Materials

873 KiB

Open AccessArticle

The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells

by Zandra George, Renee Kroon, Robert Gehlhaar, Gabin Gbabode, Angelica Lundin, Stefan Hellström, Christian Müller, Yves Geerts, Paul Heremans and Mats R. Andersson

Materials 2013, 6(7), 3022-3034; https://doi.org/10.3390/ma6073022 - 22 Jul 2013

Cited by 8 | Viewed by 6476

Abstract

A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties [...] Read more.

A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure. Full article

(This article belongs to the Section Energy Materials)

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2454 KiB

Open AccessArticle

Charged Polymers Transport under Applied Electric Fields in Periodic Channels

by Sorin Nedelcu and Jens-Uwe Sommer

Materials 2013, 6(7), 3007-3021; https://doi.org/10.3390/ma6073007 - 19 Jul 2013

Cited by 1 | Viewed by 4992

Abstract

By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added [...] Read more.

By molecular dynamics simulations, we investigated the transport of charged polymers in applied electric fields in confining environments, which were straight cylinders of uniform or non-uniform diameter. In the simulations, the solvent was modeled explicitly and, also, the counterions and coions of added salt. The electrophoretic velocities of charged chains in relation to electrolyte friction, hydrodynamic effects due to the solvent, and surface friction were calculated. We found that the velocities were higher if counterions were moved away from the polymeric domain, which led to a decrease in hydrodynamic friction. The topology of the surface played a key role in retarding the motion of the polyelectrolyte and, even more so, in the presence of transverse electric fields. The present study showed that a possible way of improving separation resolution is by controlling the motion of counterions or electrolyte friction effects. Full article

(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)

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1347 KiB

Open AccessArticle

Preparation and Characterization of New Geopolymer-Epoxy Resin Hybrid Mortars

by Francesco Colangelo, Giuseppina Roviello, Laura Ricciotti, Claudio Ferone and Raffaele Cioffi

Materials 2013, 6(7), 2989-3006; https://doi.org/10.3390/ma6072989 - 17 Jul 2013

Cited by 91 | Viewed by 8202

Abstract

The preparation and characterization of metakaolin-based geopolymer mortars containing an organic epoxy resin are presented here for the first time. The specimens have been prepared by means of an innovative in situ co-reticulation process, in mild conditions, of commercial epoxy based organic resins [...] Read more.

The preparation and characterization of metakaolin-based geopolymer mortars containing an organic epoxy resin are presented here for the first time. The specimens have been prepared by means of an innovative in situ co-reticulation process, in mild conditions, of commercial epoxy based organic resins and geopolymeric slurry. In this way, geopolymer based hybrid mortars characterized by a different content of normalized sand (up to 66% in weight) and by a homogeneous dispersion of the organic resin have been obtained. Once hardened, these new materials show improved compressive strength and toughness in respect to both the neat geopolymer and the hybrid pastes since the organic polymer provides a more cohesive microstructure, with a reduced amount of microcracks. The microstructural characterization allows to point out the presence of an Interfacial Transition Zone similar to that observed in cement based mortars and concretes. A correlation between microstructural features and mechanical properties has been studied too. Full article

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Crack Measurement Microscope images for (A) G66 (external surface); and (B) E66 (polished surface). Full article ">Figure 2
SEM micrographs of the neat geopolymer mortar (A) G66; (B) E66; and (C,D) L66. Full article ">Figure 3
TGA (continuous line) and DSC (dashed line) curves of L66 mortar cured at room temperature for 7 days in >95% relative humidity conditions. Full article ">Figure 4
Cumulative pore volume vs. pore radius as obtained by mercury intrusion poroszimetry analyses for G66, L66, E66 and G, L, E specimens. Full article ">Figure 5
SEM micrographs of (A,B) the G66; and (C,D) E66 specimens. Full article ">Figure 6
Compressive strength of G, E, L specimens as function of sand content. Full article ">Figure 7
Stress-strain curves of G, G66, E, E66, L, L66 specimens. Full article ">

805 KiB

Open AccessArticle

In Vivo Osteogenic Differentiation of Human Embryoid Bodies in an Injectable in Situ-Forming Hydrogel

by Da Yeon Kim, Yoon Young Kim, Hai Bang Lee, Shin Yong Moon, Seung-Yup Ku and Moon Suk Kim

Materials 2013, 6(7), 2978-2988; https://doi.org/10.3390/ma6072978 - 17 Jul 2013

Cited by 6 | Viewed by 7001

Abstract

In this study, we examined the in vivo osteogenic differentiation of human embryoid bodies (hEBs) by using an injectable in situ-forming hydrogel. A solution containing MPEG-b-(polycaprolactone-ran-polylactide) (MCL) and hEBs was easily prepared at room temperature. The MCL solution [...] Read more.

In this study, we examined the in vivo osteogenic differentiation of human embryoid bodies (hEBs) by using an injectable in situ-forming hydrogel. A solution containing MPEG-b-(polycaprolactone-ran-polylactide) (MCL) and hEBs was easily prepared at room temperature. The MCL solution with hEBs and osteogenic factors was injected into nude mice and developed into in situ-forming hydrogels at the injection sites; these hydrogels maintained their shape even after 12 weeks in vivo, thereby indicating that the in situ-forming MCL hydrogel was a suitable scaffold for hEBs. The in vivo osteogenic differentiation was observed only in the in situ gel-forming MCL hydrogel in the presence of hEBs and osteogenic factors. In conclusion, this preliminary study suggests that hEBs and osteogenic factors embedded in an in situ-forming MCL hydrogel may provide numerous benefits as a noninvasive alternative for allogeneic tissue engineering applications. Full article

(This article belongs to the Section Biomaterials)

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Schematic representation of in vivo osteogenic differentiation of human embryoid bodies (hEBs) in an injectable in situ-forming MPEG-b-(polycaprolactone-ran-polylactide) MCL hydrogel with osteogenic factors. Full article ">Figure 2
Relationships between the viscosity and temperature of the MCL solution at 20 wt % concentration. Full article ">Figure 3
The morphology of hEBs at (a) 1 day; (b) 7 days; and (c) 15 days. The scale bars indicate 200 µm for the ×100 magnification. Full article ">Figure 4
Image obtained (a) after the initial injection of the hEBs/F embedded in the in situ-forming MCL hydrogel; and (b) 12 weeks after hydrogel formation. Full article ">Figure 5
(a) Images of the removed MCL without (GC) or with (GCF) osteogenic factors, after 4, 8, and 12 weeks. The numbers indicate the implantation time; (b) enlarged images of the removed MCL hydrogels (GCF) and (c) volume change in the in vivo excised MCL hydrogels (GCF) after 4, 8, and 12 weeks (*p < 0.001, **p < 0.05). Full article ">Figure 6
Hematoxylin and eosin (H&E) stained sections of the MCL without (GC) or with (GCF) the osteogenic factors after 4, 8, and 12 weeks. The numbers indicate the implantation time and the scale bars indicate 100 µm for the ×400 magnification and 50 µm for the ×200 magnification. Full article ">Figure 7
von Kossa-stained sections of the MCL without (GC) and with (GCF) the osteogenic factors after 4, 8, and 12 weeks and the MCL only without hEBs and osteogenic factors as control. The numbers indicate the implantation time and the scale bars indicate 100 µm for the ×400 magnification and 50 µm for the ×200 magnification. Full article ">

