Spherical metal oxides-LAPONITE® sheets interactions: Microstructure, rheology and thixotropy of composite gels

Abstract

The composite LAPONITE®-spherical metal oxides (L-SMO) gels were characterised and compared with pure LAPONITE® gels in terms of rheology, microstructure, and time-dependent ageing behaviour. Microstructures of the L-SMO gels indicated that the LAPONITE® sheets formed bonds in an upright orientation with the negatively charged alumina and silica spheres via heterogeneous charge attraction. The bonds enhanced the strength of LAPONITE® sheets network and resulted in higher yield stress than pure LAPONITE® gel. The composite L-SMO gels displayed higher yield stress as increasing SMO content while the composite LAPONITE®-silica gel displayed higher yield stress than the LAPONITE®-alumina gel. The microstructure of composite L-SMO gels was time-dependent as reflected by increased yield stress with ageing time. The composite L-SMO gels were less time-dependent than pure LAPONITE® gel possibly due to the interruption of heterogeneous charge attraction between edges of LAPONITE® sheets and SMO particles on the EDL repulsive interaction between LAPONITE® sheets. The presence of SMO particles also shifted the location of yield stress maximum of LAPONITE® gel and caused the LAPONITE® gel less shear thinning.