Rheology and microstructure of aqueous layered double hydroxide dispersions

The rheology and microstructure of aqueous dispersions containing Mg-Al layered double hydroxides (LDHs) are considered. The thickening and gelling of such dispersions can be controlled by the addition of electrolyte or, within a certain composition range, by the application of shear. In addition to electrolyte and LDH concentration, the degree of thickening is shown to depend on both the primary crystal size of the LDH and the crystallinity of the material. XRD, particle size measurements, and direct observation by optical and electron microscopy were used to probe the microstructure of unthickened and thickened dispersions; Thickening appears to result from the interaction of predominantly rod-shaped aggregates formed by the face-to-face association of the primary LDH crystals. No interlayer swelling or delamination of the LDH crystals was observed.