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Lidia Armelao

Publications and source records attributed to Lidia Armelao.

11 recordsLinked to original sources
PubMed2006

Wetting behavior of porous silicon surfaces functionalized with a fulleropyrrolidine.

We report the immobilization of a fulleropyrrolidine, bearing a dec-9-ynyl functionality, on silicon surfaces through a thermal hydrosilylation protocol. Contact angle measurements on porous silicon (PS) surfaces reveal an unusual dependence of the angle with the PS roughness that apparently contradicts Wenzel's formula. This result has been explained by an extension of Wenzel's model in which the critical angle, which discriminates between the hydrophilic/hydrophobic character of a solid material, is substantially reduced below 90 degrees by surface roughness.

Journal Article↗
PubMed2006

Gold nanoclusters protected by conformationally constrained peptides.

The preparation and properties of a series of gold nanoclusters protected by thiolated peptides based on the alpha-aminoisobutyric acid (Aib) unit are described. The peptides were devised to form 0-3 C=O...H-N intramolecular hydrogen bonds, as required by their 3(10)-helical structure. The monolayer-protected clusters (MPCs) were prepared, using a modified version of the two-phase Brust-Schiffrin preparation, and fully characterized with (1)H NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The MPCs were obtained with core diameters in the range of 1.1-2.3 nm, depending on the reaction conditions. Structured peptides formed smaller clusters. The smallest MPC obtained is in agreement with the average formula Au(38)Pep(18). The results showed that the chemical integrity of the peptide is maintained upon monolayer formation and that the average number of peptide ligands per gold cluster is typically 75-85% the value calculated for alkanethiolate MPCs of similar sizes. The IR and NMR spectra indicated that in the monolayer the peptides are involved in both intra- and interligand C=O...H-N hydrogen bonds.

Aminoisobutyric Acids↗
PubMed2006

Polymerization processes in Al(OBu(s))3 sol-gel solutions: An investigation by laser desorption/ionization mass spectrometry.

The hydrolysis and polycondensation reactions of Al(OBu(s))3 have been studied by laser desorption/ionization (LDI), performed on the solid samples originating from different aluminum alkoxide solutions, prepared using the usual operating conditions employed in the sol-gel synthesis of Al2O3-based materials. CHCl3, CH3OH and CH3OH/H2O mixture were used as solvents. In the latter case different H2O/Al(OBu(s))3 molar ratios were adopted, i.e. 1:1, 1:2, and 1:4. The obtained hydrolysis and polycondensation species consist of polynuclear species containing < or =12 aluminum atoms. In the CHCl3 solutions, the formation of the observed hydrolysis products has been ascribed to the reaction with water present in the atmosphere during the LDI sample preparation and/or present at trace level in the solvent. When methanol is used as a solvent, extensive methanolysis reactions take place, thus originating oligomers with CH3O and OH substituents. The kinetics of formation of the various polynuclear species are dependent on the reaction environment and the reaction is faster in the presence of methanol. It is worth noticing that, regardless of the hydrolysis process, the polycondensation products can be considered as originating from a common tetrameric core [Al4O4(OBu)2(OH)2] around which different building blocks are condensed to form various oxo-polymeric species.

Journal Article↗
PubMed2006

Structural and magnetic properties of pure and Ca-doped LaCoO3 nanopowders obtained by a sol-gel route.

Pure and Ca-doped LaCoO3 nanopowders were prepared by a non-alkoxidic sol-gel route using cobalt(II) acetate, lanthanum(III) nitrate and calcium(II) acetate as oxide precursors. The structural evolution and magnetic properties of the samples were studied as a function of thermal treatments in air up to 1273 K. In particular, the microstructure and composition of the systems were analyzed by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS). Both pure and calcium-doped samples annealing at 973 K resulted in the formation of cubic LaCoO3 (average crystallite size <30 nm). This phase was fully retained in the calcium-doped materials even after annealing at higher temperatures, whereas a transition to the rhomboedral polymorph was detected in the pure samples at 1073 K. The magnetic behavior of the nanopowders was investigated as a function of temperature and applied field using both dynamic and static susceptibility measurements. Pure lanthanum cobaltite samples underwent a transition to an ordered state at 88 K, and their magnetic properties changed as a function of thermal treatments. As concerns calcium-doped samples, they ordered ferromagnetically at 171 and 185 K depending on the annealing temperature and displayed open hysteresis loops with coercive fields as large as 1.75 T at low temperatures.

Calcium↗
PubMed2006

Synthesis of copper sulphide nanoparticles in carboxylic acids as solvent.

A novel method for the preparation of CuS nanoparticles based on the fast nucleation of the sulphide has been developed. The particles have been synthesized by reaction of thioacetic acid with water and copper carboxylates (acetate, propionate) in the corresponding carboxylic acid (acetic, propionic) as a solvent. The use of carboxylic acids presents several advantages: (i) the hydrolysis of the C-S bond is favoured thus producing a fast CuS supersaturation and a high nucleation rate; (ii) the mobility of the precursor molecules is limited so that nucleation events are favoured with respect to particle growth; (iii) the low dielectric constant of the medium stabilises the nanoparticles dispersion by reducing the critical coagulation concentration. The prepared nanoparticles were investigated by UV-Vis spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and dynamic light scattering. The nanoparticle suspensions are clear and characterized by a blue-shifted adsorption edge with respect to bulk CuS. Light scattering measurements performed on acetic acid suspensions evidence the formation of monodispersed nanoparticles with an average diameter of about 5 nm.

