Electrophoretic mobility and stability of SiO2 nanoparticles in the solutions of AOT in n-hexadecane-chloroform mixtures.

Electrophoretic mobility of SiO2 nanoparticles in a n-hexadecane-chloroform mixture depending on AOT concentration and chloroform content was determined. It was shown that an increase in chloroform content and a decrease in AOT concentration cause a growth in electrophoretic mobility. The use of the values of Debye lengths (characteristic thickness) of the diffuse part of the electric double layer (EDL) that were determined previously allowed us to calculate the electrokinetic potential and to evaluate the stability of organosols. The obtained data were in good correlation with the dynamics of temporal changes of hydrodynamic radius and the intensity of light scattering. Organosols may be used for heteroaggregation (sorption) of Au and Ag nanoparticles on SiO2 .

Structure and conductivity of AOT solutions in n-hexadecane-chloroform mixtures.

The structure and conductivity of AOT (sodium bis(2-ethylhexyl) sulfosuccinate) solutions (2.5 × 10-4 -2.5 × 10-1 M) in n-hexadecane-chloroform mixture at the chloroform concentration from 50 to 100 vol% were studied. The diffusion ordered spectroscopy NMR study revealed that in the indicated range, the observed hydrodynamic diameter of micelles depends only on the AOT concentration and does not depend on the chloroform content. Molar fractions of free AOT molecules and those aggregated into micelles were calculated using the Lindman's law: at concentrations above 2.5 × 10-1 М, the solutions contain mostly the micelles, whereas at concentrations below 2.5 × 10-4 M, the solutions contain AOT molecules. The transition region contains both the AOT molecules and the micelles. Conductivity measurements were used to determine free charge carriers in the bulk of solutions and their contributions to conductivity.

The formation of free ions and electrophoretic mobility of Ag and Au nanoparticles in n-hexadecane-chloroform mixtures at low concentrations of AOT.

The electrophoretic mobility of Ag and Au nanoparticles in n-hexadecane-chloroform mixtures was studied as a function of the chloroform content (from 0 to 100 vol%). The nanoparticles were stabilized by sodium bis-(2-ethylhexyl)sulfosuccinate (AOT, Aerosol OT) with a concentration of 2.5 × 10-4 mol L-1. The obtained organosols were characterized by phase analysis light scattering, dynamic light scattering, transmission electron microscopy, diffusion-ordered spectroscopy of nuclear magnetic resonance, spectrophotometry and conductometry. The electrophoretic mobility of the nanoparticles sharply increased from 0 to 3.6 × 10-9 m2 V-1 s-1 with increasing chloroform content. The growth of the mobility was caused by an increase in the concentration of solvated AOT ions, which formed by the disproportionation reaction from uncharged molecules. Low concentrations of AOT and a considerable zeta potential (up to ∼100 mV) made it possible to use the obtained organosols for the formation of electrostatically bound aggregates of Ag and Au with negatively charged SiO2 nanoparticles.

Synthesis, characterization, and electrophoretic concentration of titanium dioxide nanoparticles in AOT microemulsions.

Stable organosols of TiO2 nanoparticles were prepared by hydrolysis of titanium tetraisopropoxide (TTIP) in microemulsions of sodium bis(2-ethylhexyl)sulfoxynate (АОТ) in n-decane with increasing the content of aqueous pseudophase from 0.15 to 0.85 vol.%. As the water content increased, the hydrodynamic diameter of nanoparticles grew from 10 to 225 nm, and the  Î¶-potential, from -6 to 18 mV (the surface of TiO2 nanoparticles was recharged when the water content was 0.45 vol.%). Nonaqueous electrophoresis in a capacitor-type cell made it possible to concentrate nanoparticles with a diameter of 60 to 225 nm (concentration factor was 10), separate 20 nm and 225 nm particles, and decrease the content of АОТ in organosol by an order of magnitude. Preparation of a concentrate of nanoparticles with a low content (0.015 M) of AOT included the following stages: (i) electrophoresis after synthesis; (ii) sampling of the concentrate and its twenty-fold dilution with pure n-decane; and (iii) repeated electrophoresis. In situ laser and spectrophotometric scanning of the interelectrode space showed the formation of a sharp boundary between the raffinate and the layer of moving nanoparticles during electrophoresis.