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Recent papers of ENMat members

Centre for Materials Science and Engineering (CISIM), University of Pisa, Italy

1) Effects of waviness on fibre-length distribution and interfacial shear strength of natural fibres reinforced composites

Authors: V. Gigante, L. Aliotta, V. Thanh Phuong, M. B. Coltelli, P. Cinelli, A. Lazzeri,
Composites Science and Technology, 152, 10, 2017, 129, doi.org/10.1016/j.compscitech.2017.09.008
Abstract:
Natural fibres are not as rigid as glass or carbon fibres. During composites extrusion and injection moulding, they tend to bend and twist in the polymeric matrix, thus resulting in fibre waviness and decreased mechanical properties of natural fibre composites. The most widely used models for the estimation of interfacial shear strength (IFSS) and elastic modulus, which consider the fibre aspect ratio and mechanical properties of the fibre and matrix, do not consider these important features.
In order to account for fibre waviness, an effective fibre length is proposed in this paper. The undulation of the fibres is approximated with a sinusoidal arc along with a calculated new length. The proposed correction factor depends on the wavelength and amplitude of the wave approximating the fibre. To verify this method, blends of polylactic acid (PLA) and polycarbonate (PC) (prepared with and without an interchange reactions catalyst) with addition to various percentages of cellulosic fibres (5 wt%, 10 wt% and 15 wt%) have been prepared and characterised. It has been demonstrated that by considering the corrected length values, it is possible to predict the mechanical properties and the effective reinforcement attained in the composites by using the most widely used models. In particular, the prediction of the elastic modulus is slightly affected by this correction, whereas the calculation of IFSS is strongly dependent on it. 

2) Pore Size Distribution and Blend Composition Affect In Vitro Prevascularized Bone Matrix Formation on Poly(Vinyl Alcohol)/Gelatin Sponges

Authors: J. Gustavo De la Ossa, L. Trombi, D. D’Alessandro, M. B. Coltelli, L. P. Serino, R. Pini, A. Lazzeri, M. Petrini, S. Danti
Macromol. Mater. Eng. 2017, 302, 1700300, https://doi.org/10.1002/mame.201700300
Abstract:
This study aims at identifying compositional and architectural (pore size and distribution) parameters of biocompatible scaffolds, which can be best suitable for both osteoblasts and endothelial cells to produce optimized 3D cocultured constructs. Spongy scaffolds are prepared using poly(vinyl alcohol) (PVA) and gelatin (G) at different weight compositions (PVA/G range: 100/0–50/50, w/w) via emulsion and freeze-drying. The higher the gelatin content, the larger is the volume occupied by higher size pores. Human umbilical vein endothelial cells and human mesenchymal stromal cells are independently differentiated on the scaffolds to select the best candidate for the coculture. The results of metabolic activity and histology on single plat-forms show both cell- and material-type dependent outcomes. PVA/G 80/20 scaffolds are finally selected and allow the formation of mineralized matrix containing organized endothelial-like structures. This study highlights the need for systematic investigations on multifactorial parameters of scaffolds to improve vascularized bone substitutes.

3) Preparation of Water Suspensions of Nanocalcite for Cultural Heritage Applications

Authors: M.B. Coltelli, D. Paolucci, V. Castelvetro, S. Bianchi, E. Mascha, L. Panariello, C. Pesce, J. Weber, A. Lazzeri
Nanomaterials 2018, 8(4), 254; https://doi.org/10.3390/nano8040254
Abstract:
The consolidation of degraded carbonate stone used in ancient monuments is an important topic for European cultural heritage conservation. The products most frequently used as consolidants are based on tetraalkoxy- or alkylalkoxy-silanes (in particular tetraethyl-orthosilicate, TEOS), resulting in the formation of relatively stable amorphous silica or alkylated (hydrophobic) silica inside the stone pores. However, silica is not chemically compatible with carbonate stones; in this respect, nanocalcite may be a suitable alternative. The present work concerns the preparation of water suspensions of calcite nanoparticles (CCNPs) by controlled carbonation of slaked lime using a pilot-scale reactor. A simplified design of experiment was adopted for product optimisation. Calcite nanoparticles of narrow size distribution averaging about 30 nm were successfully obtained, the concentration of the interfacial agent and the size of CaO being the most critical parameters. Primary nanoparticle aggregation causing flocculation could be substantially prevented by the addition of polymeric dispersants. Copolymer-based dispersants were produced in situ by controlled heterophase polymerisation mediated by an amphiphilic macro-RAFT (reversible addition-fragmentation transfer) agent. The stabilized CCNP aqueous dispersions were then applied on carbonate and silicate substrates; Scanning Electron Microscopy (SEM)analysis of cross-sections allowed the evaluation of pore penetration, interfacial binding, and bridging (gap-filling) properties of these novel consolidants.

