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  • Correlation between mechanical properties and microscopic structures of an optimized silica fraction in silicone rubber
    Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-07-19
    Dong Liu, Lixian Song, Hongtao Song, Jie Chen, Qiang Tian, Liang Chen, Liangwei Sun, Ai Lu, Chaoqiang Huang, Guangai Sun

    The mechanical properties and the hierarchical filler structures were characterized on a series silica-filled silicone rubber with a filler fraction (ΦSi) varied from 0.05 phr to 80 phr (parts per hundred rubber). Uniaxial elongation measurement suggests that there is a percolation threshold between 10 and 30 phr. Moreover, an optimum ΦSi range from 40 phr to 50 phr is found, in which the best mechanical performances of reinforcement are shown. The microscopic structures were crosschecked by small-angle neutron scattering (SANS) and scanning electron microscopy (SEM). The effects of the ΦSi and the fabrication process on the morphology of samples are unveiled. The correlation length among aggregates extracted from SANS data a monotonically decrease from 237.0 nm to 136.5 nm with increasing the ΦSi from 30 phr to 80 phr. The average radius of gyration of aggregates 〈Rg,agg〉 fitted with the Beaucage model monotonically decrease from 49.2 nm to 37.5 nm with increasing ΦSi from 10 phr to 80 phr. Providing a 10 nm thickness bound rubber as bridge, samples with optimum ΦSi yield a morphology that the radii of aggregates and the gap filled with polymer matrix in between are equivalent as both around 60 nm.

    更新日期:2018-07-20
  • Facile fabrication of POSS-Modified MoS2/PMMA nanocomposites with enhanced thermal, mechanical and optical limiting properties
    Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-07-19
    Qiaobo Liao, Qi Zhang, Xuelin Wang, Xinle Li, Guoqing Deng, Zhen Meng, Kai Xi, Peng Zhan

    A facile strategy was applied to transfer chemically exfoliated molybdenum disulphide (MoS2) nanosheets from aqueous medium to organic solvents. The MoS2 nanosheets were then modified by trisilanol-phenyl-POSS (T7POSS) which was confirmed by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and Powder X-Ray Diffraction (PXRD). The modified MoS2 nanosheets were then incorporated into poly (methyl methacrylate) (PMMA) via a simple solution blending method. The Scanning Electron Microscope (SEM) and Transmission electron microscope (TEM) were employed to demonstrate the well-dispersion of nanosheets in polymeric matrix. Compared to neat PMMA, the decomposition temperatures (Td) and the half weight decomposition temperatures (Thalf) of POSS-MoS2/PMMA nanocomposites at nanosheets concentration of 0.2 wt% were dramatically increased by 35.2 °C and 35.3 °C, respectively. Meanwhile, according to the measurements of Dynamic Mechanical Analysis (DMA), the storage modulus at 30 °C is significantly improved by 5.2 times and the glass transition temperature (Tg) is also enhanced by 6.2 °C. Remarkably, POSS-MoS2/PMMA nanocomposites possess low optical limiting differential transmittance Tc (0.5%), low nonlinear optical absorption onset threshold FON (0.02 J cm−2), low optical limiting threshold FOL (0.4 J cm−2) and high nonlinear coefficient β (297 cm GW−1), highlighting their vast potential in the development of solid-state optical limiting materials.

    更新日期:2018-07-20
  • Self-assembling diphenylalanine peptide nanotubes selectively eradicate bacterial biofilm infection
    Acta Biomater. (IF 6.383) Pub Date : 2018-07-19
    Simon L. Porter, Sophie M. Coulter, Sreekanth Pentlavalli, Thomas P. Thompson, Garry Laverty

    Biofilms present a major problem to industry and healthcare worldwide. Composed of a population of surface-attached microbial cells surrounded by a protective extracellular polysaccharide matrix, they are responsible for increased tolerance to antibiotics, treatment failure and a resulting rise in antimicrobial resistance. Here we demonstrate that self-assembled peptide nanostructures composed of a diphenylalanine motif provide sufficient antibacterial activity to eradicate mature biofilm forms of bacteria widely implicated in hospital infections. Modification of terminal functional groups to amino (-NH2), carboxylic acid (-COOH) or both modalities, and switch to d-isomers, resulted in changes in antibacterial selectivity and mammalian cell toxicity profiles. Of the three peptide nanotubes structures studied (NH2-FF-COOH, NH2-ff-COOH and NH2-FF-NH2), NH2-FF-COOH demonstrated the most potent activity against both planktonic (liquid, free-floating) and biofilm forms of bacteria, possessing minimal mammalian cell toxicity. NH2-FF-COOH resulted in greater than 3 Log10 CFU/mL viable biofilm reduction (>99.9%) at 5 mg/mL and total biofilm kill at 10 mg/mL against Staphylococcus aureus after 24 hours exposure. Scanning electron microscopy proved that antibiofilm activity was primarily due to the formation of ion channels and/or surfactant-like action, with NH2-FF-COOH and NH2-ff-COOH capable of degrading the biofilm matrix and disrupting cell membranes, leading to cell death in Gram-positive bacterial isolates. Peptide-based nanotubes are an exciting platform for drug delivery and engineering applications. This is the first report of using peptide nanotubes to eradicate bacterial biofilms and provides evidence of a new platform that may alleviate their negative impact throughout society.Statement of significanceWe outline, for the first time, the antibiofilm activity of diphenylalanine (FF) peptide nanotubes. Biofilm bacteria exhibit high tolerance to antimicrobials 10-10,000 times that of free-flowing planktonic forms. Biofilm infections are difficult to treat using conventional antimicrobial agents, leading to a rise in antimicrobial resistance. We discovered nanotubes composed of NH2-FF-COOH demonstrated potent activity against staphylococcal biofilms implicated in hospital infections, resulting in complete kill at concentrations of 10 mg/mL. Carboxylic acid terminated FF nanotubes were able to destroy the exopolysaccharide architecture of staphylococcal biofilms expressing minimal toxicity highlighting their potential for use in patients, whilst amidated (NH2-FF-NH2) forms demonstrated reduced antibiofilm efficacy and significant toxicity. These results contribute significantly to the development of innovative antibacterial technologies and peptide nanomaterials.

    更新日期:2018-07-20
  • Functionally graded multilayer scaffolds for in vivo osteochondral tissue engineering
    Acta Biomater. (IF 6.383) Pub Date : 2018-07-19
    Heemin Kang, Yuze Zeng, Shyni Varghese

    Osteochondral tissue repair remains a significant challenge in orthopedic surgery. Tissue engineering of osteochondral tissue has transpired as a potential therapeutic solution as it can effectively regenerate bone, cartilage, and the bone-cartilage interface. While advancements in scaffold fabrication and stem cell engineering have made significant progress towards the engineering of composite tissues, such as osteochondral tissue, new approaches are required to improve the outcome of such strategies. Herein, we discuss the use of a single-unit trilayer scaffold with depth-varying pore architecture and mineral environment to engineer osteochondral tissues in vivo. The trilayer scaffold includes a biomineralized bottom layer mimicking the calcium phosphate (CaP)-rich bone microenvironment, a cryogel middle layer with anisotropic pore architecture, and a hydrogel top layer. The mineralized bottom layer was designed to support bone formation, while the macroporous middle layer and hydrogel top layer were designed to support cartilage tissue formation. The bottom layer was kept acellular and the top two layers were loaded with cells prior to implantation. When implanted in vivo, these trilayer scaffolds resulted in the formation of osteochondral tissue with a lubricin-rich cartilage surface. The osteochondral tissue formation was a result of continuous differentiation of the transplanted cells to form cartilage tissue and recruitment of endogenous cells through the mineralized bottom layer to form bone tissue. Our results suggest that integrating exogenous cell-based cartilage tissue engineering along with scaffold-driven in situ bone tissue engineering could be a powerful approach to engineer analogs of osteochondral tissue. In addition to offering new therapeutic opportunities, such approaches and systems could also advance our fundamental understanding of osteochondral tissue regeneration and repair.Statement of SignificanceIn this work, we describe the use of a single-unit trilayer scaffold with depth-varying pore architecture and mineral environment to engineer osteochondral tissues in vivo. The trilayer scaffold was designed to support continued differentiation of the donor cells to form cartilage tissue while supporting bone formation through recruitment of endogenous cells. When implanted in vivo, these trilayer scaffolds partially loaded with cells resulted in the formation of osteochondral tissue with a lubricin-rich cartilage surface. Approaches such as the one presented here that integrates ex vivo tissue engineering along with endochondral cell-mediated tissue engineering can have a significant impact in tissue engineering composite tissues with diverse cell populations and functionality.

    更新日期:2018-07-20
  • An immunopotentiator, ophiopogonin D, encapsulated in a nanoemulsion as a robust adjuvant to improve vaccine efficacy
    Acta Biomater. (IF 6.383) Pub Date : 2018-07-19
    Ya-nan Tong, Liu-yang Yang, Yun Yang, Zhen Song, Liu-sheng Peng, Ji-ning Gao, Hao Zeng, Quan-ming Zou, Hong-wu Sun, Xuhu Mao

    As an ingredient of vaccines, adjuvants are indispensable for enhancing and directly inducing robust and extensive adaptive immune responses associated with vaccine antigens. In this study, we initially determined that a new molecular immunopotentiator, ophiopogonin D (OP-D), enhanced the antibody response to antigen. Because OP-D has certain disadvantages, including poor solubility, we next encapsulated OP-D in a nanoemulsion adjuvant (nanoemulsion-encapsulated OP-D, NOD) using low-energy emulsification methods. The NOD thus produced was small, with an average size of 76.45 nm, and exhibited good distribution (PdI value 0.16), significantly increasing the solubility of OP-D. Furthermore, NOD exhibited reduced cellular toxicity and acute toxicity. Our results showed that a fusion antigen of MRSA (HlaH35LIsdB348-465) formulated with NOD significantly improved humoral and cellular immune responses compared to those observed in the antigen/OP-D and antigen/AlPO4 groups. Compared with antigen/OP-D, the antigen formulated with NOD more effectively promoted antigen uptake by dendritic cells (DCs) and the activation of antigen-presenting cells (APCs). Moreover, the NOD-formulated antigen had ideal protective efficacy in a MRSA sepsis model by inducing more potent antibody responses and a Th1/Th17-biased CD4+ T cell immune response. Therefore, these results suggest that NOD is a promising and robust adjuvant platform for a MRSA vaccine.Statement of SignificanceThe importance of adjuvants to new generation vaccines can be compared with the Prometheus Fire for humans. We first identified a new powerful immunopotentiator, Ophiopogonin D, among dozens of natural products and then used nanotechnology to construct a highly efficient and low toxic adjuvant system (NOD). Our approach intersects natural medicinal chemistry, nanomaterials and immunology, revealing that a strong adjuvant activity of this adjuvant system was verified in vitro and in vivo, and the application of MRSA subunit vaccine model for survival experiments achieved a 100% protection rate. This research illustrate that NOD is a promising and robust adjuvant platform for subunit vaccines.