Carboxylic Acids↗
PubMed2005

Turning fluorescent dyes into Cu(II) nanosensors.

There is great interest in the self-organization of the proper subunits as a new strategy for the realization of fluorescent chemosensors. In this article, it is shown that commercially available fluorescent dyes, functionalized with triethoxysilane moieties, can be converted into fluorescent chemosensors by simple inclusion into silica nanostructures. Dye-doped silica nanoparticles and thin films detect Cu(II) ions in the micromolar range by the quenching of fluorescence emission. The different response toward Zn(II), Ni(II), and Co(II) metal ions was also investigated and is reported. The self-organization of the silica structures leads, at the same time, to the formation of metal ion binding sites as well as to the linking of a fluorescent reporter in their proximity. Structural features of the materials, particularly particle size and network porosity, strongly affect their ability to act as fluorescent sensors.

Journal Article↗
PubMed2005

Preparation of gold nanoparticles on silica substrate by radio frequency sputtering.

Radio frequency sputtering of gold on amorphous silica substrates was used for the preparation of Au nanoparticles on SiO2. Deposition experiments were carried out in Ar plasmas under mild conditions (RF power = 5/10 W, total pressure = 0.38 mbar, substrate temperature < or = 210 degrees C), focusing in particular on the effect of sputtering time (5/30 min) and substrate temperature on gold nucleation and coalescence, with the aim of obtaining SiO2-supported Au nanoparticles characterized by precise structural and morphological features. To this aim, several analytical techniques were employed for a thorough characterization of the systems properties, including glancing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and UV-Vis absorption spectroscopy. In particular, the evolution of optical spectra, i.e., of the surface plasmon resonance peak, was used as a probe for the structural features and was related to the results obtained by other characterization techniques. Gold nanoclusters (phi approximately 4/10 nm) dispersed uniformly on silica matrices were obtained under soft conditions, with morphology ranging from island to cluster like. The obtained results make possible a careful modulation of substrate coverage and gold nanoparticle size.

Gold↗
PubMed2005

LaCoO3 nanosystems by a hybrid CVD/sol-gel approach.

LaCoO3 nanosystems are receiving increasing attention for the development of innovative fuel cells and heterogeneous catalysts. In this report, we describe the synthesis of nanophasic LaCoO3 thin films by a hybrid chemical vapor deposition (CVD)/sol-gel (SG) approach. The adopted strategy consists in the CVD of La-O-based systems on SG cobalt oxide xerogels CoOx(OH)y at temperatures as low as 200 degrees C and in the subsequent thermal treatment in air (400-800 degrees C, 2-8 h). In this context, particular attention is devoted to achieving an intimate La/Co intermixing already in the as-prepared systems, in order to favor reactions yielding a single La-Co-O phase with uniform composition. The obtained results point out to the formation of pure and structurally homogeneous LaCoO3 nanosystems after annealing at 700 degrees C, 2 h, with a typical grain-like morphology. More severe thermal treatment resulted in the thermal decomposition of LaCoO3 nanocrystallites.

Cobalt↗
PubMed2004

Biodegradable polyesters reinforced with surface-modified vegetable fibers.

Flax fibers are investigated as reinforcing agents for biodegradable polyesters (Bionolle and poly(lactic acid) plasticized with 15 wt.-% of acetyltributyl citrate, p-PLLA). The composites are obtained either by high temperature compression molding fiber mats sandwiched between polymer films, or by batch mixing fibers with the molten polymer. Fibers in composites obtained by the latter method are much shorter (140-200 microm) than those of the mats (5,000 microm). Flax fibers are found to reinforce both p-PLLA and Bionolle (i.e. tensile modulus and strength increase) when composites based on fiber mats are investigated. Conversely, analogous composites obtained by batch mixing show poor mechanical properties. The observed behavior is attributed to the combined effect of fiber length and fiber-matrix adhesion. If flax fibers with a modified surface chemistry are used, the strength of short fiber composites is seen to improve significantly because the interface strengthens and load is more efficiently transferred. Appropriate surface modifications are performed by heterogeneous acylation reactions or by grafting poly(ethylene glycol) chains (PEG, molecular weight 350 and 750). The highest tensile strength of p-PLLA composites is reached when PEG-grafted flax fibers are used, whereas in the case of Bionolle the best performance is observed with acylated fibers.

Adipates↗
PubMed2003

Matrix-assisted laser desorption/ionisation mass spectrometry in the study of polycondensation of Ti(OBun)4 in the presence of Si(OEt)4.

The hydrolysis-polycondensation behaviour of alcoholic solutions containing Si(OEt)4 and Ti(OBun)4, in different molar ratios (Si/Ti = 10-0.2), was analysed by laser desorption/ionisation (LDI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry. The solutions were prepared using operating conditions usually employed in the sol-gel synthesis of SiO2-TiO2 materials. In accord with the well-known procedures for controlling the different chemical reactivities of the alkoxides, the pre-hydrolysis of the slower reacting silicon ethoxide and the chelation by acetylacetone of the faster reacting titanium butoxide were performed before mass spectrometric analysis. While LDI-MS did not provide evidence for the presence of mixed Si-Ti species in samples obtained from these reactions, MALDI-MS of samples diluted with chloroform and using 2,5-dihydroxybenzoic acid (DHB) as matrix led to detection of various oligomers with different contents of Si and Ti atoms. The results suggest that the formation of Si-Ti mixed oligomers seems to be the favoured process, especially for solutions in which one of the two components is diluted.

Algorithms↗