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Materials, Volume 8, Issue 4 (April 2015), Pages 1369-2042

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Open AccessArticle Preparation and Electrochemical Characterization of Mesoporous Polyaniline-Silica Nanocomposites as an Electrode Material for Pseudocapacitors
Materials 2015, 8(4), 1369-1383; doi:10.3390/ma8041369
Received: 2 February 2015 / Revised: 11 March 2015 / Accepted: 16 March 2015 / Published: 25 March 2015
Cited by 10 | PDF Full-text (1314 KB) | HTML Full-text | XML Full-text
Abstract
Mesoporous polyaniline-silica nanocomposites with a full interpenetrating structure for pseudocapacitors were synthesized via the vapor phase approach. The morphology and structure of the nanocomposites were deeply investigated by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis and nitrogen adsorption-desorption tests. The
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Mesoporous polyaniline-silica nanocomposites with a full interpenetrating structure for pseudocapacitors were synthesized via the vapor phase approach. The morphology and structure of the nanocomposites were deeply investigated by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis and nitrogen adsorption-desorption tests. The results present that the mesoporous nanocomposites possess a uniform particle morphology and full interpenetrating structure, leading to a continuous conductive polyaniline network with a large specific surface area. The electrochemical performances of the nanocomposites were tested in a mixed solution of sulfuric acid and potassium iodide. With the merits of a large specific surface area and suitable pore size distribution, the nanocomposite showed a large specific capacitance (1702.68 farad (F)/g) due to its higher utilization of the active material. This amazing value is almost three-times larger than that of bulk polyaniline when the same mass of active material was used. Full article
(This article belongs to the Special Issue Advances in Mesoporous Material 2015)
Open AccessArticle Lightweight Concrete Produced Using a Two-Stage Casting Process
Materials 2015, 8(4), 1384-1397; doi:10.3390/ma8041384
Received: 2 February 2015 / Revised: 12 March 2015 / Accepted: 16 March 2015 / Published: 25 March 2015
Cited by 2 | PDF Full-text (1851 KB) | HTML Full-text | XML Full-text
Abstract
The type of lightweight aggregate and its volume fraction in a mix determine the density of lightweight concrete. Minimizing the density obviously requires a higher volume fraction, but this usually causes aggregates segregation in a conventional mixing process. This paper proposes a two-stage
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The type of lightweight aggregate and its volume fraction in a mix determine the density of lightweight concrete. Minimizing the density obviously requires a higher volume fraction, but this usually causes aggregates segregation in a conventional mixing process. This paper proposes a two-stage casting process to produce a lightweight concrete. This process involves placing lightweight aggregates in a frame and then filling in the remaining interstitial voids with cementitious grout. The casting process results in the lowest density of lightweight concrete, which consequently has low compressive strength. The irregularly shaped aggregates compensate for the weak point in terms of strength while the round-shape aggregates provide a strength of 20 MPa. Therefore, the proposed casting process can be applied for manufacturing non-structural elements and structural composites requiring a very low density and a strength of at most 20 MPa. Full article
Open AccessArticle Nanostructured Titanium-10 wt% 45S5 Bioglass-Ag Composite Foams for Medical Applications
Materials 2015, 8(4), 1398-1412; doi:10.3390/ma8041398
Received: 18 February 2015 / Revised: 11 March 2015 / Accepted: 17 March 2015 / Published: 25 March 2015
Cited by 7 | PDF Full-text (2413 KB) | HTML Full-text | XML Full-text
Abstract
The article presents an investigation on the effectiveness of nanostructured titanium-10 wt% 45S5 Bioglass-1 wt% Ag composite foams as a novel class of antibacterial materials for medical applications. The Ti-based composite foams were prepared by the combination of mechanical alloying and a “space-holder”
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The article presents an investigation on the effectiveness of nanostructured titanium-10 wt% 45S5 Bioglass-1 wt% Ag composite foams as a novel class of antibacterial materials for medical applications. The Ti-based composite foams were prepared by the combination of mechanical alloying and a “space-holder” sintering process. In the first step, the Ti-10 wt% 45S5 Bioglass-1 wt% Ag powder synthesized by mechanical alloying and annealing mixed with 1.0 mm diameter of saccharose crystals was finally compacted in the form of pellets. In the next step, the saccharose crystals were dissolved in water, leaving open spaces surrounded by metallic-bioceramic scaffold. The sintering of the scaffold leads to foam formation. It was found that 1:1 Ti-10 wt% 45S5 Bioglass-1 wt% Ag/sugar ratio leads to porosities of about 70% with pore diameter of about 0.3–1.1 mm. The microstructure, corrosion resistance in Ringer’s solution of the produced foams were investigated. The value of the compression strength for the Ti-10 wt% 45S5 Bioglass-1 wt% Ag foam with 70% porosity was 1.5 MPa and the Young’s modulus was 34 MPa. Silver modified Ti-10 wt% 45S5 Bioglass composites possess excellent antibacterial activities against Staphylococcus aureus. Porous Ti-10 wt% 45S5 Bioglass-1 wt% foam could be a possible candidate for medical implants applications. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessArticle A Review of Pellets from Different Sources
Materials 2015, 8(4), 1413-1427; doi:10.3390/ma8041413
Received: 23 January 2015 / Revised: 3 March 2015 / Accepted: 20 March 2015 / Published: 27 March 2015
Cited by 5 | PDF Full-text (397 KB) | HTML Full-text | XML Full-text
Abstract
The rise in pellet consumption has resulted in a wider variety of materials for pellet manufacture. Thus, pellet industry has started looking for alternative products, such as wastes from agricultural activities, forestry and related industries, along with the combination thereof, obtaining a broad
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The rise in pellet consumption has resulted in a wider variety of materials for pellet manufacture. Thus, pellet industry has started looking for alternative products, such as wastes from agricultural activities, forestry and related industries, along with the combination thereof, obtaining a broad range of these products. In addition, the entry into force of EN ISO 17225 standard makes wood pellet market (among other types) possible for industry and household purposes. Therefore, wastes that are suitable for biomass use have recently increased. In this study, the main characteristics of ten kinds of laboratory-made pellets from different raw materials were analyzed. Thus, we have focused on the most limiting factors of quality standards that determine the suitability for biomass market, depending on the kind of pellet. The results showed considerable differences among the analyzed pellets, exceeding the limits established by the standard in almost all cases, especially concerning ash content and N and S composition. The requirements of the studied standard, very demanding for certain factors, disable the entry of these densified wastes in greater added value markets. Full article
(This article belongs to the Section Energy Materials)
Open AccessArticle Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses
Materials 2015, 8(4), 1428-1441; doi:10.3390/ma8041428
Received: 9 December 2014 / Revised: 4 March 2015 / Accepted: 10 March 2015 / Published: 27 March 2015
PDF Full-text (2484 KB) | HTML Full-text | XML Full-text
Abstract
Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle
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Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle Compressive Behavior of Fiber-Reinforced Concrete with End-Hooked Steel Fibers
Materials 2015, 8(4), 1442-1458; doi:10.3390/ma8041442
Received: 31 January 2015 / Revised: 14 March 2015 / Accepted: 23 March 2015 / Published: 27 March 2015
Cited by 15 | PDF Full-text (758 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize
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In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize the effect of specimen size on fiber distribution, 48 cylinder specimens 150 mm in diameter and 300 mm in height were prepared and then subjected to uniaxial compression. From the test results, it was shown that steel fiber-reinforced concrete (SFRC) specimens exhibited ductile behavior after reaching their compressive strength. It was also shown that the strain at the compressive strength generally increased along with an increase in the fiber volumetric ratio and fiber aspect ratio, while the elastic modulus decreased. With consideration for the effect of steel fibers, a model for the stress–strain relationship of SFRC under compression is proposed here. Simple formulae to predict the strain at the compressive strength and the elastic modulus of SFRC were developed as well. The proposed model and formulae will be useful for realistic predictions of the structural behavior of SFRC members or structures. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Durability Indicators Comparison for SCC and CC in Tropical Coastal Environments