923 KiB

Open AccessArticle

Order-Induced Selectivity Increase of Cu₆₀Pd₄₀ in the Semi-Hydrogenation of Acetylene

by Matthias Friedrich, Sebastián Alarcón Villaseca, László Szentmiklósi, Detre Teschner and Marc Armbrüster

Materials 2013, 6(7), 2958-2977; https://doi.org/10.3390/ma6072958 - 16 Jul 2013

Cited by 49 | Viewed by 7028

Abstract

The two structural modifications of Cu₆₀Pd₄₀ were synthesized as bulk powders and tested as unsupported model catalysts in the semi-hydrogenation of acetylene. The partly ordered low-temperature modification (CsCl type of structure) showed an outstanding ethylene selectivity of >90% over 20 [...] Read more.

The two structural modifications of Cu₆₀Pd₄₀ were synthesized as bulk powders and tested as unsupported model catalysts in the semi-hydrogenation of acetylene. The partly ordered low-temperature modification (CsCl type of structure) showed an outstanding ethylene selectivity of >90% over 20 h on stream while the disordered high-temperature modification (Cu type of structure) was 20% less selective, indicating an influence of the degree of order in the crystal structure on the catalytic properties. The results are supported by XRD and in situ XPS experiments. The latter suggest the existence of partly isolated Pd sites on the surface. In situ PGAA investigations proved the absence of metal hydride formation during reaction. Quantum chemical calculations of the electronic structure of both modifications using the CPA-FPLO framework revealed significant differences in their respective density of states, thus still leaving open the question of whether the degree of structural order or/and the electronic hybridization is the decisive factor for the observed difference in selectivity. Full article

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1873 KiB

Open AccessReview

Self-Ordered Titanium Dioxide Nanotube Arrays: Anodic Synthesis and Their Photo/Electro-Catalytic Applications

by York R. Smith, Rupashree S. Ray, Krista Carlson, Biplab Sarma and Mano Misra

Materials 2013, 6(7), 2892-2957; https://doi.org/10.3390/ma6072892 - 16 Jul 2013

Cited by 98 | Viewed by 12352

Abstract

Metal oxide nanotubes have become a widely investigated material, more specifically, self-organized titania nanotube arrays synthesized by electrochemical anodization. As a highly investigated material with a wide gamut of applications, the majority of published literature focuses on the solar-based applications of this material. [...] Read more.

Metal oxide nanotubes have become a widely investigated material, more specifically, self-organized titania nanotube arrays synthesized by electrochemical anodization. As a highly investigated material with a wide gamut of applications, the majority of published literature focuses on the solar-based applications of this material. The scope of this review summarizes some of the recent advances made using metal oxide nanotube arrays formed via anodization in solar-based applications. A general methodology for theoretical modeling of titania surfaces in solar applications is also presented. Full article

(This article belongs to the Special Issue Advances in Catalytic Materials)

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997 KiB

Open AccessArticle

Polymeric Materials Reinforced with Multiwall Carbon Nanotubes: A Constitutive Material Model

by René K. Córdova, Alex Elías-Zúiga, Luis E. Elizalde, Héctor R. Siller, José Antonio Sánchez, Ciro A. Rodríguez and Wendy Ortega

Materials 2013, 6(7), 2873-2891; https://doi.org/10.3390/ma6072873 - 16 Jul 2013

Cited by 6 | Viewed by 6573

Abstract

In this paper we have modified an existing material model introduced by Cantournet and co-workers to take into account softening and residual strain effects observed in polymeric materials reinforced with carbon nanotubes when subjected to loading and unloading cycles. In order to assess [...] Read more.

In this paper we have modified an existing material model introduced by Cantournet and co-workers to take into account softening and residual strain effects observed in polymeric materials reinforced with carbon nanotubes when subjected to loading and unloading cycles. In order to assess the accuracy of the modified material model, we have compared theoretical predictions with uniaxial extension experimental data obtained from reinforced polymeric material samples. It is shown that the proposed model follows experimental data well as its maximum errors attained are lower than 2.67%, 3.66%, 7.11% and 6.20% for brominated isobutylene and paramethylstyrene copolymer reinforced with multiwall carbon nanotubes (BIMSM-MWCNT), reinforced natural rubber (NR-MWCNT), polybutadiene-carbon black (PB-CB), and PC/ABS reinforced with single-wall carbon nanotubes (SWCNT), respectively. Full article

(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)

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1194 KiB

Open AccessArticle

Role of Fluxes in Optimizing the Optical Properties of Sr_0.95Si₂O₂N₂:0.05Eu²⁺ Green-Emitting Phosphor

by Lihong Liu, Rong-Jun Xie, Chenning Zhang and Naoto Hirosaki

Materials 2013, 6(7), 2862-2872; https://doi.org/10.3390/ma6072862 - 15 Jul 2013

Cited by 26 | Viewed by 5925

Abstract

Chlorides of NH₄Cl and SrCl₂ and fluorides of AlF₃ and SrF₂ were added to raw materials acting as the flux for preparing the SrSi₂O₂N₂:Eu²⁺ phosphor. The effects of the fluxes on [...] Read more.

Chlorides of NH₄Cl and SrCl₂ and fluorides of AlF₃ and SrF₂ were added to raw materials acting as the flux for preparing the SrSi₂O₂N₂:Eu²⁺ phosphor. The effects of the fluxes on the phase formation, particle morphology, particle size, and photoluminescence properties were investigated. The results revealed that particle size, particle morphology and photoluminescence intensity were largely dominated by the type of the flux material and its adding amount. The chloride-based flux was found to favor the formation of the SrSi₂O₂N₂:Eu²⁺ phase. Among the chloride-based fluxes, the sample added with the SrCl₂ flux presented the narrow particle distribution and cleaner surface, with enhanced emission intensity and an increased external quantum efficiency by 68% and 22%, respectively, compared with those of the sample without any flux adding. Full article

(This article belongs to the Special Issue Luminescent Materials)

