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In this study, turbulent flow characteristics of CuO-water nanofluid through heat exchanger pipe enhanced with louvered strips are numerically investigated. Nanoparticles volume fraction (ϕ) varied from 0 to 2%. The louvered strips are mounted in single and double geometries. The slant angle (θ) and the Reynolds number (Re) are within 15° − 25° and between 5000 and 14,000, respectively. (RNG) k − ϵ model is employed based on the finite volume technique. The results illustrated that strong flow disturbance between the wall and the louvered strip is the main reason for turbulent kinetic energy increment. Besides, the nanoparticles improve the thermophysical properties of the working fluid, which results in better heat transfer. The Nu number increases 15.6% by using nanofluid instead of water at Re = 14000. The highest thermal enhancement parameter of 1.99 is obtained at Re = 14000 by using double perforated louvered strip with θ = 25°. The recirculating flow inside the holes can significantly improve the thermal performance.

Zinc cobalt sulfide (ZCS) is a promising and high performance electrode material for pseudocapacitors due to its good electrical conductivity, abundant active sites and rich valence states. In this work, zinc cobalt oxide (ZCO) nanoparticles are firstly synthesized via a hydrothermal method assisted by hexadecyltrimethyl ammonium bromide (CTAB), and then transformed into zinc cobalt sulfide nanoparticles (ZCS NPs) using a facile sulfuration process. The average diameter of ZCS NPs is estimated to be about 15 nm, which is beneficial for Faradaic redox reactions in energy storage process due to their numerous active surfaces. The ZCS NPs are then coated onto a nickel foam to form the working electrode of supercapacitors. Because the ZCS electrode has lower series and charge transfer resistance, and also higher ion diffusion rate than that of the ZCO electrode, it achieves a large specific capacitance of 1269.1 F g−1 at 0.5 A g−1 in 2 M KOH electrolyte, which is four times more than that of the ZCO electrode (e.g., 295.8 F g−1 at 0.5 A g−1). In addition, an asymmetric supercapacitor using the ZCS NPs as the positive electrode and activated carbon as the negative electrode is assembled, which delivers a high energy density of 45.4 Wh kg−1 at a power density of 805.0 W kg−1, with an excellent cycling stability (91.6% retention of the initial capacitance over 5000 cycles).

Often wetting is considered from the perspective of a single surface of a rigid substrate and its topographical properties such as roughness or texture. However, many substrates, such as membranes and meshes, have two useful surfaces. Such flexible substrates also offer the potential to be formed into structures with either a double-sided surface (e.g. by joining the ends of a mesh as a tape) or a single-sided surface (e.g. by ends with a half-twist). When a substrate possesses holes, it is also possible to consider how the spaces in the substrate may be connected or disconnected. This combination of flexibility, holes and connectedness can therefore be used to introduce topological concepts, which are distinct from simple topography. Here, we present a method to create a Slippery Liquid-Infused Porous Surface (SLIPS) coating on flexible conformable doubled-sided meshes and for coating complex geometries. By considering the flexibility and connectedness of a mesh with the surface properties of SLIPS, we show it is possible to create double-sided SLIPS materials with high droplet mobility and droplet control on both faces. We also exemplify the importance of flexibility using a mesh-based SLIPS pipe capable of withstanding laminar and turbulent flows for 180 and 90 minutes, respectively. Finally, we discuss how ideas of topology introduced by the SLIPS mesh might be extended to create completely new types of SLIPS systems, such as Mobius strips and auxetic metamaterials.

In the current study a high fidelity analysis approach is used to predict the failure process of notched composite structures. Discrete cracking is explicitly modelled by incorporating cohesive interface elements along potential failure paths. These elements form an interconnected network to account for the interaction between interlaminar and intralaminar failure modes. Finite element models of these configurations were created in the commercial analysis software ABAQUS and a user defined material subroutine (UMAT) was used to describe the behaviour of the cohesive elements. The material subroutine ensured that the model remained stable despite significant damage, which is a significant challenge for implicit damage simulations. Two analysis approaches were adopted using either the as-measured or modified (in-situ) ply strengths. Both approaches were capable of closely predicting the mean ultimate strength for a range of hole diameters. However, using the measured ply properties resulted in extensive matrix cracking in the surface ply which caused a deviation from the experimentally measured surface strain. The results demonstrate that high fidelity physically based modelling approaches have the ability to complement or replace certain experimental programs focussed on the design and certification of composite structures.

Numerical investigation on latent heat thermal energy storage (LHTES) systems with phase change materials (PCMs) vertically heated from one side with novel stepped fins is presented. Transient numerical simulation by using the enthalpy-porosity method is performed to investigate the heat transfer rate and melting behaviors, while the natural convection is considered. To improve the PCM melting process, different upward and downward stepped fins with the step ratios (b/c) of 0.66, 1, 1.5, 2.33 and 4 are employed. The melt fraction and temperature contours by consideration the natural convection effects are presented. The results show that at the beginning of the melting process, the fins in the downward direction with b/c = 0.66 improve the PCM melting rate than the other cases, as the part of the heat is well transferred to the bottom of container along the fins and heat is trapped between the heated wall and the fins. The results show that the melting process in all of the tested stepped fins is faster than the conventional horizontal fins. The results show that by using downward stepped fins (b/c = 0.4) instead of conventional horizontal fins, the melting process could be enhanced up to 56.3% at t = 800 s and 65.5% at t = 3600 s.

Recently, graphene has attracted extensive research interests due to its superior mechanical, electrical and thermal performance. Small loadings of graphene can increase the properties of epoxy significantly. However, because of the large surface area of graphene, it is a challenge to disperse graphene in liquid epoxy. Strong van der Waals force causes reaggregation of graphene in the matrix. As commonly used surfactants, sodium dodecyl sulphate and gum arabic have been used a lot to de-bundle graphene, however, their dispersing efficiencies for graphene in epoxy matrix is unknown. Therefore, to evaluate their dispersing efficiencies, epoxy/graphene nanocomposites had been made and mechanical properties, dynamic mechanical analysis, thermal gravimetric analysis and scanning electron microscopy tests of nanocomposites had been conducted. The results show that the properties of nanocomposites had been enhanced largely after using sodium dodecyl sulphate and gum arabic. Sodium dodecyl sulphate shows higher dispersing effectiveness than gum arabic.

