0000000000353189
AUTHOR
Francesco Aliotta
Emerging dynamics in surfactant-based liquid mixtures: octanoic acid/bis(2-ethylhexyl) amine systems.
This work focuses on the dynamic phenomena emerging in self-assembled transient intermolecular networks formed when two different surfactants are mixed. In particular, the relaxation processes in liquid mixtures composed by bis(2-ethylhexyl)amine (BEEA) and octanoic acid (OA) in the whole composition range has been investigated by dielectric spectroscopy and Brillouin spectroscopy. A thorough analysis of all the experimental data consistently suggests that, mainly driven by acid-base interactions arising when the two surfactants are mixed, supra-molecular aggregates formation causes the slowing down of molecular dynamics. This, in turn, reflects to longer-range relaxations. These changes ha…
Study of lecithin reverse micelles by FT-IR spectroscopy
FT-IR spectra of water/lecithin/deuterated cyclohexane microemulsions as a function of water/lecithin molar ratio R (R=[water]/[lecithin]) at various lecithin volume fractions (φ) have been recorded. After elimination of the spectral contributions due to the deuterated cyclohexane and normalization, the band parameters of the CO and PO4 vibrational modes due to lecithin have been found dependent only upon R. This behaviour has been interpreted in terms of a progressive structural modification of the water/lecithin interface superimposed to the progressive hydration of CO and PO4 groups. Moreover, no correlation between the CO and PO4 band parameters and the formation of gel-like micellar so…
Structural and dynamical investigation of gelation containing water-in-oil microemulsions
The gelatin (Bloom 300)/water/AOT/n-heptane system has been investigated at fixed water/AOT molar ratioR (R=31.1) as a function of the gelatin content. Several experimental techniques (densitometry, refractometry, conductometry, rheology, dielectrometry, ultrasonics, hypersonics) have been used to investigate the role played by the gelatin molecule in the observed sol-gel transition above a critical gelatin content. The results appear consistent with the hypothesis of a rigid network of gelatin-water rods coated by surfactant molecules coexisting with gelatin-free AOT reversed micelles at the gelation point.
Hydrogen bond studies on n-pentanol and 2-methyl-2-butanol by Raman spectroscopy
Polarized Raman spectra of n-pentanol and its isomer 2-methyl-2-butanol are obtained in the liquid phase near the melting points and at superheated temperatures. The measurements are performed in the intramolecular O-H stretching region. Our analysis of the Raman data provides an interpretation of the spectral features in terms of symmetric O-H bands, originated by various degrees of intermolecular coupling, for which mechanism is different for the two isomers. Temperature dependence of the spectra is also discussed in terms of available structural and dynamical models for these H-bonded liquids.
Structural Investigation of Water/Lecithin/Cyclohexane Microemulsions by FT-IR Spectroscopy
Abstract FT-IR spectra of water/lecithin/deuterated cyclohexane microemulsions as a function of water/lecithin molar ratio R ( R = [water]/[lecithin]) at various volume fractions ( O ) of the micellar phase have been recorded at 25°C. After elimination of the small spectral contributions due to deuterated cyclohexane and normalization, the shape of the C–H stretching band due to lecithin has been found dependent upon R and O whereas that of the O–H stretching band has been found dependent only upon R . The change in shape of the C–H band was interpreted in terms of a modification of the lecithin alkyl chain packing order. The analysis of the O–H band provides evidence that the hydroxylic gr…
Dielectric properties of water/lecithin/cyclohexane gels
Dielectric relaxation measurements in the frequency range 0.1–15 GHz have been carried out on water/lecithin/cyclohexane gels using a time domain reflectometry method (TDR). Dielectric dispersions describable in terms of a power law typical of percolated systems, but with exponents significantly different from those characterizing statically or dynamically percolated systems are observed. The dielectric dispersions, attributed to water and/or lecithin head group rotational motions, indicate that these motions are characterized by a wide spectrum of relaxation times.
Calorimetric investigation of water/lecithin/cyclohexane microemulsions
The enthalpies of dilution of water/lecithin/cyclohexane microemulsion-gels at variousR values (R=[water]/[lecithin]) and molar enthalpies of solution of water in lecithin/cyclohexane at a fixed lecithin concentration were determined calorimetrically at 25°C. Through a description of the process of dilution of water/lecithin/cyclohexane microemulsion-gels as one involving mainly the scission of lecithin reversed micelles in to smaller ones, the concentration dependence of the enthalpy was rationalized. Surprisingly, in order to account for the dilution enthalpies, it was not necessary to hypothesize a thermal effect arising from the breakage of the micellar network present in the micremulsi…
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 modifica…