A. Ruggirello

FT-IR investigation of the urea state in lecithin and sodium bis(2-ethylhexyl)phosphate reversed micelles

Abstract FT-IR spectra of urea/lecithin/CCl4 and urea/sodium bis(2-ethylhexyl) phosphate (NaDEHP)/CCl4 systems as a function of the urea-to-surfactant molar ratio (Rurea) at a fixed surfactant concentration (0.1xa0molxa0kg−1) have been recorded at 25xa0°C. Analysis of the absorption spectra leads the to hypothesis that urea is confined within the hydrophilic micellar core of lecithin and NaDEHP reversed micelles. The encapsulation of urea involves some changes of the urea NH stretching band with respect to that of the pure solid urea, attributable to confinement effects. The stretching modes of the surfactant head group are affected by the presence of urea, indicating specific urea-surfactant head group interactions. On the other hand, analysis of the CO stretching band suggests that the urea CO groups are not engaged in urea-surfactant head group interactions.

Study of AOT-stabilized microemulsions of urea dispersed in carbon tetrachloride

Measurements of some physico-chemical properties (density, viscosity, permittivity) of the urea/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/CCl4 system as a function of the volume fraction of the dispersed phase (0<Φ<0.7) at various urea to AOT molar ratio (Rurea) have been carried out at 25 °C. The experimental data analysis are consistent with the hypothesis that urea is entrapped as small-size molecular clusters within the hydrophilic core of the AOT reversed micelles and that this structure is preserved well above a threshold Φ value where a percolative transition occurs. Besides, X-ray diffraction spectra of samples at Φ=1, obtained by complete evaporation under vacuum of the apolar solvent of urea/AOT/CCl4 solutions, indicates that, even in the typical two-dimensional hexagonal structure of AOT liquid crystals, urea is encapsulated as uni-dimensional molecular clusters.

Combined small-angle x-ray scattering/extended x-ray absorption fine structure study of coated Co nanoclusters in bis(2-ethylhexyl)sulfosuccinate

Chemically stable cobalt nanostructures have been prepared with Co(II) reduction in the confined space of cobalt bis(2-ethylhexyl)sulfosuccinate, Co(AOT)2, reverse micelles dispersed in n-heptane. The reaction was carried out by adding a solution of sodium borohydride in ethanol (1% weight) to a 0.2M micellar solution of Co(AOT)2 in n-heptane at a reductant to Co(II) molar ratio of 4. This procedure involves the rapid formation of surfactant-coated Co nanoparticles followed by their slow separation as nanostructures embedded in a sodium bis(2-ethylhexyl)sulfosuccinate matrix. The resulting composites, characterized by extended x-ray absorption fine structure and small-angle x-ray scattering, showed the presence of subnanometer sized cobalt nanoparticles aggregated together to form elongated structures coated by the surfactant molecules.

FT-IR Investigation of the N-methylurea State in AOT Reversed Micelles

The state of N-methylurea (NMU) confined within the hydrophilic core of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reversed micelles (radius 1.5–1.8u2009nm) has been investigated by Fourier transform infrared spectroscopy. The analysis of the spectral features leads to the hypothesis that NMU is encapsulated in the micellar core as small-sized molecular clusters. As a consequence of their small size and of NMU–AOT head group interactions, these clusters display marked departures from the H-bonded structure of the pure solid NMU even at the higher NMU to AOT molar ratio. The stretching modes of NMU CO, AOT CO and sulfonate groups indicate unambiguously specific NMU–AOT head group interactions.