Molecular weight (Mw) effects in poly(vinylidene fluoride) (PVDF) influence both processability and combustion behavior in energetic Al–PVDF filaments. Results show decreased viscosity in unloaded and fuel-lean (i.e., 15 wt% Al) filaments. In highly loaded filaments (i.e., 30 wt% Al), reduced viscosity is minimal due to higher electrostatic interaction between Al particles and low Mw chains as confirmed by Fourier-transform infrared spectroscopy. Thermal and combustion analysis further corroborates this story as exothermic activity decreases in PVDF with smaller Mw chains. Differential scanning calorimetry and Thermogravimetric analysis show reduced reaction enthalpy and lower char yield in low Mw PVDF. Enthalpy reduction trends continued in nonequilibrium burn rate studies, which confirm that burn rate decreases in the presence of low Mw PVDF. Furthermore, powder X-ray patterns of post-burn products suggest that low Mw PVDF decomposition creates a diffusion barrier near the Al particle surface resulting in negligible AlF3 formation in fuel-rich filaments.

In this work, graphene and graphene oxide were synthesized by the modified Hummers method. In order to use graphene in dye-sensitized solar cell (DSSC), TiO2–graphene was prepared by a simple chemical method and used in the DSSC photoanode at different concentrations of graphene to investigate DSSC performance. Utilizing the FE-SEM images, it was observed that accumulation of TiO2 nanoparticles disappeared and a different distribution of nanoparticles was formed on the graphene sheet. Moreover, the UV-vis spectra showed that TiO2–graphene nanocomposites can absorb a wide range of light in comparison with pure TiO2. Structural characterization of TiO2–graphene nanocomposites is confirmed by the FT-IR and Raman analysis. The results have shown that in the presence of graphene, the DSSC performance significantly improved by reducing the recombination. In addition, it has been shown that excess graphene concentration is not proper for DSSC performance. The best result for TiO2–graphene nanocomposite was obtained when the concentration of 1.5% graphene was applied.

This work describes exploration of mitigating the parasitic amorphous alumina (Al2O3) shell of aluminum nanoparticles (n-Al) and modifying the surface using different plasmas, leading to n-Al with thinner shell and different coatings including carbons and oxidizing salt called aluminum iodate hexahydrate (AIH), respectively. The approach exploits a prototype atmospheric non-thermal plasma reactor with dielectric barrier discharge (DBD) configuration for nanoparticle surface modifications using n-Al of 80 nm average diameter as an example. Preliminary results indicate that the amorphous Al2O3 shell surrounding the active aluminum core can be mitigated with inert plasmas by as much as 40% using either helium (He) or argon (Ar). The particle surface becomes carbon-rich with carbon monoxide (CO) / He plasmas. By immersing the plasma-treated n-Al in an iodic acid (HIO3) solution, AIH crystals can be formed on the n-Al surface. Transmission electron microscopy (TEM) is used as a major tool to study the details of the modified surface morphologies, diffraction patterns, and chemical composition of the modified n-Al. The results demonstrate effective surface passivation of n-Al via atmospheric plasma techniques.

Self-powered smart systems utilizing the high voltages generated by triboelectric nanogenerators (TENGs) have been systematically reviewed, with several featured applications highlighted, including electrospray, optical device, microplasma, and microfluidic.

To provide a sustainable power solution for electronics, triboelectric nanogenerator (TENG) has been developed since 2012 for high-efficiency mechanical energy harvesting from the ambient environment. TENG has very unique output characteristics including high voltage and limited current density. Thus, it is challenging to directly power most of the commercial electronics in high efficiency. However, these features also bring opportunities for high-voltage applications. Here, we will review the efforts for developing TENG as a controllable high-voltage power source for various applications. The review article will start from fundamental studies about how the high-voltage output was generated, and then, several representative research in recent years will be reviewed, including electrospray, optical devices, microplasma, field emission, and electrically responsive materials. These studies will drive the further development of TENG technology for broad applications and industrializations toward high-efficiency self-powered systems.

