Understanding Growth Kinetics of Nanorods in Microemulsion: A Combined Fluorescence Correlation Spectroscopy, Dynamic Light Scattering, and Electron Microscopy Study

Abstract

Even though nanostructures of various shapes and sizes can be controlled by microemulsions, there is substantial difficulty in understanding their growth mechanism. The evolution of nanostructures from the time of mixing of reactants to their final stage is a heterogeneous process involving a variety of intermediates. To obtain a deeper insight into these kinetic steps, we studied the slow growth kinetics (extending over eight days) of iron oxalate nanorods inside the polar core of water-in-oil microemulsion droplets made of cetyltrimethylammonium bromide/1-butanol/isooctane. Fluorescence correlation spectroscopy (FCS), dynamic light scattering (DLS), and transmission electron microscopy (TEM) have been employed to monitor the nanostructure growth at (near) the single-droplet level and in an ensemble. Analyzing FCS data with suitable kinetic model we obtain transient dimer lifetime (28 μs) and the droplet fusion rates (and fusion tendency) on each day as the reaction proceeds. The droplet fusion rate is found to directly control the nanorod growth in microemulsion solution and attains its maximum value (3.55 × 10(4) s(-1)) on day 6, when long nanorods are found in TEM data, implying that more and more reactants are fed into the growing system at this stage. Combining FCS, DLS, and TEM results, we find three distinct periods in the entire growth process: a long nucleation-dominant nanoparticle growth period which forms nanoparticles of critical (average) size of ∼53 nm, followed by a short period where isotropic nanoparticles switch to anisotropic growth to form nanorods, and finally elongation of nanorods and growth (and shrinking) of nanoparticles.

Effect of the Cationic Surfactant Moiety on the Structure of Water Entrapped in Two Catanionic Reverse Micelles Created from Ionic Liquid‐Like Surfactants

“…[1] Other surfactants used to create RMs are the cationic species benzyl-nhexadecyldimethylammonium chloride (BHDC) and hexadecyltrimethylammonium bromide (CTAB). [6][7][8][9] It is known that mixtures of surfactants can exhibit considerable synergistic advantages in their properties and applications. [6][7][8][9] It is known that mixtures of surfactants can exhibit considerable synergistic advantages in their properties and applications.…”

“…BHDC forms RMs without the addition of cosurfactants [1][2][3][4][5] but CTAB needs the presence of a cosurfactant, usually an alcohol, to generate RMs. [6][7][8][9] It is known that mixtures of surfactants can exhibit considerable synergistic advantages in their properties and applications. [10] Therefore, a new class of surfactant emerges: the catanionic surfactants.…”

Synthesis of NPs by Microemulsion Method

“…Sharma et al [20] reported a detailed and complete study on the growth kinetics of iron oxalate nanorods as they formed throughout several days inside the water pool of CTAB microdroplets (MDs) in isooctane. Authors underlined the novelty of this experimental study on nanostructure preparation in microemulsion-based reactions that could explain the key role of droplet interplay in the reaction kinetics.…”

Morphology‐Conserved Transformations of Metal‐Based Precursors to Hierarchically Porous Micro‐/Nanostructures for Electrochemical Energy Conversion and Storage

“…A porous Li[Li 0.19 Mn 0.32 Co 0.49 ]O 2 nanorod structure was synthesized by Chen et al from a Mn–Co‐oxalate nanorod precursor. Specifically, oxalate ligands were used to coordinate manganese ions and nickel ions to form a 1D bimetal nanorod structure with the help of CTAB . Then, the 1D Mn–Co‐oxalate precursor was converted to porous Mn–Co oxide under heat treatment.…”