Materials 2015, 8(4), 1459-1481; doi:10.3390/ma8041459
Received: 20 January 2015 / Revised: 16 March 2015 / Accepted: 17 March 2015 / Published: 27 March 2015
Cited by 5 | PDF Full-text (1729 KB) | HTML Full-text | XML Full-text
Abstract
Self-compacting concrete (SCC) demands more studies of durability at higher temperatures when subjected to more aggressive environments in comparison to the conventional vibrated concrete (CC). This work aims at presenting results of durability indicators of SCC and CC, having the same water/binder relations
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Self-compacting concrete (SCC) demands more studies of durability at higher temperatures when subjected to more aggressive environments in comparison to the conventional vibrated concrete (CC). This work aims at presenting results of durability indicators of SCC and CC, having the same water/binder relations and constituents. The applied methodologies were electrical resistivity, diffusion of chloride ions and accelerated carbonation experiments, among others, such as microstructure study, scanning electron microscope and microtomography experiments. The tests were performed in a research laboratory and at a construction site of the Pernambuco Arena. The obtained results shows that the SCC presents an average electrical resistivity 11.4% higher than CC; the average chloride ions diffusion was 63.3% of the CC; the average accelerated carbonation penetration was 45.8% of the CC; and the average open porosity was 55.6% of the CC. As the results demonstrated, the SCC can be more durable than CC, which contributes to elucidate the aspects related to its durability and consequent prolonged life cycle. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
Open AccessArticle Tribo-electrification and Powder Adhesion Studies in the Development of Polymeric Hydrophilic Drug Matrices
Materials 2015, 8(4), 1482-1498; doi:10.3390/ma8041482
Received: 1 March 2015 / Revised: 19 March 2015 / Accepted: 23 March 2015 / Published: 30 March 2015
Cited by 3 | PDF Full-text (2104 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The generation of tribo-electric charge during pharmaceutical powder processing can cause a range of complications, including segregation of components leading to content uniformity and particle surface adhesion. This phenomenon becomes problematical when excipients are introduced to a powder mixture alongside the highly charging
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The generation of tribo-electric charge during pharmaceutical powder processing can cause a range of complications, including segregation of components leading to content uniformity and particle surface adhesion. This phenomenon becomes problematical when excipients are introduced to a powder mixture alongside the highly charging active pharmaceutical ingredient(s) (APIs). The aim of this study was to investigate the tribo-electric charging and adhesion properties of a model drug, theophylline. Moreover, binary powder mixtures of theophylline with methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), having different polymer to drug ratios, were formed in order to study the impact of polymer concentration, particle size, substitution ratio and molecular size on the tribo-electric charging and surface adhesion properties of the drug. Furthermore, the relationship between tribo-electric charging and surface adhesion was also studied. The diversity in physicochemical properties of MC/HPMC has shown a significant impact on the tribo-electric charging and adhesion behaviour of theophylline. It was found that the magnitude of electrostatic charge and the level of surface adhesion of the API were significantly reduced with an increase in MC and HPMC concentration, substitution ratios and molecular size. In addition, the tribo-electric charge showed a linear relationship with particle surface adhesion, but the involvement of other forces cannot be neglected. Full article
(This article belongs to the Special Issue Materials for Drug Delivery)
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Open AccessArticle High-Temperature Oxidation of Fe3Al Intermetallic Alloy Prepared by Additive Manufacturing LENS
Materials 2015, 8(4), 1499-1512; doi:10.3390/ma8041499
Received: 15 January 2015 / Revised: 9 March 2015 / Accepted: 19 March 2015 / Published: 30 March 2015
Cited by 4 | PDF Full-text (3636 KB) | HTML Full-text | XML Full-text
Abstract
The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (<0.08 at%) in air atmosphere, in the temperature range of 1000 to 1200 °C, was studied. The investigation was carried out on the thin-walled (<1 mm) elements prepared by Laser
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The isothermal oxidation of Fe-28Al-5Cr (at%) intermetallic alloy microalloyed with Zr and B (<0.08 at%) in air atmosphere, in the temperature range of 1000 to 1200 °C, was studied. The investigation was carried out on the thin-walled (<1 mm) elements prepared by Laser Engineered Net Shaping (LENS) from alloy powder of a given composition. Characterization of the specimens, after the oxidation, was conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM, with back-scatter detector (BSE) and energy-dispersive X-ray spectroscopy (EDS) attachments). The investigation has shown, that the oxidized samples were covered with a thin, homogeneous α-Al2O3 oxide layers. The intensity of their growth indicates that the material lost its resistance to oxidation at 1200 °C. Structural analysis of the thin-walled components’ has not shown intensification of the oxidation process at the joints of additive layers. Full article
(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)
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Open AccessArticle The Effect of Oxygen Partial Pressure on Microstructure and Properties of Fe40Al Alloy Sintered under Vacuum
Materials 2015, 8(4), 1513-1525; doi:10.3390/ma8041513
Received: 18 February 2015 / Revised: 18 March 2015 / Accepted: 19 March 2015 / Published: 31 March 2015
Cited by 1 | PDF Full-text (4834 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the results of studies on the influence of oxygen partial pressure (vacuum level in the chamber) on the properties of FeAl intermetallics. One of the problems in the application of classical methods of prepared Fe-Al intermetallic is the occurrence of
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This paper presents the results of studies on the influence of oxygen partial pressure (vacuum level in the chamber) on the properties of FeAl intermetallics. One of the problems in the application of classical methods of prepared Fe-Al intermetallic is the occurrence of oxides. Applying a vacuum during sintering should reduce this effect. In order to analyze the effect of oxygen partial pressure on sample properties, five samples were processed (by a pressure-assisted induction sintering—PAIS method) under the following pressures: 3, 8, 30, 80, and 300 mbar (corresponding to oxygen partial pressures of 0.63, 1.68, 6.3, 16.8, and 63 mbar, respectively). The chemical and phase composition, hardness, density, and microstructure observations indicate that applying a vacuum significantly impacts intermetallic samples. The compact sintered at pressure 3 mbar is characterized by the most homogeneous microstructure, the highest density, high hardness, and nearly homogeneous chemical composition. Full article
(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications)
Open AccessArticle Covalent Binding of Heparin to Functionalized PET Materials for Improved Haemocompatibility
Materials 2015, 8(4), 1526-1544; doi:10.3390/ma8041526
Received: 18 December 2014 / Revised: 19 January 2015 / Accepted: 20 March 2015 / Published: 31 March 2015
Cited by 9 | PDF Full-text (1741 KB) | HTML Full-text | XML Full-text
Abstract
The hemocompatibility of vascular grafts made from poly(ethylene terephthalate) (PET) is insufficient due to the rapid adhesion and activation of blood platelets that occur upon incubation with whole blood. PET polymer was treated with NHx radicals created by passing ammonia through gaseous
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The hemocompatibility of vascular grafts made from poly(ethylene terephthalate) (PET) is insufficient due to the rapid adhesion and activation of blood platelets that occur upon incubation with whole blood. PET polymer was treated with NHx radicals created by passing ammonia through gaseous plasma formed by a microwave discharge, which allowed for functionalization with amino groups. X-ray photoelectron spectroscopy characterization using derivatization with 4-chlorobenzaldehyde indicated that approximately 4% of the –NH2 groups were associated with the PET surface after treatment with the gaseous radicals. The functionalized polymers were coated with an ultra-thin layer of heparin and incubated with fresh blood. The free-hemoglobin technique, which is based on the haemolysis of erythrocytes, indicated improved hemocompatibility, which was confirmed by imaging the samples using confocal optical microscopy. A significant decrease in number of adhered platelets was observed on such samples. Proliferation of both human umbilical vein endothelial cells and human microvascular endothelial cells was enhanced on treated polymers, especially after a few hours of cell seeding. Thus, the technique represents a promising substitute for wet-chemical modification of PET materials prior to coating with heparin. Full article
