A model for the γp → π + π − p reaction developed earlier is extended to account for all isospin channels. The model includes N , ∆(1232), N * (1440) and N * (1520) as intermediate baryonic states and the ρ-meson as an intermediate 2π resonance. Although many terms contribute to the cross section, some channels exhibit particular sensitivity to certain mechanisms of resonance excitation or decay and the reactions provide novel information on such mechanisms. In particular the γN → N * (1520) → ∆π process affects all the channels and is a key ingredient in the interpretation of the data. Comparison is made with all available data and the agreement is good in some channels. The remaining discrepancies in some other channels are discussed.

No abstract

The influence of the cross-linking degree on the dynamics of the segmental motions close to the glass transition of poly(methyl methacrylate), PMMA, networks was investigated by three different mechanical spectroscopy techniques: thermally stimulated recovery (TSR), dynamic mechanical analysis (DMA), and creep. The application of the time-temperature superposition principle to isothermal DMA and creep results permitted to successfully construct master curves for PMMA networks with distinct cross-linking degrees. The former results were fitted to the KWW equation. The obtained variation of KWW for the distinct networks indicated that the relaxation curves tend to broaden as the cross-linking degree increases. TSR results clearly revealed a significant shift of the R-relaxation to longer times and a broader relaxation as the cross-linking degree increases, what was also observed by DMA and creep. A change from a Vogel to an Arrhenius behavior was detected by the three techniques with the decrease of temperature below T g. The temperature dependence of the apparent activation energies (Ea) was calculated from DMA, creep, and TSR experiments; above Tg a good agreement was seen between the Ea values for all the techniques. Furthermore, the effect of the cross-linking degree on the fragility of PMMA networks was evaluated. For these materials an increase of fragility with increasing cross-linking degree was observed.

No abstract

The main electrospinning parameters, i.e., polymer concentration in the injectable solution, solvents used and their proportion, flow rate, voltage and distance to collector were herein systematically modified to analyse their particular influence in fibres diameter of electrospun membranes of poly(lactic acid), polycaprolactone and their mixture. As a result of this analysis, the procedures to obtain membranes of these polymers and blend with under-and above-micron-sized fibres were established, in which the solvents ratio (chloroform/methanol and dichloromethane/dimethylformamide) and voltage were found to play the major role. Moreover, the plausible differential effect of these fibres diameters (0.8 and 1.8 µm) in the controlled release of a molecule of interest was explored, using bovine serum albumin (BSA), proving that the most effective configuration for BSA release among those studied was the PLA-PCL combination in membranes of above-micron fibres diameter.

Films based on poly(vinylidene fluoride) (PVDF) blended with ionic liquids (ILs) comprising different cations and anions were developed to investigate the IL influence on the resulting PVDF crystalline phase. Blends with 25 wt % IL content were produced by solvent casting followed by solvent evaporation at 210 °C in an air oven. Five different ILs containing the same cation 1-ethyl-3-methylimidazolium [Emim] and five ILs containing the same anion bis(trifluoromethylsulfonyl)imide [TFSI] were selected. The formation of the different phases and the resulting thermal and dynamic mechanical properties were studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis. The incorporation of [Emim]-based ILs successfully directs the PVDF crystallization from the nonpolar α-phase toward the electroactive and highly polar β-phase. On the contrary, blends containing [TFSI] as a

No abstract

ElsevierVikingsson, LKA.; Claessens, B.; Gómez Tejedor, JA.; Gallego Ferrer, G.; Gómez Ribelles, JL. (2015). Relationship between micro-porosity, water permeability and mechanical behavior in scaffolds for cartilage engineering. that the stress response of the scaffold/hydrogel construct is a synergic effect from the performance of each of the components. This is interesting since it predicts that the in vivo outcome of the scaffold is not only depending on the material architecture but also the growing tissue inside the scaffolds pores. On the other hand, the confined compression results show that the compliance of the scaffold is mainly controlled by the micro porosity of the scaffold and less by the hydrogel density in the scaffold pores. These conclusions bring together valuable information for customizing the optimal scaffold and to predict the in vivo mechanical behavior.