The heat transfer properties of the organic molecular crystal α-RDX were studied using three phonon scattering based thermal conductivity models. It was found that the widely used Peierls-Boltzmann model for thermal transport in crystalline materials breaks down for α-RDX. We show this breakdown is due to a large degree of anharmonicity that leads to a dominance of diffusive-like carriers. Despite being developed for disordered systems, the Allen-Feldman theory for thermal conductivity actually gives the best description of thermal transport. This is likely because diffusive carriers contribute to over 95% of the thermal conductivity in α-RDX. The dominance of diffusive carriers is larger than previously observed in other fully ordered crystalline systems. These results indicate that van der Waals bonded organic crystalline solids conduct heat in a manner more akin to amorphous materials than simple atomic crystals.

Formamidinium–tin–strontium halides (CH(NH2)2Sn1−ySryX3 (FASnX3), X = I, Br and 0.0 ≤ y ≤ 0.1) were investigated. X-ray diffraction analysis revealed orthorhombic FASnI3 (space group Amm2) and SnI2 for X = I as well as cubic FASnBr3 (space group $Pm\bar{3}m$) and SnBr2 for X = Br, respectively. For X = I, the optical spectra displayed a decrease of the absorption edges with increasing Sr content (1055 nm, y = 0.0; 950–960 nm, y > 0.0) and a direct semiconducting behavior with narrow band energy gaps (1.31–1.34 eV). For X = Br, on increasing the absorption edges (492 nm, y = 0.0; 975 nm, y = 0.075), a direct semiconducting behavior with band energy gaps between 2.65 eV (y = 0.0) and 1.38 eV (y = 0.075) were observed and the emission photoluminescence (PL) spectra (excitation wavelength λexc = 380 nm) showed an increase of the luminescence response after the thermal treatment.

There is currently a need for an efficient approach to control magnetism at small scales (<1 mm). Work on these magnetoelectric concepts dates back to the 19th century, when researchers believed that a material could convert electrical to magnetic energy, similar to Oersted’s discovery, made by passing a current through a wire. Today, there are significant magnetoelectric research opportunities in both materials discovery and theoretical modeling efforts to advance this important area of magnetic control. Applications for these strain-mediated magnetoelectric materials range from replacing existing inefficient magnetic memory approaches to spearheading new discoveries, such as micrometer-size electromagnetic motors enabling robotic manipulation. This article and the other articles in this issue provide the motivation, background information, research opportunities, and novel applications for studying strain-mediated magnetoelectric materials. The issue is designed to encourage additional research on magnetoelectrics due to its potential impact on society through the efficient control of magnetism at the micro- and nanoscale.

The electrochemical behavior of TiNi(1−x)Nbx (x = 0, 0.05, 0.1, 0.2) ternary intermetallic compounds synthesized by mechanical alloying was investigated and compared to that of binary TiNi. The structure of 20-h milled product with initial stoichiometric composition of TiNi0.95Nb0.05 was found to be amorphous/nanostructured. Upon cycling, this ternary milled product exhibited the highest discharge capacity (166.1 mA h/g) after 10 cycles and best cycle stability (∼91%) while those of the binary TiNi were 147 mA h/g and ∼83%, respectively; i.e., slight amount of Nb substitution (0.05 mol) for Ni in the TiNi not only increased discharge capacity and cycle stability but also enhanced the kinetics of hydrogen absorption/desorption through increasing the exchange current density and hydrogen diffusion coefficient. However, additional Nb content was found to have negative effect on electrochemical properties; this was related to the existence of Nb element in addition to the ternary amorphous/nanocrystalline structures.

N-doped ordered mesoporous carbon (N-OMC) has been one of the most promising choices as the electrode for supercapacitors due to its large surface area and uniform mesoporous structure. However, there is still a big challenge to prepare N-OMC using a relatively simple method. Here, a straightforward preparation of N-OMC was reported in which the precursor zeoliticimidazolate framework was in situ grown in the SBA-15 template by a fast, solvent-free, and atom economic solid–solid grinding strategy. After pyrolysis and removing of the template, the N-OMC was obtained with ordered mesoporous structure, rich oxygen and nitrogen, and a large specific surface area of 1004 m2/g. As the electrode material for supercapacitors, N-OMC displayed an excellent specific capacitance of 228 F/g at 0.2 A/g and superb charge/discharge cycling stability, which is promising for high-performance energy storage. This solid–solid grinding strategy may offer a low-cost and scalable method to produce high-performance N-OMC for the electrode from the zeoliticimidazolate framework.

