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A variety of nanoparticles (NPs) (e.g., SiO 2 , TiO 2 , CeO 2 , Co 3 O 4 , etc.) and their functionalized counterparts have been intensively investigated for improving the electrochemical and mechanical durability of polymer-based proton-exchange membranes (PEMs) for use in low- and intermediate-temperature fuel cells. This study is to conduct a comprehensive review on the roles of functionalized NPs in the performance enhancement of PEMs including proton conductivity, gas crossover resistance, electrochemical and mechanical durability, etc. A brief historical review of PEM fuel cell (PEMFC) technology is made. Typical types of NPs and their functionalization techniques are retrospected and their roles in the performance improvement of PEMs are compared in detail. Consequently, the opportunities and challenges to develop high-performance functionalized NPs for use in PEMs and PEMFCs are prospected and justified. [ABSTRACT FROM AUTHOR]

An elastoplastic fracture mechanics model is formulated for determining the fracture toughness of adhesively bonded joints (ABJs) with large plastic deformations and elastic springback. The analysis is made on the basis of the post-fracture configuration of double cantilever beam (DCB) specimen consisting of two adhesively bonded thin plates of ductile metals ( e.g. , thin aluminum alloy or mild steel plates). Due to the springback after large plastic deformation, the post-fracture configuration of the adherends was noticeably different from that at the peak loading. To model the fracture process, the ductile metal adherends are treated as elastoplastic solids with power-law strain-hardening behavior, and springback of the adherends is considered in the strain energy calculation. The present model is capable of determining the fracture toughness of ABJs with extensive plastic deformation. Numerical simulations are performed to evaluate the effects of material parameters and specimen geometries on the springback and fracture toughness of the ABJs. Compared to the experimental data available in the literature, the present model can predict reliable fracture toughness of ABJs with large plastic deformations. The present study is applicable for the analysis of various fracture tests of thin ductile films with large plastic deformations and elastic springback such as peeling test, metal cutting, etc . [ABSTRACT FROM AUTHOR]

Ultrathin superhydrophobic–superoleophilic fibrous poly (vinylidene fluoride) (PVDF) membranes were prepared by means of electrospinning technique for the purpose of low-cost, high-efficiency water–oil separation. The ultrathin electrospun fibrous PVDF membranes exhibited a high water contact angle up to 153° and nearly zero oil (diesel) contact angle. The surface morphology and hydrophobicity of the membranes can be conveniently tuned by adjusting the PVDF concentration of the electrospinning solutions. The obtained ultrathin fibrous PVDF membranes showed excellent performance in separation of water-in-oil emulsions. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the fabrication and electrochemical properties of novel high-performance pseudosupercapacitor electrodes made of graphene-beaded carbon nanofibers (G/CNFs) surface-coated with nanostructured conducting polymers. The G/CNFs were produced by electrospinning the precursor graphene-beaded polymer nanofibers, followed by controlled pyrolysis. In situ polymerization in aqueous solution was utilized to coat an ultrathin layer of thorn-like polyaniline (PANI) nanorods onto the G/CNFs to form ternary PANI-coated G/CNFs (PANI-G/CNFs). The highly porous network morphology of PANI-G/CNFs exhibited a very large specific surface area, low internal resistance, and fast redox rate. Electrochemical characterization indicated that the PANI-G/CNF based pseudosupercapacitors carried a high value of specific capacitance up to 637 F g−1 at a current density of 0.15 A g−1 and still maintained the high value of specific capacitance of 478 F g−1 (only 25% decrease) even at a high current density of 6 A g−1. The pseudosupercapacitor showed a very good cycling stability of 87% after 1000 charge/discharge cycles at a very high current density of 15 A g−1. The experimental results indicated that the novel hierarchical, porous PANI-G/CNFs are a promising electrode material for use in high-performance energy storage devices. [Copyright &y& Elsevier]

Abstract: Two immiscible droplets wetting on a filament may assume engulfing, partial-engulfing, or non-engulfing morphology that depends on the wetting behavior and geometries of the resulting droplet-on-filament system. This paper studies the wetting behavior of two immiscible droplets contacting and sitting symmetrically on a straight filament. A set of ordinary differential equations (ODEs) is formulated for determining the wetting morphology of the droplet-on-filament system. In the limiting case of engulfing or non-engulfing, the morphology of the droplet-on-filament system is determined in explicit form. In the case of partial-engulfing, surface finite element method is further employed for determining the wetting morphology, surface energy, and internal pressures of droplets of the system. Numerical scaling study is performed to explore their dependencies upon the wetting properties and geometries of the system. The study can be applicable for analysis and design of textiles with tailorable wetting properties and development of novel multifunctional fibrous materials for environmental protection such as oil-spill sorption, etc. [Copyright &y& Elsevier]

