Correlation of aspect ratio of montmorillonite nanosheets with the colloidal properties in aqueous solutions

Abstract

Montmorillonite (MMT) is easily exfoliated to two-dimensional nanosheets for making multifunctional nanocomposite materials. In this work, exfoliated MMT nanosheets have been studied in order to understand the correlation of the aspect ratio with the colloidal properties. The nanosheets with various aspect ratios were prepared through controlling the number of the freezing thawing cycles and the power of the ultrasonic exfoliation, and the colloidal properties were determined through the measurements of atomic force microscope (AFM), zeta potential, acid-base back-titration, viscosity and turbidity. It has been shown that as the aspect ratio increased, the negative zeta potential of MMT nanosheets increased, and the active sites with H+ or OH− on the surfaces decreased, indicating that the MMT nanosheets with lower aspect ratio were easier to coagulate. Meanwhile, the viscosity of the MMT suspensions at high shear rate increased with increasing the aspect ratio. It suggests that the aspect ratio has a strong effect on the colloidal properties of MMT nanosheets, which might be helpful of the applications of MMT nanosheets in functional nanocomposite areas. Keywords: Montmorillonite nanosheets, Aspect ratio, Zeta potential distribution, Rheology