    更新日期:2018-07-20
  • Review of potential health risks associated with nanoscopic calcium phosphate
    Acta Biomater. (IF 6.383) Pub Date : 2018-07-19
    Matthias Epple

    Calcium phosphate is applied in many products in biomedicine, but also in toothpastes and cosmetics. In some cases, it is present in nanoparticulate form, either on purpose or after degradation or mechanical abrasion. Possible concerns are related to the biological effect of such nanoparticles. A thorough literature review shows that calcium phosphate nanoparticles as such have no inherent toxicity but can lead to an increase of the intracellular calcium concentration after endosomal uptake and lysosomal degradation. However, cells are able to clear the calcium from the cytoplasm within a few hours, unless very high doses of calcium phosphate are applied. The observed cytotoxicity in some cell culture studies, mainly for unfunctionalized particles, is probably due to particle agglomeration and subsequent sedimentation onto the cell layer, leading to a very high local particle concentration, a high particle uptake, and subsequent cell death. There is no risk from an oral uptake of calcium phosphate nanoparticles due to their rapid dissolution in the stomach. The risk from dermal or mucosal uptake is very low. Calcium phosphate nanoparticles can enter the bloodstream by inhalation, but no adverse effects have been observed, except for a prolonged exposition to high particle doses. Calcium phosphate nanoparticles inside the body (e.g. after implantation or due to abrasion) do not pose a risk as they are typically resorbed and dissolved by osteoclasts and macrophages. There is no indication for a significant influence of the calcium phosphate phase or the particle shape (e.g. spherical or rod-like) on the biological response. In summary, the risk associated with an exposition to nanoparticulate calcium phosphate in doses that are usually applied in biomedicine, health care products, and cosmetics is very low and most likely not present at all.Statement of significanceCalcium phosphate is a well-established biomaterial. However, there are occasions when it occurs in a nanoparticulate form (e.g. as nanoparticle or as nanoparticulate bone substitution material) or after abrasion from a calcium phosphate-coated metal implant. In the light of the current discussion on the safety of nanoparticles, there have been concerns about potential adverse effects of nano-calcium phosphate, e.g. in a statement of a EU study group from 2016 about possible dangers associated with non-spherical nano-hydroxyapatite in cosmetics. In the US, there was a discussion in 2016 about the dangers of nano-calcium phosphate in babyfood.In this review, the potential exposition routes for nano-calcium phosphate are reviewed, with special emphasis on its application as biomaterial.

    更新日期:2018-07-20
  • Nitrogen-doped graphene and graphene quantum dots: A review onsynthesis and applications in energy, sensors and environment
    Adv. Colloid Interface Sci. (IF 7.346) Pub Date : 2018-07-19
    Manpreet Kaur, Manmeet Kaur, Virender K. Sharma

    Doping of nitrogen is a promising strategy to modulate chemical, electronic, and structural functionalities of graphene (G)and graphene quantum dots (GQDs) for their outstanding properties in energy and environmental applications.This paper reviews various synthesis approaches of nitrogen-doped graphene (N-G) and nitrogen-doped graphene quantum dots (N-GQDs).;Thermal, ultrasonic, solvothermal, hydrothermal, and electron-beam methods have been applied to synthesize N-G and N-GQDs.These nitrogen-doped carbon materials are characterized to obtain their structural configurations in order to achieve better performance in their applications compared to only either graphene or graphene quantum dots.Both N-G and N-GQDs may be converted into functional materials by integrating with other compounds such as metal oxides/nitrides, polymers, and semiconductors.These functional materials demonstrate superior performance over N-G and N-GQDs materials.Examples of applications of N-G and N-GQDs include supercapacitors, batteries, sensors, fuel cells, solar cells, and photocatalyst.

    更新日期:2018-07-20
  • Spray Assisted Layer-by-Layer Assembled One-Bilayer Polyelectrolyte Reverse Osmosis Membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-19
    Qiang Li, George Q. Chen, Liang Liu, Sandra E. Kentish

    A single-bilayer polyelectrolyte reverse osmosis membrane was fabricated by a spray assisted layer-by-layer assembly approach using a polysulfone ultrafiltration membrane as a substrate, polyethyleneimine (PEI) as an adhesion promoter, poly(allylamine hydrochloride) (PAH) and poly(sodium-4-styrene sulfonate) (PSS) as polycation and polyanion, glutaraldehyde as a crosslinker and Pluronic F127 amphiphilic triblock copolymer as a surface modifier. The resulting active layer is ultrathin (ca. 70 nm) and has a flat, dense and uncharged surface in neutral solution. The salt rejection and permeate flux of the membrane gradually increases from 92% to 94%, and 11 L/m2h to 30 L/m2h respectively for a 2 g/L NaCl feed solution as the operating pressure increased from 1.6 MPa to 4.0 MPa. Additionally, the membrane shows good separation performance stability and protein fouling resistance using bovine serum albumin as a foulant model. The glutaradehyde plays a key role in enhancing salt rejection by forming imine bonds within the PEI layer and the PEI/PAH interlayer. The Pluronic F127 surface modifier improves the permeate flux due to its hydrophilicity and the resulting induced swelling providing channels for water flow. Further, the “brush-like” structure of the hydrophilic polyethylene oxide moieties on the membrane surface improves fouling resistance.

    更新日期:2018-07-20
  • Diamond nanothread-based 2D and 3D materials: Diamond nanomeshes and nanofoams
    Carbon (IF 7.082) Pub Date : 2018-07-19
    Julian F.R.V. Silveira, Andre R. Muniz

    Diamond nanothreads (DNTs) are one-dimensional, fully sp3-bonded carbon nanostructures resulting of covalent bonding between stacked benzene molecules in a crystal, induced by application of high pressure, as demonstrated in experiments. In this work, we used classical Molecular Dynamics simulations to propose the synthesis of analogous two- and three-dimensional porous nanostructures, which we named diamond nanomeshes (DNM) and diamond nanofoams (DNF), consistently to the definition of DNTs, and computed some of their structural and mechanical properties. Two different approaches toward creation of such materials are proposed. One of them consists in interconnecting finite domains of conventional DNTs, achieved through partial surface dehydrogenation and subsequent C-C covalent bonding. The other approach considers that the formation of sp3 C-C bonds between stacked benzene molecules under high pressure could be extended to polycyclic aromatic hydrocarbon (PAH) molecules, generating crosslinked DNT-like structures. Different atomic configurations can be achieved by varying the morphology of DNTs used in their construction, the PAH molecules, and the nature of the DNT covalent interconnections. The resulting materials exhibit an interesting combination of mechanical strength, flexibility, lightness, high porosity and high specific surface area, enabling potential applications in reinforced nanocomposites, gas storage/separation, sensors, among others.

    更新日期:2018-07-20
  • Numerical simulation of flow behavior of top-gas jet in a gas-particles bubbling fluidized bed
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    Wang Lin, Qi Guoli, Li Zhenjie, Liu Songsong, Muhammad Hassan, Lu Huilin

    Flow behavior of top-gas jet and particles is simulated by means of gas-solids two-fluid model incorporating the kinetic theory of granular flow (KTGF) in a top-gas jet bubbling fluidized bed. The RNG k-ε model is used to model gas turbulence of the top-gas jet. The effects of the top-jet gas velocity and fluidizing gas velocity on distributions of volume fractions and velocities of gas and particles are evaluated, and the results are quantified in terms of top-gas jet penetration length. Numerical simulations show that the fluidized gas-particle mixture along bed height is divided into three regions as (a) the top-gas jet region in the freeboard, (b) the concentrating region near the bed surface and (c) the diluting region near the bottom in terms of the axial distribution of solids volume fraction. By increasing the top-jet gas velocity, particles circulate through the down-flow at the center from the concentrating region to the diluting region and the up-flow near the walls from bottom to bed surface along bed height. The distributions of volume fraction and velocity of gas and particles considerably change with the variation of top-jet gas velocities. Moreover, the top-gas jet penetration length with the change of top-jet gas velocity and fluidizing gas velocity is identified and discussed.

    更新日期:2018-07-20
  • Microwave heating of magnesium silicate minerals
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    J. Forster, Y. Maham, E.R. Bobicki

    Worldwide high-grade nickel sulphide deposits are being depleted and new ones are not being discovered. Therefore, the exploitation of low-grade ultramafic nickel ores is of increasing interest. Processing these deposits, however, is a challenge, due to the high serpentine content. Serpentine minerals are anisotropic, increase the viscosity of ore slurries, dilute the concentrate, and slime-coat the valuable nickel mineral pentlandite. Microwave pre-treatment of ultramafic nickel ores has been proposed to convert the serpentine to olivine, reduce the viscosity of the ore slurry, improve ore grindability and mineral liberation, and reduce the overall energy requirements of processing. To optimize the process, an understanding of the microwave heating properties of ultramafic nickel ores and constituent minerals is necessary. The microwave heating of serpentine and olivine, the primary components of ultramafic nickel ores, is explored in this paper. Microwave heating tests and high-temperature microwave properties (real and imaginary permittivity) analysis were performed. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests were also completed to explain the permittivity data. Serpentine responded more readily to microwaves than olivine and the maximum temperatures achieved were 216 °C and 57 °C, respectively. Serpentine did not reach the temperature required for dehydroxylation (600-700 °C). The real and imaginary permittivities for serpentine and olivine varied with temperature, but overall were low, indicating these minerals cannot be expected to heat well on their own upon exposure to microwave radiation. A microwave susceptor is required for the serpentine in ultramafic nickel ores to reach dehydroxylation temperatures. It is hypothesized that the small quantities of pyrrhotite and magnetite present in ultramafic ores play this role.

    更新日期:2018-07-20
  • Experimental and computational investigation of segregation during tumblers unloading
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    S. Volpato, L. Scanferla, A.C. Santomaso

    Dry mixing is a common operation in many industrial processes. The unloading of the mixer is an essential aspect of the process which actively contributes to the final quality of the mixture. Its effect however is often underestimate or even ignored. In the present work the consequences of the unloading process on mixture quality were investigated in three different types of tumbling mixers: a symmetric double cone, an asymmetric double cone and a conic mixer were considered. The symmetric double cone mixer is a standard geometry in the pharmaceutical industry, while the other two geometries are unconventional. The effects of mixer geometry on the mixture quality were studied and related to differences in the unloading flow patterns. A segregating polydispersed mixture was used during the experiments in order to emphasize the different performances of the three tumblers. Additional quasi-2D experiments and FEM simulation of the unloading process clearly showed the ability of the unconventional geometries to mitigate the effect of segregation improving the mixture quality evaluated at the outlet of the mixer.