Highlights: [•] Formulate a semi-analytic method for determining interfacial stresses of hard coatings. [•] Investigate the dependency of interfacial stresses upon structural and material parameters. [•] Determine the spacing of progressive cracking in hard coatings based on an energy criterion with refined stress field. [Copyright &y& Elsevier]

Abstract: High interfacial stresses at the free edges of adherends are responsible for the debonding failure of adhesively bonded joints (ABJs). In this paper, a general stress-function variational method is formulated to determinate the interfacial shear and normal (peeling) stresses in ABJs in high accuracy. By extending authors’ prior work in stress analysis of bonded joints (Wu and Jenson, 2011), all the planar stress components in the adherends and adhesive layer of an ABJ are expressed in terms of four unknown interfacial stress functions, which are introduced at the upper and lower surfaces of the adhesive layer. A set of governing ordinary differential equations (ODEs) of the four interfacial stress functions is obtained via minimizing the complimentary strain energy of the ABJ, which is further solved by using eigenfunctions. The obtained semi-analytic stress field can satisfy all the traction boundary conditions (BCs) of the ABJ, especially the stress continuity across the bonding lines and the shear-free condition at the ends of adherends and adhesive layer. As an example, the stress field in an adhesively single-sided strap joint is determined by the present method, whose numerical accuracy and reliability are validated by finite element method (FEM) and compared to existing models in the literature. Parameter studies are performed to examine the dependencies of the interfacial stresses of the exemplified ABJ upon the geometries, moduli and temperature change of the adherends and adhesive layer, respectively. The present method is applicable for scaling analysis of joint strength, optimal design of ABJs, etc. [Copyright &y& Elsevier]

Abstract: This paper studies the synthesis and electrochemical characterization of novel graphene-beaded carbon nanofibers (G/CNFs) as electrode material for use in supercapacitor. The porous G/CNF films were prepared by electrospinning polyacrylonitrile (PAN)/N,N-dimethylformamide (DMF) solution dispersed with oxidized graphene nanosheets, followed by carbonization at 800 °C in a tubular quartz furnace. The morphology and chemical structure of the porous G/CNF films were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The electrochemical behavior of the synthesized G/CNF films as supercapacitor electrodes was characterized by means of cyclic voltammetry (CV), galvanotactic charge/discharge, and electrochemical impedance test in a 6 m KOH aqueous electrolyte. Electrochemical measurements revealed that the maximum specific capacitance of the porous G/CNF electrodes reached up to 263.7 F g− 1 at a discharge current density 100 mA g− 1. Furthermore, the supercapacitor exhibited very good cycling stability of energy storage with the retention ratio of 86.9% after 2000 cycles. The high electrochemical performance of the G/CNF electrodes was attributed to the unique nanostructural configuration, high electrical conductivity, and large specific surface area of the graphene nanosheets. [Copyright &y& Elsevier]

Abstract: Droplet wetting on two parallel filaments may assume a barrel-shaped morphology or a liquid bridge depending upon the filament diameter and spacing, droplet volume, and contact angle. This paper is aimed to examine the dependency of droplet wetting length upon the above parameters. In the process, morphology of either a barrel-shaped droplet or a liquid bridge sitting on two parallel filaments is determined numerically by using surface finite element method (SFEM). Variation of wetting length with contact angle is examined at varying droplet volume, filament spacing, and droplet morphology. It is found that the droplet wetting length increases with decreasing filament spacing ratio as well as contact angle while it also increases with the growth of droplet volume. The dependency of wetting length upon contact angle behaves sensitive to filament spacing in the case of stable liquid bridges, while it exhibits nearly constant sensitivity to the contact angle in the case of barrel-shaped droplets. The quantitative relations yielded in this study can be considered as characteristic curves applicable for a variety of droplet-on-filament systems, particularly useful to wetting property characterization of filaments, micro liquid delivery, biological cell manipulation, etc. [Copyright &y& Elsevier]

