Strategy to obtain nm size crystals through precipitation in the presence of polyelectrolyte

Crystals of lead sulfate were precipitated in solutions of various polyelectrolyte polymers (acidic, neutral, and basic polymers) using a double-jet crystallizer. Polyetyleneimine (PEI) basic polymer controlled both the nucleation rate and crystal growth rate, and enabled the production of fine monodispersed crystals. The on-line measurement of the variation in the lead concentration indicated that PEI lost its effect when a certain amount of the reactants N_tot was supplied. Interaction between lead ions and PEI was detected by NMR analysis, which suggested that lead ions made some kind of complex with PEI. The values of N_tot correlated well with the weight of PEI in the solution, regardless of the feed flow rate and reactant concentration, as shown in the correlative equation N_tot = k W^0.49. It was suggested that PEI could no longer control the precipitation rate when the amount of reactants supplied exceeded N_tot. Thereafter, rapid nucleation occurred. Precipitation with PEI could be controlled by a certain amount of PEI in a ground solution in order to produce monodispersed fine crystals. These results give an effective idea of how to create various nm size crystals.