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Longhi G.,University of Brescia | Longhi G.,Consorzio Interuniversitario Science Fisiche della Materia | Abbate S.,University of Brescia | Abbate S.,Consorzio Interuniversitario Science Fisiche della Materia | And 4 more authors.
Physical Chemistry Chemical Physics | Year: 2011

Positively charged supramolecular aggregates formed in vacuo by n AOTNa (sodium bis(2-ethylhexyl)sulfosuccinate) molecules and n c additional sodium ions, i.e. [AOT nNa n+nc]n c, have been investigated by molecular dynamics (MD) simulations for n = 1-20 and n c = 0-5. Statistical analysis of physical quantities like gyration radii, atomic B-factors and moment of inertia tensors provides detailed information on their structural and dynamical properties. Even for n c = 5, all stable aggregates show a reverse micelle-like structure with an internal solid-like core including sodium counterions and surfactant polar heads surrounded by an external layer consisting of the surfactant alkyl chains. Moreover, the aggregate shapes may be approximated by rather flat and elongated ellipsoids whose longer axis increases with n and n c. The fragmentation patterns of a number of these aggregates have also been examined and have been found to markedly depend on the aggregate charge state. In one particular case, for which experimental findings are available in the literature, a good agreement is found with the present fragmentation data. © 2011 the Owner Societies.

Longhi G.,University of Brescia | Longhi G.,Consorzio Interuniversitario Science Fisiche della Materia | Ceselli A.,University of Milan | Fornili S.L.,University of Milan | And 5 more authors.
Journal of Mass Spectrometry | Year: 2013

The behavior of aqueous solutions of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N0 AOT AOT- anions (N0 AOT = 0, 5, 10) and N0 Na sodium ions (N0 Na = 0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N0 AOT and N 0 Na eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.

Zanotto A.,Centro Grandi Apparecchiature | Spinella A.,Centro Grandi Apparecchiature | Nasillo G.,Centro Grandi Apparecchiature | Caponetti E.,Centro Grandi Apparecchiature | And 2 more authors.
Express Polymer Letters | Year: 2012

This paper examines the results of the characterization of two functional composites: Poly(methyl methacrylate) (PMMA)-Ce:YAG (yttrium aluminium garnet doped with cerium) and PMMA-cobalt hexacyanoferrate (CoHCF). The composites were prepared as possible emitters in the fields of lighting thermal sensors. The prepared composites were characterized using transmission electron microscopy (TEM), nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) analyses to study the correlation between micro and macro characteristics. We found that the molecular interactions of the two different fillers with the matrix were localized in different sites of the polymer chains. Moreover, the composites showed an increased thermal strength and stiffness, in particular the PMMA-Ce:YAG composite. © BME-PT.

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