Abstract: This paper considers the explicit solutions of free-edge stresses near circumferential cracks in surface coatings of circular torsion bars and their application in determining the progressive cracking density in the coating layers. The problem was formulated within the framework of linear elastic fracture mechanics (LEFM). The free-edge stresses near crack tip and the shear stresses in the cross-section of the torsion bar were approached in explicit forms based on the variational principle of complementary strain energy. Criterion for progressive cracking in the coating layer was established in sense of strain energy conservation, and the crack density is thereby estimated. Effects of external torque, aspect ratio, and elastic properties on the density of progressive cracking were examined numerically. The present study shows that, in the sense of inducing a given crack density, compliant coating layer with lower modulus has much higher critical torque than that of a stiffer one with the same geometries and substrate material, i.e., compliant coating layer has greater cracking tolerance. Meanwhile, the study also indicates that thicker surface coating layer is more pliant to cracking than the thinner ones. The present model can be used for analyzing the damage mechanism and cracking tolerance of surface coatings of torsion shafts and for data reduction of torsional fracture test of brittle surface coatings, etc. [Copyright &y& Elsevier]

Abstract: Dispersion relation of antiplane surface acoustic waves (SAWs) propagating in elastic half-space coated with an anisotropic laminate was determined explicitly by means of Stroh’s formalism within the subsonic range, where is no energy leakage into the substrate. During the procedure, the governing dynamic equation in each anisotropic layer and the displacement–traction continuity at interfaces were exactly satisfied by Stroh’s functions. Explicit algebraic equation was derived for determining the dispersion relation. As an example, the wave number vs. phase velocity diagram for steel half-space coated with a graphite-fiber/epoxy laminate with a lay-up was demonstrated. The given method can be used for the study of SAW properties of anisotropic coating systems and non-destructive evaluation based on surface/guided wave methods. [Copyright &y& Elsevier]

Abstract: Probabilistic edge-delamination strength of a thermosetting polymer composite was studied experimentally in this work. During the procedure, by means of edge-delamination tensile test, the graphite–fiber/epoxy laminate made of unidirectional Toray P7051S-20Q-1000 prepregs with an optimized lay-up of [122/–122/02]S was used for examining its probabilistic distributions of the edge-delamination onset stress and the ultimate tensile strength. Acoustic emission (AE) equipment and optical microscope were utilized to capture the edge-delamination initiation and characterize the failure modes during delaminating. Fractographical analysis based on scanning electron microscope (SEM) was conducted for the characterization of the microscopic failure mechanisms of the composite laminate during edge delaminating. Probabilistic models were introduced for data reduction. Test results show that the edge-delamination onset stress and the ultimate tensile strength of the laminate tested satisfy two two-parameter Weibull distributions very well. AE signals show the main failure mode during edge delaminating is interlaminar shear failure, corresponding to that predicted by numerical simulation and confirmed by SEM fractographical results in this study. [Copyright &y& Elsevier]

This paper is concerned with the electroelastic potentials and the fracture parameters of a twin-edge-cracked piezoelectric bimaterial strip with a screw dislocation. By means of conformal mapping technique and the known dislocation solution, the antiplane displacement and inplane electric potentials are obtained in closed-form. The intensity factors and the energy release rate are extracted explicitly. In some limiting cases, the present solutions cover those in the literature. [Copyright &y& Elsevier]

A closed-form solution is obtained for the problem of a mode-III interfacial edge crack between two bonded semi-infinite dissimilar elastic strips. A general out-of-plane displacement potential for the crack interacting with a screw dislocation or a line force is constructed using conformal mapping technique and existing dislocation solutions. Based on this displacement potential, the stress intensity factor (SIF, KIII) and the energy release rate (ERR, GIII) for the interfacial edge crack are obtained explicitly. It is shown that, in the limiting special cases, the obtained results coincide with the results available in the literature. The present solution can be used as the Green’s function to analyze interfacial edge cracks subjected to arbitrary anti-plane loadings. As an example, a formula is derived correcting the beam theory used in evaluation of SIF (KIII) and ERR (GIII) of bimaterials in the double cantilever beam (DCB) test configuration. [Copyright &y& Elsevier]