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XRD patterns of SrSi2O2N2:Eu2+ sintered at various temperatures with 1% flux (a) NH4Cl; (b) AlF3; (c) SrCl2; (d) SrF2; (e) none. Full article ">Figure 2
Emission intensities of the SrSi2O2N2:Eu2+ sintered at various temperatures with 1% flux. Full article ">Figure 3
XRD patterns of SrSi2O2N2:Eu2+ adding various amounts flux (a) NH4Cl (1550 °C); (b) SrCl2 (1500 °C); (c) SrF2 (1500 °C); (d) AlF3 (1400 °C). Full article ">Figure 4
Effects of flux adding amounts on the emission intensity of SrSi2O2N2:Eu2+ phosphor with various kinds of flux. Full article ">Figure 5
Effects of various kinds of flux on the emission intensity of SrSi2O2N2:Eu2+ phosphors. Full article ">Figure 6
Particle size distribution of SrSi2O2N2:Eu2+ with various kinds of flux (a) none (1550 °C); (b) NH4Cl (1550 °C, 2%); (c) SrCl2 (1500 °C, 5%); (d) SrF2 (1500 °C, 3%); (e) AlF3 (1400 °C, 1%). Full article ">Figure 7
SEM images of SrSi2O2N2:Eu2+ with various kinds of flux (a) none (1550 °C); (b) NH4Cl (1550 °C, 2%); (c) SrCl2 (1500 °C, 5%); (d) SrF2 (1500 °C, 3%); (e) AlF3 (1400 °C, 1%). Full article ">Figure 8
Effects of various kinds of flux on the external quantum efficiencies of SrSi2O2N2:Eu2+ phosphors. Full article ">

467 KiB

Open AccessArticle

Synthesis and Enhanced Phosphate Recovery Property of Porous Calcium Silicate Hydrate Using Polyethyleneglycol as Pore-Generation Agent

by Wei Guan, Fangying Ji, Qingkong Chen, Peng Yan and Ling Pei

Materials 2013, 6(7), 2846-2861; https://doi.org/10.3390/ma6072846 - 15 Jul 2013

Cited by 40 | Viewed by 7493

Abstract

The primary objective of this paper was to synthesize a porous calcium silicate hydrate (CSH) with enhanced phosphate recovery property using polyethyleneglycol (PEG) as pore-generation agent. The formation mechanism of porous CSH was proposed. PEG molecules were inserted into the void region of [...] Read more.

The primary objective of this paper was to synthesize a porous calcium silicate hydrate (CSH) with enhanced phosphate recovery property using polyethyleneglycol (PEG) as pore-generation agent. The formation mechanism of porous CSH was proposed. PEG molecules were inserted into the void region of oxygen–silicon tetrahedron chains and the layers of CSH. A steric hindrance layer was generated to prevent the aggregation of solid particles. A porous structure was formed due to the residual space caused by the removal of PEG through incineration. This porous CSH exhibited highly enhanced solubility of Ca²⁺and OH⁻ due to the decreased particle size, declined crystalline, and increased specific surface area (S_BET) and pore volume. Supersaturation was increased in the wastewater with the enhanced solubility, which was beneficial to the formation of hydroxyapatite (HAP) crystallization. Thus, phosphate can be recovered from wastewater by producing HAP using porous CSH as crystal seed. In addition, the regenerated phosphate-containing products (HAP) can be reused to achieve sustainable utilization of phosphate. The present research could provide an effective approach for the synthesis of porous CSH and the enhancement of phosphate recovery properties for environmental applications. Full article

(This article belongs to the Section Porous Materials)

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N2 adsorption–desorption isotherms (a) and pore-size distribution curves (b) of the synthesized CSH samples. Full article ">Figure 2
X-ray diffraction (XRD) patterns of CSH samples before and after modified by PEG. Full article ">Figure 3
Fourier transform infrared spectroscopy (FI-IR) spectra of CSH (PEG-0) and CSH (PEG-0.6%). Full article ">Figure 4
Field emission scanning electron microscopy (FESEM) photographs and schematic diagrams of CSH (PEG-0) and CSH (PEG-0.6%) during the modification process. (a) CSH (PEG-0), and the pore structure of this sample was dense before modification; (b) PEG molecules insert into the void region of oxygen–silicon tetrahedron chain or the layers of CSH (c,d); (e) CSH (PEG-0.6%), and porous structure was formed due to the residual space caused by the removal of PEG through incineration (f). Full article ">Figure 5
Particle size distributions of as-prepared CSH samples. Full article ">Figure 6
Variations of concentration of Ca2+ released from CSH samples (a) and pH values in deionized water (b). Full article ">Figure 7
Changes of residual phosphate concentration by recycling phosphate removal of CSH samples. Full article ">Figure 8
XRD patterns of regenerated product obtained by CSH (PEG-0.6%) and CSH (PEG-0). Full article ">

358 KiB

Open AccessArticle

Self-Healing of Microcracks in Engineered Cementitious Composites (ECC) Under a Natural Environment

by Emily N. Herbert and Victor C. Li

Materials 2013, 6(7), 2831-2845; https://doi.org/10.3390/ma6072831 - 15 Jul 2013

Cited by 138 | Viewed by 8754

Abstract

This paper builds on previous self-healing engineered cementitious composites (ECC) research by allowing ECC to heal outdoors, in the natural environment, under random and sometimes extreme environmental conditions. Development of an ECC material that can heal itself in the natural environment could lower [...] Read more.

This paper builds on previous self-healing engineered cementitious composites (ECC) research by allowing ECC to heal outdoors, in the natural environment, under random and sometimes extreme environmental conditions. Development of an ECC material that can heal itself in the natural environment could lower infrastructure maintenance costs and allow for more sustainable development in the future by increasing service life and decreasing the amount of resources and energy needed for repairs. Determining to what extent current ECC materials self-heal in the natural environment is the first step in the development of an ECC that can completely heal itself when exposed to everyday environmental conditions. This study monitored outdoor ECC specimens for one year using resonant frequency (RF) and mechanical reloading to determine the rate and extent of self-healing in the natural environment. It was found that the level of RF, stiffness, and first cracking strength recovery increased as the duration of natural environment exposure increased. For specimens that underwent multiple damage cycles, it was found that the level of recovery was highly dependent on the average temperature and amount of precipitation between each damage event. However, RF, stiffness, and first cracking strength recovery data for specimens that underwent multiple loading cycles suggest that self-healing functionality can be maintained under multiple damage events. Full article

(This article belongs to the Special Issue Self-healing Concrete)

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517 KiB

Open AccessArticle

Optical Constants of Crystallized TiO₂ Coatings Prepared by Sol-Gel Process

by Xiaodong Wang, Guangming Wu, Bin Zhou and Jun Shen

Materials 2013, 6(7), 2819-2830; https://doi.org/10.3390/ma6072819 - 12 Jul 2013

Cited by 88 | Viewed by 10017

Abstract

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and [...] Read more.

