Kaolinite Aggregation in Book-Like Structures from Non-Aqueous Media

Abstract

AbstractTo control a vast spectrum of applications and processes, an understanding of the morphologies of clay mineral assemblies dispersed in aqueous or non-aqueous media is important. As such, the objective of this study was to verify the relationship between dispersion medium type and the size and morphology of the clay aggregates that are formed, which can increase knowledge on the assembly formation process. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy were used in an attempt to describe kaolinite platelet organization in non-aqueous media and to compare it to the organization in aqueous media or in media with or without a selection of dissolved organic polymers. The SEM images indicated that the kaolinite platelet assembly process occurs during slow evaporation of the solvent. Because the experimental procedure was rigorously identical for all cases in this study, the SEM images compared how the effects of various media and environments on kaolinite platelet interactions can lead to different morphologies. Quite spectacular morphological differences were indeed observed between samples dispersed in aqueous and non-aqueous media, particularly when the kaolinite platelets were dispersed in an organic solvent with dissolved organic polymers. For kaolinite dispersed in water, only small aggregates were observed after slow evaporation. In contrast, large kaolinite booklets or vermiform aggregates were formed by slow solvent evaporation when kaolinite was first dispersed into some organic solvents. The aggregates were particularly large when an organic polymer was dissolved in the organic solvent. For example, kaolinite aggregates dispersed in a binary cyclohexane/toluene mixture with dissolved ethyl cellulose (EC) had top apparent surface areas (i.e. stacking length × width) of more than 3,000 µm2. Other dissolved polymers, such as polystyrene or the polysaccharide, guar gum, gave similar results. Kaolinite platelet aggregation resulted from face-to-face interactions as well as edge-to-face and edge-to-edge interactions. The XRD results showed that ethyl cellulose led to the formation of smaller kaolinite platelets with an increased tendency to form larger aggregates, which is due to the ability of EC to chemically interact with silanol and/or the aluminol groups of kaolinite.