Interaction of polycarboxylate ether with silica fume

The interaction of silica fume with negatively charged polycarboxylate ethers in comparison to a polyacrylate and two non-ionic polyethylene glycols is investigated by adsorption and streaming potential measurements at slight alkaline pH value. The results indicate that polyethylene glycol is adsorbed on the silica fume in a flat conformation. Increased molecular weight however favours network formation. In contrast, the polyacrylate is adsorbed only in a very low amount due to a mutual electrostatic repulsion of the negative charged silica surface and the carboxylate groups. Polycarboxylate ether, which combine both structural features, a negative charged backbone and non-ionic polyethylene glycol side chains, adsorb via hydrogen bonding mechanism of the side chains with the silica particles. The adsorption rate of the polycarboxylate ethers predominantly increases with decreasing carboxylic equivalent. However, the adsorption affinity is determined by both, the carboxylic equivalent and the side chain length of the polycarboxylate ether.