The effect of adsorbed fumaric acid on dispersions of rough titania particles

Abstract

Molecules with a rigid backbone and limited spatial conformation were previously reported to participate in “highly directed bridging”. As such, fumaric acid is hypothesized to have high potential for highly directed bridging. In this study, the effect of adsorbed fumaric acid on titania dispersions was investigated as a function of pH and concentration. The surface chemistry was investigated via zeta potential measurements. The vane-yield stress technique was employed to probe the interparticle strength between colloid particles in bulk dispersions. The pure titania dispersion displayed a maximum yield stress at the isoelectric point. The presence of adsorbed fumaric acid reduced the maximum yield stress of the titania dispersions with rough particles and the extent of reduction increased with fumaric acid concentration. Despite its molecular structure being conducive to highly directed bridging, the extreme surface roughness of the titania particles severely reduced the amount of bridging interactions. As a result, the additional attractive contribution to yield stress by highly directed bridging was unable to compensate for the steric contribution arising from the adsorbed layer; thus leading to the reduction in maximum yield stress. On the other hand, adsorbed fumaric acid caused a small increase in yield stress in the titania dispersion with smoother particles; thus supporting the role played by surface roughness. It is important to recognise that in addition to molecular structure, surface roughness also plays an important role in determining how adsorbed dicarboxylic acids influence interparticle interaction.