Titanium oxide coatings have been deposited by the sol-gel dip-coating method. Crystallization of titanium oxide coatings was then achieved through thermal annealing at temperatures above 400 °C. The structural properties and surface morphology of the crystallized coatings were studied by micro-Raman spectroscopy and atomic force microscopy, respectively. Characterization technique, based on least-square fitting to the measured reflectance and transmittance spectra, is used to determine the refractive indices of the crystallized TiO₂ coatings. The stability of the synthesized sol was also investigated by dynamic light scattering particle size analyzer. The influence of the thermal annealing on the optical properties was then discussed. The increase in refractive index with high temperature thermal annealing process was observed, obtaining refractive index values from 1.98 to 2.57 at He-Ne laser wavelength of 633 nm. The Raman spectroscopy and atomic force microscopy studies indicate that the index variation is due to the changes in crystalline phase, density, and morphology during thermal annealing. Full article

(This article belongs to the Special Issue Advances in Surface Coatings 2013)

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Flow chart of TiO2 sol synthesis process. Full article ">Figure 2
Raman spectra of TiO2 coatings annealed at different temperatures. Full article ">Figure 3
Transmittance spectra of TiO2 coatings annealed at different temperatures. Full article ">Figure 4
Refractive index dispersion of TiO2 coatings annealed at different temperatures. Full article ">Figure 5
Plot of (αhν)1/m vs. (hν) for the estimation of the band gap energy value (400 °C annealed TiO2 coating): (a) indirect gap and (b) direct gap. Full article ">Figure 6
2D AFM images of TiO2 coatings annealed at (a) 300 °C; (b) 500 °C; (c) 700 °C; (d) 900 °C. Full article ">Figure 7
Particle size distribution of TiO2 sol. Full article ">

647 KiB

Open AccessReview

Persistent Luminescence in Non-Eu²⁺-Doped Compounds: A Review

by Koen Van den Eeckhout, Dirk Poelman and Philippe F. Smet

Materials 2013, 6(7), 2789-2818; https://doi.org/10.3390/ma6072789 - 12 Jul 2013

Cited by 295 | Viewed by 16032

Abstract

During the past few decades, the research on persistent luminescent materials has focused mainly on Eu²⁺-doped compounds. However, the yearly number of publications on non-Eu²⁺-based materials has also increased steadily. By now, the number of known persistent phosphors has [...] Read more.

During the past few decades, the research on persistent luminescent materials has focused mainly on Eu²⁺-doped compounds. However, the yearly number of publications on non-Eu²⁺-based materials has also increased steadily. By now, the number of known persistent phosphors has increased to over 200, of which over 80% are not based on Eu²⁺, but rather, on intrinsic host defects, transition metals (manganese, chromium, copper, etc.) or trivalent rare earths (cerium, terbium, dysprosium, etc.). In this review, we present an overview of these non-Eu²⁺-based persistent luminescent materials and their afterglow properties. We also take a closer look at some remaining challenges, such as the excitability with visible light and the possibility of energy transfer between multiple luminescent centers. Finally, we summarize the necessary elements for a complete description of a persistent luminescent material, in order to allow a more objective comparison of these phosphors. Full article

(This article belongs to the Special Issue Luminescent Materials 2013)

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Number of papers published on non-Eu2+-doped persistent luminescent compounds, according to the Web of Science. Full article ">Figure 2
(a) Green persistent luminescence in a Playmobil® ghost toy based on ZnS:Cu, Co. (b) Afterglow emission spectrum of ZnS:Cu, Co centered around 540 nm. Full article ">Figure 3
(a) Excitation and emission spectrum of Zn3Ga2Ge2O10:0.5%Cr3+; (b) Effectiveness of excitation wavelength (energy) for persistent luminescence of Zn3Ga2Ge2O10:0.5%Cr3+. The afterglow intensity after 10 s is monitored as a function of the excitation wavelength (Reprinted with permission from [<a href="#B2-materials-06-02789" class="html-bibr">2</a>]). Full article ">Figure 4
Energy level diagram for CaAl2O4: Ce3+, showing the positions of the Ce3+ levels relative to the bandgap of the host and the proposed trapping mechanism. After excitation in the conduction band, trapping occurs through the conduction band. After excitation in the lower 5d levels, trapping occurs through tunneling (Reprinted with permission from [<a href="#B77-materials-06-02789" class="html-bibr">77</a>]. Copyright 2003 The Electrochemical Society). Full article ">Figure 5
Thermoluminescence (TL)-emission mapping: the emission spectrum is monitored during the thermoluminescence experiment, showing which traps are related to which activators. An example is shown for Mn2+-emission in CaMgSi2O6 (Reprinted with permission from [<a href="#B33-materials-06-02789" class="html-bibr">33</a>]. Copyright 2010 Elsevier) Full article ">Figure 6
TL-excitation mapping: the TL measurement is repeated for different excitation wavelengths, showing which wavelengths are suited for trap filling. An example is shown for Cu+-emission in ZnS (presented earlier in [<a href="#B258-materials-06-02789" class="html-bibr">258</a>]). It can be seen that different kinds of traps are being filled by short (<340 nm) and longer (>340 nm) wavelengths, where 340 nm corresponds to the band gap of the ZnS host compound. Full article ">

752 KiB

Open AccessArticle

Amino Alcohol Oxidation with Gold Catalysts: The Effect of Amino Groups

by Alberto Villa, Sebastiano Campisi, Marco Schiavoni and Laura Prati

Materials 2013, 6(7), 2777-2788; https://doi.org/10.3390/ma6072777 - 12 Jul 2013

Cited by 13 | Viewed by 6998

Abstract

Gold catalysts have been prepared by sol immobilization using Tetrakis(hydroxymethyl) phosphonium chloride (THPC) as a protective and reducing agent or by deposition on different supports (Al₂O₃, TiO₂, MgAl₂O₄, and MgO). The catalytic systems [...] Read more.

Gold catalysts have been prepared by sol immobilization using Tetrakis(hydroxymethyl) phosphonium chloride (THPC) as a protective and reducing agent or by deposition on different supports (Al₂O₃, TiO₂, MgAl₂O₄, and MgO). The catalytic systems have been tested in the liquid phase oxidation of aminoalcohols (serinol and ethanolamine) and the corresponding polyols (glycerol and ethylene glycol). This comparison allowed us to state that the presence of amino groups has a crucial effect on the catalytic performance, in particular decreasing the durability to the catalysts, but did not substantially vary the selectivity. A support effect has been as well established. Full article

(This article belongs to the Special Issue Advances in Catalytic Materials)

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1122 KiB

Open AccessArticle

Synthesis of New RE³⁺ Doped Li_1+xTa_1−xTi_xO₃ (RE: Eu, Sm, Er, Tm, and Dy) Phosphors with Various Emission Colors

by Hiromi Nakano, Shiho Suehiro, Shohei Furuya, Hiroyuki Hayashi and Shinobu Fujihara

Materials 2013, 6(7), 2768-2776; https://doi.org/10.3390/ma6072768 - 11 Jul 2013

Cited by 11 | Viewed by 5757

Abstract

New phosphors with various emission colors for RE³⁺doped Li_1+xTa_1−xTi_xO₃ (LTT) (RE: Eu, Sm, Er, Tm, and Dy) were synthesized by electric furnace at 1423 K for 15 h. The microstructure of the [...] Read more.