(This article belongs to the Section Biomaterials)
Open AccessCommunication Enhanced Thermoelectric Performance of Bi2O2Se with Ag Addition
Materials 2015, 8(4), 1568-1576; doi:10.3390/ma8041568
Received: 9 February 2015 / Revised: 5 March 2015 / Accepted: 6 March 2015 / Published: 1 April 2015
Cited by 4 | PDF Full-text (1148 KB) | HTML Full-text | XML Full-text
Abstract
Polycrystalline Bi2O2Se/Ag nanocomposites were synthesized by spark plasma sintering process. Their thermoelectric properties were evaluated from 300 to 673 K. With the addition of silver, the conductive second phase Ag2Se and Ag can be observed, which results
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Polycrystalline Bi2O2Se/Ag nanocomposites were synthesized by spark plasma sintering process. Their thermoelectric properties were evaluated from 300 to 673 K. With the addition of silver, the conductive second phase Ag2Se and Ag can be observed, which results in a significant enhancement of electrical conductivity. The maximum conductivity is 691.8 S cm−1 for Bi2O2Se/20 vol.% Ag, which increased nearly 500 higher times than the pure Bi2O2Se bulk. ZT value can be enhanced greatly, ~0.07, for Bi2O2Se/5 vol.% Ag at 673 K, which is two times larger than the pure sample. Full article
(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)
Open AccessArticle All-Ceramic Single Crown Restauration of Zirconia Oral Implants and Its Influence on Fracture Resistance: An Investigation in the Artificial Mouth
Materials 2015, 8(4), 1577-1589; doi:10.3390/ma8041577
Received: 23 February 2015 / Revised: 20 March 2015 / Accepted: 27 March 2015 / Published: 1 April 2015
Cited by 3 | PDF Full-text (1032 KB) | HTML Full-text | XML Full-text
Abstract
The aim of the current investigation was to evaluate the fracture resistance of one-piece zirconia oral implants with and without all-ceramic incisor crowns after long-term thermomechanical cycling. A total of 48 implants were evaluated. The groups with crowns (C, 24 samples) and without
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The aim of the current investigation was to evaluate the fracture resistance of one-piece zirconia oral implants with and without all-ceramic incisor crowns after long-term thermomechanical cycling. A total of 48 implants were evaluated. The groups with crowns (C, 24 samples) and without crowns (N, 24 samples) were subdivided according to the loading protocol, resulting in three groups of 8 samples each: Group “0” was not exposed to cyclic loading, whereas groups “5” and “10” were loaded with 5 and 10 million chewing cycles, respectively. This resulted in 6 different groups: C0/N0, C5/N5 and C10/N10. Subsequently, all 48 implants were statically loaded to fracture and bending moments were calculated. All implants survived the artificial aging. For the static loading the following average bending moments were calculated: C0: 326 Ncm; C5: 339 Ncm; C10: 369 Ncm; N0: 339 Ncm; N5: 398 Ncm and N10: 355 Ncm. To a certain extent, thermomechanical cycling resulted in an increase of fracture resistance which did not prove to be statistically significant. Regarding its fracture resistance, the evaluated ceramic implant system made of Y-TZP seems to be able to resist physiological chewing forces long-term. Restauration with all-ceramic single crowns showed no negative influence on fracture resistance. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessArticle A Six-Fold Symmetric Metamaterial Absorber
Materials 2015, 8(4), 1590-1603; doi:10.3390/ma8041590
Received: 12 January 2015 / Revised: 24 March 2015 / Accepted: 30 March 2015 / Published: 3 April 2015
Cited by 8 | PDF Full-text (984 KB) | HTML Full-text | XML Full-text
Abstract
A novel microwave metamaterial absorber design is introduced along with its manufacturing and characterization. Significant results considering both bandwidth and angular stability are achieved. Parametric analysis and simplified equivalent circuit are provided to give an insight on the key elements influencing the absorber
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A novel microwave metamaterial absorber design is introduced along with its manufacturing and characterization. Significant results considering both bandwidth and angular stability are achieved. Parametric analysis and simplified equivalent circuit are provided to give an insight on the key elements influencing the absorber performance. In addition, the constitutive parameters of the effective medium model are obtained and related to the absorber resonant behavior. Moreover, a new thinner and more flexible absorber version, preserving broad bandwidth and angular insensitive performance, is simulated, and an 8 × 8 unit-cells prototype is manufactured and measured for a limited angular margin in an anechoic chamber. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Effect of Different Luting Agents on the Retention of Lithium Disilicate Ceramic Crowns
Materials 2015, 8(4), 1604-1611; doi:10.3390/ma8041604
Received: 17 January 2015 / Revised: 28 March 2015 / Accepted: 31 March 2015 / Published: 7 April 2015
Cited by 1 | PDF Full-text (1412 KB) | HTML Full-text | XML Full-text
Abstract
No studies are available that evaluate the retention of disilicate crowns according to different cementation procedures. The purpose of this study was to measure the retention of lithium disilicate crowns cemented using two different cementation systems. Twenty extracted mandibular premolars were prepared. Anatomic
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No studies are available that evaluate the retention of disilicate crowns according to different cementation procedures. The purpose of this study was to measure the retention of lithium disilicate crowns cemented using two different cementation systems. Twenty extracted mandibular premolars were prepared. Anatomic crowns were waxed and hot pressed using lithium disilicate ceramic. Teeth were divided into two groups (n = 10): (1) self-curing luting composite and (2) glass-ionomer cement (GIC). After cementation, the crowns were embedded in acrylic resin block with a screw base. Each specimen was pulled along the path of insertion in Universal Testing Machine. Failure load in Newtons (N) and failure mode were recorded for each specimen. Failure mode was classified as decementation or fracture. Failure load data were analyzed using one-way analysis of variance (ANOVA). Failure modes were compared using Pearson’s Chi-square test. Mean failure load was 306.6(±193.8) N for composite group and 94.7(±48.2) N for GIC group (p = 0.004). Disilicate crown cemented with luting composite most often failed by fracture; otherwise, crown cemented with glass-ionomer cement most often failed by decementation (p = 0.02). Disilicate full crown cemented with luting composite showed higher failure load compared with conventional cementation with glass-ionomer cement. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessArticle Effect of Alkali-Acid-Heat Chemical Surface Treatment on Electron Beam Melted Porous Titanium and Its Apatite Forming Ability
Materials 2015, 8(4), 1612-1625; doi:10.3390/ma8041612
Received: 28 January 2015 / Revised: 23 March 2015 / Accepted: 30 March 2015 / Published: 8 April 2015
Cited by 5 | PDF Full-text (607 KB) | HTML Full-text | XML Full-text
Abstract
Advanced additive manufacturing techniques such as electron beam melting (EBM), can produce highly porous structures that resemble the mechanical properties and structure of native bone. However, for orthopaedic applications, such as joint prostheses or bone substitution, the surface must also be bio-functionalized to
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Advanced additive manufacturing techniques such as electron beam melting (EBM), can produce highly porous structures that resemble the mechanical properties and structure of native bone. However, for orthopaedic applications, such as joint prostheses or bone substitution, the surface must also be bio-functionalized to promote bone growth. In the current work, EBM porous Ti6Al4V alloy was exposed to an alkali acid heat (AlAcH) treatment to bio-functionalize the surface of the porous structure. Various molar concentrations (3, 5, 10M) and immersion times (6, 24 h) of the alkali treatment were used to determine optimal parameters. The apatite forming ability of the samples was evaluated using simulated body fluid (SBF) immersion testing. The micro-topography and surface chemistry of AlAcH treated samples were evaluated before and after SBF testing using scanning electron microscopy and energy dispersive X-ray spectroscopy. The AlAcH treatment successfully modified the topographical and chemical characteristics of EBM porous titanium surface creating nano-topographical features ranging from 200–300 nm in size with a titania layer ideal for apatite formation. After 1 and 3 week immersion in SBF, there was no Ca or P present on the surface of as manufactured porous titanium while both elements were present on all AlAcH treated samples except those exposed to 3M, 6 h alkali treatment. An increase in molar concentration and/or immersion time of alkali treatment resulted in an increase in the number of nano-topographical features per unit area as well as the amount of titania on the surface. Full article
