Immersion microcalorimetry and C-13 CP/MAS NMR study of the structure of organoclays

The organoclays as dimethyldistearyl ammonium montmorillonite (DDA-Mt) are interstratified clays in which pure organic sheets and silicate layers coexist, The stacking disorder depends on the conformation of the DDA within the interlayer, This conformation depends on the quantity of sorbed vapor methanol, Immersion microcalorimetry of DDA-Mt in liquid methanol data shows endothermic reactions, The CH2/CH2 bonds between two adjacent alkyl chains are disrupted at P/P-0 < 0.6 corresponding to two methanol molecules for one polar head, Beyond this value Delta H is constant. C-13 CP/MAS NMR data show, by correlation, that the mobility of the chains is strongly increased at P/P-0 > 0.6. Mobility and distance between alkyl chains vary in the same direction and correspond to an increase in the stacking order of the sheets within a particle. (C) 1996 Academic Press, Inc.