New phosphors with various emission colors for RE³⁺doped Li_1+xTa_1−xTi_xO₃ (LTT) (RE: Eu, Sm, Er, Tm, and Dy) were synthesized by electric furnace at 1423 K for 15 h. The microstructure of the host material and the photoluminescence (PL) property were determined and compared to those of RE³⁺doped Li_1+xNb_1−xTi_xO₃ (LNT)_. In the LTT phosphor, the highest PL intensity was achieved for the mixture composition Li_1.11Ta_0.89Ti_0.11O₃ with a LiTaO₃ structure, although it has an M-phase superstructure. In the LTT host material, the effective activators were Eu³⁺ and Sm³⁺ ions, in contrast to the LNT host material. Here, we discuss the relationship between PL property and the host material’s structure. Full article

(This article belongs to the Special Issue Luminescent Materials 2013)

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Relationships among PL intensity, internal quantum efficiency, and TiO2 content in Li1+xTa1−xTixO3 host material. Full article ">Figure 2
Structures of Li1.11M0.89Ti0.11O3 (M: Nb or Ta) host material: (a–b) LNT; and (c) LTT. Full article ">Figure 3
Relationship between PL intensity and annealing time in Li1.11Ta0.89Ti0.11O3:Eu3+ phosphor. Full article ">Figure 4
XRD patterns of Li1.11Ta0.89Ti0.11O3:Eu3+ phosphors for various annealing times. Full article ">Figure 5
XRD patterns of Li1.11Ta0.89Ti0.11O3:RE3+ (RE: Dy. Tm, Er, Sm, Eu) for 15 h annealing. Full article ">Figure 6
Comparison of PL intensity between LNT:RE3+ and LTT:RE3+. Dotted line: LNT:RE3+, solid line: LTT:RE3+. Full article ">

342 KiB

Open AccessReview

The Influence of Processing and the Polymorphism of Lignocellulosic Fillers on the Structure and Properties of Composite Materials—A Review

by Dominik Paukszta and Slawomir Borysiak

Materials 2013, 6(7), 2747-2767; https://doi.org/10.3390/ma6072747 - 11 Jul 2013

Cited by 49 | Viewed by 6697

Abstract

Cellulose is the most important and the most abundant plant natural polymer. It shows a number of interesting properties including those making it attractive as a filler of composite materials with a thermoplastic polymer matrix. Production of such composite materials, meeting the standards [...] Read more.

Cellulose is the most important and the most abundant plant natural polymer. It shows a number of interesting properties including those making it attractive as a filler of composite materials with a thermoplastic polymer matrix. Production of such composite materials, meeting the standards of green technology, has increased from 0.36 million tons in 2007 to 2.33 million tons in 2012. It is predicted that by 2020 their production will reach 3.45 million tons. Production of biocomposites with lignocellulosic components poses many problems that should be addressed. This paper is a review of the lignocellulosic materials currently used as polymer fillers. First, the many factors determining the macroscopic properties of such composites are described, with particular attention paid to the poor interphase adhesion between the polymer matrix and a lignocellulosic filler and to the effects of cellulose occurrence in polymorphic varieties. The phenomenon of cellulose polymorphism is very important from the point of view of controlling the nucleation abilities of the lignocellulosic filler and hence the mechanical properties of composites. Macroscopic properties of green composites depend also on the parameters of processing which determine the magnitude and range of shearing forces. The influence of shearing forces appearing upon processing the supermolecular structure of the polymer matrix is also discussed. An important problem from the viewpoint of ecology is the possibility of composite recycling which should be taken into account at the design stage. The methods for recycling of the composites made of thermoplastic polymers filled with renewable lignocellulosic materials are presented and discussed. This paper is a review prepared on the basis of currently available literature which describes the many aspects of the problems related to the possibility of using lignocellulosic components for production of composites with polymers. Full article

(This article belongs to the Special Issue Advances in Cellulosic Materials)

1206 KiB

Open AccessArticle

Fractional Factorial Design Study on the Performance of GAC-Enhanced Electrocoagulation Process Involved in Color Removal from Dye Solutions

by Marius Sebastian Secula, Igor Cretescu, Benoit Cagnon, Liliana Rozemarie Manea, Corneliu Sergiu Stan and Iuliana Gabriela Breaban

Materials 2013, 6(7), 2723-2746; https://doi.org/10.3390/ma6072723 - 10 Jul 2013

Cited by 64 | Viewed by 8514

Abstract

The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted [...] Read more.

The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted using a two-level fractional factorial design (FFD) for a given dye solution. Three textile dyes: Acid Blue 74, Basic Red 1, and Reactive Black 5 were used. Experimental factors used and their respective levels were: current density (2.73 or 27.32 A/m²), initial pH of aqueous dye solution (3 or 9), electrocoagulation time (20 or 180 min), GAC dose (0.1 or 0.5 g/L), support electrolyte (2 or 50 mM), initial dye concentration (0.05 or 0.25 g/L) and current type (Direct Current—DC or Alternative Pulsed Current—APC). GAC-enhanced electrocoagulation performance was analyzed statistically in terms of removal efficiency, electrical energy, and electrode material consumptions, using modeling polynomial equations. The statistical significance of GAC dose level on the performance of GAC enhanced electrocoagulation and the experimental conditions that favor the process operation of electrocoagulation in APC regime were determined. The local optimal experimental conditions were established using a multi-objective desirability function method. Full article

(This article belongs to the Special Issue Advances in Colorants)

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480 KiB

Open AccessArticle

Cytotoxic Effects of Hydroxylated Fullerenes in Three Types of Liver Cells

by Kumiko Shimizu, Reiji Kubota, Norihiro Kobayashi, Maiko Tahara, Naoki Sugimoto, Tetsuji Nishimura and Yoshiaki Ikarashi

Materials 2013, 6(7), 2713-2722; https://doi.org/10.3390/ma6072713 - 9 Jul 2013

Cited by 14 | Viewed by 5225

Abstract

Fullerenes C₆₀ have attracted considerable attention in the biomedical field due to their interesting properties. Although there has been a concern that C₆₀ could be metabolized to hydroxylated fullerenes (C₆₀(OH)_x) in vivo, there is little information [...] Read more.