(This article belongs to the Section Structure Analysis and Characterization)
Open AccessArticle Preparation of High Density Polyethylene/Waste Polyurethane Blends Compatibilized with Polyethylene-Graft-Maleic Anhydride by Radiation
Materials 2015, 8(4), 1626-1635; doi:10.3390/ma8041626
Received: 20 January 2015 / Revised: 13 March 2015 / Accepted: 30 March 2015 / Published: 8 April 2015
Cited by 5 | PDF Full-text (1890 KB) | HTML Full-text | XML Full-text
Abstract
Polyurethane (PU) is a very popular polymer that is used in a variety of applications due to its good mechanical, thermal, and chemical properties. However, PU recycling has received significant attention due to environmental issues. In this study, we developed a recycling method
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Polyurethane (PU) is a very popular polymer that is used in a variety of applications due to its good mechanical, thermal, and chemical properties. However, PU recycling has received significant attention due to environmental issues. In this study, we developed a recycling method for waste PU that utilizes the radiation grafting technique. Grafting of waste PU was carried out using a radiation technique with polyethylene-graft-maleic anhydride (PE-g-MA). The PE-g-MA-grafted PU/high density polyethylene (HDPE) composite was prepared by melt-blending at various concentrations (0–10 phr) of PE-g-MA-grafted PU. The composites were characterized using fourier transform infrared spectroscopy (FT-IR), and their surface morphology and thermal/mechanical properties are reported. For 1 phr PU, the PU could be easily introduced to the HDPE during the melt processing in the blender after the radiation-induced grafting of PU with PE-g-MA. PE-g-MA was easily reacted with PU according to the increasing radiation dose and was located at the interface between the PU and the HDPE during the melt processing in the blender, which improved the interfacial interactions and the mechanical properties of the resultant composites. However, the elongation at break for a PU content >2 phr was drastically decreased. Full article
(This article belongs to the Special Issue Smart Materials)
Open AccessArticle Characterization of Fibrin and Collagen Gels for Engineering Wound Healing Models
Materials 2015, 8(4), 1636-1651; doi:10.3390/ma8041636
Received: 27 February 2015 / Revised: 27 March 2015 / Accepted: 2 April 2015 / Published: 10 April 2015
Cited by 12 | PDF Full-text (3343 KB) | HTML Full-text | XML Full-text
Abstract
Hydrogels are used for 3D in vitro assays and tissue engineering and regeneration purposes. For a thorough interpretation of this technology, an integral biomechanical characterization of the materials is required. In this work, we characterize the mechanical and functional behavior of two specific
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Hydrogels are used for 3D in vitro assays and tissue engineering and regeneration purposes. For a thorough interpretation of this technology, an integral biomechanical characterization of the materials is required. In this work, we characterize the mechanical and functional behavior of two specific hydrogels that play critical roles in wound healing, collagen and fibrin. A coherent and complementary characterization was performed using a generalized and standard composition of each hydrogel and a combination of techniques. Microstructural analysis was performed by scanning electron microscopy and confocal reflection imaging. Permeability was measured using a microfluidic-based experimental set-up, and mechanical responses were analyzed by rheology. We measured a pore size of 2.84 and 1.69 μm for collagen and fibrin, respectively. Correspondingly, the permeability of the gels was 1.00·10−12 and 5.73·10−13 m2. The shear modulus in the linear viscoelastic regime was 15 Pa for collagen and 300 Pa for fibrin. The gels exhibited strain-hardening behavior at ca. 10% and 50% strain for fibrin and collagen, respectively. This consistent biomechanical characterization provides a detailed and robust starting point for different 3D in vitro bioapplications, such as collagen and/or fibrin gels. These features may have major implications for 3D cellular behavior by inducing divergent microenvironmental cues. Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
Open AccessArticle Tuning the Pore Geometry of Ordered Mesoporous Carbons for Enhanced Adsorption of Bisphenol-A
Materials 2015, 8(4), 1652-1665; doi:10.3390/ma8041652
Received: 25 February 2015 / Revised: 26 March 2015 / Accepted: 31 March 2015 / Published: 10 April 2015
Cited by 5 | PDF Full-text (1002 KB) | HTML Full-text | XML Full-text
Abstract
Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with
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Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with fine pores of 3 nm and less. The hard templated carbon (CMK-3) material had an even higher BET-surface of 1420 m2/g with an average pore size of 4 nm. The soft templated carbon (SMC) reached a BET-surface of 476 m2/g and a pore size of 7 nm. The maximum observed adsorption capacity (qmax) of CMK-3 was the highest with 474 mg/g, compared to 290 mg/g for PAC and 154 mg/g for SMC. The difference in adsorption capacities was attributed to the specific surface area and hydrophobicity of the adsorbent. The microporous PAC showed the slowest adsorption, while the ordered mesopores of SMC and CMK-3 enhanced the BPA diffusion into the adsorbent. This difference in adsorption kinetics is caused by the increase in pore diameter. However, CMK-3 with an open geometry consisting of interlinked nanorods allows for even faster intraparticle diffusion. Full article
(This article belongs to the Special Issue Advances in Mesoporous Material 2015)
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Open AccessArticle A Thin C-Band Polarization and Incidence Angle-Insensitive Metamaterial Perfect Absorber
Materials 2015, 8(4), 1666-1681; doi:10.3390/ma8041666
Received: 30 January 2015 / Revised: 16 March 2015 / Accepted: 2 April 2015 / Published: 13 April 2015
Cited by 5 | PDF Full-text (1789 KB) | HTML Full-text | XML Full-text
Abstract
A novel metamaterial absorber design able to operate in the C frequency band is presented, along with an analysis and a method to improve both its bandwidth and its angular stability. Simulation results for a FR4-based design are shown for comparison with existing
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A novel metamaterial absorber design able to operate in the C frequency band is presented, along with an analysis and a method to improve both its bandwidth and its angular stability. Simulation results for a FR4-based design are shown for comparison with existing designs. In addition, a simplified equivalent circuit is provided for a better understanding of the great angular stability and wide bandwidth exhibited by the proposed structure. Moreover, simulations, manufacturing and measurements of a thinner and more flexible metamaterial absorber, keeping the angular stability of the former one, while providing a wide bandwidth, are presented. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Teflon/SiO2 Bilayer Passivation for Improving the Electrical Reliability of Oxide TFTs Fabricated Using a New Two-Photomask Self-Alignment Process
Materials 2015, 8(4), 1704-1713; doi:10.3390/ma8041704
Received: 7 January 2015 / Revised: 13 March 2015 / Accepted: 26 March 2015 / Published: 13 April 2015
Cited by 6 | PDF Full-text (895 KB) | HTML Full-text | XML Full-text
Abstract
This study proposes a two-photomask process for fabricating amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) that exhibit a self-aligned structure. The fabricated TFTs, which lack etching-stop (ES) layers, have undamaged a-IGZO active layers that facilitate superior performance. In addition, we demonstrate a bilayer
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This study proposes a two-photomask process for fabricating amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) that exhibit a self-aligned structure. The fabricated TFTs, which lack etching-stop (ES) layers, have undamaged a-IGZO active layers that facilitate superior performance. In addition, we demonstrate a bilayer passivation method that uses a polytetrafluoroethylene (Teflon) and SiO2 combination layer for improving the electrical reliability of the fabricated TFTs. Teflon was deposited as a buffer layer through thermal evaporation. The Teflon layer exhibited favorable compatibility with the underlying IGZO channel layer and effectively protected the a-IGZO TFTs from plasma damage during SiO2 deposition, resulting in a negligible initial performance drop in the a-IGZO TFTs. Compared with passivation-free a-IGZO TFTs, passivated TFTs exhibited superior stability even after 168 h of aging under ambient air at 95% relative humidity. Full article