With the development of metal matrix composites (MMCs), the mechanical properties of MMCs with a small volume fraction of nano-sized particles were found to be even superior to that with a larger content of micron-sized particles. However, the improved mechanical properties of MMCs bring tremendous challenges such as premature tool failure in Ti machining process. This study exhibits an investigation on tool wear in micro milling of magnesium-based MMCs reinforced with 1.98 Vol.% of nano-sized titanium particles using 0.5-mm diameter two-flute tungsten carbide micro endmills. The tool wear was characterised both quantitatively and qualitatively by observing tool wear patterns and analysing the effect of cutting parameters on flank wear, reduction in tool diameter, cutting forces, surface roughness, and burr formation. A finite element model was established to understand matrix deformation and interaction between tool-particle and further explain the tool wear phenomena observed. Additionally, cutting performance using AlTiN coated and uncoated was also investigated. The results indicated that the main wear mechanisms were identified as flank wear and edge chipping due to abrasive wear and chip adhesion in uncoated micro endmills. These wear mechanisms were confirmed by chip formation process produced by finite element modelling (FEM). It was also observed that the largest tool wear occurred at the smallest feed per tooth (0.75 μm/tooth) and smallest wear occurred at the largest feed per tooth (3 μm/tooth). Also, the effect of BUE on tool wear and surface generation was studied.

Kesterite (CZTSe) is a promising thin film photovoltaic absorber material due to its composition of more earth abundant materials compared to mature thin film photovoltaic technologies. Up to now, power conversion efficiencies are still lower and its main problem is the low open circuit voltage (Voc). Recently, a novel sintering approach using a nanometric Ge layer showed a large increase in device performance and especially in Voc. In this work, in-depth solar cell characterization as well as Raman and photoluminescence studies of devices employing different Ge doped CZTSe absorber layers is presented. The main focus is to reveal the beneficial effects of Ge doping and furthermore investigate the interaction of Ge and Na. For low Ge doping an increase in charge carrier concentration is observed, resulting in devices with a Voc of 460 mV, which corresponds to a Voc deficit (Eg/q − Voc) of 596 mV, a value comparable to current record devices. For high Ge amounts, admittance spectroscopy measurements identified the appearance of a deep defect which can explain the observed deterioration of solar cell performance. Additional Na provided during crystallization of high Ge doped devices can reduce the density of this deep defect and recover device performance. These results indicate that Na plays an important role in defect passivation and we propose a defect model based on the interaction of group IV elements and Na with Cu vacancies.

The effect of nickel additions to tune the wear performance of CuZrAl at.% alloy has been studied to present a new strategy for preventing excessive wear rate at high loads in metallic glass composites. This strategy consists on proper selection of a doping element in controlled concentrations with the ability to decrease the glass transition temperature (T) of the alloy so that the friction temperature during sliding is close to the T. This enables the formation of crystalline phases and their subsequent oxidation (lubricating layer) on the contact surface during sliding thus enhancing the wear resistance. Proper doping can also contribute towards the wear resistance when the content of the doping element promotes the martensitic transformation. The results show that the main wear mechanism for the three studied alloys (CuZrAl, CuZrAlNi and CuZrAlNi at.%) is governed by delamination and the mass loss increases with increasing load from 1 to 10 N. However, for the maximum load of 15 N, the calculated friction temperature is close to T for the Ni-containing alloys and partial crystallization and oxidation take place resulting in a mass loss decrease from about 2.6 mg (at 10 N) to about 2.1 mg (at 15 N)., SG is grateful to the Royal Society for the grant RG2015R2. V.M.V. and S.G. acknowledge research support from Northumbria University. Partial financial support from RG2015R2 is acknowledged. J. Medina and P. Pérez would like to acknowledge the expert support of A. García and A. Tomás for assistance with SEM/TEM observations.

Future energy demand can be addressed by using renewable and inexhaustible solar energy, providing clean, unlimited, economical and green energy. Electricity generation from the sun employing PV technology is currently dominated by Si-based PV and requires expensive equipment and process and schemes for cost reduction on a large scale are limited. Thin film technologies such as CdTe and Cu(In,Ga)Se2, provide a lower cost alternative primarily due to the use of in-line and low-temperature processes. While considerable efforts have been made to increase efficiency and reduce costs, thin film PV currently relies on scarce and therefore expensive resources and/or toxic elements. Alternative thin film materials would therefore provide routes to reduce PV cost-per-watt while still exhibiting lower input energy requirements. Solar cells based on Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers offer such an alternative. \ud \ud Despite its young history CZTSSe record efficiency stands at 12.6% and the major limitations are (i) a lower than expected open circuit voltage accompanied by a low efficiency at converting and collecting carriers from low energy photons; (ii) the difficulty in controlling the kesterite crystal structure throughout the fabrication process; and (iii) the use of hydrazine, a highly toxic chemical, in the fabrication process to achieve the record efficiencies. This project uses nanocrystal dispersions (inks) of CZTS synthesised from hot injection as the starting material. This technique can reliably control crystal structure, composition and doping and does not present any environmental risks. Inks are easily spin coated or sprayed on substrates and a heat treatment under selenium rich atmosphere promotes grain growth without loss of the crystal structure. In order to fabricate record efficiencies using this technique the microstructure of the absorber and back contact layers need to be engineered to provide large grains extending the full thickness of the absorber combined with a small interfacial layer to ensure a good ohmic contact.

