Flow behaviour of titanium dioxide dispersions in the presence of 2-hydroxyethyl cellulose

The effects of 2-hydroxyethyl cellulose (HEC) of weight-average molecular w eight 15,000, 90,000 and 7,20,000 on the rheological properties of TiO2 dis persions were evaluated. For all three HECs, the maximum yield stress, tau( ymax), (occurred at zero zeta potential), decreased with increasing HEC con centration. Interestingly, the largest reduction in tau(ymax) was observed with the HEC with the highest molecular weight. This reduction was attribut ed to steric interaction arising from adsorbed HEC. Adsorbed high-molecular -weight HEC formed an effectively thicker steric barrier because of its lar ger size and higher adsorption capacity. Bridging interactions that were ex pected to be important for the high-molecular-weight HEC were found to be u nimportant here. In the flocculated regime, HEC enhanced the shear-thinning characteristics of the TiO2 dispersions.