EFFECT OF SURFACTANT CONCENTRATION ON THE STABILITY OF AQUEOUS TITANIUM-DIOXIDE SUSPENSIONS

The effect of a surfactant (polyoxyethylene diethylenetriamine dialkylamide) on the stability of aqueous titanium dioxide (TiO2) dispersion was studied by measuring adsorption and ζ potentials. It was found that as the surfactant concentration increases, stability decreases initially and then increases, showing a minimum. As the concentration increases further, stability decreases, showing a maximum. The ζ potential changes from negative to positive as the adsorption increases and reaches a maximum when the adsorption reaches a plateau value. The dispersion flocculated when the absolute values of the ζ potential dropped below 10 mV, indicating that the destabilization by the surfactant in the low surfactant concentration is due to reduction of the electrical repulsion. Destabilization at the higher surfactant concentration is likely caused by the depletion effect since there is no change in adsorption and ζ potential in the concentration range, and the surfactant molecules are not sufficiently large to form bridges between particles. © 1991.