Unlike metal electrodes such as Al and Au, aluminum doped zinc oxide (AZO) with high conductivity and transparency can be used as transparent electrodes for surface acoustic wave (SAW) resonators, and thus realize fully transparent and invisible ZnO SAW devices on glass. This paper reports the fabrication of transparent SAW resonators using AZO as the transparent electrode and investigation of effects of deposition parameters on the crystal structures of the AZO thin films deposited by magnetron sputtering. Results show that a low sputtering pressure and an optimal sputtering power are beneficial for the deposition of (0002) orientation of AZO. The optimal deposition parameters are found to be: deposition pressure of 0.3 Pa, sputtering power of 300 W, substrate temperature of 200 °C. The fabricated transparent SAW devices have different wavelengths (from 16 to 32 μm) and all the devices exhibit two types of wave modes: Rayleigh and Sezawa waves. Compared with Sezawa wave, the Rayleigh wave has a large signal amplitude up to 25 dB. In addition, as the wavelength increases, the resonant frequencies of both the Rayleigh and Sezawa waves increase whereas their phase velocities decrease. The transparent SAW devices have also demonstrated their ability to induce a strong acoustic streaming in a water droplet with a streaming velocity up to 2.27 cm/s. This research opens a door for further exploration of the SAW devices in transparent electronics.

The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the environmental stress cracking resistance of the nano-composites. The storage modulus of nano-composites measured by dynamic mechanical analysis increased remarkably as a function of halloysite nanoclay content. At 0.7 wt% nanoclay, the Tg improved from 72°C to 76°C. The fracture toughness increased up to 33% and time to failure improved 155% with the addition of 0.7 wt% of halloysite nanoclay. The maximum microhardness was found 119% higher for the same nano-filler concentration compared to monolithic polyester. The reinforcement with 1 wt% showed lower fracture toughness due to agglomerations of nanoclay which act as flaws. The presence of agglomerates weakened the bond between nano-particles and matrix hence reduces the environmental stress cracking resistance by halloysite nanoclay reinforcement.

A novel tweakable nanocomposite was prepared by spark plasma sintering followed by systematic oxidation of carbon nanotube (CNT) molecules to produce alumina/carbon nanotube nanocomposites with surface porosities. The mechanical properties (flexural strength and fracture toughness), surface area, and electrical conductivities were characterized and compared. The nanocomposites were extensively analyzed by field emission scanning electron microscopy (FE-SEM) for 2D qualitative surface morphological analysis. Adding CNTs in ceramic matrices and then systematically oxidizing them, without substantial reduction in densification, induces significant capability to achieve desirable/application oriented balance between mechanical, electrical, and catalytic properties of these ceramic nanocomposites. This novel strategy, upon further development, opens new level of opportunities for real-world/industrial applications of these relatively novel engineering materials.

In this paper, we present a method to create a highly sensitive piezoelectric quasi 1&ndash, 3 composite using a thermoplastic material filled with a piezoelectric powder. An up-scalable high-temperature dielectrophoresis (DEP) process is used to manufacture the quasi 1&ndash, 3 piezoelectric polymer-ceramic composites. For this work, thermoplastic cyclic butylene terephthalate (CBT) is used as a polymer matrix and PZT (lead zirconium titanate) ceramic powder is chosen as the piezoelectric active filler material. At high temperatures, the polymer is melted to provide a liquid medium to align the piezoelectric particles using the DEP process inside the molten matrix. The resulting distribution of aligned particles is frozen upon cooling the composite down to room temperature in as little as 10 min. A maximum piezoelectric voltage sensitivity (g33) value of 54 &plusmn, 4 mV&middot, m/N is reported for the composite with 10 vol% PZT, which is twice the value calculated for PZT based ceramics.

The conduction mechanisms in metal-insulator-metal (MIM) junctions where the insulator consists of a self-assembled monolayer are investigated. Temperature dependence measurements from 2.5 to 300 K, show that the conduction is dominated by tunnelling only for temperatures below 20 K, while at higher temperatures surface-limited and bulk-limited mechanisms are observed. The experimental results are explained using a combination of direct (Simmons) tunnelling, Schottky emission, and Poole-Frenkel theory. Further insight is gained through numerical simulations based on the non-equilibrium Green-function formalism.

This paper demonstrates a unique way of creating heterogeneous layered structures of soft functional materials for advanced transducer applications. Hydrogel droplets with different composites were patterned by a "two-parallel plate" configuration used in microfluidics applications. Resulted heterogeneous layered structures of hydrogel were created, generating reconfigurable 3D (3-dimensional) deformation responding to discrete levels of stimulation inputs.

Flexibility plays a vital role in wearable electronics. Repeated bending often leads to the dramatic decrease of conductivity because of the numerous microcracks formed in the metal coating layer, which is undesirable for flexible conductors. Herein, conductive textiles based tactile sensors and metal-coated polyurethane (PU) sponges based bending sensors with superior flexibility for monitoring human touch and arm motions are proposed, respectively. Tannic acid, a traditional mordant, is introduced to attach to various flexible substrates, providing a perfect platform for catalyst absorbing and subsequent electroless deposition (ELD). By understanding the nucleation, growth and structure of electroless metal deposits, the surface morphology of metal nanoparticles can be controlled in nanoscale with simple variation of the plating time. When the electroless plating time is 20 min, the normalized resistance (R/R0) of our as-made conductive fibers is only 1.6, which is much lower than a 60 min ELD sample at the same conditions (R/R0 ≈ 5). This is because a large number of unfilled gaps between nanoparticles prevent metal films from cracking under bending. Importantly, the Kelvin problem is relevant to deposited conductive coatings because metallic cells have a honeycomb-like structure, which is a rationale to explain the relationships of conductivity and flexibility.