    更新日期:2018-07-20
  • Particle scale modelling of solid flow characteristics in liquid fluidizations of ellipsoidal particles
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    E. Abbaszadeh Molaei, A.B. Yu, Z.Y. Zhou

    Particle shape is one of the most important parameters that can cause significant changes of flow characteristics in liquid fluidized beds, which however has not been well studied in the past. In this work, CFD-DEM approach is used to investigate the hydrodynamics of ellipsoidal particles in liquid fluidizations. The non-uniformity distributions of pressure gradient and porosity with bed height are successfully captured for ellipsoids at high liquid superficial velocities, consistent with those reported in literature. The results also show that ellipsoids intend to enter the freeboard region and entrainment may occur. Disc-shape particles expand more significantly than spherical and elongated particles. The force analysis indicates that with particle aspect ratio deviating from 1.0, the drag force acting on ellipsoids increases while pressure gradient force reduces. Particle shape effects shown above are closely related to particle orientations which can significantly affect particle-fluid interaction force and particle terminal velocities.

    更新日期:2018-07-20
  • Random forest regression prediction of solid particle Erosion in elbows
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    Peyman Zahedi, Saeid Parvandeh, Alireza Asgharpour, Brenton S. McLaury, Siamack A. Shirazi, Brett A. McKinney

    Solid particle erosion is an inevitable problem in oil and gas production and transportation systems, and it can cause severe damage in pipe fittings in which the flow direction changes suddenly. Erosion occurs in a variety of fittings, and one common fitting which is one of the most vulnerable to erosion is the elbow. Repair and/or replacement of pipe fittings in the appropriate period can avoid catastrophic disasters such as hydrocarbon release events. Therefore, accurate prediction of erosion is a subject of interest for the oil and gas industry. Both experimental and modeling approaches have been conducted in the past under different flow conditions and materials. The goal of this study is to use relevant experimental parameters as predictor variables and utilize a machine learning algorithm to predict erosion rate and validate the prediction under different conditions with test data. It is assumed that important parameters in erosion magnitude are material characteristics, pipe diameter, particles properties and size and carrier fluid properties. 201 experimental data points with a broad range of conditions were selected for the analysis. Predicted erosion rates through different machine learning techniques were compared, and Random Forest regression model was selected as an effective and alternative approach for erosion prediction. This method was examined on data points and compared with experimental results. Good agreement was observed in this method with experiments which provides the framework for a new way to predict solid particle erosion which is simpler yet accurate in comparison with available prediction models.

    更新日期:2018-07-20
  • Effect of dodecylamine-frother blend on bubble rising characteristics
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    Hongzheng Zhu, Alejandro López Valdivieso, Jinbo Zhu, Fanfei Min, Shaoxian Song, Dianqiang Huang, Shanmin Shao

    Bubble aspect ratios and rising velocities of dodecylamine (DDA), methyl isobutyl carbinol (MIBC), sec-octyl alcohol (2-octanol), DDA-MIBC blend, and DDA-2-octanol blend were investigated for different concentrations. The bubble aspect ratio of these individual reagents was found to follow the same order as molecular weight: DDA>2-octanol>MIBC. DDA addition further increased the aspect ratio of the bubbles in the individual MIBC and 2-octanol solutions, and the aspect ratio of the DDA-MIBC blend was found to be smaller than that of the DDA-2-octanol blend for a random but identical reagent concentration. The bubble rising velocity of these individual reagents followed the order MIBC>2-octanol>DDA. DDA addition had a significant effect in terms of decreasing the rising velocity of the bubbles in the individual MIBC and 2-octanol solutions; meanwhile, the bubble rising velocity of the DDA-MIBC blend was larger than that of the DDA-2-octanol blend. Bubble rising velocity showed a negative linear correlation with aspect ratio that was independent of reagent type, concentration, and blend.

    更新日期:2018-07-20
  • Spherical α-Al2O3 suspensions layered sequentially with anionic and cationic polyelectrolytes: Chemistry, rheology and TEM images
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    Wei Zhang, Pek-Ing Au, X. Zhang, H. Fan, Chunbao Sun, M. Saunders, Yee-Kwong Leong

    The zeta potential-pH and yield stress-pH behaviour of washed spherical α-Al2O3 suspensions with and without adsorbed multilayer polyelectrolytes up to 4 layers of poly(styrene sulphonic acid) sodium salt or PSSNa (100 kDa) and polyethyleneimine or PEI (70 kDa) adsorbed sequentially were characterised. The maximum yield stress (τymax) of washed spherical α-Al2O3 is 81.8 Pa located at pHξ=0 at ~9.2. Particles with the first layer (layer 1) of PSSNa displayed negative zeta potential over the whole pH range of 3 to 8. Particles containing 3 layers with layer 3 being PSSNa also displayed negative zeta potential over the same pH range. The magnitude of the Layer 3 PSSNa is smaller. Similarly, the zeta potential remained positive for layer 2 and layer 4 PEI over the whole pH range of 3 to 8. At the dosage of 0.5 dwb% PSSNa and 0.1 dwb% PEI, monolayer coverage of PSSNa for layer 1 and 3 and of PEI for layer 2 and 4 should be achieved if the adsorption is uniform. The maximum yield stress of layer 1 PSSNa and layer 2 PEI was much larger than that without adsorbed additives despite the zeta potential being not zero. Additional attractive forces such as bridging, hydrophobic and hydrogen bonding must be present. TEM images showed that the adsorbed PSSNa-PEI layer surface is undulating and not uniform in thickness. This suggests that adsorption of these polyelectrolyes is not uniform. Extensive particle bridging showing the merging of layers at the interacting surface of the particles was observed from these TEM images. In contrast, α-Al2O3 suspensions with bilayer DIBMA-PEI, trilayer DIBMA-PEI-DIBMA and 4 layers DIBMA-PEI-DIBMA-PEI formed by 14 kDa DIBMA and 1.8 kDa PEI performed effectively as steric layer reducing the maximum yield stress significantly. TEM image of α-Al2O3 particles with bilayer DIBMA-PEI did not show the presence of polyelectrolyte layer suggesting that the polyelectrolyte layer is too thin to be observable.

    更新日期:2018-07-20
  • Reuse of Powder Feedstock for Directed Energy Deposition
    Powder Technol. (IF 3.23) Pub Date : 2018-07-19
    Benjamin E. MacDonald, James C. Haley, Julie M. Schoenung

    The deposition efficiency of metal based additive manufacturing processes, particularly with directed energy deposition (DED) equipment which requires powder feedstock, is often <50%. While reuse of the remaining powder is common in industry, the precise effects on build quality resulting from possible morphological, microstructural, and chemical changes in the powder remain poorly understood. In this study, the reuse of 316 L stainless steel powder in the Laser Engineered Net Shaping (LENS®) machine was investigated through multiple deposition cycles. Particular attention was paid to the influence of reusing powder on: particle morphology, flowability, agglomeration, chemical composition and microstructure, via scanning electron microscopy, particle size analysis and mechanical testing of deposited parts from select reuse cycles. Results show that, for the range of parameters studied in this investigation, the physical properties of powder particles vary over multiple deposition cycles without significantly effecting the build quality of deposited parts.

    更新日期:2018-07-20
  • Novel reactive dyes with intramolecular color matching combination containing different chromophores
    Dyes Pigments (IF 3.767) Pub Date : 2018-07-19
    Hongjuan Zhang, Han Yang, Kongliang Xie, Aiqin Hou, Aiqin Gao

    Five novel reactive dyes by intramolecular color matching combination based on azo and anthraquinone multiple chromophores were designed and synthesized. They were obtained by using 1-amino-8-naphthol-3,6-disulfonicacid (H-acid) or 2-amino-5-naphthol-7-sulfonic Acid (J-acid) as the coupling component, 4-(ethylsulfurate sulfonyl) aniline as the diazo component and 1-amino-2-sulfonic acid-4-(3-amino-2,4,6-trimethyl-5-sulfonic acid phenylamine) anthraquinone sodium salt derivatives as the anthraquinone chromophore. The chemical structures of the synthesized dyes were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (1H NMR) and ultraviolet–visible spectra (UV–Vis). The dyes containing both azo and anthraquinone chromophores showed novel and beautiful color, including taupe, violet, brown, rosy and claret-red. The synthesized dyes showed good dyeing performances and fastness on cotton fabric. Because of the intramolecular color matching, the new reactive dyes have significant advantage in the colors and the reproducibility. The problem of low dyeing compatibility may be resolved. This work has important significance for the synthesis and applications of new dyes by intramolecular color matching.

    更新日期:2018-07-20
  • A dicyanoisophorone-based near-infrared fluorescent probe and its application for detecting thiophenols in water and living cells
    Dyes Pigments (IF 3.767) Pub Date : 2018-07-19
    Jiaxin Hong, Qingfeng Xia, Weiyong Feng, Guoqiang Feng

    We report herein a new dicyanoisophorone-based colorimetric and near-infrared (NIR) fluorescent probe for rapid detection of thiophenols. This probe possesses a remarkable large Stokes shift (208 nm) and works in almost pure aqueous solution under mild conditions. More importantly, it displays a rapid, highly selective and sensitive dual colorimetric and NIR fluorescent turn-on signal responses for thiophenols and allows the detection of thiophenols in the presence of analytes including amino acids, biothiols and aliphatic thiols. Moreover, the fluorescence of this probe at 655 nm displays a good linear relationship with the thiophenol concentration ranging from 0 to 20 μM, and the detection limit is as low as 12 nM. Furthermore, the practicability of this new probe has been successfully proved by detection of thiophenol in real water samples and bioimaging of thiophenol in living cells.

    更新日期:2018-07-20
  • Optical anti-counterfeiting of a single molecule by two solvents based on intra- and intermocular excited state proton transfer mechanisms
    Dyes Pigments (IF 3.767) Pub Date : 2018-07-19
    Hang Yin, Yu-Mo Zhang, Hui-Fang Zhao, Guo-Jian Yang, Ying Shi, Sean Xiao-An Zhang, Da-Jun Ding

    Organic dye molecules with excited state proton transfer property gain huge scientific interest owing to the design flexibility and functional diversity. However, the anti-counterfeiting of a single dye molecule through intra- and intermocular excited state proton transfer (ESIPT and ESPT) has yet to be achieved. This study demonstrates a simple and efficient approach to realize the anti-counterfeiting of a single dye molecule in a PMMA film. We control the 1-hydroxypyrene-2-carbaldehyde (HP) to be fluorescent or not through two different solvents based on ESIPT and ESPT mechanisms. Furthermore, we investigate the detailed information of excited-state dynamics for HP in two solvents, aiming at exploring the mechanisms of totally different luminescence property, through the femtosecond transient absorption spectroscopy. Meanwhile, the theoretical TDDFT research sheds light on the correlation between molecular structure and luminescence character. Specifically, the fluorescence of the molecule in acetonitrile is quenched by an ESIPT (127 fs) induced intersystem crossing (11.8 ps) whereas the ESPT (195 fs) and following aldehyde group rotation (26.5 ps) make the molecule to exhibit a strong luminescence property in dimethyl sulfoxide. The results are promising and offer new avenues to realize the greener and sustainable anti-counterfeiting of a single dye molecule.

