A STUDY OF THE DISPERSING EFFECTS OF POLYCARBOXYLATE-BASED DISPERSANT ON FINE PARTICLES

摘要

Polycarboxylate-based superplasticizers (air-entraining and high-range water-reducing a-gents) contain a polycarboxylate-based dispersant (PA) and a dispersion retainer. The PA adsorbs to the surface of the binding material particles. Due to steric effects, the particles are well dispersed, resulting in a high level of water reduction and high fluidity (1), (2). It is considered that in the study of the dispersion effects of superplasticizers, it is important to understand the adsorption properties of the PA. We focused on the molecular size and adsorbed number of PA molecules. Based on the chemical structure and molecular weight of the PA, we calculated its molecular size and determined that the maximum length of the extended trunk polymer was 20 nm and that of the side chain was 7 nm. Considering the effective volume based on thermodynamics, one PA molecule is adsorbed to every 400 nm~2 of particle surface. However, according to calculations based on the actual measurement of specific surface area and adsorption amounts, one PA molecule is adsorbed to every 100 nm~2 of the particle surface. It is suggested that PA molecules shrink and are adsorbed on the surface of binding materials more densely than expected.