Biological Liquid Crystal, a rich set of soft materials with rod-like structures widely existed in nature, possess typical lyotropic liquid crystalline phase properties both in vitro (e.g. cellulose, peptides and protein assemblies), and in vivo (e.g. cellular lipid membrane, packed DNA in bacteria and aligned fibroblasts). Given the ability to undergo phase transition in response to various stimuli, numerous practices have been exercised to spatially arrange biological liquid crystals. In this mini-review, the fundamental understanding of interactions between rod-shaped biological building blocks and their orientational ordering across multiple length scales is addressed. Discussions are made with regard to the dependence of physical properties of non-motile objects on the first-order phase transition and the coexistence of multi-phases in passive liquid crystalline systems. This review also focuses on how the applied physical stimuli drives the reorganization of constituent passive particles for a new steady-state alignment. A number of recent progresses in the dynamics behaviours of active liquid crystals are presented, and particular attention has been given to those self-propelled animate elements, like the formation of motile topological defects, active turbulence, correlation of orientational ordering and cellular functions. Finally, future implications and potential applications of the biological liquid crystalline materials are discussed.

Recent advancements in electronics engineering require materials with the resiliency and sustainability to extend their life time. With this regard, we presented a sustainable multi-functional nanocomposites strategy by introducing dynamic imine bonds based polyazomethine (PAM) as molecular interconnects and Fe3O4-loaded multiwalled carbon nanotubes as electromagnetic (EM) wave absorbing units. Driven by the reversible dynamic imine bonds, our materials show robust spontaneous self-healing with excellent healing efficiencies of 95% for PAM and 90% for nanocomposite, and an accelerated recovery under a moderate mechanical stimulus. By adding Fe3O4-loaded multiwalled carbon nanotubes, the hybrids show excellent EM wave absorbing properties with 50% increment on minimum reflection coefficient (−40.6 dB) than the reported value. We demonstrate a full degradability by decomposing a nanocomposite sheet of 100 mg in an acidic solution within 90 min at room temperature. The nanofillers and monomers after degradation can be re-used to synthesis nanocomposites. The testing results for recoverable nanocomposites show a good retention on mechanical property. This novel strategy may shed a light on the downstream applications in EM wave absorbing devices and smart structures with great potential to accelerate circular economy.

International audience; Kesterite solar cells based on chalcogenide Cu2ZnSn(S,Se)4 (CZTSSe) are a viable approach to thin film photovoltaics, utilising Earth-abundant, non-toxic elements. CZTSSe films produced from nanoparticle inks offer a cost-effective solution-based method of fabrication. However, improving efficiency in these devices has proved challenging, in part due to the presence of detrimental complex defects within the bulk of the CZTSSe absorber. In this study, the behaviour of nanoparticle-based CZTSSe absorbers and solar cells made from relatively low and high quality grade chemicals is investigated with a view to improving cost-effectiveness of the ink-based fabrication process. Photoluminescence spectroscopy revealed the presence of similar shallow acceptor plus shallow donor states in both low and high purity precursor absorbers. We demonstrate a relationship between the average depth of energy band-edge potential fluctuations and absorber quality where the higher grade chemical precursor-based absorber outperforms the lower purity version. In addition, the low purity precursor absorber had a higher total defect density resulting in a 10 meV increase in the average electrostatic potential fluctuations. Deep level transient spectroscopy in solar devices indicated the presence of detrimental deep defect states in both types of absorber. Notwithstanding the high purity precursor absorber with lower defect density, the power conversion efficiencies of both types of CZTSSe solar cells were similar (~5%), implying an issue other than defects in the absorber bulk inhibits device performance as evidenced by quantum efficiency analysis and current–voltage measurements.

Based on theoretical analysis, finite element simulation and experimental verifications, we have systematically investigated evolution, hybridization and decoupling of multiple acoustic wave modes and vibration patterns generated from piezoelectric film acoustic wave devices fabricated on flexible thin foils/plates. ZnO piezoelectric films deposited on flexible and bendable Al foil and plates were selected for this particular study. The ZnO/Al acoustic wave devices were chosen with wavelengths varied from 12 to 800 μm, ZnO film thickness from 2 to 10 μm and Al foil/plate thickness from 10 to 600 μm. Multiple acoustic wave modes (including symmetrical and asymmetrical Lamb waves, Rayleigh waves and higher harmonic/Sezawa wave modes) were generated, hybridized occasionally with each other, and then easily decoupled by changing the ratios of the substrate/film thicknesses to wavelengths. Ratios between device wavelength and substrate/film thickness have been identified to be the dominant parameter in determining the evolution and hybridization of multiple wave modes and their vibration patterns, which provide useful design guidance for both sensing and microfluidic applications using these flexible and bendable acoustic wave devices.

External surfaces of stones used in historic buildings often carry high artistic value and need to be preserved from the damages of time, especially from the detrimental effects of the weathering. This study aimed to test the effectiveness and compatibility of some new environmentally-friendly materials for stone consolidation, as the use thereof has been so far poorly investigated. The treatments were based on combinations of an aqueous solution of di-ammonium phosphate (DAP) and two calcium-based nanomaterials, namely a commercial nanosuspension of Ca(OH)2 and a novel nanosuspension of calcite. The treatments were applied to samples of two porous stones: a limestone and a sandstone. The effectiveness of the treatments was assessed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, ultrasound pulse velocity test, colour measurements, and capillary water absorption test. The results suggest that the combined use of DAP and Ca-based nanosuspensions can be advantageous over other commonly used consolidants in terms of retreatability and physical-chemical compatibility with the stone. Some limitations are also highlighted, such as the uneven distribution and low penetration of the consolidants.

Smart materials with self-growing and tailorable mechanical strength have wide-range potential applications in self-healing, self-repairing, self-assembly, artificial muscle, soft robots and intelligent devices. However, their working mechanisms and principles are not fully understood yet and mathematically and physical modeling is a huge challenge, as traditionally synthesized materials cannot self-grow and reconstruct themselves once formed or deformed. In this study, a phenomenological constitutive model was developed to investigate the working mechanisms of self-growing and tailorable mechanical strength in double-network (DN) hydrogel composites, induced by mechanochemical transduction of dynamic-modal mechanophore. An extended Maxwell model was firstly employed to characterize the mechanical unzipping of hydrogel composites, and then mechanochemically induced destruction and reconstruction processes of brittle network in the hydrogel composite were formulated. The enhanced mechanical strength of brittle network has been identified as the key driving force to generate self-growing and tailorable mechanical strength in the hydrogel composite. Finally, a stress-strain constitutive relationship was developed for the dynamic-modal mechanophorein the hydrogel composite. Simulation results obtained from the proposed model were compared with the experimental data, and a good agreement has been achieved. This study provides an effective strategy for modelling and exploring the working mechanism in the mechanoresponsive DN hydrogel composites with self-growing and tailorable mechanical strength.