This paper reports the fabrication and filtration characterization of advanced fibrous cellulose acetate (CA) membranes for high-flux water filtration. The ultrathin nonwoven fibrous CA membranes with varying fiber diameter and areal weight were produced by electrospinning and post-processed by hot-press. The filtration efficiency of the ultrathin fibrous CA membranes was characterized by controlled water-filtration tests based on artificial colloids prepared via dispersing polystyrene (PS) particles of the diameters of 5 μm, 2 μm, 500 nm, and 100 nm in water, respectively. Natural river water was further used for evaluating the filtration capability of the electrospun fibrous CA membranes. Experimental results show that the rejection rate of the present fibrous CA membranes to PS particles with the diameter of 2 μm was up to 99.8%. In addition, the filtration efficiency of the electrospun fibrous CA membranes increased with increasing areal weight of the membranes. In the case of the filtering electrospun fibrous CA membranes with the fiber diameter of ∼800 nm and membrane areal weight ∼0.005 g/cm 2 , the measured turbidity of natural river water after filtration can reach as low as 0.135 nephelometric turbidity unit (NTU) while the initial flow flux can reach up to 20,455 L/m 2 h at the feed pressure 14 psi. The study suggests that low-cost electrospun fibrous membranes can be used for stable, high-flux water microfiltration with the filtration efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Mechanically flexible mats consisting of electrospun carbon nanofibers (ECNFs) were prepared by first electrospinning aqueous mixtures containing a natural product of alkali lignin together with polyvinyl alcohol (PVA) into composite nanofiber mats followed by stabilization in air and carbonization in an inert environment. Morphological and structural properties, as well as specific surface area, total pore volume, average pore size, and pore size distribution, of the lignin-based ECNF mats were characterized; and their electrochemical performances (i.e., capacitive behaviors) were evaluated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The lignin-based ECNF mats exhibited outstanding performance as free-standing and/or binder-free electrodes of supercapacitors. For example, the ECNFs made from the composite nanofibers with mass ratio of lignin/PVA being 70/30 (i.e., ECNFs (70/30)) had the average diameter of ∼100 nm and the Brunauer–Emmett–Teller (BET) specific surface area of ∼583 m2 g−1. The gravimetric capacitance of ECNFs (70/30) electrode in 6 M KOH aqueous electrolyte exhibited 64 F g−1 at current density of 400 mA g−1 and 50 F g−1 at 2000 mA g−1. The ECNFs (70/30) electrode also exhibited excellent cycling durability/stability, and the gravimetric capacitance merely reduced by ∼10% after 6000 cycles of charge/discharge. [Copyright &y& Elsevier]

Abstract: This letter reports a method to produce lignin and cellulose nanofibrils (CNFs) based porous core-shell carbon fibers via co-electrospinning followed by controlled carbonization. Lignin formed the shell of the fiber while CNF network formed the porous core. Polyacrylonitrile (PAN) was added to the lignin solution to increase its electrospinability. CNFs were surface acetylated and dispersed in silicon oil to obtain a homogenous dispersion for electrospinning the porous core. Hollow lignin fibers were also electrospun using glycerin as the core material. FT-IR measurements confirmed the CNF acetylation. SEM micrographs showed the core-shell and hollow fiber nanostructures before and after carbonization. The novel carbon fibers synthesized in this study exhibited increased surface area and porosity that are promising for many advanced applications. [Copyright &y& Elsevier]

Abstract: This paper reports the fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon fiber (CF) fabrics surface-attached with electrospun carbon nanofiber (ECN) mats. The ECNs were prepared via thermal treatments of polyacrylonitrile copolymer nanofibers, which were produced by the electrospinning technique and collected as overlaid mats on the T300 CF fabrics. The ECN-CF fabrics/mats were used as innovative reinforcement fillers for the fabrication of hybrid multi-scale composites (with SC-15 epoxy resin) through the composite-manufacturing technique of vacuum assisted resin transfer molding. Three-point bending test and short-beam shear test were carried out to evaluate the strengthening/toughening effects of ECNs on mechanical properties of the novel composites. The results indicated that out-of-plane mechanical properties of the ECN-CF/epoxy composites were considerably higher than the control sample of traditional CF/epoxy composites. [Copyright &y& Elsevier]

Abstract: In this study, hybrid multi-scale composites were developed from glass microfiber fabrics (GFs) and nano-epoxy resins containing electrospun glass nanofibers (EGNFs). The hypothesis was that, through dispersing a small amount of EGNFs into epoxy resin, mechanical properties (particularly out-of-plane mechanical properties) of the resulting hybrid multi-scale composites would be significantly improved. The composites were fabricated by the technique of vacuum assisted resin transfer molding (VARTM). The interlaminar shear strength, flexural properties, impact absorption energy, and tensile properties of the composites were evaluated, and the results were compared to those acquired from GFs/epoxy composite as well as GFs/epoxy composites containing chopped glass microfibers (GMFs); additionally, the reinforcement and/or toughening mechanisms were investigated. The study revealed that the nano-epoxy resin with 0.25wt.% of EGNFs resulted in substantial improvements on mechanical properties of the resulting hybrid multi-scale composites. [Copyright &y& Elsevier]

Abstract: A universal technique is developed to coat uniform layer of catalyst on any targeted substrate. The technique is based on a novel concept of catalyst deposition by using polymer–metal complexes in the form of invertible polymeric nanostructures through molecular self-assembly. Growth of carbon nanofibres on carbon microfibres was demonstrated to show this technique. [Copyright &y& Elsevier]