This work is part of the interlaboratory collaboration to study the stability of organic solar cells containing PCDTBT polymer as a donor material. The varieties of the OPV devices with different device architectures, electrode materials, encapsulation, and device dimensions were prepared by seven research laboratories. Sets of identical devices were aged according to four different protocols: shelf lifetime, laboratory weathering under simulated illumination at ambient temperature, laboratory weathering under simulated illumination, and elevated temperature (65 °C) and daylight outdoor weathering under sunlight. The results generated in this study allow us to outline several general conclusions related to PCDTBT-based bulk heterojunction (BHJ) solar cells. The results herein reported can be considered as practical guidance for the realization of stabilization approaches in BHJ solar cells containing PCDTBT.

The fundamentals and applications of ferroic materials—ferromagnetic, ferroelectric, and ferroelastic—are common subjects discussed in just about every graduate course related to functional materials. Looking beyond today’s traditional uses, such as in permanent magnets, capacitors, and shape-memory alloys, there are worthwhile and interesting questions common to the caloric properties of these ferroic materials. Can ferroic materials be used in a cooling cycle? Why are these materials susceptible to external fields? Which combination of properties is required to make some of them suitable for efficient cooling and heat pumping? We address these questions in this introduction to ferroic cooling, which comprises magnetocaloric, electrocaloric, elastocaloric and barocaloric approaches and combinations thereof (i.e., multicalorics). These are addressed in greater detail in the articles in this issue.

The human body is a challenging platform for energy harvesting. For thermoelectrics, the small temperature differences between the skin and air necessitate materials with low thermal conductivities in order to maintain useful output powers. For kinetic harvesting, human motion is not strongly tonal, the frequencies are very low, and the accelerations are modest. Kinetic harvesting can be split into two categories—inertial, in which human motion excites an inertial mass–the motion of which is transduced to electricity, and clothing integrated, in which the harvesting material is integrated with a garment or other flexible wearable system. In the first case, key issues are the electromechanical dynamics of the system and materials with improved electromechanical transduction figures of merit. In the second case, materials that provide flexibility, stretchability, and comfort are of primary importance.

Morphological control of energetic materials (EM) is highly desired because ill-defined morphology arising from variations in processing method and supplier make it impossible to reproducibly engineer their physicochemical properties. As the most powerful, non nuclear energetic material to date, 2,4,6,8,10,12-hexanitro -2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) has been the subject of significant interest for improved applications in military grade explosives. Here we report a new method for recrystallization of CL-20 from irregular bulk EMs using a surfactant assisted self-assembly process to produce uniform spherical micron-sized particles. Detailed electron microscopy studies indicate that surfactant plays a critical role in controlling CL-20 morphology. Combined X-ray diffraction and Raman spectroscopy results reveal that the resultant spherical CL-20 particles exhibit an orthorhombic β-phase crystal structure. This material is expected to display enhanced functional reproducibility due to its monodisperse nature as well as decreased shock sensitivity due to their sub-micron particle size.

A brief review of the status of our understanding of the occupation of the Pu 5f states is provided herein, with an emphasis upon experimental measurements.

The atmospheric pressure plasma sources with a coaxial geometry were used for generation of the radio frequency, microwave and pulsed dc plasmas inside water and aqueous solutions. Pulsed dc plasma generated in ethanol-water mixtures leads to production of the hydrogen-rich synthesis gas with hydrogen content up to 65 %. The effect of various plasma generation regimes on the performance of plasma, on the hydrogen production efficiency and on the hydrogen-rich synthesis gas production was examined. A role of the composition of the ethanol-water mixture was investigated.