For an efficient single-photon source a high-count rate into a well-defined spectral and spatial mode is desirable. Here we have developed a hybrid planar Fabry-Perot microcavity by using a two-photon polymerization process (2PP) where coupling between single-photon sources (diamond colour centres) and resonance modes is observed. The first step consists of using the 2PP process to build a polymer table structure around previously characterized nitrogen-vacancy (NV) centres on top of a distributed Bragg reflector (DBR) with a high reflectivity at the NV zero-phonon line (ZPL). Afterwards, the polymer structure is covered with a silver layer to create a weak (low Q) cavity where resonance fluorescence measurements from the NVs are shown to be in good agreement with analytical and Finite Difference Time Domain (FDTD) results.

The topographical features of fractured tensile, flexural, K1C, and impact specimens of 1.0 wt% multi-layered graphene/nanoclay-epoxy nanocomposites have been investigated. The topographical features studied include maximum roughness height ( Rmax or Rz), root mean square value ( Rq), roughness average ( Ra), and waviness ( Wa). Due to deflection and bifurcation of the cracks by nanofillers, specific fracture patterns are observed. Although these fracture patterns seem aesthetically appealing, however, if delved deeper, they can further be used to estimate the influence of nanofiller on the mechanical properties. By a meticulous examination of topographical features of fractured patterns, various important aspects related to fillers can be approximated such as dispersion state, interfacial interactions, presence of agglomerates, and overall influence of the incorporation of filler on the mechanical properties of nanocomposites. In addition, treating the nanocomposites with surfaces of specific topography can help improve the mechanical properties of nanocomposites.

Influence of topography on the variation in mechanical performance of 1.0 wt% multi-layer graphene (MLG)/nanoclay-epoxy samples has been investigated. Three different systems were produced: 1.0 wt% MLG-EP, 1.0 wt% nanoclay-EP, and 0.5 wt% MLG-0.5 wt% nanoclay-EP. The influence of synergistic effect on mechanical performance in case of hybrid nanocomposites is also studied. Various topography parameters studied include maximum roughness height (Rz or Rmax), root mean square value (Rq), roughness average (Ra), and surface waviness (Wa). The Rz of as-cast 1.0 wt% multi-layer graphene, nanoclay, and 0.5 wt% MLG-0.5 wt% nanoclay-EP nanocomposites were 41.43 µm, 43.54 µm, and 40.28 µm, respectively. The 1200P abrasive paper and the velvet cloth decreased the Rz value of samples compared with as-cast samples. In contrary, the 60P and 320 P abrasive papers increased the Rz values. Due to the removal of material from the samples by erosion, the dimensions of samples decreased. The weight loss due to erosion was commensurate with the coarseness of abrasive papers. It was recorded that multi-layer graphene is more influential in enhancing the mechanical performance of epoxy nanocomposites than nanoclay. Additionally, it was observed that mechanical performance of hybrid nanocomposites did not show a marked difference suggesting that synergistic effects are not strong enough in multi-layer graphene and nanoclay.

One of the main issues in the production of polymer nanocomposites is the dispersion state of filler as multilayered graphene (MLG) and carbon nanotubes (CNTs) tend to agglomerate due to van der Waals forces. The agglomeration can be avoided by using organic solvents, selecting suitable dispersion and production methods, and functionalizing the fillers. Another proposed method is the use of hybrid fillers as synergistic effects can cause an improvement in the dispersion state of the fillers. In this review article, various aspects of each process that can help avoid filler agglomeration and improve dispersion state are discussed in detail. This review article would be helpful for both current and prospective researchers in the field of MLG- and CNT-based polymer nanocomposites to achieve maximum enhancement in mechanical, thermal, and electrical properties of produced polymer nanocomposites.

Metal–insulator–metal (MIM) diodes have attracted much attention in recent years because of the possibility of operating at very high frequencies (HFs), well into the terahertz range, a promise first highlighted over 30 years ago. The MIM diode is a quantum device wherein a thin dielectric is sandwiched between two metal electrodes with dissimilar work functions, which cause an asymmetric electric current to flow through the dielectric with respect to the polarity of the electrodes. The asymmetry at zero bias can be further increased by maximizing the work function difference between the two electrodes. This increases the possibility for the diode to operate without the need for an externally applied bias, making it a useful component in a wide range of applications, including radio-frequency identification tags, thermal-energy harvesting, and HF detectors and mixers.\ud \ud The fabrication of MIM diodes has been reported in the literature using several fabrication techniques. In this paper, the device has been fabricated using a low-cost technique where the dielectric layer consists of octadecyltrichlorosilane (OTS), an amphiphilic molecule consisting of an alkyl chain and a polar head group, commonly used to functionalize the surface of silicon dioxide (SiO2). Its thickness is essentially determined by the length of the alkyl chain, rather than process conditions, with a typical value of approximately 2 nm. An OTS layer was sandwiched between titanium and platinum, which have a work function difference of 1.4 eV thereby resulting in a strong nonlinear current–voltage (J –V) characteristic.

Lithium ion batteries have attained great success in commercialization owing to their high energy density. However, the relatively delaying discharge/charge severely hinders their high power applications due to intrinsically diffusion-controlled lithium storage of the electrode. This study demonstrates an ever-increasing surface redox capacitive lithium storage originating from an unique microstructure evolution during cycling in a novel RGO–MnO–RGO sandwich nanostructure. Such surface pseudocapacitance is dynamically in equilibrium with diffusion-controlled lithium storage, thereby achieving an unprecedented rate capability (331.9 mAh g−1 at 40 A g−1, 379 mAh g−1 after 4000 cycles at 15 A g−1) with outstanding cycle stability. The dynamic combination of surface and diffusion lithium storage of electrodes might open up possibilities for designing high-power lithium ion batteries.

