Seed‐Assisted Synthesis of BaCrO4 Nanoparticles and Nanostructures in Water‐in‐Oil Microemulsions

Isooctane dispersions of discrete isometric BaCrO₄ nanoparticles or self‐assembled linear chains of prismatic BaCrO₄ nanoparticles were added as surfactant‐coated seed crystals/nanostructures to Na₂CrO₄/NaAOT/Ba(AOT)₂/isooctane microemulsion reaction solutions prepared at w = 10 with molar ratios favoring the de novo synthesis of either nanoparticle chains ([Ba²⁺]/ [CrO₄^2–] = 1:1) or isolated nanoparticles ([Ba²⁺]/[CrO₄^2–] = 1:5.5). Addition of BaCrO₄ nanoparticles or chains under particle‐ or chain‐producing conditions, respectively, resulted in preferential growth of the seeds with retention of particle morphology and nanostructure architecture. In contrast, addition of linear chains to microemulsion reaction solutions under particle‐producing conditions resulted in disruption of the seed nanostructure and overgrowth of the released prismatic nanoparticles to produce discrete oval‐shaped or cuboidal nanocrystals depending on the seed concentration used. Discrete faceted nanoparticles were also produced by seed‐assisted synthesis when isometric nanoparticles were added at relatively high concentrations to chain‐producing microemulsion reaction solutions; however, decreasing the seed population resulted in intact self‐assembled linear chains and superlattices that consisted of interlinked prismatic nanoparticles with end‐capped pseudo‐hexagonal morphology. Growth of the seeds and their assembly/disassembly was consistent with a model of coupled synthesis and self‐organization based on the strength of electrostatic interactions at the surfactant‐crystal interface. The results suggest that microemulsion‐based processes could be of general importance for controlling the secondary growth of pre‐organized nanoparticle‐based superstructures, as well as the morphological refinement of their constituent building blocks.