    更新日期:2018-07-20
  • Flexural and torsional properties of a glass fiber-reinforced composite diaphyseal bone model with multidirectional fiber orientation
    J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-07-18
    Kalle A. Dahl, Niko Moritz, Pekka K. Vallittu

    Although widely used, metallic implants have certain drawbacks in reconstructive bone surgery. Their high stiffness in respect to cortical bone can lead to complications which include periprosthetic fractures and aseptic loosening. In contrast to metallic alloys, fiber-reinforced composites (FRC) composed of a thermoset polymer matrix reinforced with continuous E-glass fibers have elastic properties matching those of bone. We investigated the mechanical properties of straight FRC tubes and FRC bone models representing the diaphysis of rabbit femur prepared from glass fiber/bisphenol A glycidyl methacrylate (BisGMA) - triethylene glycol dimethacrylate (TEGDMA) composite in three-point bending and torsion. Three groups of straight FRC tubes with different fiber orientations were mechanically tested to determine the best design for the FRC bone model. Tube 1 consisted most axially oriented unidirectional fiber roving and fewest bidirectional fiber sleevings. Fiber composition of tube 3 was the opposite. Tube 2 had moderate composition of both fiber types. Tube 2 resisted highest stresses in the mechanical tests and its fiber composition was selected for the FRC bone model. FRC bone model specimens were then prepared and the mechanical properties were compared with those of cadaver rabbit femora. In three-point bending, FRC bone models resisted 39%-54% higher maximum load than rabbit femora with similar flexural stiffness. In torsion, FRC bone models resisted 31% higher maximum torque (p<0.001) and were 38% more rigid (p=0.001) than rabbit femora. Glass fiber-reinforced composites have good biocompatibility and from a biomechanical perspective, they could be used even in reconstruction of segmental diaphyseal defects. Development of an implant applicable for clinical use requires further studies.

    更新日期:2018-07-19
  • How important is sample alignment in planar biaxial testing of anisotropic soft biological tissues? A finite element study
    J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-07-18
    Heleen Fehervary, Julie Vastmans, Jos Vander Sloten, Nele Famaey

    Finite element models of biomedical applications increasingly use anisotropic hyperelastic material formulations. Appropriate material parameters are essential for a reliable outcome of these simulations, which is why planar biaxial testing of soft biological tissues is gaining importance. However, much is still to be learned regarding the ideal methodology for performing this type of test and the subsequent parameter fitting procedure. This paper focuses on the effect of an unknown sample orientation or a mistake in the sample orientation in a planar biaxial test using rakes. To this end, finite element simulations were conducted with various degrees of misalignment. Variations to the test method and subsequent fitting procedures are compared and evaluated. For a perfectly aligned sample and for a slightly misaligned sample, the parameters of the Gasser-Ogden-Holzapfel model can be found to a reasonable accuracy using a planar biaxial test with rakes and a parameter fitting procedure that takes into account the boundary conditions. However, after a certain threshold of misalignment, reliable parameters can no longer be found. The level of this threshold seems to be material dependent. For a sample with unknown sample orientation, material parameters could theoretically be obtained by increasing the degrees of freedom along which test data is obtained, e.g. by adding the data of a rail shear test. However, in the situation and the material model studied here, the inhomogeneous boundary conditions of the test set-ups render it impossible to obtain the correct parameters, even when using the parameter fitting method that takes into account boundary conditions. To conclude, it is always important to carefully track the sample orientation during harvesting and preparation and to minimize the misalignment during mounting. For transversely isotropic samples with an unknown orientation, we advise against parameter fitting based on a planar biaxial test, even when combined with a rail shear test.

    更新日期:2018-07-19
  • An investigation of the anisotropic mechanical properties and anatomical structure of porcine atrioventricular heart valves
    J. Mech. Behav. Biomed. Mater. (IF 3.239) Pub Date : 2018-07-18
    Samuel Jett, Devin Laurence, Robert Kunkel, Anju R. Babu, Katherine Kramer, Ryan Baumwart, Rheal Towner, Yi Wu, Chung-Hao Lee

    Valvular heart diseases are complex disorders, varying in pathophysiological mechanism and affected valve components. Understanding the effects of these diseases on valve functionality requires a thorough characterization of the mechanics and structure of the healthy heart valves. In this study, we performed biaxial mechanical experiments with extensive testing protocols to examine the mechanical behaviors of the mitral valve and tricuspid valve leaflets. We also investigated the effect of loading rate, testing temperatures, species (porcine versus ovine hearts), and age (juvenile vs adult ovine hearts) on the mechanical responses of the leaflet tissues. In addition, we evaluated the structure of chordae tendineae within each valve and performed histological analysis on each atrioventricular leaflet. We found all tissues displayed a characteristic nonlinear anisotropic mechanical response, with radial stretches on average 30.7% higher than circumferential stretches under equibiaxial physiological loading. Tissue mechanical responses showed consistent mechanical stiffening in response to increased loading rate and minor temperature dependence in all five atrioventricular heart valve leaflets. Moreover, our anatomical study revealed similar chordae quantities in the porcine mitral (30.5 ± 1.43 chords) and tricuspid valves (35.3 ± 2.45 chords), but significantly more chordae in the porcine than the ovine valves (p<0.010). Our histological analyses quantified the relative thicknesses of the four distinct morphological layers in each leaflet. This study provides a comprehensive database of the mechanics and structure of the atrioventricular valves, which will be beneficial to development of subject-specific atrioventricular valve constitutive models and toward multi-scale biomechanical investigations of heart valve function to improve valvular disease treatments.

    更新日期:2018-07-19
  • Application of GRAAL model to the resumption of International Simple Glass alteration
    npj Mater. Degrad. Pub Date : 2018-07-18
    Maxime Fournier, Pierre Frugier, Stéphane Gin

    The methodology developed for predicting nuclear waste behavior under disposal conditions combines experimental approaches and modeling. A waste glass canister placed in contact with water undergoes irreversible chemical processes leading to its degradation into more stable phases. This transformation occurs in three kinetic stages: the initial alteration rate (stage I), the residual rate (stage II), and, in some cases, a resumption of alteration (stage III) related to zeolites precipitation. Affinity effects based on the transition state theory are used to account for the rate drop from stage I to stage II. However, modeling of stage III has not been extensively studied. This study investigates the ability of the "glass reactivity with allowance for the alteration layer" (GRAAL) model to describe the effect of zeolite precipitation on the dissolution kinetics of the international simple glass (ISG). The GRAAL model-based description of the alteration layer was adapted to account for alkaline pH alteration mechanisms. A model describing the nucleation and growth kinetics of zeolites was proposed based on simple formalisms whose parameters can be inferred from previous studies’ results. These improvements give a description of the moment where a resumption of alteration occurs. As the predictive capacity of the GRAAL model is strongly dependent on the appropriateness of the alteration layers’ description, this work shows the need to develop new functions to describe the evolution of their compositions and solubilities with pH changes. Calculations also show the importance of Al and Ca activities and the effect of Al on the silica solubility.

    更新日期:2018-07-19
  • Publisher Correction: Two-dimensional materials with piezoelectric and ferroelectric functionalities
    npj 2D Mater. Appl. Pub Date : 2018-07-18
    Chaojie Cui, Fei Xue, Wei-Jin Hu, Lain-Jong Li

    Publisher Correction: Two-dimensional materials with piezoelectric and ferroelectric functionalities Publisher Correction: Two-dimensional materials with piezoelectric and ferroelectric functionalities, Published online: 18 July 2018; doi:10.1038/s41699-018-0067-1 Publisher Correction: Two-dimensional materials with piezoelectric and ferroelectric functionalities

    更新日期:2018-07-19
  • Experimental and modeling study of calcium carbonate precipitation and its effects on the degradation of oil well cement during carbonated brine exposure
    Cem. Concr. Res. (IF 5.43) Pub Date : 2018-07-18
    Edward N. Matteo, Bruno Huet, Carlos F. Jové-Colón, George W. Scherer

    Decalcification of cement in solutions of carbonated brine is important to a host of engineering applications, especially in subsurface service environments where cementitious materials are frequently utilized as engineered barriers for wellbore seals, as well as shaft and drift seals and waste forms for nuclear waste disposal. Analysis of leaching simulations and experiments shows that, depending on solution compositions (dissolved CO2 concentration, pH, Ca ion concentration), calcite precipitation occurring during leaching of cement in contact with carbonated brine can have a significant impact on cement reactivity, in some instances leading to complete arrest of reactivity via calcium carbonate “pore-clogging”. We present modeling and experimental results that examine the range of solution conditions that can lead to pore-clogging. Analysis of the results shows that distinct regimes of leaching behavior, based on pH and pCO2, can be used to form a framework to better understand the occurrence of pore-clogging.

    更新日期:2018-07-19
  • May reversible water uptake/release by hydrates explain the thermal expansion of cement paste? — Arguments from an inverse multiscale analysis
    Cem. Concr. Res. (IF 5.43) Pub Date : 2018-07-18
    Hui Wang, Christian Hellmich, Yong Yuan, Herbert Mang, Bernhard Pichler

    Quasi-instantaneous thermal expansion of cement pastes is governed by the relative humidity (RH) within their air-filled pores and by the decrease/increase of this internal RH resulting from a temperature decrease/increase. The latter effect is traced back to quasi-instantaneous water uptake/release by cement hydrates, using microporomechanics and a three-scale representation of mature cement pastes. Partially saturated gel and capillary pores are considered to be connected and spherical, with radii following exponential distributions. The Mori-Tanaka scheme provides the scale transition from effective pore pressures to eigenstrains at the cement paste level. This modeling approach, together with considering mass conservation of water, allows for downscaling macroscopic thermal expansion coefficients, so as to identify the molecular water uptake/release characteristics of the hydrates. The latter characteristics are mixture-independent, as shown by their use for predicting the thermal expansion coefficients of different mature cement pastes, with w/c-ratios ranging from 0.50 to 0.70.