Influence of topography on the variation in mechanical performance of 0.5 wt% multi-layer graphene (MLG)/nanoclay-epoxy nanocomposites has been studied. Three different systems were produced: 0.5 wt% MLG-EP, 0.5 wt% nanoclay-EP, and 0.25 wt% MLG-0.25 wt% nanoclay-EP. The influence of synergistic effect on mechanical performance in case of hybrid nanocomposites is also studied. Various topography parameters studied include maximum roughness height (Rz or Rmax),root mean square value (Rq),roughness average (Ra), and surface waviness (Wa).The Rz of as-cast 0.5 wt% MLG, nanoclay, and 0.25 wt% MLG-0.25 wt% nanoclay-EP nanocomposites were 41.43 μm, 43.54 μm, and 40.28 μm, respectively. The 1200P abrasive paper and the velvet cloth decreased the Rzvalue of samples compared with as-cast samples. In contrary, the 60P and 320P abrasive papers increased the Rz values. Due to the removal of material from the samples by erosion, the dimensions of samples decreased. The weight loss due to erosion was commensurate with the coarseness of abrasive papers. It was observed that MLG is more influential in enhancing the mechanical performance of epoxy nanocomposites than nanoclay. In addition, it was observed that mechanical performance of hybrid nanocomposites did not show a marked difference suggesting that synergistic effects are not strong enough in MLG and nanoclay.

The topographical features of fractured tensile, flexural, K1C, and impact specimens of0.5 wt% multi-layer graphene (MLG)/nanoclay-epoxy (EP) nanocomposites have been investigated.The topographical features studied include maximum roughness height (Rmax or Rz),root meansquare value (Rq), roughness average (Ra), and waviness (Wa).Due to the deflection and bifurcationof cracks by nano-fillers, specific fracture patterns are observed. Although these fracture patternsseem aesthetically appealing, however, if delved deeper, they can further be used to estimate theinfluence of nano-filler on the mechanical properties. By a meticulous examination of topographicalfeatures of fractured patterns, various important aspects related to fillers can be approximated such asdispersion state, interfacial interactions, presence of agglomerates, and overall influence of theincorporation of filler on the mechanical properties of nanocomposites. In addition, treating thenanocomposites with surfaces of specific topography can help improve the mechanical properties ofnanocomposites.

A series of Co 3 O 4 /Ketjen Black cathodes are fabricated by electrostatic spray deposition technique for Li–O 2 batteries. A sluggish kinetics of oxygen reduction reaction and oxygen evolution reaction processes is noted either when Co 3 O 4 is lacked or Ketjen Black is insufficient, which leads to much higher overpotentials between charge and discharge profiles. By contrast, with the optimal design in terms of electric conduction and catalytic activity, the Co 3 O 4 /Ketjen Black (80 wt%) composite achieves enhanced electrochemical performance with an initial discharge capacity of 2044 mAh g −1 and maintaining 33 cycles at a fixed capacity of 500 mAh g −1 . The electrochemical characterization indicates that the improved Li–O 2 battery performance may benefit from the highest oxygen reduction reaction and oxygen evolution reaction activity under this electro-chemically optimized composite. This work may shed light on the design principle of future cathode materials for Li–O 2 batteries.

The effects of annealing treatment between 400 °C and 540 °C on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO4) thin films are investigated in this work. The results show that higher temperature leads to larger grain size, improved crystallinity, and better crystal orientation for the BiVO4 thin film electrodes. Under air-mass 1.5 global (AM 1.5) solar light illumination, the BiVO4 thin film prepared at a higher annealing temperature (500–540 °C) shows better PEC OER performance. Also, the OER photocurrent density increased from 0.25 mA cm−2 to 1.27 mA cm−2 and that of the oxidation of sulfite, a hole scavenger, increased from 1.39 to 2.53 mA cm−2 for the samples prepared from 400 °C to 540 °C. Open-circuit photovoltage decay (OCPVD) measurement indicates that BiVO4 samples prepared at the higher annealing temperature have less charge recombination and longer electron lifetime. However, the BiVO4 samples prepared at lower annealing temperature have better EC performance in the absence of light illumination and more electrochemically active surface sites, which are negatively related to electrochemical double-layer capacitance (Cdl). Cdl was 0.0074 mF cm−2 at 400 °C and it decreased to 0.0006 mF cm−2 at 540 °C. The OER and sulfide oxidation are carefully compared and these show that the efficiency of charge transport in the bulk (ηbulk) and on the surface (ηsurface) of the BiVO4 thin film electrode are improved with the increase in the annealing temperature. The mechanism behind the light-condition-dependent role of the annealing treatment is also discussed.

Orthorhombic Nb2O5 (T-Nb2O5) nanocrystallites are successfully fabricated through an evaporation induced self-assembly (EISA) method guided by a commercialised triblock copolymer – Pluronic F127. We demonstrate a morphology transition of T-Nb2O5 from continuous porous nanofilms to monodisperse nanoparticles by changing the content of Pluronic F127. The electrochemical results show that the optimized monodisperse Nb-2 with a particle size of 20 nm achieves premier Li-ion intercalation kinetics and higher rate capability than mesoporous T-Nb2O5 nanofilms. Nb-2 presents an initial intercalation capacity of 528 and 451 C g−1 at current densities of 0.5 and 5 A g−1 and exhibited a stable capacity of 499 C g−1 after 300 charge/discharge cycles and 380 C g−1 after 1000 cycles, respectively. We would expect this copolymer guided monodispersion of T-Nb2O5 nanoparticles with high Li+ intercalation performance to open up a new window for novel EES technologies.

