Dynamics and role of rosin acid molecules for preparation of well-dispersed CaCO₃ colloidal suspensions

We studied the dynamics and role of rosin acid molecules for the preparation of well-dispersed calcium carbonate (CaCO₃) colloidal aqueous suspensions. We investigated a quantitative determination method of the amounts of free diffused surfactant molecules in H₂O particle dispersion using the pulsed field gradient nuclear magnetic resonance (PFG-NMR). The diffusion phenomena of rosin acid surfactant molecules in a CaCO₃ aqueous dispersion were directly observed using the PFG-NMR method. It was clearly found that the observed diffusion of rosin acid surfactant molecules was attributed to the micelle-like agglomerated rosin acid molecules in the CaCO₃ aqueous dispersion using PFG-NMR method. Large amounts of rosin acid molecules were strongly bound onto CaCO₃ particles, contributing to the well-dispersed primary size of CaCO₃ in colloidal secondary particles. The free diffused micelle-like agglomerated rosin acid molecules were found to play an important role in maintaining the stability of the CaCO₃ in a dispersion of colloidal secondary particles. The CaCO₃/rosin acid secondary particles were estimated to be larger than submicron size using dynamic light scattering (DLS). The structure of the CaCO₃/rosin acid secondary particle observed by scanning transmission electron microscopy under extremely low pressure supported the results from PFG-NMR and DLS measurements. The well-dispersed primary CaCO₃ particles were found to be surrounded by a large amount of rosin acid surfactant molecules. The observed zeta potentials of this secondary particle dispersion were between −70 and −60 mV, indicating again that the CaCO₃ was covered with rosin acid. The PFG-NMR method is found to be a powerful tool to investigate the role of surfactant molecules for preparation of well-dispersed colloidal suspensions.