Open AccessArticle High Throughput Screening of Valganciclovir in Acidic Microenvironments of Polyester Thin Films
Materials 2015, 8(4), 1714-1728; doi:10.3390/ma8041714
Received: 1 December 2014 / Revised: 19 March 2015 / Accepted: 30 March 2015 / Published: 13 April 2015
Cited by 1 | PDF Full-text (635 KB) | HTML Full-text | XML Full-text
Abstract
Ganciclovir and valganciclor are antiviral agents used for the treatment of cytomegalovirus retinitis. The conventional method for administering ganciclovir in cytomegalovirus retinitis patients is repeated intravitreal injections. In order to obviate the possible detrimental effects of repeated intraocular injections, to improve compliance and
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Ganciclovir and valganciclor are antiviral agents used for the treatment of cytomegalovirus retinitis. The conventional method for administering ganciclovir in cytomegalovirus retinitis patients is repeated intravitreal injections. In order to obviate the possible detrimental effects of repeated intraocular injections, to improve compliance and to eliminate systemic side-effects, we investigated the tuning of the ganciclovir pro-drug valganciclovir and the release from thin films of poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), or mixtures of both, as a step towards prototyping periocular valganciclovir implants. To investigate the drug release, we established and evaluated a high throughput fluorescence-based quantification screening assay for the detection of valganciclovir. Our protocol allows quantifying as little as 20 ng of valganciclovir in 96-well polypropylene plates and a 50× faster analysis compared to traditional HPLC measurements. This improvement can hence be extrapolated to other polyester matrix thin film formulations using a high-throughput approach. The acidic microenvironment within the polyester matrix was found to protect valganciclovir from degradation with resultant increases in the half-life of the drug in the periocular implant to 100 days. Linear release profiles were obtained using the pure polyester polymers for 10 days and 60 days formulations; however, gross phase separations of PCL and acid-terminated PLGA prevented tuning within these timeframes due to the phase separation of the polymer, valganciclovir, or both. Full article
(This article belongs to the Special Issue Materials for Drug Delivery)
Open AccessArticle Direct Ink Writing of Three-Dimensional (K, Na)NbO3-Based Piezoelectric Ceramics
Materials 2015, 8(4), 1729-1737; doi:10.3390/ma8041729
Received: 11 March 2015 / Revised: 31 March 2015 / Accepted: 8 April 2015 / Published: 14 April 2015
Cited by 1 | PDF Full-text (1244 KB) | HTML Full-text | XML Full-text
Abstract
A kind of piezoelectric ink was prepared with Li, Ta, Sb co-doped (K, Na)NbO3 (KNN) powders. Piezoelectric scaffolds with diameters at micrometer scale were constructed from this ink by using direct ink writing method. According to the micro-morphology and density test, the
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A kind of piezoelectric ink was prepared with Li, Ta, Sb co-doped (K, Na)NbO3 (KNN) powders. Piezoelectric scaffolds with diameters at micrometer scale were constructed from this ink by using direct ink writing method. According to the micro-morphology and density test, the samples sintered at 1100 °C for 2 h have formed ceramics completely with a high relative density of 98%. X-ray diffraction (XRD) test shows that the main phase of sintered samples is orthogonal (Na0.52K0.4425Li0.0375)(Nb0.87Sb0.07Ta0.06)O3. The piezoelectric constant d33 of 280 pC/N, dielectric constant ε of 1775, remanent polarization Pr of 18.8 μC/cm2 and coercive field Ec of 8.5 kV/cm prove that the sintered samples exhibit good electrical properties. The direct ink writing method allows one to design and rapidly fabricate piezoelectric structures in complex three-dimensional (3D) shapes without the need for any dies or lithographic masks, which will simplify the process of material preparation and offer new ideas for the design and application of piezoelectric devices. Full article
Open AccessArticle Preparation and Tribological Study of Biodegradable Lubrication Films on Si Substrate
Materials 2015, 8(4), 1738-1751; doi:10.3390/ma8041738
Received: 30 January 2015 / Revised: 23 March 2015 / Accepted: 7 April 2015 / Published: 14 April 2015
Cited by 8 | PDF Full-text (3797 KB) | HTML Full-text | XML Full-text
Abstract
A novel method for preparing eco-biodegradable lubricant based on hydroxypropyl methylcellulose (HPMC) via hydration process is demonstrated. The smooth and homogeneous HPMC coating has a uniform thickness (~35 μm). It has been demonstrated that the preparation parameters play a critical role in controlling
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A novel method for preparing eco-biodegradable lubricant based on hydroxypropyl methylcellulose (HPMC) via hydration process is demonstrated. The smooth and homogeneous HPMC coating has a uniform thickness (~35 μm). It has been demonstrated that the preparation parameters play a critical role in controlling the lubricating behavior of the coating; in addition, excess HPMC and water concentration suppress the tribology properties. Nevertheless, a remarkable friction-reduction and anti-wear performance has been obtained. Impressively, the preparation parameter of 5% HPMC + 30 mL water significantly improves lubricant performance and durability. A simple approach for the water-degradability evaluation of HPMC is proposed. Full article
(This article belongs to the Special Issue Selected Papers from ICETI2014)
Open AccessArticle Spherical V-Fe-MCM-48: The Synthesis, Characterization and Hydrothermal Stability
Materials 2015, 8(4), 1752-1765; doi:10.3390/ma8041752
Received: 14 February 2015 / Revised: 30 March 2015 / Accepted: 31 March 2015 / Published: 14 April 2015
Cited by 5 | PDF Full-text (3981 KB) | HTML Full-text | XML Full-text
Abstract
Spherical MCM-48 mesoporous sieve co-doped with vanadium and iron was successfully synthesized via one-step hydrothermal method. The material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, inductively coupled plasma (ICP), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-vis spectra,
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Spherical MCM-48 mesoporous sieve co-doped with vanadium and iron was successfully synthesized via one-step hydrothermal method. The material was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, inductively coupled plasma (ICP), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV-vis spectra, and X-ray photoelectron spectra (XPS) techniques. Results indicated that the V-Fe-MCM-48 showed an ordered 3D cubic mesostructure with spherical morphology, narrow pore size distribution and high specific surface area. Most of vanadium and iron atoms existing as tetrahedral V4+ and Fe3+ species were co-doped into the silicate framework. The particle sizes of V-Fe-MCM-48 were smaller and the specific area was much higher than those of of V-MCM-48. Additionally, the synthesized V-Fe-MCM-48 exhibited improved hydrothermal stability compared with the pure MCM-48. Full article
(This article belongs to the Special Issue Advances in Mesoporous Material 2015)
Open AccessArticle Effect of Heat Treatment on the Physical Properties of Provisional Crowns during Polymerization: An in Vitro Study
Materials 2015, 8(4), 1766-1777; doi:10.3390/ma8041766
Received: 12 December 2014 / Revised: 2 April 2015 / Accepted: 7 April 2015 / Published: 15 April 2015
Cited by 1 | PDF Full-text (1980 KB) | HTML Full-text | XML Full-text
Abstract
This study concerned the effect of heat treatment during setting on the physical properties of four resin-based provisional restorative materials: Duralay (polymethyl methacrylate), Trim II (polyethyl methacrylate), Luxatemp (bis-acrylic composite), and Protemp 4 (bis-acrylic composite). Specimens were prepared at 23, 37, or 60
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This study concerned the effect of heat treatment during setting on the physical properties of four resin-based provisional restorative materials: Duralay (polymethyl methacrylate), Trim II (polyethyl methacrylate), Luxatemp (bis-acrylic composite), and Protemp 4 (bis-acrylic composite). Specimens were prepared at 23, 37, or 60 °C for evaluation of flexural strength, surface roughness, color change and marginal discrepancy. Flexural strength was determined by a three-point bending test. Surface profile was studied using atomic force microscopy. Color change was evaluated by comparing the color of the materials before and after placement in coffee. A travelling microscope helped prepare standardized crowns for assessment of marginal discrepancy. Flexural strength of all tested materials cured at 23 °C or 37 °C did not significantly change. The surface roughness and marginal discrepancy of the materials increased at 60 °C curing temperature. Marginal discrepancies, color stability, and other physical properties of materials cured at 23 °C or 37 °C did not significantly change. Flexural strength of certain provisional materials cured at 60 °C increased, but there was also an increase in surface roughness and marginal discrepancy. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessArticle Conductive Polymer Porous Film with Tunable Wettability and Adhesion
