JOURNAL OF COLLOID AND INTERFACE SCIENCE 183, 148–154 (1996) ARTICLE NO. 0529 Immersion Microcalorimetry and 13 C CP/MAS NMR Study of the Structure of Organoclays K. KHATIB,* M. FRANCOIS,* P. TEKELY,² L. J. M ICHOT,* J. Y. BOTTERO,‡ ,1 AND I. BAUDIN§ * Laboratoire Environnement Mine ´ralurgie, URA 235 CNRS, INPL. B.P. 40, 54 501 Vandoeuvre Cedex, France; ² Laboratoire d’Etude sur les Solutions Organiques et Colloidales, UA 406 CNRS, Universite ´ de Nancy I, B.P. 239, 54 506 Vandoeuvre Cedex, France; ‡ Laboratoire des Ge ´osciences de l’Environnement, URA 132 CNRS, Cerege fu 17, Universite ´ Aix-Marseille III, Europole Me ´diterrane ´en de l’Arbois B.P. 80, 13545 Aix-EnProvence Cedex 04, France; and §CIRSEE, Lyonnaise des Eaux, 38 rue du Pre ´sident Wilson, 78230 Le Pecq, France Received December 27, 1994; accepted March 1, 1996 presence of a cosolvent such as methanol increases the reten- The organoclays as dimethyldistearyl ammonium montmoril- tion of micropollutants like atrazine (9). Methanol helps in lonite (DDA-Mt) are interstratified clays in which pure organic the penetration of the pollutant by modifying the material’s sheets and silicate layers coexist. The stacking disorder depends texture. Recently it has been shown that in the presence of on the conformation of the DDA within the interlayer. This confor- water or methanol vapor, or liquid methanol, the interlayer mation depends on the quantity of sorbed vapor methanol. Immer- distance remains the same but the stacking order of the sheets sion microcalorimetry of DDA-Mt in liquid methanol data shows increases and the material behaves as an ordered system endothermic reactions. The CH 2 /CH 2 bonds between two adjacent (10–13). The structure of the clay particles, formed with alkyl chains are disrupted at P / P 0 õ 0.6 corresponding to two turbostratic stacking of the sheets, is closely related to the methanol molecules for one polar head. Beyond this value DH is constant. 13 C CP/MAS NMR data show, by correlation, that the structure of the organic phase in the interlayer space. The mobility of the chains is strongly increased at P / P 0 ú 0.6. Mobility CH 2 groups in short-chain ( tetramethylammonium) and and distance between alkyl chains vary in the same direction and long-chain ( hexadecylammonium) surfactants have a high correspond to an increase in the stacking order of the sheets within local mobility as revealed by 13 C cross-polarization /magic- a particle.  1996 Academic Press, Inc. angle spinning (CP/MAS) NMR (14). The cross-polariza- tion time values T CH  10 ms indicate that the short-chain surfactants are in a pseudo-liquid state (15, 16). The move- INTRODUCTION ments become anisotropic when the length of the alkyl chain increases. Numerous studies concerning the structure and the appli- In the case of a long-chain surfactant such as dimethyldis- cations of organoclays, especially alkylammonium benton- tearyl ammonium (DDA), the steric effects seem to be pre- ites, have been done (1). These materials have a texture dominant (2). which depends on the length of the alkyl chain and swells The purpose of this paper is to study the mobility of DDA in presence of polar molecules like alcohols. The interlayer molecules within the interlayer space of a montmorillonite distances change with the length of the alkyl chain (2). Its and adsorbed onto external surfaces (17) versus the partial value is 13.6 A ˚ with C n £ 13 and 17.6 A ˚ with 14 £ C n £ pressure of methanol by using 13 C CP /MAS NMR and meth- 18 ( 3 ) . Depending of the number of carbon atoms, the alkyl anol immersion calorimetry. chains arrange themselves parallel to the sheets as a mono- layer or a bilayer ( 4, 5 ) . When there are more than 18 carbon MATERIALS AND METHODS atoms the resulting structure is pseudotrimolecular (6, 7). These authors observe the increase of the interlayer dis- Materials tance with the increasing of the partial pressure of alcohol. The swelling decreases as the molecular weight of the alco- The organoclay used in this study is the same as that studied hol increases. In the presence of water these materials show in a previous work (17). We recall only a few specifications a strong affinity for non- or weakly polar solvents (8). The of the organoclay: the cationic exchange capacity (CEC ) was determined at 85 meq/100 g using Remy and Orsini’s 1 To whom correspondence should be addressed. method (18 ) and the structural formula of the montmorillonite 148 0021-9797/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved.