Molecular Motions, Surface Interactions, and Stacking Disorder in Kaolinite Intercalates

-Intercalates of Georgia well-crystallized kaolinite with formamide, N-methylformamide (NMF), and dimethylsulfoxide (DMSO) were prepared at room temperature by dispersing the clay in the organic liquid. Several physical and chemical properties of the intercalated organic molecules and the clay, while intercalated and after de-intercalation, were examined using nuclear magnetic resonance (NMR), infrared (IR), and electron paramagnetic resonance spectroscopy (EPR), and specific heat (Cp) measurements. The chemical bonding between the inner-surface hydroxyls and the organic molecules, as indicated by IR, was strongest for DMSO and weakest for formamide. The distortion of the kaolinite layer, as shown by EPR, also was greatest for DMSO and least for formamide. NMR T 1 measurements indicated a relatively strong DMSO-kaolinite surface interaction that slowed down the methyl group reorientation comparable to that in bulk solid DMSO. T~ measurements indicated a weaker interaction for NMF. De-intercalation by mild heating did not return the kaolinite to its original structural state as shown by EPR and Cp. The greatest disorder was found for the DMSO de-intercalate and the least for the formamide de-intercalate. These experiments show that for sufficiently strong bonding between the clay inner surface and the intercalating molecule, the structure of the clay is capable of distortion, which is partly temporary and partly permanent. The permanent changes probably involve the introduction of stacking faults. Key Words--Dimethyl sulfoxide, Electron paramagnetic resonance, Formamide, Infrared spectroscopy, Intercalate, Kaolinite, N-methylformamide, Nuclear magnetic resonance, Specific heat. I N T R O D U C T I O N Study of the static and dynamic properties of an intercalated molecule can yield information about the environment of the molecules, and, indirectly, about the surface properties and structure of the clay. Few studies of intercalated kaolins have attempted to examine the range of time scales which are available with modem experimental techniques. Costanzo et al. (1984) and Lipsicas et aL (1985) used very long (X-ray powder diffraction and heat-capacity measurements), medium (nuclear magnetic resonance relaxation-time measurements), and very short (infrared absorption) time scales to study the static and dynamic properties of water intercalated into kaolinite. A similarly broad examination of the properties of intercalated organic molecules has not been carried out. This is unfortunate because of the importance of clay-organic interactions in catalysis and clay diagenesis, in the use of intercalation to distinguish types of kaolins, and perhaps, even in the origin of organic life. The present study was designed to investigate the degree of interaction between a single kaolinite mineral and several organic intercalating molecules. The range of time scales was broad and included infrared (IR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and heat capacity (Cp) measurements. The aim was to determine the relative strengths of interaction between the organic molecule Copyright 9 1986, The Clay Minerals Society and the clay over a wide time scale and to correlate these strengths with the properties of the organic molecules.