Nanoenergetic composites are of overwhelming interest to the Department of Defense because of the higher power output and the ability to finely tune the ignition thresholds of these composites. Recently, several variants of a nanoaluminum-poly(perfluorinated methacrylate) (AlFA) have been synthesized and optimized for a variety of applications including reactive warhead liners and bullet spotters. While conventional techniques such as thermal analysis and bomb calorimetry can be used to characterize the reaction mechanism and energy output of AlFA composites, characterizing their dynamic behaviour is more challenging. Bullet spotter applications require a material to be impact sensitive at very low velocities, yet be adequately insensitive. Several live-fire tests were conducted which revealed the AlFA50 material reacted consistently upon target impact at high velocities, but unreliably at very low velocities. In an effort to better understand the fundamental impact ignition mechanism and to determine the impact velocity threshold of AlFA50 a series of Taylor gas gun experiments were conducted. It was determined that the light-initiation mechanism was consistent with a pinch mechanism, and that the ignition velocity threshold was near 74 m/s. Based on these results, it was hypothesized that the addition of a filler material could be used to sensitize the AlFA50, and that Asay shear impact testing could be used to determine a more optimal shape of such inclusions. Experiments performed using the Asay shear impact test setup confirmed the pinch ignition mechanism, but observations also revealed that the size of the pinch point was important. Finally, it was shown that the addition of large glass beads (> 1mm in diameter) was effective at sensitizing the AlFA50 material at high and low velocities, with ignition observed at impact velocities as low as 35 m/s.

Schwarzites are crystalline, 3D porous structures with a stable negative curvature formed of sp2-hybridized carbon atoms. These structures present topologies with tunable porous size and shape and unusual mechanical properties. In this work, we have investigated the mechanical behavior under compressive strain and energy absorption of four different Schwarzites. We considered two Schwarzites families, the so-called Gyroid and Primitive and two structures from each family. We carried out reactive molecular dynamics simulations, using the ReaxFF force field as available in the LAMMPS code. Our results also show they exhibit remarkable resilience under mechanical compression. They can be reduced to half of their original size before structural failure (fracture) occurs.

Lithium–sulphur (Li–S) batteries are one of the most promising candidates for the next generation of energy storage systems to alleviate the energy crisis. However, Li–S batteries’ commercialization faces the challenges of low active materials utilization, poor cycling life, and low energy density. Recently, tremendous progress has been achieved in improving the electrode performances and tap density by using the nanostructured metal compounds in Li–S batteries. In this review, we not only present the latest various nanostructured metal compounds applications in Li–S batteries, including metal oxides, metal sulphides, metal carbides, metal nitrides, and metal organic frameworks, but also we focus on the interaction mechanisms between these polar metal compounds with polysulphides. The issues and bottlenecks of these metal compounds are concluded and the corresponding available solutions to address these issues are proposed. This systematic discussion and proposed strategies can offer avenues to the practical application of Li–S batteries in the near future.

High iodine containing oxides are of interest as biocidal components in energetic applications requiring fast exothermic reactions with metallic fuels. Aerosol techniques offer a convenient route and potentially direct route for preparation of small particles with high purity, and are a method proven to be amenable and economical to scale-up. Here, we demonstrate the synthesis of various iodine oxide/iodic acid microparticles by a direct one-step aerosol method from iodic acid. By varying temperature and humidity, we produced near phase pure δ-HIO3, HI3O8, and I2O5 as determined by X-ray diffraction. δ-HIO3, a previously unknown phase, was confirmed in this work. In addition, scanning electron microscopy was used to examine the morphology and size of those prepared iodine oxide/iodic acid particles and the results show that all particles have an irregularly spherical shape. Thermogravimetric/differential scanning calorimetry measurement results show that HIO3 dehydrates endothermically to HI3O8, and then to I2O. I2O5 decomposes to I2 and O2.

Many simple diatomic and triatomic molecules such as N2 and CO2 have the potential to form extended “polymeric” solids under extreme conditions, which can store a large sum of chemical energy in its three-dimensional network structures made of strong covalent bonds. Diatomic nitrogen is particularly of interest because of the uniquely large energy difference between that of the single bond (160 kJ/mol) and that of the triple bond (954 kJ/mol). As such, the transformation of a singly bonded polymeric nitrogen back to triply-bonded diatomic nitrogen molecules can release nearly 5 times the energy of TNT without any negative environmental impact. In this paper, we will describe our recent research efforts to synthesize novel extended phases of isoelectronic systems of N2 and CO, as well as those of N2+CO mixtures to lower the transition pressures and enhance the stability of recovered products at ambient condition.