Fullerenes C₆₀ have attracted considerable attention in the biomedical field due to their interesting properties. Although there has been a concern that C₆₀ could be metabolized to hydroxylated fullerenes (C₆₀(OH)_x) in vivo, there is little information on the effect of hydroxylated C₆₀ on liver cells. In the present study, we evaluated the cytotoxic effects of fullerene C₆₀ and various hydroxylated C₆₀ derivatives, C₆₀(OH)₂, C₆₀(OH)_6–12, C₆₀(OH)₁₂ and C₆₀(OH)₃₆, with three different types of liver cells, dRLh-84, HepG2 and primary cultured rat hepatocytes. C₆₀, C₆₀(OH)₂ and C₆₀(OH)₃₆ exhibited little or no cytotoxicity in all of the cell types, while C₆₀(OH)_6–12 and C₆₀(OH)₁₂ induced cytotoxic effects in dRLh-84 cells, accompanied by the appearance of numerous vacuoles around the nucleus. Moreover, mitochondrial activity in liver cells was significantly inhibited by C₆₀(OH)_6–12 and C₆₀(OH)₁₂. These results indicate that the number of hydroxyl groups on C₆₀(OH)_x contribute to the difference of their cytotoxic potential and mitochondrial damage in liver cells. Full article

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Chemical formulas of C60 (A); C60(OH)6–12 or 36 (B); and C60(OH)2 (C). Full article ">Figure 2
Mass Spectra of C60(OH)12 and C60(OH)6–12. Full article ">Figure 3
Cytotoxicity of fullerene and hydroxylated fullerenes in liver cells after exposure for 3 days. HepG2 (A); dRLh-84 (B); and primary cultured rat hepatocytes (C) were exposed to C60, C60(OH)2, C60(OH)6–12, C60(OH)12, and C60(OH)36 at concentrations of 0.3–100 μg/mL. After exposure, cytotoxicities were evaluated by the cell viability assay and the values are reported as % viability. Each data represents the mean ± SD (n = 3). * Significantly different from the control: p < 0.05. Full article ">Figure 4
Numerous vacuoles of dRLh-84 cells treated with C60(OH)6–12 and C60(OH)12 for 24 h. After dRLh-84 cells were exposed to 30 μg/mL of C60(OH)6–12 and C60(OH)12, photographs were taken using an optical microscope. Scale bar: 50 μm. The arrows indicate cytoplasmic vacuoles. Full article ">Figure 5
Mitochondrial activity of fullerene and hydroxylated fullerenes in liver cells after exposure for 3 days. Three types of cells, HepG2 (A); dRLh-84 (B); and primary cultured rat hepatocytes (C) were treated with fullerene and hydroxylated fullerenes with the same concentrations as employed in the cell viability assay (the sample symbols are the same as in <a href="#materials-06-02713-f003" class="html-fig">Figure 3</a>). After exposure for 3 days, the inhibition rate (%) of mitochondrial activity was evaluated. Each data represents the mean ± SD (n = 3). * Significantly different from the control: p < 0.05. Full article ">Figure 5 Cont.
Mitochondrial activity of fullerene and hydroxylated fullerenes in liver cells after exposure for 3 days. Three types of cells, HepG2 (A); dRLh-84 (B); and primary cultured rat hepatocytes (C) were treated with fullerene and hydroxylated fullerenes with the same concentrations as employed in the cell viability assay (the sample symbols are the same as in <a href="#materials-06-02713-f003" class="html-fig">Figure 3</a>). After exposure for 3 days, the inhibition rate (%) of mitochondrial activity was evaluated. Each data represents the mean ± SD (n = 3). * Significantly different from the control: p < 0.05. Full article ">

498 KiB

Open AccessArticle

Millimeter Wave Radiations Affect Membrane Hydration in Phosphatidylcholine Vesicles

by Amerigo Beneduci, Katia Cosentino and Giuseppe Chidichimo

Materials 2013, 6(7), 2701-2712; https://doi.org/10.3390/ma6072701 - 9 Jul 2013

Cited by 6 | Viewed by 6030

Abstract

A clear understanding of the response of biological systems to millimeter waves exposure is of increasing interest for the scientific community due to the recent convincing use of these radiations in the ultrafast wireless communications. Here we report a deuterium nuclear magnetic resonance [...] Read more.

A clear understanding of the response of biological systems to millimeter waves exposure is of increasing interest for the scientific community due to the recent convincing use of these radiations in the ultrafast wireless communications. Here we report a deuterium nuclear magnetic resonance spectroscopy (²H-NMR) investigation on the effects of millimeter waves in the 53–78 GHz range on phosphocholine bio-mimetic membranes. Millimeter waves significantly affect the polar interface of the membrane causing a decrease of the heavy water quadrupole splitting. This effect is as important as inducing the transition from the fluid to the gel phase when the membrane exposure occurs in the neighborhood of the transition point. On the molecular level, the above effect can be well explained by membrane dehydration induced by the radiation. Full article

(This article belongs to the Special Issue Biointerfaces and Materials)

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Graphical abstract
Full article ">Figure 1
Exposure set-up showing the millimeter-waves applicator connected to a diamagnetic cylindrical waveguide inserted into to the nuclear magnetic resonance (NMR) magnet (A); The waveguide terminates with a dielectric Teflon antenna located in the NMR probe over the sample (B). Model of the scenario for the dosimetric assessment: the millimeter waves (MMWs) applicator inserted into a cuvette with the exposed sample. Full article ">Figure 2
Effects of millimeter waves (53–78 GHz) on deuterium labeled 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) vesicles measured as real-time changes of the 2H-NMR line shapes at 37 °C (A) and 27 °C (B) during exposure. The heavy water quadrupole splitting (∆νq) is defined as the distance (in Hz) between the peaks of the spectrum. Quadrupole splitting behavior of DMPC/2H2O multilamellar vesicles (MLVs) (nw = 11) under sham (<math display="inline"> <semantics> <mrow> <mstyle mathcolor="red"> <mo>●</mo> </mstyle> </mrow> </semantics> </math>) and MMWs exposure (■) in the transition region (Tm = phase transition temperature). Full article ">Figure 3
Temperature effect on the heavy water quadrupole splitting (∆νq) of DMPC vesicles with a water/lipid mole ratio n = 12 in the range 30–50 °C. (A) Heating (<math display="inline"> <semantics> <mrow> <mstyle mathcolor="red"> <mo>○</mo> </mstyle> </mrow> </semantics> </math>) and cooling (□) curves and (B) corresponding 2H-NMR lineshape changes for selected temperatures. Full article ">Figure 4
Heavy water quadrupole splitting reduction induced by 4 h MMWs exposure in the wide-band mode on DMPC/2H2O MLVs samples with different water/mole lipid ratio (nw). Points and error bars are, respectively, means and standard deviations relative to three independent experiments. Full article ">

1056 KiB

Open AccessArticle

Effect of Ni Core Structure on the Electrocatalytic Activity of Pt-Ni/C in Methanol Oxidation

by Jian Kang, Rongfang Wang, Hui Wang, Shijun Liao, Julian Key, Vladimir Linkov and Shan Ji

Materials 2013, 6(7), 2689-2700; https://doi.org/10.3390/ma6072689 - 8 Jul 2013

Cited by 19 | Viewed by 7169

Abstract

Methanol oxidation catalysts comprising an outer Pt-shell with an inner Ni-core supported on carbon, (Pt-Ni/C), were prepared with either crystalline or amorphous Ni core structures. Structural comparisons of the two forms of catalyst were made using transmission electron microscopy (TEM), X-ray diffraction (XRD) [...] Read more.

