Synthesis of hollow BaSO4 nanospheres templated by core–shell–corona type polymeric micelles

Hollow barium sulfate (BaSO₄) nanospheres were synthesized by templating a polymeric micelle of a triblock copolymer poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG). This polymer is known to form a micelle with a PS core, a PAA shell and a PEG corona in aqueous solutions. Barium chloride and sodium sulfate were used as precursors of BaSO₄. In the synthesis, the PS core acts as a template for cavities of the hollow particles, the PAA shell is beneficial for arresting Ba²⁺ ions to produce BaSO₄, and the PEG corona stabilizes the BaSO₄/polymer nanocomposite to prevent secondary aggregate formation. Hollow BaSO₄ nanospheres were obtained by removing the polymeric template from the BaSO₄/polymer nanocomposite by calcination. The hollow BaSO₄ nanospheres thus fabricated were characterized by various techniques including transmission electron microscopy and X-ray diffraction analysis. The average diameter of the spheres is around 25 nm and the average cavity diameter is around 16 nm. The significance of the present method is that it can avoid formation of large crystals which is generally unavoidable in other methods.