Calcite is dispersed into nanoparticles with the use of polysodium acrylate, PAANa. The molecular weight distribution of PAANa greatly influences the characteristics of the dispersion. Near-monodisperse PAANa adsorbs irreversibly and totally onto the CaCO3 surface, but for polydisperse PAANa, a mass segregation occurs, where only chains with a selected molecular weight are adsorbed. With polydisperse samples, small spherical CaCO3 particles are generated in addition to calcite crystals. This bimodal dispersion is less viscous than the dispersion containing only calcite crystals. (c) 2005 Elsevier Ltd. All rights reserved.