Preparation of Stable Suspensions of Delaminated Kaolinite by Combined Dimethylsulfoxide-ammonium Fluoride Treatment

The separation of kaolinite crystallites into their layer components involves two problems, namely, overcoming the bonding energy which holds these layers together, and imparting the latter with a new surface potential that prevents their reunion, once they are separated. To chemical this author's knowledge, the separation of kaolinite into its lamellae to form a stable suspension has never been reported. It is the purpose of the present note to demonstrate experimentally (1) the dissociation of kaolinite crystallites into their lamellar components, and (2) the formation of stable suspensions by such lamellae. The key to the successful delamination of a kaolinite crystallite into its isolated layers is the initial use of an intercalating agent, which opens up the crystallite and decreases the cohesion energy. Additional steps are then needed to continue this separation and bring about a complete removal of the lamellae from each other, as is shown below. Intercalation of molecules by kaolinite has been studied quite intensively during recent decades, and the list of intercalated species includes organic as well as water molecules (for review of early works, see Theng, 1974; more recent works include Constanzo et al., 1984; Sugahara et al., 1988) and ionic species (Yariv, 1986). Consider the intercalation reaction of dimethylsulfoxide (DMSO), with kaolinite. According to Cruz et al. (1973), the hydrogen bonds between the DMSO and the kaolinite internal hydroxyls are stronger than the initial hydrogen bonds. Due to the high dielectric constant of the DMSO (compared to that of the crystal lattice), a chemical driving force causes the intercalation of the DMSO molecules (presumably starting at the crystal edges; see also Giese, 1978), followed by diffusion of the intercalated molecules into the interlayer zones. As the distance between the unit layers increases, the energy needed to bring about a complete separation of two adjacent layers to a distance of zero attraction is now lower than before the intercalation. To reduce the attraction energy between the unit layers further, some of the hydroxyls can be exchanged by fluoride (Giese, 1973; Constanzo et al., 1984). The presence of DMSO attached to the layer surfaces gives them a new surface potential, which causes them to repel each other; once they are separated, their re-as-