Formation of BaSO₄ Whiskers in Microemulsion

Abstract

Several shapes of BaSO₄ particles were synthesized by the reaction of Ba(AOT)₂ microemulsion with NaAOT microemulsion containing SO₄^2– at differing [Ba²⁺]/[SO₄^2–] mole ratios. BaSO₄ nanofilaments were obtained under an excess of Ba²⁺ with the same mole ratio to that of Li and Mann (2000). A plasma replica SEM revealed that the nanofilaments were formed exactly in the microemulsion. Further excess Ba²⁺ resulted in the formation of short rags and thick spirals rather than nanofilaments. In contrast, fine particles were formed under a shortage of Ba²⁺. By addition of excess Ba²⁺ to the microemulsion after the generation of the fine particles under a shortage of Ba²⁺, whisker-like rods were obtained. These results suggest a new mechanism for formation of the whisker-like rods through an anisotropic aggregation of the fine particles.