P. Calandra

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.

FT-IR and dielectric study of water/AOT liquid crystals

Abstract In order to explore the influence of microwave radiation on highly viscous microheterogeneous systems, the evolution of structural and dynamical properties of the water/sodium bis(2-ethylhexyl) sulfosuccinate (AOT) liquid crystals as a function of the molar ratio R ( R =[water]/[AOT]) has been investigated by FT-IR spectroscopy and time domain reflectometry. The study emphasises how the progressive hydration of the surfactant head groups is mainly responsible for the structural and dynamical evolution of water/AOT liquid crystals. In particular, it has been found that the state of water at lower R values is strongly perturbed, bulk-like water appears only at R >23 and the water/AOT interface polarisation is controlled by the fast translational dynamics of sodium counterions and the slow orientational dynamics of the AOT ionic head groups.

Anti-Arrhenian behaviour of conductivity in octanoic acid–bis(2-ethylhexyl)amine systems: a physico-chemical study

Pure surfactant liquids and their binary mixtures, owing to the amphiphilic nature of the molecules involved, can exhibit nano-segregation and peculiar transport properties. The structural and dynamic properties of octanoic acid (OA)–bis(2-ethylhexyl)amine (BEEA) liquid mixtures at various compositions have been studied by Wide Angle X-ray Scattering (WAXS), 1H-NMR and broadband dielectric spectroscopy as a function of temperature. It was found that the self-assembly occurs via proton exchange between the OA COOH group and the BEEA NH one; such self-assembled local structures are affected anisotropically by a temperature increase so that the thermal dilatation is more marked in a direction perpendicular to the molecular axis whereas it is practically unaffected along its axis. Interestingly, an anti-Arrhenian behaviour of the conductivity has been found at the OA molar ratio (XOA) of around 0.66. This behaviour has been interpreted as the overall result of the competition between the tendency of OA surfactant molecules to aggregate through OA–OA H-bond formation and the establishment of hetero-adducts OA–BEEA joined to the temperature disordering effect. The potentialities of such systems as proton conducting water-free organic-based liquid systems enable them to be tailored for their direct use as liquid membranes in fuel cells but also, from a more general perspective, for the piloted design of smart materials for specific applications.

Self-assembly in surfactant-based liquid mixtures: Octanoic acid/Bis(2-ethylhexyl)amine systems

The physico-chemical properties of Bis(2-ethylhexyl)amine (BEEA) plus octanoic acid (OA) mixtures have been investigated by IR, SAXS, WAXS, viscosimetry, and AC complex impedance spectroscopy in the whole composition range. Mainly driven by proton transfer from the acidic OA to the basic BEEA, the formation of stoichiometrically well-defined adducts takes place in the mixtures. This causes the slowing down of molecular dynamics and the increase in charge carrier number density. Interestingly, while the pure components possess no significant conductivity (about 10(-12) S cm(-1) at 25 °C), their mixtures show a composition-dependent enhanced conductivity (up to about 10(-5) S cm(-1)), i.e., more than seven orders of magnitude higher than that of the pure components. The comparison of the composition dependence of viscosity, direct-current conductivity, and static permittivity indicates the concurrence of contributions of different adducts and that the dynamics controlling molecular reorientation and momentum and charge transfer, even if ultimately related to the proton transfer from OA to BEEA, are different. The results can be used not only to design novel materials for application purposes, but also to shed more light on the principles regulating molecular self-assembly in surfactant-based liquid systems.

Folate targeted coated SPIONs as efficient tool for MRI

The development of more sensitive diagnostic tools allowing an early-stage and highly efficient medical imaging of tumors remains a challenge. Magnetic nanoparticles seem to be the contrast agents with the highest potential, if properly constructed. Therefore, in this study, hybrid magnetic nanoarchitectures were developed using a new amphiphilic inulin-based graft copolymer (INU-LAPEG-FA) as coating material for 10-nm spinel iron oxide (magnetite, Fe3O4) superparamagnetic nanoparticles (SPION). Folic acid (FA) covalently linked to the coating copolymer in order to be exposed onto the nanoparticle surface was chosen as the targeting agent because folate receptors are upregulated in many cancer types. Physicochemical characterization and in vitro biocompatibility study was then performed on the prepared magnetic nanoparticles. The improved targeting and imaging properties of the prepared FA-SPIONs were further evaluated in nude mice using 7-Tesla magnetic resonance imaging (MRI). FA-SPIONs exhibited the ability to act as efficient contrast agents in conventional MRI, providing a potential nanoplatform not only for tumor diagnosis but also for cancer treatment, through the delivery of anticancer drug or locoregional magnetic hyperthermia.

Decoupling of dynamic processes in surfactant-based liquid mixtures: the case of lithium-containing bis(2-ethylhexyl)phosphoric acid/bis(2-ethylhexyl)amine systems.

Pure surfactant liquids and their binary mixtures, because of the amphiphilic nature of the molecules involved, can exhibit nanosegregation and peculiar transport properties. The idea that inspired this work is that the possibility of including in such media salts currently used for technological applications should lead to a synergy between the properties of the salt and those of the medium. Therefore, the dynamic features of bis(2-ethylhexyl)amine (BEEA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) liquid mixtures were investigated as a function of composition and temperature by (1)H nuclear magnetic resonance (NMR) spectroscopy and rheometry. Inclusion of litium trifluoromethanesulfonate (LiT) has been investigated by infrared spectroscopy, pulsed field gradient NMR, and conductimetry methods to highlight the solubilizing and confining properties of these mixtures as well as the lithium conductivity. It was found that BEEA/HDEHP binary liquid mixtures show zero-threshold percolating self-assembly with a maximum in viscosity and a minimum in molecular diffusion at a 1:1 composition. Dissolution of LiT in such system can occur via confinement in the locally self-assembled polar domains. Despite this confinement, Li(+) conduction is scarcely dependent on the medium composition because of the possibility of a field-induced hopping decoupled by the structural and dynamical features of the medium.

Sensitization of nanocrystalline TiO2 with 3,4,9,10-perylene tetracarboxylic acid

Optical properties of 3,4,9,10-perylene tetracarboxylic acid (PTCA) in the presence of nanocrystalline TiO2 (nominal diameter 15xa0nm) have been investigated in ethanol solution and in the solid state by UV–Vis absorption spectroscopy and steady-state and time-resolved fluorescence. Experimental results show that, in ethanol, the presence of TiO2 nanoparticles causes significant changes in the typical absorption and fluorescence bands of PTCA and in the fluorescence relaxation time. Similar effects are also detected in solid samples, obtained by electrospray deposition technique. The nonlinear optical properties of the PTCA–TiO2 in ethanol solutions were investigated using the single-beam Z-scan techniques at 532xa0nm. It was found that, at high TiO2 nanoparticles content, PTCA exhibits a reverse saturable absorption with significant nonlinear absorption and intensity-dependent negative nonlinear refractive coefficient, indicating self-defocusing behaviour. The third-order nonlinear susceptibility and optical limiting threshold were also determined. Data analysis leads consistently to attribute the observed behaviours to chemical adsorption of PTCA to the TiO2 surface both in liquid and solid samples. Potentialities of these novel luminescent nanostructured composites as components of dye-sensitized solar cells or components where the nonlinear optical behaviour is requested have been highlighted.