BaSO<SUB>4</SUB> crystals grown at an expanding liquid-liquid interface in a radial hele-shaw cell show spontaneous large-scale assembly into filaments

Control over the crystallography, morphology, and spontaneous organization of ceramic crystals are important goals in advanced materials engineering with important application potential. Most studies hitherto have concentrated on static charged interfaces as templates for the controlled nucleation and growth of ceramic crystals. In this communication, we show that BaSO<SUB>4</SUB> crystals grown at a steadily expanding liquid-liquid interface populated by fatty acid molecules spontaneously organize themselves into highly linear superstructures over large length-scales. This experiment is realized in a radial Hele-Shaw cell where the liquid-liquid interfacial growth rate and consequently time scales such as arrival of surfactant molecules to the interface etc. may be readily modulated. Possible reasons for the regular assembly of barite crystals are discussed