M. Goffredi

Study of the growth of ZnS nanoparticles in water/AOT/n-heptane microemulsions by UV-absorption spectroscopy

Abstract ZnS nanoparticles were synthesized at 25°C using water-containing AOT reversed micelles as nanoreactors and characterized by UV–vis spectroscopy. The time dependence of the spectra emphasizes a slow growing process of the ZnS nanoparticles coupled with a change of their photophysical properties. Both processes are well described by power laws. The nanoparticle size can be controlled by the molar ratio R ( R =[water]/[AOT]), i.e. by the micellar size. The deposits obtained by evaporation of the volatile components of the microemulsions are found to be composed of a surfactant matrix containing ZnS nanoparticles smaller and more stable than that in the corresponding microemulsions.

Study of AOT-stabilized microemulsions of formamide and n-methylformamide dispersed in n-heptane

Abstract A wide investigation of some physicochemical properties (density, viscosity, conductance, IR spectra, permittivity) of AOT-stabilized dispersions of formamide and n -methylformamide in n -heptane has been performed. The experimental data are consistent with the hypothesis that these highly hydrophilic substances are encapsulated within AOT reversed micelles and that this structure is maintained for both systems well above the volume fraction of the dispersed phase where a percolative transition occurs. In addition, the observed properties of these microemulsions reveal the pivotal role of intermicellar attractive interactions in driving the percolative transition. A marked modification of the structural and dynamical properties of formamide and n -methylformamide accompanying their solubilization within AOT reversed micelles has also been observed.

Refractive index of water-AOT-n-heptane microemulsions

Refractive index measurements on water/AOT/n-heptane microemulsions as a function of the volume fraction ϕ of the dispersed phase (water plus AOT) and of the water/AOT molar ratio R have been performed at 25°C. The refractive index was found to vary monotonically with ϕ without any change in rate during the crossover of the percolation threshold. Such a behavior suggested that, well above the percolation threshold, the water-AOT-n-heptane microemulsions are still formed by water-containing AOT reversed micelles dispersed in the oil phase. The analysis of the experimental data allowed an evaluation the fraction of the water molecules bonded to the AOT head group as a function of R.

Calorimetric investigation of the formation of ZnS nanoparticles in w/o microemulsions

The enthalpies of precipitation of ZnS nanoparticles within water containing reversed micelles of sodium bis(2-ethylhexyl) solfosuccinate, L-α phosphatidylcholine, tetraethyleneglycol-mono-n-dodecyl ether and didodecyldimethylammonium bromide as a function of the molar concentration ratioR (R=[water]/[surfactant]) were measured by calorimetric technique. The results indicate that the energetic state of ZnS nanoparticles confined in the aqueous core of the reversed micelles is different from that in bulk water. Effects due to nanoparticle size, adsorption of HS− ions on the nanoparticle surface and interactions between nanoparticles and water/surfactant interfaces are discussed.

Electrical conductivity and permittivity of water-AOT-n-heptane microemulsions

Measurements of the electrical conductivity and of the complex permittivity of water-sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-n-heptane microemulsions are reported. The experimental results are rationalized in terms of a hopping mechanism of AOT anions within clusters of reversed micelles. The dependence of the hopping rate and of the cluster dimensions upon the ratio [water]/[AOT] and temperature is discussed.

Volumetric and transport properties of aerosol-OT reversed micelles containing light and heavy water

Densities and viscosities of sodium bis(2-ethylhexyl) sulfosuccinate (AOT in-heptane system containing light and heavy water, as a function of the molar ratio R (R=[H2O or D2O]/[AOT]) were measured at 0, 5, 25 and 40°C. At low R values, the apparent molar volume of deuterium oxide is smaller than that of light water. The difference is related to the strength of the hydrogen bonding H2O and D2O. The viscosities of both H2O-AOT-n-heptane and D2O-AOT-n-heptane systems were explained in terms of intermicellar interactions mainly governed by hydration of the head groups of AOT.

Viscoelastic behavior of water/AOT/n‐heptane microemulsions by ultrasonic absorption investigation

The ultrasonic absorption in water/sodium bis(2‐ethylhexyl) sulfosuccinate (AOT)/n‐heptane system has been measured at 25 °C, as a function of the water/AOT molar ratio (X) and of the volume fraction (φ) of the micellar phase. The ultrasonic spectra have been found strongly dependent on φ and nearly independent on X. In particular, as φ increases, ultrasonic dynamics shifts from a single to a distribution of relaxation times with occurrence of viscoelastic effects. Such findings have been correlated to the increased connectivity of the micellar network.

Effect of water on proton migration in alcoholic solvents—I. the conductance of hydrogen chloride in n-butanol and iso-butanol at 25°C

Conductance measurements at 25°C on dilute solutions of hydrochloric acid in n-butanol and iso-butanol containing small amounts of water are reported. The data were analysed with a computer programmed for the linearized 1965 theoretical Fuoss-Onsager equation. The equivalent conductance at infinite dilution and the association constant in absolute n-butanol and iso-butanol respectively, have been determined by graphical extrapolation. In agreement with previous experiments in alcohol-water mixtures the limiting equivalent conductance decreases when water is added to the alcohol and then increases again. The equilibrium constant and the standard free energy change for ROH2+ + H2O ⇄ ROH + H3O+ have been determined.

Physico-chemical characterization of Pd nanoparticles synthesized in w/o microemulsions

Abstract The long time stability of surfactant-coated Pd nanoparticles in w/o microemulsions has been investigated. It has been proven that in suitable conditions, the use of the functionalized surfactant Pd(AOT)2 allows to obtain very stable nanosized Pd particles and to finely control their average size.

Effects of water on proton migration in alcoholic solvents. Part 4.—Conductance of hydrogen chloride in butan-2-ol and in ethanol at 25°C

Data are reported on the conductances of dilute solutions of hydrogen chloride in wet ethanol and wet butan-2-ol at 25°C.From these and supplementary data in other homologous alcohols of the CnH2n+1 OH series the correlation between monomer concentration and proton limiting conducatance/viscosity product is discussed in terms of the structure of the solvent.