Materials 2015, 8(4), 1817-1830; doi:10.3390/ma8041817
Received: 7 January 2015 / Revised: 25 March 2015 / Accepted: 1 April 2015 / Published: 16 April 2015
Cited by 7 | PDF Full-text (2171 KB) | HTML Full-text | XML Full-text
Abstract
A conductive polymer porous film with tunable wettability and adhesion was fabricated by the chloroform solution of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid-methyl-ester (PCBM) via the freeze drying method. The porous film could be obtained from the solution of 0.8 wt%, whose pore diameters ranged
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A conductive polymer porous film with tunable wettability and adhesion was fabricated by the chloroform solution of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid-methyl-ester (PCBM) via the freeze drying method. The porous film could be obtained from the solution of 0.8 wt%, whose pore diameters ranged from 50 nm to 500 nm. The hydrophobic porous surface with a water contact angle (CA) of 144.7° could be transferred into a hydrophilic surface with CA of 25° by applying a voltage. The water adhesive force on the porous film increased with the increase of the external voltage. The electro-controllable wettability and adhesion of the porous film have potential application in manipulating liquid collection and transportation. Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
Open AccessArticle The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions
Materials 2015, 8(4), 1831-1840; doi:10.3390/ma8041831
Received: 30 January 2015 / Revised: 23 March 2015 / Accepted: 10 April 2015 / Published: 16 April 2015
Cited by 4 | PDF Full-text (1425 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was
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In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles. Full article
(This article belongs to the Special Issue Selected Papers from ICETI2014)
Open AccessArticle Collagen Fibrils in Skin Orient in the Direction of Applied Uniaxial Load in Proportion to Stress while Exhibiting Differential Strains around Hair Follicles
Materials 2015, 8(4), 1841-1857; doi:10.3390/ma8041841
Received: 4 March 2015 / Revised: 9 April 2015 / Accepted: 14 April 2015 / Published: 20 April 2015
Cited by 9 | PDF Full-text (1185 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast
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We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast Fourier Transforms (FFT) while strain inhomogeneity was determined at different distances from hair follicles using Digital Image Correlation (DIC). A parameter, defined as the Collagen Orientation Index (COI), is introduced that accounts for the increasingly ellipsoidal nature of the FFT amplitude images upon loading. We show that the COI demonstrates two distinct mechanical regimes, one at low strains (0%, 2.5%, 5% strain) in which randomly oriented collagen fibrils align in the direction of applied deformation. In the second regime, beginning at 5% strain, collagen fibrils elongate in response to applied deformation. Furthermore, the COI is also found to be linearly correlated with the applied stress indicating that collagen fibrils orient to take the applied load. DIC results indicated that major principal strains were found to increase with increased load at all locations. In contrast, minimum principal strain was dependent on distance from hair follicles. These findings are significant because global and local changes in collagen deformations are expected to be changed by disease, and could affect stem cell populations surrounding hair follicles, including mesenchymal stem cells within the outer root sheath. Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
Open AccessArticle Impact of Different Surface Ligands on the Optical Properties of PbS Quantum Dot Solids
Materials 2015, 8(4), 1858-1870; doi:10.3390/ma8041858
Received: 12 February 2015 / Revised: 7 April 2015 / Accepted: 9 April 2015 / Published: 21 April 2015
Cited by 16 | PDF Full-text (2858 KB) | HTML Full-text | XML Full-text
Abstract
The engineering of quantum dot solids with low defect concentrations and efficient carrier transport through a ligand strategy is crucial to achieve efficient quantum dot (QD) optoelectronic devices. Here, we study the consequences of various surface ligand treatments on the light emission properties
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The engineering of quantum dot solids with low defect concentrations and efficient carrier transport through a ligand strategy is crucial to achieve efficient quantum dot (QD) optoelectronic devices. Here, we study the consequences of various surface ligand treatments on the light emission properties of PbS quantum dot films using 1,3-benzenedithiol (1,3-BDT), 1,2-ethanedithiol (EDT), mercaptocarboxylic acids (MPA) and ammonium sulfide ((NH4)2S). We first investigate the influence of different ligand treatments on the inter-dot separation, which mainly determines the conductivity of the QD films. Then, through a combination of photoluminescence and transient photoluminescence characterization, we demonstrate that the radiative and non-radiative recombination mechanisms in the quantum dot films depend critically on the length and chemical structure of the surface ligands. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
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Open AccessArticle Additively Manufactured Open-Cell Porous Biomaterials Made from Six Different Space-Filling Unit Cells: The Mechanical and Morphological Properties
Materials 2015, 8(4), 1871-1896; doi:10.3390/ma8041871
Received: 18 January 2015 / Revised: 8 April 2015 / Accepted: 14 April 2015 / Published: 21 April 2015
Cited by 42 | PDF Full-text (3621 KB) | HTML Full-text | XML Full-text
Abstract
It is known that the mechanical properties of bone-mimicking porous biomaterials are a function of the morphological properties of the porous structure, including the configuration and size of the repeating unit cell from which they are made. However, the literature on this topic
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It is known that the mechanical properties of bone-mimicking porous biomaterials are a function of the morphological properties of the porous structure, including the configuration and size of the repeating unit cell from which they are made. However, the literature on this topic is limited, primarily because of the challenge in fabricating porous biomaterials with arbitrarily complex morphological designs. In the present work, we studied the relationship between relative density (RD) of porous Ti6Al4V EFI alloy and five compressive properties of the material, namely elastic gradient or modulus (Es20–70), first maximum stress, plateau stress, yield stress, and energy absorption. Porous structures with different RD and six different unit cell configurations (cubic (C), diamond (D), truncated cube (TC), truncated cuboctahedron (TCO), rhombic dodecahedron (RD), and rhombicuboctahedron (RCO)) were fabricated using selective laser melting. Each of the compressive properties increased with increase in RD, the relationship being of a power law type. Clear trends were seen in the influence of unit cell configuration and porosity on each of the compressive properties. For example, in terms of Es20–70, the structures may be divided into two groups: those that are stiff (comprising those made using C, TC, TCO, and RCO unit cell) and those that are compliant (comprising those made using D and RD unit cell). Full article
(This article belongs to the Special Issue Mechanics of Biomaterials) Printed Edition available
Open AccessArticle Setup of Extruded Cementitious Hollow Tubes as Containing/Releasing Devices in Self-Healing Systems
Materials 2015, 8(4), 1897-1923; doi:10.3390/ma8041897
Received: 27 February 2015 / Revised: 6 April 2015 / Accepted: 14 April 2015 / Published: 21 April 2015
Cited by 6 | PDF Full-text (3611 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this research is to produce self-healing cementitious composites based on the use of cylindrical capsules containing a repairing agent. Cementitious hollow tubes (CHT) having two different internal diameters (of 2 mm and 7.5 mm) were produced by extrusion and used
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The aim of this research is to produce self-healing cementitious composites based on the use of cylindrical capsules containing a repairing agent. Cementitious hollow tubes (CHT) having two different internal diameters (of 2 mm and 7.5 mm) were produced by extrusion and used as containers and releasing devices for cement paste/mortar healing agents. Based on the results of preliminary mechanical tests, sodium silicate was selected as the healing agent. The morphological features of several mix designs used to manufacture the extruded hollow tubes, as well as the coatings applied to increase the durability of both core and shell materials are discussed. Three-point bending tests were performed on samples produced with the addition of the above-mentioned cementitious hollow tubes to verify the self-healing effectiveness of the proposed solution. Promising results were achieved, in particular when tubes with a bigger diameter were used. In this case, a substantial strength and stiffness recovery was observed, even in specimens presenting large cracks (>1 mm). The method is inexpensive and simple to scale up; however, further research is needed in view of a final optimization. Full article