Cu2ZnSn(S,Se)4 (CZTSSe) thin film photovoltaic absorber layers are fabricated by selenizing Cu2ZnSnS4 (CZTS) nanoparticle thin films in a selenium rich atmosphere. The selenium vapor pressure is controlled to optimize the morphology and quality of the CZTSSe thin film. The largest grains are formed at the highest selenium vapor pressure of 226mbar. Integrating this photovoltaic absorber layer in a conventional thin film solar cell structure yields a champion short circuit current of 37.9mA/cm2 without an antireflection coating. This stems from an improved external quantum efficiency characteristic in the visible and near-infrared part of the solar spectrum. The physical basis of this improvement is qualitatively attributed to a substantial increase in the minority carrier diffusion length.

A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.

High-performance perovskite solar cells have attracted increased attention for photovoltaic applications and potentially replacing the predecessor generations. Nevertheless, the stability issues and the lead content has always been among the major concerns that barriers perovskite solar cells from commercialization. This review presents the discussion towards the inherent instability of perovskite solar cells and the development towards replacing lead with discussion towards their performance and challenges. The degradation of perovskite active layer would release toxic substance into the environment. The development towards low-toxic, lead-free and efficient perovskite solar cells is the key for a sustainable solar energy generation with the application of perovskite solar cells.

Effects of partial pressure of methane on deposition rate, hardness, bonding strength and friction coefficient of TiAlN/TiAlC0.37N0.63 multilayer coating were investigated. The TiAlN coating was deposited at a N2 flow rate of 70 sccm, and TiAlC0.37N0.63 coating were deposited at a N2 flow rate of 35 sccm and a CH4 flow rate of 35 sccm. TiAlN/TiAlC0.37N0.63 multilayer coatings with different modulation periods but the same total thickness of 3.56 μm were deposited on high speed steel (HSS) substrates using multi-arc ion plating technology. Microhardness and tribological measurement show that the multilayer coating with a modulating ratio of 1:1 and a modulation period of 68 nm had a hardness of 2793.9 HV0.10, an excellent bonding strength of 52 N, and the minimum friction coefficient of 0.46 and a relatively low wear rate.

International audience; The performance of organic-inorganic hybrid thermoelectric thin films can be dramatically enhanced by optimizing energy filtering and carrier transport states at the organic-inorganic interfaces. In this work, p-type "Sb2Te3/CH3NH3I/Sb2Te3" multilayer thin films were firstly fabricated with varied contents of CH3NH3I, and then an annealing process was used in order to form homogeneous organic-inorganic hybrid thin films. The results revealed that the introduced organic component can promote thin film growth and develop a dense nanostructure with improved crystallinity, thus resulting in a significantly increased Seebeck coefficient and a reduced thermal conductivity as a result of the optimized electronic transport characteristics and enhanced effects of phonon scattering. As is expected, the thermoelectric performance of the hybrid-nanocomposite films is enhanced, achieving the maximum ZT value of 1.55 at a temperature of 413 K, which is several times higher than that of the as-fabricated film, thereby suggesting that the proposed strategy can be applied as an efficient method for the preparation of high-performance thermoelectric thin films.

A platinum-coated singlemode-multimode (SM) structure is investigated in this paper as an optical fibre sensor (OFS) to monitor the phase transition of a phase change material (PCM). Paraffin wax has been used as an example to demonstrate the sensor’s performance and operation. Most materials have the same temperature but different thermal energy levels during the phase change process, therefore, sole dependency on temperature measurement may lead to an incorrect estimation of the stored energy in PCM. The output spectrum of the reflected light from the OFS is very sensitive to the bend introduced by the PCM where both liquid and solid states exist during the phase transition. The measurement of strain experienced by the OFS during the phase change of the PCM is utilized for identifying the phase transition of paraffin wax between the solid and liquid states. The experimental results presented in this paper show that the OFS with a shorter multimode fibre section has better performance for monitoring the phase transition of paraffin wax with a measured phase transition temperature range of 41.5 ºC – 57.7 ºC for the SM based OFS with a 5 mm long multimode fibre section.

We show that micron-scale two-dimensional (2D) honeycomb microwells can significantly improve the stability of blue phase liquid crystals (BPLCs). Polymeric microwells made by direct laser writing improve various features of the blue phase (BP) including a dramatic extension of stable temperature range and a large increase both in reflectivity and thermal stability of the reflective peak wavelength. These results are mainly attributed to the omni-directional anchoring of the isotropically oriented BP molecules at the polymer walls of the hexagonal microwells and at the top and bottom substrates. This leads to an omni-directional stabilization of the entire BPLC system. This study not only provides a novel insight into the mechanism for the BP formation in the 2D microwell but also points to an improved route to stabilize BP using 2D microwell arrays., Comment: 16 pages, 5 figures

Graphene has recently attracted significant academic and industrial interest because of its excellent performance in mechanical, electrical and thermal applications. Graphene can significantly improve physical properties of epoxy at extremely small loading when incorporated appropriately. Herein, the structure, preparation and properties of epoxy/graphene nanocomposites are reviewed in general, along with detailed examples drawn from the key scientific literature. The modification of graphene and the utilization of these materials in the fabrication of nanocomposites with different processing methods have been explored. This review has been focused on the processing methods and mechanical, electrical, thermal, and fire retardant properties of the nanocomposites. The synergic effects of graphene and other fillers in epoxy matrix have been summarised as well.

A heat transfer model of polymer composite reinforced by buckypaper was established in this study to analyze how the shapes, heating power and thermal conductivity of polymer matrix affect the temperature distribution and heating uniformity. Thermal responses of the polymer composites reinforced by flat and pulse bending buckypaper were systematically studied, and the heating mechanisms of multiple-field coupling were investigated. The shapes and dimensions of the buckypaper are crucial in the optimization of such the polymer composites for heat generation. Results showed that the polymer composites reinforced by the flat buckypaper had relatively higher maximum and average temperatures in a steady heated state compared with those by the pulse bending ones, whereas the minimum temperature of the composites reinforced by the flat buckypaper was relatively lower, so the temperature distribution in those flat ones was more non-uniform. The overall heating temperature of the polymer composites reinforced by both the flat and pulse bending buckypaper was increased linearly with the applied power. The larger the thermal conductivity of the polymer is, the lower the maximum and average temperatures are.

