Abstract: The rheological properties of single-component clay dispersions and clay/MMH mixed dispersions containing oppositely charged colloidal particles have been investigated. As the clay concentration is increased, the clay suspensions develop from the newtonian form of flow behavior to a yielding type of response. At^w(clay) is between 2%-4%, upon addition of MMH to clay dispersions, the magnitude of yield value and storage modulus increase monotonically, indicating enhanced gel strength. Adding NaCl to clay/MMH mixed suspensions causes the decrease of storage modulus, yield values and apparent viscosities. In the structural recovery measurements, the time dependence of viscoelastic properties of clay/MMH mixed dispersions shows only very small variations of the storage moduli over 3 h, in contrast to unusual thixotropic properties of aqueous single-component dispersions of laponite or MMH. The above results are interpreted based on attractive electrostatic interactions between clay and MMH particles due to their opposite charges, similar to the edge(+)/face(-) interactions in single-component clay dispersions under a low pH value.

Key words: Clay, Mixed metal hydroxides, Thixotropy, Rheology, Suspension