In Situ Crystallization and Growth Dynamics of Acentric Iron Iodate Nanocrystals in w/o Microemulsions Probed by Hyper-Rayleigh Scattering Measurements

Abstract

A detailed experimental investigation of the formation mechanisms of acentric iron iodate [Fe(IO 3 ) 3 ] nanocrystals in AOT-based reverse micelles according to the water-in-oil (w/o) microemulsion (ME) composition and temperature was performed. A low chemical reaction rate was first demonstrated by means of UV-vis absorption spectroscopy. Attainment of iron iodate crystalline nanorods was then attributed to an oriented aggregation mechanism of 10-20-nm amorphous primary nanoparticles. As for the intermicellar exchange of reactants, the aggregation mechanism was also found to be determined by the ME composition because clear effects of the surfactant and reactant concentrations, the nature of the oil phase, and the water droplet size were observed. Moreover, a combination of dynamic light scattering, X-ray diffraction, and transmission electron microscopy experiments revealed that hyper-Rayleigh scattering is a fast, valuable, and nondestructive alternative to probe, in real time, the crystallization and formation dynamics of acentric nanoparticles in microemulsions. This experimental approach can be extended to studies dealing with the formation of metal nanoparticles for which scattering of second-harmonic light is readily observed.

Harmonic nanoparticles: noncentrosymmetric metal oxides for nonlinear optics

“…For the production of Fe(IO 3 ) 3 , co-precipitation between iron nitrate and iodic acid has been used in homogeneous solutions and from mini [29]-and micro-emulsions [30,31].…”

Preparation of transparent PMMA/Fe(IO3)3 nanocomposite films from microemulsion polymerization

“…Besides, after such a period, the viscosity is high and prevents any spin‐coating. We demonstrated earlier that an increase in temperature and in the concentration of reactants and surfactants strongly reduces the crystallization time but such variations are not conceivable here . Another possibility is to reduce the strong binding interactions at the organic–inorganic interface between surfactants and the surface of primary amorphous precursors .…”

“…The domains of existence of microemulsions being identified, in situ crystallization of iron iodate nanorods in microemulsions is then probed by time‐dependent hyper‐rayleigh scattering (HRS) measurements. The experimental setup was already detailed in a previous work . After centrifugation (Sigma 2–16 centrifuge) of the reaction medium, the crystalline structure of nanorods is confirmed by X‐Ray Diffraction (XRD) with Co‐Kα (INEL CPS 120 with a position sensitive detector).…”

“…Detection of a nonlinear optical response is performed using the Maker‐fringes technique. The experimental setup is the same as the one used for HRS except that the signal at 2ω is detected in transmission (and not perpendicularly to the incident laser beam) and that the sample is placed on a rotation plate. Piezoelectric performances of the different films are assessed with a piezo‐d meter (SS01‐01, Sensor Technology limited, Canada ) to estimate the d 33 piezoelectric coefficient and also with laser vibrometry (SIOS SP‐S 120, Polytec ) .…”

“…On the other hand, the needle‐like Fe(IO 3 ) 3 crystalline nanoparticles obtained so far by coprecipitation of Fe(NO 3 ) 3 9H 2 O and HIO 3 in various sodium bis (2‐ethylhexyl) sulfosuccinate (AOT)/alkane/water ternary systems are good candidates to prepare transparent functional polymers with optimized piezoelectric response . The growth mechanism from water‐in‐oil microemulsions, clearly associated to an aggregation‐induced crystallization of 10–20 nm amorphous precursor particles, leads to the formation of small crystalline nanorods with diameter and length below 30 and 200 nm, respectively . The nanometer size and the absence of aggregation are strong requirements in order to keep the transparency of the resulting nanocomposite material …”