Mechanistic understanding of growth of nanorods in microemulsions

Abstract

One-dimensional (1D) nanostructures have garnered enormous attention because of applications in plasmonics, optoelectronics, sensors, electronics, spintronics, catalysts, energy conversion and storage, medical diagnostics, drug delivery, therapeutics and also act as key units to construct nano-dimensional electronic and photonic devices. One of the versatile and successful methodologies to obtain such 1D nanostructures is microemulsions based reaction scheme. Microemulsions are thermodynamically stable oil-water systems stabilized by surfactant and cosurfactant and form reverse micelles (RMs) under appropriate concentration of each component. CTAB (Cetyltrimethylammoniumbromide)-based quaternary reverse micelles (RMs), a tunable soft template has turned out to be a successful method to synthesize nanorods with tailored structural characteristics (size and aspect ratio) of a variety of materials. Herein, we present a comprehensive overview of the growth mechanism of the heterogeneous evolution of nanorods inside the polar core of CTAB RMs. Such 1D nanostructure growth requires a symmetry-breaking mechanism to be operative that usually leads to directional characteristics i.e. preferential selection of growth along the longitudinal axis over the lateral axis that finally results in nanorod based anisotropic structures. We show the generality of the proposed microemulsion based heterogeneous growth mechanism by its validation for both slow and relatively fast kinetics for nanorod synthesis.