Single Kaolinite Nanometer Layers Prepared by an In Situ Polymerization-Exfoliation Process in the Presence of Ionic Liquids

A simple chemical route for the exfoliation of kaolinite in the presence of polymerizable ionic liquids and the resulting obtainment of exfoliated nanocomposites is reported. The exfoliation was achieved using three different ionic liquids structurally bearing a vinyl group: 1-methyl-3-(4-vinylbenzyl)imidazolium chloride salt (IL_1), 1-methyl-1-(4-vinylbenzyl)pyrrolidinium chloride (IL_2), and 1-methyl-3-vinyl imidazolium iodide (IL_3) and a urea-kaolinite intercalate as precursor. The reaction was done in one step by an in situ polymerization-exfoliation process. C-13 CP/MAS NMR spectra confirmed the spontaneous polymerization of the ionic liquid during the exfoliation process to afford atactic polystyrene derivatives in the case of IL_1 and IL_2. The amount of organic material in the exfoliated nanocomposite was close to 30% as shown by thermal gravimetric analysis. This amount is small in comparison to the amount obtained when the exfoliation was done using sodium polyacrylate (Letaief and Detellier, Langmuir 2009, 25, 10975). XRD as well as SEM analysis confirmed a total exfoliation of the kaolinite when the reaction was done using urea kaolinite, whereas a mic:rocomposite, made predominantly of kaolinite platelet aggregates dispersed in the polymeric matrix, was formed when dimethylsulfoxide kaolinite was used as the precursor.