Methanol oxidation catalysts comprising an outer Pt-shell with an inner Ni-core supported on carbon, (Pt-Ni/C), were prepared with either crystalline or amorphous Ni core structures. Structural comparisons of the two forms of catalyst were made using transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and methanol oxidation activity compared using CV and chronoamperometry (CA). While both the amorphous Ni core and crystalline Ni core structures were covered by similar Pt shell thickness and structure, the Pt-Ni(amorphous)/C catalyst had higher methanol oxidation activity. The amorphous Ni core thus offers improved Pt usage efficiency in direct methanol fuel cells. Full article

(This article belongs to the Special Issue Advances in Catalytic Materials)

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X-ray diffraction patterns of (a) NiA/C; (b) NiC/C; (c) Pt-NiC/C and (d) Pt-NiA/C; the vertical dot lines correspondent to the positions of diffraction peaks for the home-made Pt/C sample. Full article ">Figure 2
Pt 4f X-ray photoelectron spectroscopy (XPS) spectra of the Pt-NiC/C and Pt-NiA/C catalysts. Full article ">Figure 3
Lorentzian curves of Pt 4f XPS spectra of the Pt-NiA/C (a) and Pt-NiC/C (b) catalysts respectively. Full article ">Figure 4
Transmission electron microscopy (TEM), high-resolution TEM (HRTEM) images and EDS spectrum of Pt-NiC/C (a–c) and Pt-NiA/C (d–f) catalysts, respectively. Inset of (a) and (d) show the selected area electron diffraction (SAED) patterns of Pt-NiC/C and Pt-NiA/C catalysts. Full article ">Figure 5
Cyclic voltammograms of Pt-NiA/C and Pt-NiC/C catalysts in 0.5 mol L−1 H2SO4 solution under N2 atmosphere at room temperature; Scan rate: 50 mV s−1. Full article ">Figure 6
Cyclic voltammograms of the Pt-NiA/C and Pt-NiC/C catalysts in 0.5 mol L−1 H2SO4 + 0.5 mol L−1 CH3OH solution saturated by N2 at room temperature with scan rate of 50 mV s−1. Full article ">Figure 7
Chronoamperometric curves for methanol oxidation at 0.6 V vs. Ag/AgCl on Pt-NiA/C and Pt-NiC/C in 0.5 mol L−1 CH3OH + 0.5 mol L−1 H2SO4 solution at room temperature. Full article ">

1216 KiB

Open AccessArticle

Diffusion Study by IR Micro-Imaging of Molecular Uptake and Release on Mesoporous Zeolites of Structure Type CHA and LTA

by Mauricio Rincon Bonilla, Tobias Titze, Franz Schmidt, Dirk Mehlhorn, Christian Chmelik, Rustem Valiullin, Suresh K. Bhatia, Stefan Kaskel, Ryong Ryoo and Jörg Kärger

Materials 2013, 6(7), 2662-2688; https://doi.org/10.3390/ma6072662 - 4 Jul 2013

Cited by 29 | Viewed by 7727

Abstract

The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular [...] Read more.

The presence of mesopores in the interior of microporous particles may significantly improve their transport properties. Complementing previous macroscopic transient sorption experiments and pulsed field gradient NMR self-diffusion studies with such materials, the present study is dedicated to an in-depth study of molecular uptake and release on the individual particles of mesoporous zeolitic specimens, notably with samples of the narrow-pore structure types, CHA and LTA. The investigations are focused on determining the time constants and functional dependences of uptake and release. They include a systematic variation of the architecture of the mesopores and of the guest molecules under study as well as a comparison of transient uptake with blocked and un-blocked mesopores. In addition to accelerating intracrystalline mass transfer, transport enhancement by mesopores is found to be, possibly, also caused by a reduction of transport resistances on the particle surfaces. Full article

(This article belongs to the Special Issue Diffusion in Micropores and Mesopores 2013)

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1536 KiB

Open AccessArticle

Spinnability and Characteristics of Polyvinylidene Fluoride (PVDF)-based Bicomponent Fibers with a Carbon Nanotube (CNT) Modified Polypropylene Core for Piezoelectric Applications

by Benjamin Glauß, Wilhelm Steinmann, Stephan Walter, Markus Beckers, Gunnar Seide, Thomas Gries and Georg Roth

Materials 2013, 6(7), 2642-2661; https://doi.org/10.3390/ma6072642 - 3 Jul 2013

Cited by 49 | Viewed by 9995

Abstract

This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 [...] Read more.

This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 wt % carbon nanotubes (CNTs) and 2 wt % sodium stearate (NaSt). The sodium stearate is added to lower the viscosity of the melt. The compound constitutes the fiber core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of an all-trans conformation β phase, caused by draw-winding of the fibers. The core and sheath materials, as well as the bicomponent fibers, are characterized through different analytical methods. These include wide-angle X-ray diffraction (WAXD) to analyze crucial parameters for the development of a crystalline β phase. The distribution of CNTs in the polymer matrix, which affects the conductivity of the core, was investigated by transmission electron microscopy (TEM). Thermal characterization is carried out by conventional differential scanning calorimetry (DSC). Optical microscopy is used to determine the fibers’ diameter regularity (core and sheath). The materials’ viscosity is determined by rheometry. Eventually, an LCR tester is used to determine the core’s specific resistance. Full article

(This article belongs to the Special Issue Smart Polymers and Polymeric Structures)

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283 KiB

Open AccessCommunication

A Fundamental Limitation of Small Diameter Single-Walled Carbon Nanotube Synthesis—A Scaling Rule of the Carbon Nanotube Yield with Catalyst Volume

by Shunsuke Sakurai, Masayasu Inaguma, Don N. Futaba, Motoo Yumura and Kenji Hata

Materials 2013, 6(7), 2633-2641; https://doi.org/10.3390/ma6072633 - 2 Jul 2013

Cited by 27 | Viewed by 5947

Abstract

Understanding the fundamental mechanisms and limiting processes of the growth of single-walled carbon nanotube (SWCNT) would serve as a guide to achieve further control on structural parameters of SWCNT. In this paper, we have studied the growth kinetics of a series of SWCNT [...] Read more.