Open AccessArticle Three-Dimensional Imaging of Dislocations in a Ti–35mass%Nb Alloy by Electron Tomography
Materials 2015, 8(4), 1924-1933; doi:10.3390/ma8041924
Received: 5 January 2015 / Revised: 9 April 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
Cited by 1 | PDF Full-text (6857 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We have studied three-dimensional (3D) configurations of dislocations in the β phase of a Ti–35mass%Nb alloy by means of single-axis tilt tomography using bright-field scanning transmission electron microscopy (BF-STEM). To visualize dislocations, the hh0 systematic reflections were excited throughout tilt-series acquisition with
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We have studied three-dimensional (3D) configurations of dislocations in the β phase of a Ti–35mass%Nb alloy by means of single-axis tilt tomography using bright-field scanning transmission electron microscopy (BF-STEM). To visualize dislocations, the hh0 systematic reflections were excited throughout tilt-series acquisition with the maximum tilt angle of 70°. Dislocations in the β grains were clearly reconstructed by the weighted back-projection algorithm. The slip planes of the dislocations were deduced by rotating the reconstructed volumes with the aid of selected area electron diffraction patterns. It was found that BF-STEM images with relatively low contrasts, taken along low-order zone axes, are capable to reproduce and preserve the quality of reconstructed image of dislocations. We also found that tilt angles as low as 40° are practically acceptable to visualize 3D configurations of dislocations, while there exists limitation in resolution due to the existence of a large missing wedge. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle Flexural Behavior of HPFRCC Members with Inhomogeneous Material Properties
Materials 2015, 8(4), 1934-1950; doi:10.3390/ma8041934
Received: 30 January 2015 / Revised: 10 April 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
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Abstract
In this paper, the flexural behavior of High-performance Fiber-Reinforced Cementitious Composite (HPFRCC) has been investigated, especially focusing on the localization of cracks, which significantly governs the flexural behavior of HPFRCC members. From four points bending tests with HPFRCC members, it was observed that
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In this paper, the flexural behavior of High-performance Fiber-Reinforced Cementitious Composite (HPFRCC) has been investigated, especially focusing on the localization of cracks, which significantly governs the flexural behavior of HPFRCC members. From four points bending tests with HPFRCC members, it was observed that almost evenly distributed cracks formed gradually, followed by a localized crack that determined the failure of the members. In order to investigate the effect of a localized crack on the flexural behavior of HPFRCC members, an analytical procedure has been developed with the consideration of intrinsic inhomogeneous material properties of HPFRCC such as cracking and ultimate tensile strengths. From the comparison, while the predictions with homogeneous material properties overestimated flexural strength and ductility of HPFRCC members, it was found that the analysis results considering localization effect with inhomogeneous material properties showed good agreement with the test results, not only the flexural strength and ductility but also the crack widths. The test results and the developed analysis procedure presented in this paper can be usefully applied for the prediction of flexural behaviors of HPFRCC members by considering the effect of localized cracking behavior. Full article
(This article belongs to the Section Advanced Composites)
Open AccessArticle Gas Permeation Properties of Soluble Aromatic Polyimides Based on 4-Fluoro-4,4'-Diaminotriphenylmethane
Materials 2015, 8(4), 1951-1965; doi:10.3390/ma8041951
Received: 26 January 2015 / Revised: 26 March 2015 / Accepted: 9 April 2015 / Published: 21 April 2015
Cited by 4 | PDF Full-text (415 KB) | HTML Full-text | XML Full-text
Abstract
A series of new organic polyimides were synthesized from 4-fluoro-4'4"-diaminotriphenylmethane and four different aromatic dianhydrides through a one-step, high-temperature, direct polycondensation in m-cresol at 180–200 °C, resulting in the formation of high-molecular-weight polyimides (inherent viscosities ~ 1.0–1.3 dL/g). All the resulting polyimides exhibited
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A series of new organic polyimides were synthesized from 4-fluoro-4'4"-diaminotriphenylmethane and four different aromatic dianhydrides through a one-step, high-temperature, direct polycondensation in m-cresol at 180–200 °C, resulting in the formation of high-molecular-weight polyimides (inherent viscosities ~ 1.0–1.3 dL/g). All the resulting polyimides exhibited good thermal stability with initial decomposition temperatures above 434 °C, glass-transition temperatures between 285 and 316 °C, and good solubility in polar aprotic solvents. Wide-angle X-ray scattering data indicated that the polyimides were amorphous. Dense membranes were prepared by solution casting and solvent evaporation to evaluate their gas transport properties (permeability, diffusivity, and solubility coefficients) toward pure hydrogen, helium, oxygen, nitrogen, methane, and carbon dioxide gases. In general, the gas permeability was increased as both the fractional free volume and d-spacing were also increased. A good combination of permeability and selectivity was promoted efficiently by the bulky hexafluoroisopropylidene and 4-fluoro-phenyl groups introduced into the polyimides. The results indicate that the gas transport properties of these films depend on both the structure of the anhydride moiety, which controls the intrinsic intramolecular rigidity, and the 4-fluoro-phenyl pendant group, which disrupts the intermolecular packing. Full article
(This article belongs to the Section Energy Materials)
Open AccessArticle Modification of pH Conferring Virucidal Activity on Dental Alginates
Materials 2015, 8(4), 1966-1975; doi:10.3390/ma8041966
Received: 13 February 2015 / Revised: 26 March 2015 / Accepted: 13 April 2015 / Published: 21 April 2015
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Abstract
To formulate an alginate dental impression material with virucidal properties, experimental alginate dental impression materials were developed and the formulations adjusted in order to study the effect on pH profiles during setting. Commercially available materials served as a comparison. Eight experimental materials were
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To formulate an alginate dental impression material with virucidal properties, experimental alginate dental impression materials were developed and the formulations adjusted in order to study the effect on pH profiles during setting. Commercially available materials served as a comparison. Eight experimental materials were tested for antiviral activity against Herpes Simplex Virus type 1 (HSV-1). Changing the amount of magnesium oxide (MgO) used in the experimental formulations had a marked effect on pH. Increasing MgO concentration corresponded with increased pH values. All experimental materials brought about viral log reductions ranging between 0.5 and 4.0 over a period of 4 h. The material with the lowest pH was the most effective. The current work highlights the very important role of MgO in controlling pH profiles. This knowledge has been applied to the formulation of experimental alginates; where materials with pH values of approximately 4.2–4.4 are able to achieve a significant log reduction when assayed against HSV-1. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessArticle Properties of Exchange Coupled All-garnet Magneto-Optic Thin Film Multilayer Structures
Materials 2015, 8(4), 1976-1992; doi:10.3390/ma8041976
Received: 3 February 2015 / Revised: 13 April 2015 / Accepted: 15 April 2015 / Published: 21 April 2015
PDF Full-text (2510 KB) | HTML Full-text | XML Full-text
Abstract
The effects of exchange coupling on magnetic switching properties of all-garnet multilayer thin film structures are investigated. All-garnet structures are fabricated by sandwiching a magneto-soft material of composition type Bi1.8Lu1.2Fe3.6Al1.4O12 or Bi3Fe
