THE RHEOLOGICAL AND COLLOIDAL PROPERTIES OF BENTONITE DISPERSIONS IN THE PRESENCE OF ORGANIC-COMPOUNDS .1. FLOW BEHAVIOR OF SODIUM-BENTONITE IN WATER-ALCOHOL

Addition of methanol, ethanol, and n-propanol to aqueous dispersions o f Namontmorillonite (2% w/w) reduces the apparent viscosity and the yi eld value. In the presence of NaCl the flow parameters increase to a m aximum at medium alcohol concentration. Thus, the gel strength of Nabe ntonite dispersions can greatly change with the alcohol content of the dispersion. This is probably caused by the transition of dispersed cl ay mineral particles (individual silicate layers or lamellae of a few of these layers) to band-type networks with optical homogeneity and we akly attractive particle-particle interaction. When attraction between the particles becomes too strong at high alcohol concentrations, the bands are condensed to short fragments and, eventually, freely moving particles, reducing the viscosity and the yield value. The interpartic le interaction energy is calculated for the constant charge model by v an Olphen's (1977) method. Agreement with the experimental results is only obtained when the Stern layer adsorption is governed by a specifi c adsorption energy mu, which increases with decreasing dielectric con stant.