D. Cannoletta

Monitoring Wood Degradation during Weathering by Cellulose Crystallinity

The degree of crystallinity of cellulose was used for assessing the degradation level of coated and uncoated samples of pine wood after weathering. X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy measured the changes in the surface crystallinity of cellulose resulting from weathering, both natural and artificial. Both techniques revealed an increase in the crystallinity index (CI) of cellulose when wood was subjected to weathering. An increase in the size of crystallites was also observed by XRD measurements. These results were related to the reduction of the amorphous fractions of wood, and, consequently, to the enrichment of the relative crystalline content. Thanks to FT-IR analysis, the degradation of hemicellulose was observed for uncoated samples after exposure to artificial weathering. The effect of weathering was less evident on coated samples because of the protective action of the coating. A good correlation between the crystallinity indexes obtained from FT-IR and XRD was found. The experimental results proved that the proposed method may be a very useful tool for a rapid and accurate estimation of the degradation level of wood exposed to weathering. This methodology can find application in the field of conservation and restoration of wooden objects or in the industry of wood coatings.

Experimental and Computational Studies on Non-Covalent Imprinted Microspheres as Recognition System for Nicotinamide Molecules

Molecularly imprinted microspheres obtained by precipitation polymerization using nicotinamide (nia) as template have been prepared and characterised by SEM. How various experimental parameters can affect microsphere morphology, reaction yield and re-binding capacity have been evaluated. Pre-polymerization interactions between template and functional monomer in chloroform and MeCN have been studied by 1H-NMR. The results suggest that the interaction between nia and methacrylic acid (MAA) is mainly based on hydrogen-bonding between amide protons and MAA. Computational density functional theory (DFT) studies on MAA-nia complexes have been also performed to better understand hydrogen-bonding interactions. The imprinted activity of the microspheres, synthesized in chloroform or acetonitrile (MeCN), has been evaluated by spectrophotometric analysis of nia solutions when chloroform or MeCN are used as incubation solvents. The results suggest that MeCN interferes with hydrogen bonding between template and MAA during either the polymerization step or re-binding process as also observed from theoretical results. Finally, the selectivity towards selected nia analogues has been also confirmed.

Effects of the spontaneous polarization and piezoelectric fields on the luminescence spectra of GaN/Al0.15Ga0.85N quantum wells

Abstract We have investigated the well width dependence of the ground level emission of GaN/AlGaN quantum wells. We find that the fundamental electron–heavy-hole transition red-shifts well below the GaN bulk gap for well widths larger than 3 nm and that the luminescence intensity reduces with increasing well thickness. These effects originate from the quantum confined Stark effect caused by the strong built-in electric field induced by the spontaneous polarization charge at the GaN/AlGaN interfaces and, to a minor extent, by the piezoelectric charge, with typical strength in the MV/cm range. The experimental data are quantitatively explained by means of a self-consistent tight-binding approach which includes screening (either dielectric or by free carriers) and spontaneous polarization field.

Optical and Transport Properties of GaN/Al0.15Ga0.85N Quantum Wells

We have investigated the optical and phototransport properties of GaN/AlGaN quantum wells by photoluminescence and photovoltage spectroscopy. We show that the internal piezoelectric and spontaneous polarization fields cause a strong red-shift of the ground level energy of the quantum wells. Furthermore, identical quantum wells grown on different buffer layers (GaN or AlGaN) exhibit different emission energies, but similar well-width dependence of the n = 1 state, due to the different distribution of strain between well and barrier. The built-in field also causes a strong reduction of the exciton oscillator strength, which is not observable in photovoltage spectra. A long-living (thousands of seconds) charge storage effect is observed in the phototransport spectra due to the presence of point defects, presumably associated to Ga vacancies.