Geometrical dependence of thermal conductivity in elliptical and rectangular nanowires

The aim of this work is to analyze the shape dependence of the effective thermal conductivity of nanowires, based on the model of phonon hydrodynamics. In particular, we consider elliptical and rectangular nanowires, and we compare their respective thermal conductivities with those of circular nanowires and of wide thin plates.     

Cross-linked soy protein as material for biodegradable films: Synthesis, characterization and biodegradation

The modification of soy protein isolate (SPI) with different amounts of a naturally occurring cross-linking agent (genipin, Gen) and glycerol used as plasticizer was carried out in this work. The films yielded were cast from heated and alkaline aqueous solution of SPI, glycerol and Gen and then dried in an oven. Total soluble matter, water vapor permeability and mechanical properties were improved by adding small amounts of Gen. These properties were not significantly affected (P ? 0.05) by additions exceeding 2.5% (w/w of SPI). The opacity and cross-linking degree were linearly increased with the addition of Gen, whereas the swelling ratios in water were decreased. All the films were submitted to degradation under indoor soil burial conditions and the weight loss of the films was measured at different times. This study revealed that the film biodegradation time can be controlled or modified from at least 14 to 33 days. The tests performed showed the potential of Gen to improve the SPI film properties, in which the possibility of employing such new films as biodegradable food packaging was raised.     

Removal of heavy metals from wastewater using magnetic nanocomposites: Analysis of the experimental conditions

This contribution provides insight on the elimination of heavy metals from water resources using magnetic separation. Nanocomposites based on magnetite and chitosan were prepared. An exhaustive characterization of the magnetic adsorbents was developed. Adsorption assays were performed in batch using Cu, Zn, Cd, and Cr as model heavy metals. The efficiency of magnetic adsorbents followed the order: Cu > Cd > Zn > Cr, with maximum values of 188, 159, 72, and 46 mg of Me/g of nanocomposite, respectively. Kinetics and mechanistic issues were studied. The magnetic materials were efficient for five to eight cycles using Cu(II),Cd(II), and Cr(VI).     

Gallium gradients in Cu(In,Ga)Se2 thin‐film solar cells

The gallium gradient in Cu(In,Ga)Se₂ (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe₂ and CuGaSe₂ were calculated using density functional theory. The migration barrier for the In_Cu antisite in CuGaSe₂ is significantly lower compared with the Ga_Cu antisite in CuInSe₂, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.     

Time‐resolved investigation of Cu(In,Ga)Se2 growth and Ga gradient formation during fast selenisation of metallic precursors

Ga segregation at the backside of Cu(In,Ga)Se₂ solar cell absorbers is a commonly observed phenomenon for a large variety of sequential fabrication processes. Here, we investigate the correlation between Se incorporation, phase formation and Ga segregation during fast selenisation of Cu–In–Ga precursor films in elemental selenium vapour. Se incorporation and phase formation are analysed by real‐time synchrotron‐based X‐ray diffraction and fluorescence analysis. Correlations between phase formation and depth distributions are gained by interrupting the process at several points and by subsequent ex situ cross‐sectional electron microscopy and Raman spectroscopy. The presented results reveal that the main share of Se incorporation takes place within a few seconds during formation of In–Se at the top part of the film, accompanied by outdiffusion of In out of a ternary Cu–In–Ga phase. Surprisingly, CuInSe₂ starts to form at the surface on top of the In–Se layer, leading to an intermediate double graded Cu depth distribution. The remaining Ga‐rich metal phase at the back is finally selenised by indiffusion of Se. On the basis of a proposed growth model, we discuss possible strategies and limitations for the avoidance of Ga segregation during fast selenisation of metallic precursors. Solar cells made from samples selenised with a total annealing time of 6.5 min reached conversion efficiencies of up to 14.2 % (total area, without anti‐reflective coating). The evolution of the Cu(In,Ga)Se₂ diffraction signals reveals that the minimum process time for high‐quality Cu(In,Ga)Se₂ absorbers is limited by cation ordering rather than Se incorporation. Copyright © 2014 John Wiley & Sons, Ltd.     

Ionic liquid recovery alternatives in ionic liquid‐based three‐phase partitioning (ILTPP)

Ionic liquid‐based three‐phase partitioning (ILTPP) is a promising technique to recover high‐added value proteins at the liquid–liquid interface. Its economic and environmental performance highly depends on the net ionic liquid consumption. Alternatives to maximize the fraction of ionic liquid that can be recycled are studied. It is demonstrated that the addition of extra salt, previously proposed in literature, has a very limited effect on ionic liquid recovery for relatively high protein concentrations in the feed stream, and that it may even lead to an increase of the ionic liquid losses under certain conditions. However, small additions of salt are shown to be effective and profitable from an economic point of view. Vacuum evaporation is shown to allow for the complete ionic liquid and salt recovery, reinforcing the sustainability and viability of ILTPP processes. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3577–3586, 2014     

Biodegradable nanocomposites based on starch/polycaprolactone/compatibilizer ternary blends reinforced with natural and organo‐modified montmorillonite

In this article, biodegradable polymer/clay nanocomposites were prepared. The matrices used were based on blends of Polycaprolactone (PCL) and Anhydride‐Functional Polycaprolactone (PCL‐gMA) with Thermoplastic Starch (TPS). Nanocomposites films based on PCL/TPS and PCL/PCL‐g‐MA/TPS blends reinforced with 1 and 3 wt % of natural montmorillonite and two organo‐modified ones were prepared by melt intercalation followed by compression molding. The study was designed focusing on packaging applications. Grafting maleic anhydride onto PCL was efficient to improve PCL/TPS compatibility but did not modify matrix/nanoclay interaction. Matrix compatibilization and nanoclays increased the Youn?s modulus and slightly decreased the maximum stress of the TPS/PCL matrix. Nanoclay functionalization improved nanoclay dispersion in the blends but it was not reflected in mechanical properties improvements. The water adsorption of the compatibilized matrix was reduced after clay incorporation. A slight decrease in the biodegradation rate was observed with the addition of nanoclay. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44163.