It is generally recognized that dimethylformamide (DMF) and ethanol are good media to uniformly disperse graphene, and therefore have been used widely in the preparation of epoxy/graphene nanocomposites. However, as a solvent to disperse graphene, dichlorobenzene (DCB) has not been fully realized by the polymer community. Owing to high values of the dispersion component ( δ d ) of the Hildebrand solubility parameter, DCB is considered as a suitable solvent for homogeneous graphene dispersion. Therefore, epoxy/graphene nanocomposites have been prepared for the first time with DCB as a dispersant; DMF and ethanol have been chosen as the reference. The colloidal stability, mechanical properties, thermogravimetric analysis, dynamic mechanical analysis and scanning electron microscopic images of nanocomposites have been obtained. The results show that with the use of DCB, the tensile strength of graphene has been improved from 64.46 to 69.32 MPa, and its flexural strength has been increased from 97.17 to 104.77 MPa. DCB is found to be more effective than DMF and ethanol for making stable and homogeneous graphene dispersion and composites.

The influence of short-term water absorption on the mechanical properties of halloysite nanotubes-multi layer graphene reinforced polyester hybrid nanocomposites has been investigated. The addition of nano-fillers significantly increased the flexural strength, tensile strength, and impact strength in dry and wet conditions. After short-term water exposure, the maximum microhardness, tensile, flexural and impact toughness values were observed at 0.1 wt % multi-layer graphene (MLG). The microhardness increased up to 50.3%, tensile strength increased up to 40% and flexural strength increased up to 44%. Compared to dry samples, the fracture toughness and surface roughness of all types of produced nanocomposites were increased that may be attributed to the plasticization effect. Scanning electron microscopy revealed that the main failure mechanism is caused by the weakening of the nano-filler-matrix interface induced by water absorption. It was further observed that synergistic effects were not effective at a concentration of 0.1 wt % to produce considerable improvement in the mechanical properties of the produced hybrid nanocomposites.

Ferromagnetic materials have been utilized as recording media in data storage devices for many decades. The confinement of a material to a two-dimensional plane is a significant bottleneck in achieving ultra-high recording densities, and this has led to the proposition of three-dimensional (3D) racetrack memories that utilize domain wall propagation along the nanowires. However, the fabrication of 3D magnetic nanostructures of complex geometries is highly challenging and is not easily achieved with standard lithography techniques. Here, we demonstrate a new approach to construct 3D magnetic nanostructures of complex geometries using a combination of two-photon lithography and electrochemical deposition. The magnetic properties are found to be intimately related to the 3D geometry of the structure, and magnetic imaging experiments provide evidence of domain wall pinning at the 3D nanostructured junction.

The fabrication and testing of metal-insulator-metal (MIM) diodes on a flexible substrate for microwave and mm-wave applications are presented. The diodes utilized octadecyltrichlorosilane (OTS), which self assembles to form a thin, pin holes free insulator. Preliminary electrical analysis shows that the diodes have a typical zero bias resistance of approximately 80 kΩ, zero-bias curvature coefficient (γ_ ZB ) of approximately 5.5 V−1, and voltage responsivity of 3.1 kV/W at a frequency of 1 GHz, and are produced with over 90% device yield. The fabrication process is simple and cost effective, environmentally friendly, and demonstrates the possibility of roll-to-roll volume manufacturing of MIM diodes.

Antimony selenide (Sb2Se3) is regarded as one of the key alternative absorber materials for conventional thin film solar cells due to its excellent optical and electrical properties. Here, we proposed a Sb2Se3 thin film solar cell fabricated using a two-step process magnetron sputtering followed by a post-selenization treatment, which enabled us to optimize the best quality of both the Sb2Se3 thin film and the Sb2Se3/CdS heterojunction interface. By tuning the selenization parameters, a Sb2Se3 thin film solar cell with high efficiency of 6.06% was achieved, the highest reported power conversion efficiency of sputtered Sb2Se3 planar heterojunction solar cells. Moreover, our device presented an outstanding open circuit voltage (VOC) of 494 mV which is superior to those reported Sb2Se3 solar cells. State and density of defects showed that proper selenization temperature could effectively passivate deep defects for the films and thus improve the device performance.

This paper describes an experimental programme which examines the reinforcement in flexure of timber beams with composite materials based on natural fibers in the form of fabrics made from hemp, flax, basalt and bamboo fibers. The industrial use of natural fibers has been continuously increasing since 1990s due to their advantages in terms of production costs, pollution emissions and energy consumption for production and disposal. The technique allows the reinforcement of the intrados of beams, avoiding the dismantling of the overlying part of the structure with significant savings in terms of costs and work time. The test program consists of three phases incorporating 45 beams. The bending tests on the wooden elements made it possible to measure the increase in capacity and stiffness resulting from the composite reinforcement. This was applied to beams, creating different arrangements and using different quantities (number of layers). Despite the diversity of the various tests carried out, the results obtained in some cases showed significant increases in terms of load-carrying capacity and in deflection ductility.

The topographical features of fractured tensile, flexural, K1C, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of samples before fracture. The topographical features studied include waviness (Wa), roughness average (Ra), root mean square value (Rq), and maximum roughness height (Rmax or Rz). As surface notches generate triaxial state of stress, therefore, the crack propagation is precipitated resulting in catastrophic failure. Although surfaces can be examined before fracture for any deleterious topographical elements, however, fractured surfaces can reveal finer details about the topography. It is because, as discussed in this article, surfaces with specific topography produce fracture patterns of peculiar aesthetics, and if delved deeper, they can further be used to estimate about the topography of surfaces before fracture. In addition, treating the samples with surfaces of specific topography can help improve the mechanical properties of monolithic epoxy.