    更新日期:2018-07-19
  • Smart cord-rubber composites with integrated sensing capabilities by localised carbon nanotubes using a simple swelling and infusion method
    Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-07-18
    Yinping Tao, Yi Liu, Han Zhang, Christopher A. Stevens, Emiliano Bilotti, Ton Peijs, James J.C. Busfield

    Smart self-sensing composites with integrated damage detection capabilities are of particular interests in various applications ranging from aerospace and automotive structural components, to wearable electronics and healthcare devices. Here, we demonstrate a feasible strategy to introduce and localise conductive nanofillers into existing elastomeric coatings of reinforcing cords for interfacial damage detection in cord-rubber composites. A simple swelling and infusion method was developed to incorporate carbon nanotubes (CNTs) into the elastomeric adhesive coating of glass cords. Conductive CNT-infused glass cords with good self-sensing functions were achieved without affecting the bonding provided by the coating with rubber matrix. The effectiveness of using these smart cords as interfacial strain and damage sensors in cord-rubber composites was demonstrated under static and cyclic loading. It showed the possibility to identify both reversible deformation and irreversible interfacial damage. The simplicity of the proposed swelling and infusion methodology provides great potential for large-scale industrial production or modification of CNT functionalised elastomeric products such as cord-rubber composites.

    更新日期:2018-07-19
  • Effect of thermal cycles on delayed hydride cracking in Zr-2.5Nb alloy
    J. Nucl. Mater. (IF 2.447) Pub Date : 2018-07-18
    M.E. De Las Heras, S.A. Parodi, L.M.E. Ponzoni, J.I. Mieza, S.C. Müller, S.D. Alcantar, G. Domizzi

    Delayed Hydride Cracking, DHC, is a mechanism that affects Zr and its alloys. Among other factors, thermal cycles may influence the occurrence of DHC process due to the difference between the hydrogen dissolution and precipitation solvus curves. In this work, DHC propagation rate (VP) was measured in Zr-2.5Nb alloy, after different thermal cycles: 1) by cooling to the Test temperature (Ttest); 2) by heating to Ttest; 3) after cooling to different temperatures (Tcool) and subsequent heating to Ttest = 253 °C and 154 °C. VP measured after cooling followed Arrhenius behavior, and a change in the activation energy was detected around 170 °C. It was confirmed that, under the conditions tested in this report, DHC is not possible at temperatures higher than TA = 210 °C when Ttest is approached by heating. An undercooling of 25 °C was enough to avoid DHC at Ttest = 253 °C. If Ttest = 154 °C DHC could not be stopped by any undercooling. Experimental results of VP and critical temperatures presented good agreement with values calculated with theoretical models reported in literature.

    更新日期:2018-07-19
  • An effective numerical algorithm for intra-granular fission gas release during non-equilibrium trapping and resolution
    J. Nucl. Mater. (IF 2.447) Pub Date : 2018-07-18
    G. Pastore, D. Pizzocri, C. Rabiti, T. Barani, P. Van Uffelen, L. Luzzi

    Fission gas release and gaseous swelling in nuclear fuel are driven by the transport of fission gas from within the fuel grains to grain boundaries (intra-granular fission gas release). The process involves gas atom diffusion in conjunction with trapping in and resolution from intra-granular bubbles, and is described mathematically by a system of two partial differential equations (PDE). Under the assumption of equilibrium between trapping and resolution (quasi-stationary approximation) the system can be reduced to a single diffusion equation with an effective diffusion coefficient. Numerical solutions used in engineering fuel performance calculations invariably rely on this simplification. First, we investigate the validity of the quasi-stationary approximation compared to the solution of the general system of PDEs. Results demonstrate that the approximation is valid under most conditions of practical interest, but is inadequate to describe intra-granular fission gas release during rapid transients to relatively high temperatures such as postulated reactivity-initiated accidents (RIA). Then, we develop a novel numerical algorithm for the solution of the general PDE system in time-varying conditions. We verify the PolyPole-2 algorithm against a reference finite difference solution for a large number of randomly generated operation histories including prototypical RIA transients. Results demonstrate that PolyPole-2 captures the solution of the general system with a high accuracy and a low computational cost. The PolyPole-2 algorithm overcomes the quasi-stationary approximation and the concept of an effective diffusion coefficient for the solution of the intra-granular fission gas release problem in nuclear fuel analysis.

    更新日期:2018-07-19
  • The effect of He ions irradiation on the micro-structure and property of CLF-1 steel
    J. Nucl. Mater. (IF 2.447) Pub Date : 2018-07-18
    Xiaonan Zhang, Xianxiu Mei, Xingzhong Cao, Younian Wang, Jianrong Sun, Pengfei Zheng

    The irradiation resistance of CLF-1 steel was investigated by using He ion irradiation with an energy of 300 keV. After the irradiation, the structure of CLF-1 steel mainly remained martensitic structure, while the lattice distortion and grain refinement occurred in the irradiation damaged layer. As irradiation fluence increased, the number of vacancies in CLF-1 steel increased, and the vacancies combined with the He atoms to form a bubble layer with the thickness of about 300 nm which located at the end of the He ions range. In the bubble layer, local amorphous region formed and the carbide particles showed a tendency to decompose. When the irradiation fluence was up to 1 × 1018ions/cm2, extensive blisters and a small amount of peelings appeared on the surface of CLF-1 steel. Due to grain refinement and dispersion of small carbide particles, the hardness of CLF-1 steel increased after the irradiation.

    更新日期:2018-07-19
  • An investigation of the chemical durability of hydrous and anhydrous rare-earth phosphates
    J. Nucl. Mater. (IF 2.447) Pub Date : 2018-07-18
    Mohamed Ruwaid Rafiuddin, Andrew P. Grosvenor

    Geological disposal of nuclear waste relies upon a multiple barrier approach in which canisters containing nuclear wasteforms are proposed to be stored in geological repositories. In the event of a failed container situation, the groundwater present near the repository may penetrate the waste containment system and eventually come in contact with the nuclear wasteform. Assessing the chemical durability of nuclear wasteforms is of utmost importance and in this study, leaching experiments were conducted on rare-earth phosphate materials adopting the monazite- (LaPO4), xenotime- (YbPO4), and rhabdophane- (GdPO4.H2O) type structures. Monazite and xenotime are abundant rare-earth minerals containing varying amounts of actinides incorporated within their crystal structure and are proposed as a potential host matrix for the immobilization of actinides. Rhabdophane is a hydrous rare-earth mineral that forms on the surface of chemically altered monazite mineral and is proposed to act as a protective barrier by preventing the release of actinides to the biosphere. The as-synthesized materials were exposed to deionized water for a total period of seven months and the concentration of the leached elements in the water solution were determined using inductively coupled plasma – mass spectrometry (ICP-MS). In this study, the normalized leach rates of LaPO4, YbPO4, and GdPO4.H2O materials were found to be low and indicate the chemical durability of these materials. Structural characterization of materials before and after leaching was performed using powder X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES). Analysis of the powder XRD diffractograms and XANES spectra has shown that the long-range and local structures of monazite-, xenotime-, and rhabdophane-type materials remain unaffected after exposure to water for seven months.

    更新日期:2018-07-19
  • A novel chemical reduction method to fabricate tunable selenium nanosphere and nanobelt based on cellulose nanocrystals
    Mater. Lett. (IF 2.687) Pub Date : 2018-07-18
    Duanchao Wang, Houyong Yu, Ying Guan, Maihao Zhu, Shanshan Liu, Juming Yao

    A novel chemical reduction method was reported to prepare tunable spherical or belted morphologies of nano-selenium (Se) based on cellulose nanocrystal (CNC). The homogeneous Se nanospheres with size of about 36 nm can be found for Se-Sphere-12H by adding ascorbic acid (VC) as assisted reducing agent. The Se nanobelt with a length of about 800 nm can be observed for Se-Belt-12H through one-pot reaction of CNC with sodium selenite (Na2SeO3) under hydrothermal conditions. Moreover, Se-Belt-12H exhibited the higher crystallinity of 96.10% and maximum thermal degradation temperature (Tmax) of 479.4 oC, the highest capacitance and the smallest internal resistance.

    更新日期:2018-07-19
  • ZnO nanoparticles enhanced hydrophobicity for starch film and paper
    Mater. Lett. (IF 2.687) Pub Date : 2018-07-18
    Shuzhen Ni, Hui Zhang, Patrick M. Godwin, Hongqi Dai, Huining Xiao

    Since hydrophobicity can improve the usability and functionality of materials in humid condition, enhancing the hydrophobic behavior of starch films or papers is of importance. In this work, ZnO nanoparticles (NPs) were introduced into the starch solution under ultrasonic and magnetic-stirring, followed by cast filming and paper coating. The contact angles of resulting film and coated paper containing 2% (wt) NPs were increased from 85.73° to 121.45°, 64.47° to 103.94°, respectively. The results from comprehensive characterizations confirmed the hierarchical structure created by ZnO nanoparticles on the surface of starch film as well as the formation of intact layers on coated paper. The excellent miscibility between starch and ZnO NPs was also achieved. The approach developed is promising and facilitates the hydrophobic modification of green-based materials.

    更新日期:2018-07-19
  • Biogenic green synthetic route for Janus type Ag:SnO2 asymmetric nanocomposite arrays: Plasmonic activation of wide band gap semiconductors towards photocatalytic degradation of Doripenem
    Mater. Lett. (IF 2.687) Pub Date : 2018-07-18
    Dipyaman Mohanta, Sauvik Raha, Md. Ahmaruzzaman

    In the present study, Janus type Ag: SnO2 heterojunction has been synthesized by a green route and has been utilized as a photocatalyst for the degradation of Doripenem, a prototype for emerging antibiotic pollutant. The kinetics of photodegradation of Doripenem was studied in aqueous solutions under solar and UV irradiation conditions. The rate constant for the photodegradation under UV irradiation was found to be 1.39 x 10-2 min-1. The obtained results, under the adopted conditions, indicated a marked influence of heterojuction structure and frequency of irradiation on the photodegradation rates of Doripenem.

    更新日期:2018-07-19
  • Mineralization of plasma treated polymer surfaces from super-saturated simulated body fluids
    Mater. Lett. (IF 2.687) Pub Date : 2018-07-18
    Phong A. Tran, Hiep T. Nguyen, Philip J. Hubbard, Hoang Phuc Dang, Dietmar W. Hutmacher

    This study aims to obtain mechanistic understanding of the formation and development of biomedical CaP coating on a model polymer surface of plasma treated polycaprolactone (PCL). Oxygen plasma treatment changed the surface morphology at nanometre scale and introduced negatively charged groups to PCL surface. Nucleation of CaP on the treated PCL surface occurred via two modes of growth, Volmer–Weber and Stranski–Krastanov. EDX and FTIR analysis suggested that the coating progressed from compositions with low Ca/P ratios and solubility to the phases of higher ratios and stability. The results also indicated that CaP clusters formed through Volmer–Weber mode were rich in the CaP phases of the higher Ca/P ratios. This study thus provided mechanistic insights into the coating process of CaP from solution onto functionalized surfaces which could be useful in designing coatings to suit different requirements.

