Control of barite morphology by double-hydrophilic block copolymers

Barite particles with a rich variety of well-defined morphologies have been synthesized by using double-hydrophilic block copolymers (which consist of a hydrophilic solvating block and a hydrophilic binding block) as crystal growth modifiers to direct the controlled precipitation of barium sulfate from aqueous solution. The influences of variation in functional group and molecular structure of the copolymers as well as variation of pH condition on the particle size and morphology were investigated. It was revealed that in the presence of copolymers containing carboxylic acid groups at a pH above 5, the obtained BaSO4 particles always exhibit a nanocrystalline structure due to the large inhibition effect oft;he polyanionic chain on the barite crystallization. With decreasing pH, the particle size essentially increases, and the particle morphology generally varies from ovals through peanuts to peaches. In the presence of the phosphonated copolymer PEG-b-PMAA-PO3H2 at pH 5, large bundles of barite nanofilaments ranging from 20 to 30 nm in diameter, each of which is a single crystal elongated along the crystallographic [1 (2) over bar 0] axis, can be produced due to the strong and specific interaction between the phosphonate groups of the copolymer and the crystallizing BaSO4 particles. The obtained results demonstrate the tremendous potential of double-hydrophilic block copolymers as tools for the controlled synthesis of inorganic crystals with unusual, well defined morphologies.