Microemulsions as Reaction Media for the Synthesis of Mixed Oxide Nanoparticles: Relationships between Microemulsion Structure, Reactivity, and Nanoparticle Characteristics

Abstract

Phase behavior, dynamics, and structure of W/O microemulsions of the system aqueous solution/Synperonic 13_6.5/1-hexanol/isooctane were studied, with the goal of determining their effect on Mn-Zn ferrite nanoparticle formation, kinetics and characteristics. Microemulsion structure and dynamics were studied systematically by conductivity, dynamic light scattering (DLS), differential scanning calorimetry (DSC), and small-angle neutron scattering (SANS). The main effect of cosurfactant 1-hexanol was a decrease in microemulsion regions as compared to the systems without cosurfactant; nevertheless, overlap of microemulsion regions in the systems with precursor salts (PS) and precipitating agent (PA) was achieved at lower S/O ratios, compared to the system without cosurfactant. At 50 °C, PA microemulsions are nonpercolated, while PS microemulsions are percolated. SANS indicates small prolate ellipsoidal micelles with the absence of free water up to 18 wt % PS solution; DSC studies confirm the absence of free water in this composition range. Kinetic studies show an increase in the reaction rate with increasing concentration of the aqueous solution; but the most significant effect in reaction kinetics was noted when cosurfactant was used, regardless of microemulsion dynamics and structure. On the other hand, the main difference regarding the characteristics of the obtained nanoparticles was observed when bicontinuous microemulsions were used as reaction media which resulted in 8 nm nanoparticles, versus a constant size of ~4 nm obtained with all other microemulsions regardless of aqueous solution content, dynamics, and presence or absence of cosurfactant. The latter effect of constant size is attributed to the fact that the water present is dominantly bound to the EO units of the surfactant.

Oriented attachment of ultra-small Mn(1−x)ZnxFe2O4nanoparticles during the non-aqueous sol–gel synthesis

“…As an alternative to this process various other methods have been developed for the preparation on a laboratory scale, such as the micoemulsion synthesis, 14 co-precipitation, 15 sol-gel synthesis 16 and hydrothermal synthesis. Fax: +49 (0)531 3919633; Tel: +49 (0)531 3919615; E-mail: g.garnweitner@tubraunschweig.de b Institute for Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, Karlsruhe, Germany.…”

Introductory Chapter: Microemulsions

“…Here, the measurement is the fluctuation of scattered laser light intensity, which is related to the Brownian motion of particles (droplets) in the medium. Fitting the autocorrelation of the scattered light intensity to models of particles in specific media can lead to determining the diffusion constant, particle size distribution, and in some cases, shape anisotropy [9][10][11].…”

Controlling Mesopore Size and Processability of Transparent Enzyme-Loaded Silica Films for Biosensing Applications

“…19−22 Templating materials, e.g., molecular surfactants or block copolymers (BCP), microemulsions, 23 etc., self-organize into large size 3D structures (e.g., micelles). Simultaneously, sol−gel chemistry is used to build a metal oxide framework around them.…”