 

Institute of Research on Electron Microscopy and Materials (IMEYMAT), University of Cádiz, Spain

1) Direct Measurement of Polarization-Induced Fields in GaN/AlN by Nano-Beam Electron Diffraction

Authors: Daniel Carvalho, Knut Müller-Caspary, Marco Schowalter, Tim Grieb, Thorsten Mehrtens, Andreas Rosenauer, Teresa Ben, Rafael García, Andrés Redondo-Cubero, Katharina Lorenz, Bruno Daudin & Francisco M. Morales.
Sci. Rep. 6, 28459; https://doi: 10.1038/srep28459 (2016)
Abstract:
The built-in piezoelectric fields in group III-nitrides can act as road blocks on the way to maximizing the efficiency of opto-electronic devices. In order to overcome this limitation, a proper characterization of these fields is necessary. In this work nano-beam electron diffraction in scanning transmission electron microscopy mode has been used to simultaneously measure the strain state and the induced piezoelectric fields in a GaN/AlN multiple quantum well system.

2) Hybrid Perovskite, CH3NH3PbI3, for Solar Applications: An Experimental and Theoretical Analysis of Substitution in A and B Sites

Authors: Antonio Sánchez-Coronilla, Javier Navas, Juan Jesús Gallardo, Elisa I. Martín, Desireé De los Santos, Norge C. Hernández, Rodrigo Alcántara, José Hidalgo Toledo, and Concha Fernández-Lorenzo.
Journal of Nanomaterials, Volume 2017, Article ID 9768918, 10 pages, https://doi.org/10.1155/2017/9768918
Abstract:
The effect of the incorporation of NH4+ into the CH3NH3+ sites of the tetragonal perovskite CH3NH3PbI3 is analysed. Also, how it affects the introduction of Cd2+ cations into Pb2+ sites for a perovskite with 25 at.% of NH4+ is addressed. The incorporation of NH4+ into perovskite leads to a dramatic loss of crystallinity and to the presence of other phases. Moreover, the NH4PbI3 was not found. The less formation of perovskite when NH4+ is incorporated is due to geometrical factors and not changes in the chemical state bonding of the ions. Also, the samples where perovskite is formed show similar band gap values. A slight increase is observed for samples with  and 0.75. For the sample with , a drastic increase of the band gap is obtained. Periodic-DFT calculations agree with the experimental structural tendency when NH4+ is incorporated and the density of states analysis confirmed the experimental band gap. The perovskite with 25 at.% of NH4+ was selected for studying the effect of the concentration of Cd on the structural and electronic properties. The theoretical band gap values decreased with the Cd concentration where the narrowing of Cd s-states in the conduction band plays an important role.

3) Sub-nanometer surface chemistry and orbital hybridization in lanthanum-doped ceria nano-catalysts revealed by 3D electron microscopy

Authors: Sean M. Collins, Susana Fernandez-Garcia, José J. Calvino & Paul A. Midgley.
Scientific Reports volume 7, Article number: 5406 (2017), https://doi.org/10.1038/s41598-017-05671-9
Abstract:
Surface chemical composition, electronic structure, and bonding characteristics determine catalytic activity but are not resolved for individual catalyst particles by conventional spectroscopy. In particular, the nano-scale three-dimensional distribution of aliovalent lanthanide dopants in ceria catalysts and their effect on the surface electronic structure remains unclear. Here, we reveal the surface segregation of dopant cations and oxygen vacancies and observe bonding changes in lanthanum-doped ceria catalyst particle aggregates with sub-nanometer precision using a new model-based spectroscopic tomography approach. These findings refine our understanding of the spatially varying electronic structure and bonding in ceria-based nanoparticle aggregates with aliovalent cation concentrations and identify new strategies for advancing high efficiency doped ceria nano-catalysts.

Reacties op de inhoud: Els Van der Burght. Laatste wijziging 2018-08-20
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