    更新日期:2018-07-19
  • Hydroxyapatite Nanocrystals Synthesized from Calcium rich Bio-wastes
    Mater. Lett. (IF 2.687) Pub Date : 2018-07-18
    Dariela Núñez, Elizabeth Elgueta, Kokkarachedu Varaprasad, Patricio Oyarzún

    Hydroxyapatite nanocrystals were synthesized by wet chemical precipitation using bio-waste shells of mollusk (clam and mussel) and egg as feedstock materials. The powdered shells were calcined, dissolved in water, and the resulting product was reacted with phosphoric acid. X-ray diffraction analysis identified pure phase of hydroxyapatite for the three different raw materials. Transmission electron microscopy observations of hydroxyapatite indicated that rod-like crystals were produced in nanometric scale, which showed pH-dependent surface charges using zeta potential analysis. Overall, this study proved that calcium-rich bio-wastes are valuable materials to be used as feedstock for production of high purity and economically feasible hydroxyapatite nanocrystals for biomedical and technological applications.

    更新日期:2018-07-19
  • Injectable and tunable hyaluronic acid hydrogels releasing chemotactic and angiogenic growth factors for endodontic regeneration
    Acta Biomater. (IF 6.383) Pub Date : 2018-07-18
    Cristiana R. Silva, Pedro S. Babo, Maurizio Gulino, Lígia Costa, Joaquim M. Oliveira, Joana Silva-Correia, Rui M.A. Domingues, Rui L. Reis, Manuela E. Gomes

    Bioengineered soft tissues on any meaningful scale or complexity must incorporate aspects of the functional tissue, namely a vasculature, providing cells oxygen and nutrients critical for their survival. However, the ability of tissue engineering strategies to promote a fast revascularization is critically limited. Particularly in endodontic regenerative therapies, the complicated anatomy of the root canal system, and the narrow apical access limit the supply of new blood vessels and pulp tissue ingrowth. Here we characterize the viscoelastic and microstructural properties of a class of injectable hyaluronic acid (HA) hydrogels formed in situ, reinforced with cellulose nanocrystals (CNCs) and enriched with platelet lysate (PL), and test its ability to promote cells recruitment and proangiogenic activity in vitro. The incorporation of CNCs enhanced the stability of the materials against hydrolytic and enzymatic degradation. Moreover, the release of the chemotactic and pro-angiogenic growth factors (GFs) (PDGF and VEGF) from the PL-laden hydrogels showed an improved sustained profile proportional to the amount of incorporated CNCs. The PL-laden hydrogels exhibited preferential supportive properties of encapsulated human dental pulp cells (hDPCs) in in vitro culture conditions. Finally, PL-laden hydrogels stimulated chemotactic and pro-angiogenic activity by promoting hDPCs recruitment and cell sprouting in hDPCs/human umbilical vein endothelial cell co-cultures in vitro, and in an ex vivo model. These results support the use of the combined system as a scaffold for GFs delivery and cells recruitment, thereby exhibiting great clinical potential in treating injuries in vascularized tissues. Statement of Significance Innovative strategies for improved chemotactic and pro-angiogenic features of TE constructs are needed. In this study, we developed an injectable HA/CNC/PL hydrogel with improved structural and biologic properties, that not only provide a sustained release of chemotactic and proangiogenic GFs from PL but also enhance the cells’ viability and angiogenic activity. As a result of their unique traits, the developed hydrogels are ideally suited to simultaneously act as a GFs controlled delivery system and as a supportive matrix for cell culture, recruitment, and revascularization induction, holding great potential for the regeneration of vascularized soft tissues, such as the dentin-pulp complex.

    更新日期:2018-07-19
  • Effect of Y doping on microstructure and thermophysical properties of yttria stabilized hafnia ceramics
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Chun Li, Yue Ma, Zhaolu Xue, Yonghong Yang, Jianhua Chen, Hongbo Guo

    A series of Y2O3-doped HfO2 ceramics (Hf1-xYxO2-0.5×, x=0, 0.04, 0.08, 0.12, 0.16 and 0.2) were synthesized by solid-state reaction at 1600 °C. The microstructure, thermophysical properties and phase stability were investigated. Hf1-xYxO2-0.5× ceramics were comprised of monoclinic (M) phase and cubic (C) phase when Y3+ ion concentration ranged from 0.04 to 0.16. The thermal conductivity of Hf1-xYxO2-0.5× ceramic decreased as Y3+ ion concentration increased and Hf0.8Y0.2O1.9 ceramic revealed the lowest thermal conductivity of ~1.8 W/m⁎K at 1200 °C. The average thermal expansion coefficient (TEC) of Hf1-xYxO2-0.5× between 200 °C and 1300 °C increased with the Y3+ ion concentration. Hf0.8Y0.2O1.9 yielded the highest TEC of ~10.4×10−6 K−1 while keeping good phase stability between room temperature and 1600 °C.

    更新日期:2018-07-19
  • Carbon Nanotube/Titanium Carbide Sol-gel Coated Zirconium Diboride Composites Prepared by Spark Plasma Sintering
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Yang Miao, Xiaojing Wang, Yi-Bing Cheng

    With combination of a powder processing technique and a sol-gel process, carbon nanotube/titanium carbide coated zirconium diboride matrix composite was fabricated. Zirconium diboride (ZrB2) powders were coated with a functionalized carbon nanotubes (CNTs) mixed titanium carbide (TiC) sol-gel precursor. As the results suggests, the carbothermal reduction produced nanosized TiC grains at the surface of the ZrB2 particles with a homogenous distribution of CNTs. The densification of the CNT/TiC coated ZrB2 matrix composite was achieved via 1900 °C spark plasma sintering(SPS). The TiC grains and the CNTs were primarily concentrated in the grain boundaries of the ZrB2 and showed the pinning effects that restrained the growth of ZrB2 grain. The TiC grain diffusion in the sintering coarsened the grains from nanosizes to 1–2 μm, which improved the densification of the ZrB2. Due to the difference in coefficient of thermal expansion, CNTs bridged the gaps between the TiC and the ZrB2 matrix, which formed a weak-bonding interface. The major toughening mechanism found was crack deflection via the TiC grains on the ZrB2 matrix.

    更新日期:2018-07-19
  • Influence of Pore Distribution on the Equivalent Thermal Conductivity of Low Porosity Ceramic Closed-cell Foams
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Meijie Zhang, Miaolin He, Huazhi Gu, Ao Huang, Wuguo Xiang

    The microstructures of porous alumina materials with different porosities were established by introducing the departure factor of pore position and acentric factor of pore diameter to describe the distribution of pores in space and in size, respectively. The contribution of radiation and influence of pore distribution on the equivalent thermal conductivity were discussed based on numerical simulations by the finite volume method (FVM) considering both thermal conduction and radiation. When the pore diameter was less than 10 μm, the radiation component was less than 2%, and radiation could be neglected. Radiative heat transfer played a dominant role for materials with high porosity and large pore size at high temperatures. For micro pore materials (<100 μm), broad pore size and non-uniform pore space distribution decreased the thermal conductivity across the entire temperature range. For materials with macro pores (>1 mm), broad pore distribution decreased the thermal conductivity at low temperatures and increased it at high temperatures. The basic prediction model of effective thermal conductivity for a two-component material, the Maxwell–Eucken model (ME1) and its modified model were corrected by introducing the pore structure factor. The results from experiments prove that the numerical values were satisfactory.

    更新日期:2018-07-19
  • Appropriate thickness of pyrolytic carbon coating on SiC fiber reinforcement to secure reasonable quasi-ductility on NITE SiC/SiC composites
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Naofumi Nakazato, Hirotatsu Kishimoto, Joon-Soo Park

    Pyrolytic carbon (PyC) coating of silicon carbide (SiC) fibers is an important technology that creates quasi-ductility to SiC/SiC composites. Nano-infiltration and transient eutectic-phase (NITE) process is appealing for the fabrication of SiC/SiC composites for use in high temperature system structures. However, the appropriate conditions for the PyC coating of the composites have not been sufficiently tested. In this research, SiC fibers, with several thick PyC coatings prepared using a chemical vapor infiltration continuous furnace, were used in the fabrication of NITE SiC/SiC composites. Three point bending tests of the composites revealed that the thickness of the PyC coating affected the quasi-ductility of the composites. The composites reinforced by 300 nm thick coated SiC fibers showed a brittle fracture behavior; the composites reinforced 500 and 1200 nm thick PyC coated SiC fibers exhibited a better quasi-ductility. Transmission electron microscope research revealed that the surface of the as-coated PyC coating on a SiC fiber was almost smooth, but the interface between the PyC coating and SiC matrix in a NITE SiC/SiC composite was very rough. The thickness of the PyC coating was considered to be reduced maximum 400 nm during the composite fabrication procedure. The interface was possibly damaged during the composite fabrication procedure, and therefore, the thickness of the PyC coating on the SiC fibers should be thicker than 500 nm to ensure quasi-ductility of the NITE SiC/SiC composites.

    更新日期:2018-07-19
  • Recover of C3N4 Nanoparticles Under High-Pressure by Shock Wave Loading
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Yi-Gao Wang, Fu-Sheng Liu, Qi-Jun Liu, Xu-Yu Ling, Wen Peng Wang, Zhong Mi

    Theory predicts that β-C3N4 with its dense structure is a superhard material. In order to synthesize this material, light-gas gun loading and shock recovery technology were used to perform experiments. The amorphous nitrogen-enriched g-C3N4, produced by the thermal decomposition of melamine, was used as a precursor. The shock synthesis experiment was completed under the pressure of 50 GPa. A high-density phase with a β-C3N4 structure was detected only in the desired product. It is suspected that the elemental composition and synthetic pressure of precursors may be the main factors affecting the phase composition of products. This has significant potential for the synthesis of pure superhard carbonitride compounds.

    更新日期:2018-07-19
  • Mechanical properties of hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) materials after aging treatments
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Hae-Yong Jeong, Hae-Hyoung Lee, Yu-Sung Choi

    The purpose of this study was to evaluate and compare the changes in the various mechanical properties of hybrid and conventional CAD/CAM materials after accelerated aging using hydrothermal processes. Five kinds of hybrid and ceramic CAD/CAM blocks were selected. A total of 225 specimens were prepared with highly polished surfaces, in the form of round discs (diameter 12 mm, thickness 1.2 mm), and were divided into three groups (the control group, thermal cycling group, and autoclave group [n=15, each]). The nanoindentation hardness and Young's modulus (nanoindenter), biaxial flexural strength (ball-on-ring test system), surface roughness (atomic force microscopy), surface texture (scanning electron microscopy (SEM)), and elemental concentrations (energy dispersive spectroscopy) were evaluated. The Kruskal–Wallis test and Mann–Whitney U test were used to determine statistical significance (P< 0.05). The nanoindentation hardness and Young's modulus of the hybrid CAD/CAM materials were lower than those of ceramic materials, and they decreased after autoclave treatment. Among the hybrid CAD/CAM materials, Vita Enamic alone showed no significant difference in the Young's modulus after autoclave treatment; it also exhibited the highest nanoindentation hardness and modulus. There were significant changes in the biaxial flexural strength of hybrid CAD/CAM materials after aging. However, there was no change in the biaxial flexural strength of ceramic materials. The surface roughness of all materials, except CeraSmart, changed after aging. The SEM observations indicated a loss of filler particles in Lava Ultimate and morphological changes in IPS e.max ZirCAD, after aging. The ceramic CAD/CAM materials are superior to hybrid CAD/CAM materials in terms of the mechanical properties. The accelerated aging procedure induced changes in the mechanical properties of some hybrid CAD/CAM materials. Therefore, when using hybrid CAD/CAM materials, it is important to understand the behaviors of the various properties of each material as time progresses, and long-term follow up is necessary.