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The effects of exchange coupling on magnetic switching properties of all-garnet multilayer thin film structures are investigated. All-garnet structures are fabricated by sandwiching a magneto-soft material of composition type Bi1.8Lu1.2Fe3.6Al1.4O12 or Bi3Fe5O12:Dy2O3 in between two magneto-hard garnet material layers of composition type Bi2Dy1Fe4Ga1O12 or Bi2Dy1Fe4Ga1O12:Bi2O3. The fabricated RF magnetron sputtered exchange-coupled all-garnet multilayers demonstrate a very attractive combination of magnetic properties, and are of interest for emerging applications in optical sensors and isolators, ultrafast nanophotonics and magneto-plasmonics. An unconventional type of magnetic hysteresis behavior not observed previously in magnetic garnet thin films is reported and discussed. Full article
Open AccessArticle Crystal Quality and Light Output Power of GaN-Based LEDs Grown on Concave Patterned Sapphire Substrate
Materials 2015, 8(4), 1993-1999; doi:10.3390/ma8041993
Received: 17 February 2015 / Revised: 8 April 2015 / Accepted: 10 April 2015 / Published: 22 April 2015
Cited by 2 | PDF Full-text (2029 KB) | HTML Full-text | XML Full-text
Abstract
The crystal quality and light output power of GaN-based light-emitting diodes (LEDs) grown on concave patterned sapphire substrate (CPSS) were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage
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The crystal quality and light output power of GaN-based light-emitting diodes (LEDs) grown on concave patterned sapphire substrate (CPSS) were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage of c-plane). However, when the pattern space decreased to 0.41 μm (S0.41-GaN), the GaN crystallinity dropped. On the other hand, the light output power of GaN-based LEDs was increased with the decrease of the pattern space due to the change of the light extraction efficiency. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
Open AccessArticle Evaluation of Contact Heat Transfer Coefficient and Phase Transformation during Hot Stamping of a Hat-Type Part
Materials 2015, 8(4), 2030-2042; doi:10.3390/ma8042030
Received: 21 January 2015 / Revised: 16 April 2015 / Accepted: 17 April 2015 / Published: 22 April 2015
Cited by 2 | PDF Full-text (2227 KB) | HTML Full-text | XML Full-text
Abstract
Using an inverse analysis technique, the heat transfer coefficient on the die-workpiece contact surface of a hot stamping process was evaluated as a power law function of contact pressure. This evaluation was to determine whether the heat transfer coefficient on the contact surface
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Using an inverse analysis technique, the heat transfer coefficient on the die-workpiece contact surface of a hot stamping process was evaluated as a power law function of contact pressure. This evaluation was to determine whether the heat transfer coefficient on the contact surface could be used for finite element analysis of the entire hot stamping process. By comparing results of the finite element analysis and experimental measurements of the phase transformation, an evaluation was performed to determine whether the obtained heat transfer coefficient function could provide reasonable finite element prediction for workpiece properties affected by the hot stamping process. Full article
(This article belongs to the Section Manufacturing Processes and Systems)

Review

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Open AccessReview Heterogeneous Catalysis of Polyoxometalate Based Organic–Inorganic Hybrids
Materials 2015, 8(4), 1545-1567; doi:10.3390/ma8041545
Received: 5 January 2015 / Revised: 8 March 2015 / Accepted: 25 March 2015 / Published: 31 March 2015
Cited by 24 | PDF Full-text (3077 KB) | HTML Full-text | XML Full-text
Abstract
Organic–inorganic hybrid polyoxometalate (POM) compounds are a subset of materials with unique structures and physical/chemical properties. The combination of metal-organic coordination complexes with classical POMs not only provides a powerful way to gain multifarious new compounds but also affords a new method to
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Organic–inorganic hybrid polyoxometalate (POM) compounds are a subset of materials with unique structures and physical/chemical properties. The combination of metal-organic coordination complexes with classical POMs not only provides a powerful way to gain multifarious new compounds but also affords a new method to modify and functionalize POMs. In parallel with the many reports on the synthesis and structure of new hybrid POM compounds, the application of these compounds for heterogeneous catalysis has also attracted considerable attention. The hybrid POM compounds show noteworthy catalytic performance in acid, oxidation, and even in asymmetric catalytic reactions. This review summarizes the design and synthesis of organic–inorganic hybrid POM compounds and particularly highlights their recent progress in heterogeneous catalysis. Full article
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Open AccessReview Nanophotonics: Energy Transfer towards Enhanced Luminescent Chemosensing
Materials 2015, 8(4), 1682-1703; doi:10.3390/ma8041682
Received: 9 January 2015 / Revised: 24 March 2015 / Accepted: 30 March 2015 / Published: 13 April 2015
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Abstract
We discuss a recently proposed novel photonic approach for enhancing the fluorescence of extremely thin chemosensing polymer layers. We present theoretical and experimental results demonstrating the concept of gain-assisted waveguided energy transfer (G-WET) on a very thin polymer nanolayer spincoated on an active
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We discuss a recently proposed novel photonic approach for enhancing the fluorescence of extremely thin chemosensing polymer layers. We present theoretical and experimental results demonstrating the concept of gain-assisted waveguided energy transfer (G-WET) on a very thin polymer nanolayer spincoated on an active ZnO thin film. The G-WET approach is shown to result in an 8-fold increase in polymer fluorescence. We then extend the G-WET concept to nanostructured media. The benefits of using active nanostructured substrates on the sensitivity and fluorescence of chemosensing polymers are discussed. Preliminary theoretical results on enlarged sensing surface and photonic band-gap are presented. Full article
(This article belongs to the Special Issue Luminescent Materials and Devices)
Open AccessReview Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers
Materials 2015, 8(4), 1778-1816; doi:10.3390/ma8041778
Received: 20 January 2015 / Revised: 24 March 2015 / Accepted: 27 March 2015 / Published: 15 April 2015
Cited by 9 | PDF Full-text (871 KB) | HTML Full-text | XML Full-text
Abstract
Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily
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Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration. Full article
(This article belongs to the Special Issue Dental Materials)
Open AccessReview Misfit Layer Compounds and Ferecrystals: Model Systems for Thermoelectric Nanocomposites
Materials 2015, 8(4), 2000-2029; doi:10.3390/ma8042000
Received: 6 February 2015 / Revised: 3 April 2015 / Accepted: 7 April 2015 / Published: 22 April 2015
Cited by 13 | PDF Full-text (4023 KB) | HTML Full-text | XML Full-text
Abstract
A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by
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A basic summary of thermoelectric principles is presented in a historical context, following the evolution of the field from initial discovery to modern day high-zT materials. A specific focus is placed on nanocomposite materials as a means to solve the challenges presented by the contradictory material requirements necessary for efficient thermal energy harvest. Misfit layer compounds are highlighted as an example of a highly ordered anisotropic nanocomposite system. Their layered structure provides the opportunity to use multiple constituents for improved thermoelectric performance, through both enhanced phonon scattering at interfaces and through electronic interactions between the constituents. Recently, a class of metastable, turbostratically-disordered misfit layer compounds has been synthesized using a kinetically controlled approach with low reaction temperatures. The kinetically stabilized structures can be prepared with a variety of constituent ratios and layering schemes, providing an avenue to systematically understand structure-function relationships not possible in the thermodynamic compounds. We summarize the work that has been done to date on these materials. The observed turbostratic disorder has been shown to result in extremely low cross plane thermal conductivity and in plane thermal conductivities that are also very small, suggesting the structural motif could be attractive as thermoelectric materials if the power factor could be improved. The first 10 compounds in the [(PbSe)1+δ]m(TiSe2)n family (m, n ≤ 3) are reported as a case study. As n increases, the magnitude of the Seebeck coefficient is significantly increased without a simultaneous decrease in the in-plane electrical conductivity, resulting in an improved thermoelectric power factor. Full article
(This article belongs to the Special Issue Low-Dimensional Anisotropic Thermoelectrics)
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