Rheology of colloidal dispersions of positively charged Al-Mg MMH particles

The theology of aqueous Al-Mg MMH (mixed metal hydroxide) dispersions and e lectrophoretic mobility of MMH colloidal particles were studied by theologi cal and electrokinetic measurements as a function of MMH concentration, pH of dispersion and NaCl concentration, It was found that the suspensions are Newtonian at low MMH concentrations, while increasing MMH concentration gi ves rise to the suspensions with a yielding type of behavior. However, a tr ansition from Newtonian to non-Newtonian flow curves may occur at relativel y low MMH concentration (2%) when suspensions was formulated near the isoel ectric point (pH(iep)) for MMH or with NaCl being added to MMH suspensions below pH(iep). It appears that the theology of MMH dispersions is closely c orrelated to the MMH concentration and the surface charge of MMH particle. When the recovery experiments with a relatively high vigorous stirring and at a low shear rate were performed on inherent MMH suspensions consisting o f positively charged platelike particles, the evolution of the gel structur e is very slow, similar to the result for aqueous Laponite system consistin g of negatively charged platelike particles. This result suggests that it i s also the long-range electrostatic double layer forces that lead to the fo rmation of a repulsive gel in MMH suspensions, similar to aqueous Laponite system at a high pH.