The effect of pH on morphological control of barium hydrogen phosphate crystal by a double-hydrophilic copolymer

A new double-hydrophilic copolymer, poly(ethylene glycol) acrylate-copoly(methacrylic acid), is synthesized and used to control the morphology of barium hydrogen phosphate, which gives different shapes at different pH values: hexagon (pH=7.26), sphere cluster (pH=8), sphere with rough surface (pH=9), sphere with relatively smooth surface (pH=10), and small sphere (pH=11). The order of the particles increases with the pH value increases. The products vary from the out-of-order particles obtained at low pH to the uniform spherical particles at high pH. The results of X-ray diffraction (XRD) indicate that the structures of the particles controlled by copolymers are mainly BaHPO4 when pH<11. Weak diffraction peaks of Ba5(PO4)3OH (112) and (211) appear when pH=11, which means that precipitates are also mainly BaHPO4 but with minor Ba5(PO4)3OH. The results can be explained by the results of calculating distribution coefficients of ions (δ).