organization in a lamellar phase changes the interaction potential between C10E3 and Mt, a surface that favors the aggregation of normal bilayers which expands the interlayer space at wide values (>40 A) while keeping the exchangeable Na+ cations conferring dual hydrophilic–hydrophobic behavior for the hybrid layered materials. Depending on the C10E3 phase state (in monomers or in a lamellar phase), the adsorption leads to four distinct surfactant arrangements (lateral layers to normal tilted bilayers) within the interlayer space of Mt. The hybrid layered materials show a thermal stability at 350 °C with a collapse of their interlayer space at 13 A due to the degradation of the hydrocarbon chains of C10E3. FTIR during thermogravimetry analysis permits the identification of the portions of C10E3 corresponding to ethylene oxide groups in close interaction with the Mt surface.