Electrokinetic Potential of Nanoparticles in Reverse AOT Micelles: Photometric Determination and Role in the Processes of Heterocoagulation, Separation, and Concentration

Abstract

A simple photometric method for determining the electrophoretic mobility of nano- and microparticles in reverse micelles and in solvents with a low dielectric permittivity (2-5) has been developed. The method is based on the use of a thermostatically controlled diaphragm-based optical cell (length 2 cm) with three vertical plane-parallel electrodes (2 x 3 cm; interelectrode gap, 0.3 cm) placed into a standard photocolorimeter. When an electrostatic field (100-600 V) is applied, the particles begin to move away from the electrode of the same polarity. The path traveled by the particles for a given time (2-30 s) is calculated from the change in the optical density of the solution in the near-electrode zone. The electrophoretic potential of nanoparticles in the model systems, calculated from the values of electrophoretic mobility by Huckel-Onsager theory, varied from 70 (Ag nanoparticles in AOT micelles in decane) to -73 mV (aggregated SiO(2) nanoparticles in a decane-chloroform mixture). Calculations by the classical Deryaguin-Landau-Verwey-Overbeek (DLVO) theory determined the contribution of the electrostatic interaction to the stability of the studied systems. We have shown that the surface charge of nanoparticles permits: (1) an electrophoretic concentration of the charged nanoparticles (Ag) with an enrichment factor of up to 10(4), (2) the separation of nanoparticles with zero (C(60)) and a high (Ag) electrokinetic potentials, and (3) the formation of electrostatically bound aggregates (Ag-SiO(2)) through the heterocoagulation of oppositely charged particles.

Di-(2-ethylhexyl) dithiophosphoric acid surface protected gold nanoparticles: micellar synthesis, stabilization, isolation, and properties

“…During the reduction of Au III and Ag I by hydrazine in AOT micelles, the charge of Au and Ag NPs is positive, too, and it increases with the dilution of AOT solution in decane by chloroform [14,38]. On the basis of the results reported in the present work and those obtained previously, we can propose the following hypothetical mechanism of double sequential stabilization.…”

Effect of the organic solvent polarity on the structure of the gold nanoparticle adsorption layer as observed by photon-correlation spectroscopy

“…Synthesized organosol was placed into an electrophoretic cell (a glass cuvette of 40×20 mm) with horizontally oriented plane-parallel copper electrodes with an interelectrode gap of 10 mm. The voltage on electrodes was 200 V. When the field was switched on, the particles moved towards the cathode located at the bottom of the cell [7]. In 20-30 min the particles accumulated on the cathode as a dark layer.…”

Obtaining electrostatically bound CdS-SiO2 aggregates from electrophoretic concentrates of CdS nanoparticles

“…The electrophoretic mobilities of the CdS and SiO 2 nanoparticles were determined using the original photometric technique developed by the authors and described in detail in [14]. A capacitor-type electrophoretic cell with three vertically oriented copper electrodes and an inter-electrode gap of 3 mm was used.…”

“…As in [14], we associate the adsorption of nanoparticles on SiO 2 with electrostatic interaction. To perform calculations with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, we must determine particle size and the zeta potential.…”

“…In [14], silver nanoparticles were prepared reducing silver nitrate with hydrazine in the reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The nanoparticles were positively charged, allowing us to conduct additional electrophoretic concentration and separate them from the reaction byproducts and excess surface-active substances (surfactants).…”