    更新日期:2018-07-19
  • Evidence of enhanced ferromagnetic nature and hyperfine interaction studies of Ce-Sm doped Co-Ni ferrite nanoparticles for microphone applications
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    K.M. Srinivasamurthy, V.Jagadeesha Angadi, S.P. Kubrin, Shidaling Matteppanavar, P. Mohan Kumar, B. Rudraswamy

    We present the results of the structural, Magnetic and low temperature Mössbauer spectroscopy studies of Co0.5Ni0.5Fe2-(x+y)CexSmyO4 (where x,y = 0.0, 0.01, 0.015 and 0.02) which was prepared by the solution combustion route using mixture of glucose and urea as fuel. The prepared samples were subjected to X-Ray Diffractometer (XRD), Transmission Electron Spectroscopy (TEM), Vibrating Sample Magnetometry (VSM) and Mössbauer Spectroscopy at room temperature and low temperature (15 K) to understand the phase, structure and magnetic behavior of the samples. The results of XRD reveals the formation of a single phase spinel cubic structure with space group Fd 3 ̅ m. The crystallite sizes are found to be increasing with increasing Ce3+ and Sm3+ content. This is due to the fact that bigger ionic radii of Ce3+ and Sm3+ replace Fe3+ ions at B site. The lattice parameter is found to be increasing with the increasing Ce3+ and Sm3+ content due to increased internal strain upon doping. The TEM micrographs reveals that the particles almost appear as spherical and agglomerated. Magnetic measurements show that all the obtained samples exhibit higher saturation magnetization (MS), remanence (Mr), coercivity (HC), anisotropy constant (K) and magneton number (ηB). This is due to the increase in A-B super exchange interaction in the samples. Further the increase in HC with the dopant concentration is interpreted as the enhanced magnetic pinning and ferromagnetic behavior in the samples. The room temperature Mössbauer spectra consist of broadened magnetic sextet and paramagnetic quadrupole-split lines. The presence of the magnetic sextet and doublet component on the Mössbauer spectra indicate the presence of superparamagnetic relaxation with a higher TB than the room temperature. The obtained results suggest that the rare earth doped Co-Ni ferrites are potential candidates for microphone applications.

    更新日期:2018-07-19
  • The electrical, magnetic and 57Fe Mössbauer studies of Al doped PrFeO3 polycrystalline materials
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    J. Ramesh, S.S.K. Reddy, N. Raju, M. Sreenath Reddy, Ch. Gopal Reddy, P. Yadagiri Reddy, K. Rama Reddy, V. Raghavendra Reddy

    The structural, electrical, magnetic and 57Fe Mössbauer studies of sol-gel synthesized polycrystalline Pr1-xAlxFeO3 (x= 0, 0.1, 0.2, 0.3, 0.4 and 0.5) samples are reported in this paper and the phase purity of the materials was confirmed from Rietveld refinement of XRD pattern. From the magnetization studies it is observed that the Al doping at Pr site changed the magnetic ordering of the systemat both room and low temperatures. The observed isomer-shift values from room temperature Mössbauer spectroscopy confirmed the charge state of the Fe ions and magnetic ordering in the compounds. Leakage current is observed to decrease with Al doping in the present work. From the leakage current density (J-E) measurements, it is observed that the space charge limited conduction (SCLC) dominates the conductionin lower and higher field regions for all the samples.

    更新日期:2018-07-19
  • Study of structural transformation and hysteresis behavior of Mg-Sr substituted X-type hexaferrites
    Ceram. Int. (IF 3.057) Pub Date : 2018-07-18
    Syeda Rabia Ejaz, Muhammad Azhar Khan, Muhammad Farooq Warsi, Majid Niaz Akhtar, Altaf Hussain

    Effect of Mg-Sr substitution on thermal, structural, spectral, dielectric and magnetic properties were explored in the X-type hexagonal ferrites having composition of Ba2-xMgxCo2-ySry Fe28O46 (x = y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) synthesized via a sol-gel auto-combustion process. The sintered material was characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), dielectric measurement and vibrating sample magnetometer (VSM) techniques. The sintering temperature necessary for the entire degradation of nitrates and the hexagonal phase development was found 1250 °C which was determined from thermo-gravimetric analysis. The formation of the single phase hexagonal was confirmed from XRD patterns. The lattice constants and cell volume were found to be decreased. This decreased was attributed to the lower ionic size of the substituted metal ions. The porosity of the synthesized material was found to be decreased from 0.463 to 0.417 with the increase in the substitution. FTIR spectroscopy of Mg-Sr doped material revealed the characteristics absorption bands of hexa-ferrites and it was investigated in the frequency range of 400–1000 cm−1. The dielectric measurement has been explored as the function of frequency and composition. Ac conductivity was found to be increased from 1.46 to 2.029 Ω cm−1. The Cole-Cole graphs of prepared materials revealed the promising role of grain boundaries in the conduction mechanism. The improvement in the coercivity was observed with the increase in the Mg-Sr cations, while the saturation magnetization was decreased with the increase in the substitution. The higher value of the coercivity of these synthesized material proposed their use in longitudinal recording media.

    更新日期:2018-07-19
  • Energy storage properties of NaNbO3-CaZrO3 ceramics with coexistence of ferroelectric and antiferroelectric phases
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-07-18
    Zhiyong Liu, Jinshan Lu, Yuqing Mao, Pengrong Ren, Huiqing Fan

    Anti-ferroelectric materials with large saturated polarization, small remnant polarization, and moderate breakdown strength are receiving increasing attention for modern high-power electrical systems. Here we demonstrated that by incorporating CaZrO3 into NaNbO3 ceramics, the antiferroelectricity in NaNbO3-CaZrO3 solid solutions could be stabilized at room temperature. The effects of phase constitution and microstructure on the dielectric properties, electrical breakdown strength, and energy storage properties of the NaNbO3-CaZrO3 ceramics were investigated. Ferroelectric and antiferroelectric phase coexistence in the NaNbO3-CaZrO3 was confirmed by XRD and TEM analyses. With increasing CaZrO3 content, the grain size was reduced, and the dielectric breakdown strength was improved. Therefore, a high energy density of 0.55 J/cm3 and efficiency of 63% was obtained in the NaNbO3-0.04CaZrO3 ceramics. These lead-free NaNbO3-CaZrO3 antiferroelectrics with good electrical energy storage can be exploited for high-power storage devices.

    更新日期:2018-07-19
  • Effect of technological parameters on densification of reaction bonded Si/SiC ceramics
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-07-18
    P.S. Grinchuk, M.V. Kiyashko, H.M. Abuhimd, M.S. Alshahrani, M.O. Stepkin, V.V. Toropov, A.A. Khort, D.V. Solovei, A.V. Akulich, M.D. Shashkov, M.Yu Liakh

    Si/SiC composite ceramics was produced by reaction sintering method in process of molten silicon infiltration into porous C/SiC preform fabricated by powder injection molding followed by impregnation with phenolic resin and carbonization. To optimize the ceramics densification process, effect of slurry composition, debinding conditions and the key parameters of all technological stages on the Si/SiC composite characteristics was studied. At the stage of molding the value of solid loading 87.5% was achieved using bimodal SiC powder and paraffin-based binder. It was found that the optimal conditions of fast thermal debinding correspond to the heating rate of 10 °C/min in air. The porous C/SiC ceramic preform carbonized at 1200 °C contained 4% of pyrolytic carbon and ∼25% of open pores. The bulk density of Si/SiC ceramics reached 3.04 g/cm3, silicon carbide content was 83–85 wt.% and residual porosity did not exceed 2%.

    更新日期:2018-07-19
  • Creep behaviour of dense and porous SrTi0.75Fe0.25O3-δ for oxygen transport membranes and substrates
    J. Eur. Ceram. Soc. (IF 3.794) Pub Date : 2018-07-18
    R. Oliveira Silva, J. Malzbender, F. Schulze-Küppers, S. Baumann, M. Krüger, O. Guillon

    Considering challenging conditions imposed by application of membranes in an asymmetric design, in particular creep resistance of the substrate material is an important parameter for the stability in long-term operation. As promising material, in terms of chemical stability, the perovskite SrTi0.75Fe0.25O3-δ has been identified in previous works. Porous supports with different microstructures have been produced using different manufacturing methods and compared to the material in its fully dense state regarding creep behaviour. The creep deformation of pressed, porous tape-cast and freeze-dried SrTi0.75Fe0.25O3-δ specimens has been investigated in the application relevant temperature range of 850 – 1000 °C under compressive stresses of 15, 30 and 45 MPa A global fitting method considering all experimental data was used to derive stress exponent and activation energy of SrTi0.75Fe0.25O3-δ, which are 2.9 ± 0.4 and 402 ± 25 kJ/mol, respectively. Thus, it is suggested that the mechanism controlling creep is mainly related to dislocation climb/glide.

    更新日期:2018-07-19
  • Towards the development of electrospun mats from poly(ε-caprolactone)/poly(ester amide)s miscible blends
    Polymer (IF 3.483) Pub Date : 2018-07-18
    Miguel L. Lamas, Mafalda S. Lima, Ana C. Pinho, David Tugushi, Ramaz Katsarava, Elisabete C. Costa, Ilídio J. Correia, Arménio C. Serra, Jorge F.J. Coelho, Ana C. Fonseca

    In this work, electrospun mats made from miscible poly(ε-caprolactone) (PCL)/poly(ester amide) (PEA) blends were prepared, for the first time. The well-known immiscibility issues between these two type of polymers were overcome through the synthesis of a novel tailor-made compatibilizer blocky PEA, comprising well defined PCL and PEA8L6 blocks (PCL-PEA8L6). The PCL-PEA8L6 was synthesized for the first time in this work and was characterized in terms of its chemical structure and thermal properties. Regarding the mats, it was found that their properties (morphology, porosity, wettability, thermomechanical) can be easily adjusted by the ratio of the components of the mixture to be electrospun. Increasing amounts of PEA led to more hydrophilic mats, with enhanced in vitro degradability, both hydrolytic and enzymatic. The in vitro cytotoxicity tests carried out with normal human dermal fibroblasts (NHDF) revealed that the samples do not elicit any acute adverse effect on the cells. Moreover, the NHDF were able to grow and proliferate in the surface of the electrospun mats. The data presented in this contribution is a proof-of-concept that can be used to address immiscibility issues between different types of polymers broadly used in biomedical applications.

