Structural Organization of syndiotactic polystyrene films crystallized in the β form

Syndiotactic polystyrene (sPS) films were obtained either by casting or by melt crystallization in the β form. Different thermal treatments of the melt led to mixed α and β forms. The structural organization was investigated by x-rays, transport properties, and Fourier transform infrared analysis. The β form is characterized by chains in zigzag planar conformation. For samples prevalently in β form, the fraction of impermeable phase, derived from sorption measurements, was found coincident with the fraction of crystalline phase derived from x-rays. In samples with mixed α and β forms, however, a fraction of mesophase is also present. The β form of sPS is stable to dichloromethane, whereas the α form is transformed into a crystalline form with the chains in helical conformation. Nevertheless, when the relative fraction of β form is lower than a critical value, it also dissolves in liquid dichloromethane, undergoing the conformational transition into the helical form.     

Effect of thermal treatments on the structure of syndiotactic polystyrene

Syndiotactic polystyrene films were prepared from the melt with different thermal treatments. Amorphous or crystalline films were obtained; x-ray analysis shows that in the crystalline samples two crystalline forms can be present and that the phase composition depends on the thermal conditions. The two forms show a different stability to liquid methylene chloride, one being stable while the other can be dissolved or transformed to a completely different crystalline structure. In all the analyzed samples the study of transport properties of CH₂ Cl₂ at low activity indicates that the amorphous component behaves as atactic polystyrene. This allows the determination of the crystallinity in the different samples.     

The Express heuristic for probabilistically constrained integer problems

Integer problems under joint probabilistic constraints with random coefficients in both sides of the constraints are extremely hard from a computational standpoint since two different sources of complexity are merged. The first one is related to the challenging presence of probabilistic constraints which assure the satisfaction of the stochastic constraints with a given probability, whereas the second one is due to the integer nature of the decision variables. In this paper we present a tailored heuristic approach based on alternating phases of exploration and feasibility repairing which we call Express (Explore and Repair Stochastic Solution) heuristic. The exploration is carried out by the iterative solution of simplified reduced integer problems in which probabilistic constraints are discarded and deterministic additional constraints are adjoined. Feasibility is restored through a penalty approach. Computational results, collected on a probabilistically constrained version of the classical 0–1 multiknapsack problem, show that the proposed heuristic is able to determine good quality solutions in a limited amount of time.     

Atomic scale design and control of cation distribution in hexagonal ferrite

Using a novel alternating target laser ablation deposition technique, Mn cations were placed in specific interstitial sites of BaFe12O19 thin films as opposed to being distributed throughout the unit cell as in conventional bulk materials. The distribution of Mn cations has been confirmed experimentally and predicted theoretically. As a result of site selection, the saturation magnetization increased 12%-22%, and the Néel temperature increased by 40-60 K compared to bulk materials. This technique implies a new methodology to design and process a new generation of ferrite, oxide, and alloy materials.     

Excess of proton mean kinetic energy in supercooled water

We find, by means of a deep inelastic neutron scattering experiment, a significant excess of proton mean kinetic energy E_(k) in supercooled water, compared with that measured in stable liquid and solid phases. The measured values of E_(k) at moderate degrees of supercooling do not fit the predicted linear increase with temperature observed for the water stable phases. This anomalous behavior is confirmed by the shape of the measured momentum distribution, thus supporting a likely occurrence of ground-state quantum delocalization of a proton between the O atoms of two neighboring molecules. These results strongly suggest a transition from a single-well to a double-well potential felt by the delocalized proton, with a reduced first neighbor O-O distance, in the supercooled state, as compared to ambient condition.     

Electrospun tin-carbon nanocomposite as anode material for all solid state lithium-ion batteries

Journal of Solid State Electrochemistry - All-solid-state batteries represent the next generation of electrochemical energy storage systems. A tin-carbon nanocomposite material is prepared by the...     

Immobilized TiO<Subscript>2</Subscript> nanoparticles produced by flame spray for photocatalytic water remediation

Anatase/rutile mixed-phase titanium dioxide (TiO₂) photocatalysts in the form of nanostructured powders with different primary particle size, specific surface area, and rutile content were produced from the gas-phase by flame spray pyrolysis (FSP) starting from an organic solution containing titanium (IV) isopropoxide as Ti precursor. Flame spray-produced TiO₂ powders were characterized by means of X-ray diffraction, Raman spectroscopy, and BET measurements. As-prepared powders were mainly composed of anatase crystallites with size ranging from 7 to 15 nm according to the synthesis conditions. TiO₂ powders were embedded in a multilayered fluoropolymeric matrix to immobilize the nanoparticles into freestanding photocatalytic membranes. The photocatalytic activity of the TiO₂-embedded membranes toward the abatement of hydrosoluble organic pollutants was evaluated employing the photodegradation of rhodamine B in aqueous solution as test reaction. The photoabatement rate of best performing membranes significantly overcomes that of membranes produced by the same method and incorporating commercial P25-TiO₂.     

Physical aging of syndiotactic polypropylene

Syndiotactic polypropylene (sPP) was quenched from the melt in an ice‐water bath, and changes in the structural organization, during the aging time, were followed by X‐rays, differential scanning calorimetry, and transport properties of dichloromethane at low activities. After 1 month, an increase of crystallinity from 19 to 26% was observed. In addition, the results of sorption and diffusion indicated a consistent increase of an intermediate phase not crystalline, yet impermeable to the vapors. The study of the mechanical properties showed that there is a remarkable increase of all the mechanical parameters with the aging time, and this effect was associated to the increase of the intermediate phase. The elastic modulus increased three times in the first hours of aging. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 173–180, 1999     

Studies of the γ ← α transition in syndiotactic polystyrene

In this work we compare calorimetric and X-ray diffraction experiments realized on annealed sPS in helical γ forms resulting by different treatements: From clathrate δ form and from interaction of amorphous sample with acetone. The experimental results show that the γ form obtained by acetone converts into the more ordered final α” form modification; while the γ form, obtained by thermal treatments of δ form, transforms into the poorly ordered final α' form.     

Drawing behaviour of syndiotactic polystyrene (sPS)

The drawing behaviour of amorphous and solvated structure of syndiotactic polystyrene has been analysed. By means of X-ray analysis and infra-red spectrometry we have studied the conformational transitions induced by the drawing processing.