Understanding the fundamental mechanisms and limiting processes of the growth of single-walled carbon nanotube (SWCNT) would serve as a guide to achieve further control on structural parameters of SWCNT. In this paper, we have studied the growth kinetics of a series of SWCNT forests continuously spanning a wide range of diameters (1.9–3.2 nm), and have revealed an additional fundamental growth limiting process where the mass of the individual SWCNT is determined by the individual catalyst volume. Calculation of the conversion rate of carbon atoms into CNTs per Fe atom is 2 × 10² atoms per second. This rate limiting process provides an important understanding where the larger diameter SWCNT would grow faster, and thus be more suited for mass production. Full article

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(a) Conceptual representation of the process flow of the synthesis of a series of single-walled carbon nanotube (SWCNT) forest with a continuous and wide range of structural properties. Structural control of SWCNT forests was achieved by decoupling the catalyst nanoparticle formation process from the CNT growth process; (b) Schimatic representation of the series of conditions for catalyst formation process. Conditions shown by red/blue arrows (large/low H2 flow rate and low/high temperature) resulted in high/low density and small/large diameter SWCNT forest. Full article ">Figure 2
(a) Plot of the yield versus the diameter of SWCNT; (b) Plot of the forest height versus the diameter of SWCNT; (c) A plot of the catalyst number density as a function of the SWCNT diameter. Dotted line represents an inverse cubic power law: <math display="inline"> <semantics> <mrow> <mi>n</mi> <mo>=</mo> <msub> <mi>n</mi> <mn>0</mn> </msub> <msup> <mrow> <mrow> <mo>(</mo> <mrow> <mrow> <mi>d</mi> <mo>/</mo> <mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mrow> </mrow> </mrow> <mo>)</mo> </mrow> </mrow> <mrow> <mo>−</mo> <mn>3.4</mn> </mrow> </msup> </mrow> </semantics> </math>, where n0 = 2.2 × 1013 cm−2 and d0 is 1 nm. Inset shows the Plot of linear mass density as a function of diameter; (d) Plot of the individual SWCNT mass versus the catalyst volume. Dotted line represents a linear relationship with a slope of 2 × 10−16 g/nm3. Full article ">Figure 2 Cont.
(a) Plot of the yield versus the diameter of SWCNT; (b) Plot of the forest height versus the diameter of SWCNT; (c) A plot of the catalyst number density as a function of the SWCNT diameter. Dotted line represents an inverse cubic power law: <math display="inline"> <semantics> <mrow> <mi>n</mi> <mo>=</mo> <msub> <mi>n</mi> <mn>0</mn> </msub> <msup> <mrow> <mrow> <mo>(</mo> <mrow> <mrow> <mi>d</mi> <mo>/</mo> <mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mrow> </mrow> </mrow> <mo>)</mo> </mrow> </mrow> <mrow> <mo>−</mo> <mn>3.4</mn> </mrow> </msup> </mrow> </semantics> </math>, where n0 = 2.2 × 1013 cm−2 and d0 is 1 nm. Inset shows the Plot of linear mass density as a function of diameter; (d) Plot of the individual SWCNT mass versus the catalyst volume. Dotted line represents a linear relationship with a slope of 2 × 10−16 g/nm3. Full article ">Figure 3
(a) The evolutions of two forest heights as a function of time measured by in-situ height monitor using a commercially available telecentric optical system. Blue and red lines represent small diameter (1.9 nm) and large diameter (2.6 nm) SWCNT forest, respectively; (b) The evolutions of forest yield, which was obtained by multiplying the heights with the densities. Full article ">

1017 KiB

Open AccessArticle

Localized Overheating Phenomena and Optimization of Spark-Plasma Sintering Tooling Design

by Diletta Giuntini, Eugene A. Olevsky, Cristina Garcia-Cardona, Andrey L. Maximenko, Maria S. Yurlova, Christopher D. Haines, Darold G. Martin and Deepak Kapoor

Materials 2013, 6(7), 2612-2632; https://doi.org/10.3390/ma6072612 - 25 Jun 2013

Cited by 61 | Viewed by 8544

Abstract

The present paper shows the application of a three-dimensional coupled electrical, thermal, mechanical finite element macro-scale modeling framework of Spark Plasma Sintering (SPS) to an actual problem of SPS tooling overheating, encountered during SPS experimentation. The overheating phenomenon is analyzed by varying the [...] Read more.

The present paper shows the application of a three-dimensional coupled electrical, thermal, mechanical finite element macro-scale modeling framework of Spark Plasma Sintering (SPS) to an actual problem of SPS tooling overheating, encountered during SPS experimentation. The overheating phenomenon is analyzed by varying the geometry of the tooling that exhibits the problem, namely by modeling various tooling configurations involving sequences of disk-shape spacers with step-wise increasing radii. The analysis is conducted by means of finite element simulations, intended to obtain temperature spatial distributions in the graphite press-forms, including punches, dies, and spacers; to identify the temperature peaks and their respective timing, and to propose a more suitable SPS tooling configuration with the avoidance of the overheating as a final aim. Electric currents-based Joule heating, heat transfer, mechanical conditions, and densification are imbedded in the model, utilizing the finite-element software COMSOL™, which possesses a distinguishing ability of coupling multiple physics. Thereby the implementation of a finite element method applicable to a broad range of SPS procedures is carried out, together with the more specific optimization of the SPS tooling design when dealing with excessive heating phenomena. Full article

(This article belongs to the Special Issue Progress in Net-shaped PM (Powder Metallurgical) Parts)

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918 KiB

Open AccessReview

A Review of Luminescent Anionic Nano System: d¹⁰ Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts

by Xiaobo Li and Howard H. Patterson

Materials 2013, 6(7), 2595-2611; https://doi.org/10.3390/ma6072595 - 25 Jun 2013

Cited by 20 | Viewed by 6408

Abstract

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in [...] Read more.

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration. Full article

(This article belongs to the Special Issue Luminescent Materials 2013)

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1446 KiB

Open AccessArticle

Influence of Fracture Width on Sealability in High-Strength and Ultra-Low-Permeability Concrete in Seawater

by Daisuke Fukuda, Yoshitaka Nara, Daisuke Hayashi, Hideo Ogawa and Katsuhiko Kaneko

Materials 2013, 6(7), 2578-2594; https://doi.org/10.3390/ma6072578 - 25 Jun 2013

Cited by 13 | Viewed by 6178

Abstract

For cementitious composites and materials, the sealing of fractures can occur in water by the precipitation of calcium compounds. In this study, the sealing behavior in a macro-fractured high-strength and ultra-low-permeability concrete (HSULPC) specimen was investigated in simulated seawater using micro-focus X-ray computed [...] Read more.

For cementitious composites and materials, the sealing of fractures can occur in water by the precipitation of calcium compounds. In this study, the sealing behavior in a macro-fractured high-strength and ultra-low-permeability concrete (HSULPC) specimen was investigated in simulated seawater using micro-focus X-ray computed tomography (CT). In particular, the influence of fracture width (0.10 and 0.25 mm) on fracture sealing was investigated. Precipitation occurred mainly at the outermost parts of the fractured surface of the specimen for both fracture widths. While significant sealing was observed for the fracture width of 0.10 mm, sealing was not attained for the fracture width of 0.25 mm within the observation period (49 days). Examination of the sealed regions on the macro-fracture was performed using a three-dimensional image registration technique and applying image subtraction between the CT images of the HSULPC specimen before and after maintaining the specimen in simulated seawater. The temporal change of the sealing deposits for the fracture width of 0.10 mm was much larger than that for the fracture width of 0.25 mm. Therefore, it is concluded that the sealability of the fracture in the HSULPC is affected by the fracture width. Full article

(This article belongs to the Section Advanced Composites)

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Materials, Volume 6, Issue 7 (July 2013) – 25 articles , Pages 2578-3034

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