    更新日期:2018-07-19
  • Preparation of novel polyimide nanocomposites with high mechanical and tribological performance using covalent modified carbon nanotubes via Friedel-Crafts reaction
    Polymer (IF 3.483) Pub Date : 2018-07-18
    Chunying Min, Dengdeng Liu, Zengbao He, Songjun Li, Kan Zhang, Yudong Huang

    Novel polyimide nanocomposites with excellent mechanical and tribological properties were achieved using amine functionalized multi-walled carbon nanotubes (MWCNT-NH2). MWCNT-NH2 was successfully obtained through Friedel-Crafts acylation and nitroreduction. PI nanocomposites with different contents of MWCNT-NH2 were prepared via in-situ polymerization. In contrast with the properties of pure PI or PI/MWCNT blends, the tribological properties, mechanical properties, and thermal performance of PI/MWCNT-NH2 nanocomposites were evidently improved due to the homogeneous dispersion of MWCNT-NH2 in PI matrix as well as the strong interfacial covalent bonds between MWCNT-NH2 and the PI matrix. Notably, it was demonstrated that the PI/MWCNT-NH2 nanocomposite adding with 0.7 wt% MWCNT-NH2 exhibited the best tribological properties in consideration of the friction coefficient (0.310) and wear rate (2.234 × 10−4 mm3/Nm) under dry sliding condition. Furthermore, the resulting PI/MWCNT-NH2 nanocomposites possessed the combined excellent tribological and mechanical properties, evidencing their potential applications in the field of the friction materials and other high-performance areas.

    更新日期:2018-07-19
  • Facile Assembly of a Large‐Area BNNSs Film for Oxidation/Corrosion‐Resistant Coatings
    Adv. Mater. Interfaces (IF 4.834) Pub Date : 18 July 20
    Chao Teng; Yucai Lin; Yanli Tan; Jian Liu; Lei Wang
    更新日期:2018-07-19
  • Progress in Powder Coating Technology Using Atomic Layer Deposition
    Adv. Mater. Interfaces (IF 4.834) Pub Date : 2018-07-18
    Sangeeta Adhikari; Seenivasan Selvaraj; Do‐Heyoung Kim
    更新日期:2018-07-19
  • Self‐Healing Asphalt Review: From Idea to Practice
    Adv. Mater. Interfaces (IF 4.834) Pub Date : 2018-07-18
    Shi Xu; Alvaro García; Junfeng Su; Quantao Liu; Amir Tabaković; Erik Schlangen
    更新日期:2018-07-19
  • Investigation on Structural, Electrical and Magnetic Properties of Titanium substituted Cobalt Ferrite nanocrystallites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-07-18
    Persis Amaliya, S. Anand, S. Pauline

    The doping of parent compound with selective dopants usually enhances the properties of the parent compound. In this paper, Titanium doped cobalt ferrite nanoparticles (Co1-xTixFe2O4 with x=0-0.075) via the sol-gel route is reported. The effect of titanium ions on the properties of cobalt ferrite is detailed. Structural evolution is confirmed using XRD technique and the titanium ion induced changes are given in terms of lattice constant, grain size, X-ray density, tetrahedral and octahedral hopping length and tetrahedral and octahedral bond length. The X-ray diffraction pattern displayed the formation of cubic inverse spinal structure belonging to the Fd3m space group. FTIR analysis confirmed the presence of characteristic peaks of ferrites around 400 cm-1 and 600 cm-1. Raman spectroscopy revealed reduction in peak intensities of Raman active modes. SEM characterization had shown the formation of well resolved spherical particles. Elemental composition was evaluated by EDAX spectrum. TEM images also confirmed the spherical morphology of the nanocrystallites and crystallite size calculated is in agreement with that calculated from the XRD analysis. The SAED pattern shows uniform fringes of width 0.428 nm belonging (222) plane. The diffraction pattern of HRTEM confirmed cubic spinel structure of the samples. Magnetic properties are evaluated from room temperature hysteresis loops. Increase in the saturation magnetization and coercivity was observed with increasing titanium content. Gradual increase in impedance with the increase in titanium concentration was estimated by impedance spectroscopy.

    更新日期:2018-07-19
  • Cluster-Glass-Like Behavior in Zinc Ferrite Nanograins
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-07-18
    E.F. Procopio, C. Larica, E.P. Muniz, F.J. Litterst, E.C. Passamani

    Structural and magnetic properties of ZnFe2O4 nanograins, prepared by high-energy ball milling and annealed, were systematically studied by X-ray diffraction, 57Fe Mössbauer spectroscopy and AC magnetic susceptibility measurements. Disordered spinel-like structure, with a grain size of 12 nm, is established after 200 h of milling. While the 300 K Mössbauer spectrum of the as-milled sample ( 200 h ) displays broad magnetic absorption lines, characteristic of a disordered system, the magnetization data do not show a magnetic phase transition between 4 and 300 K. At low temperatures, the Mössbauer spectra suggest the presence of two distinct ferrite magnetic phases: one attributed to the grain core (crystalline-like phase), with magnetic ordering temperature of about 90 K, and one showing a magnetic hyperfine field distribution; the latter is associated with a chemically disordered phase (grain boundary contributions). Annealing the 200 h sample at 973 K leads to an improvement of atomic ordering of the spinel structure (reduction of cationic inversion) and average grain size of about 17 nm. AC magnetic susceptibility shows a cusp at about T ≈ 30 K, whilst Mössbauer experiments in the same sample reveal magnetic blocking in the same temperature range. The frequency dependence of susceptibility suggests the formation of a cluster-glass-like state. High temperature susceptibility can be described with a Fulcher law of interacting magnetic clusters.

    更新日期:2018-07-19
  • Layer-by-layer assembled iron oxide based polymeric nanocomposites
    J. Magn. Magn. Mater. (IF 3.046) Pub Date : 2018-07-18
    Maria A.G. Soler

    Hybrid nanocomposites are nowadays the focus of intensive scientific and industrial research motivated by expectations from fields as diverse as microelectronics and medicine. One of the challenges faced by these materials, before getting into applications, is the development of methodologies capable of processing them in the form of thin planar nanostructures. To achieve this, bottom-up manipulation, such as the layer-by-layer approach capable of growing nano-objects while controlling position and inter-particle distances, has made possible the construction of assemblies with properties tailored on the nanoscale level. This review will summarize the new initiatives taken in the area of colloidal iron oxide nanoparticles and their arrays in polymeric matrix employing the layer-by-layer technique related research. Aiming to understand fundamental issues such as the effect of nanocomposite morphology on the collective magnetic properties, experiments and simulations performed to assess both the nanocomposite’s morphology and the corresponding magnetic signatures, will be discussed. Applications leading to future developments related with these nanostructures, as for instance chemical sensors and storage devices, will also be highlighted.

    更新日期:2018-07-19
  • Carbazole/α-carboline hybrid bipolar compounds as electron acceptors in exciplex, non-exciplex mixed cohosts and exciplex- emitters for high-efficiency OLEDs
    J. Mater. Chem. C (IF 5.976) Pub Date : 2018-07-18
    Youtian Tao, Qingjing Wu, Menghan Wang, Xudong Cao, Di Zhang, Ning Sun, Shigang Wan

    Two cyanopyridine derivatives CzPyCN and CbPyCN are designed and synthesized through a simple catalyst free aromatic nucleophilic substitution reaction by using 2-cyano-3,5-difluorpyridine as electrophiles and carbazole (Cz) or α-carboline (Cb) as nucleophiles. CbPyCN exhibits blue-shifted emission (λmax at 420 nm), wider optical band-bap (Eg: 3.15 eV) and higher triplet energy (ET: 2.79 eV) than CzPyCN (454 nm, 3.02 and 2.69 eV). The HOMO/LUMO energy levels were -5.77/-2.75 and -5.58/-2.38 eV for CzPyCN and CbPyCN, respectively. With sufficient HOMO/LUMO energy levels offsets, CzPyCN and CbPyCN could functionalize as electron acceptors to form exciplex with the typical electron-donor of di-[4-(N,N-ditolyl-amino)-phenyl] cyclohexane (TAPC), showing broad exciplex emission with peak at 530 and 520 nm, long decay lifetime of 1097 and 1014 ns, respectively. However, when mixed with 1,3-di(9H-carbazol-9-yl)-benzene (mCP), no exciplex whereas only typical CzPyCN or CbPyCN deep blue emission with decay lifetime of 14.3 or 12.1 ns is observed. Blue phosphorescent OLEDs by using mCP (TAPC)/CzPyCN as mixed cohosts shows maximum EQE of 19.1 (6.2)%, lower than 21.4 (13.3)% of mCP (TAPC)/CbPyCN, respectively, which is probably due to the better electron-transport properties as well as higher triplet energy levels for the electron-deficient α-carboline containing CbPyCN. Similarly, exciplex-type green fluorescent OLEDs based on TAPC/CzPyCN shows lower maximum efficiency of 22.0 cd A-1 and 7.4% than 27.5 cd A-1 and 9.1% of TAPC/CbPyCN.

    更新日期:2018-07-19
  • Electrical Characteristics of Heterogeneous Polymer Layers in PEDOT:PSS Films
    J. Mater. Chem. C (IF 5.976) Pub Date : 2018-07-18
    Yunryeol Kim, Wonseok Cho, Youngno Kim, Hangyeol Cho, Jung Hyun Kim

    (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a representative conducting polymer, is environment-friendly, and offers easy processing and flexibility owing to its hydro-dispersive property. In this study, we investigated the electrical properties of PEDOT:PSS films by H2SO4/DMSO post-treatment. PEDOT:PSS is an electrolyte complex that has been attracting attention as a next-generation transparent electrode. The PEDOT:PSS films are composed of two heterogeneous phases: a PEDOT-rich layer and a PSS-rich layer. The PSS-rich layer is observed to be a homogeneous phase that does not impact the electrical properties. Thus, the PSS-rich layer, which occupies a large area on the PEDOT:PSS films, was removed to obtain films having high electrical properties. Both the layers exhibit a homogeneous phase regardless of their electrical properties. In particular, the PSS-rich layer without the PEDOT chains does not affect the electrical properties, since it does not contribute to hole transport. The heterogeneity of the PEDOT:PSS films with high electrical properties has been demonstrated by eliminating the unnecessary PSS-rich layers. The highest electrical conductivity obtained is 2239 S cm-1, which is about 4.1 times higher than that of the pristine PEDOT:PSS films, for the films involving 15 M H2SO4/DMSO post-treatment.

    更新日期:2018-07-19
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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