Negative stiffness honeycombs are architected metamaterials that utilize elastic buckling to absorb mechanical energy. Relative to conventional honeycomb materials, they offer several advantages, including the ability to recover their initial configuration and offer consistently repeatable mechanical energy absorption. In this paper, fully recoverable negative stiffness honeycombs are fabricated from thermoplastic and metallic parent materials. The honeycombs are subjected to quasistatic and impact loading to demonstrate the predictability and repeatability of their energy absorption characteristics across a variety of loading conditions. Results indicate that these honeycombs offer nearly ideal shock isolation by thresholding the acceleration of an isolated mass at a predetermined level and that this thresholding behavior is highly repeatable as long as the magnitude of the mechanical energy imparted to the system does not exceed the energy absorption capacity of the honeycomb.

The temperature programmed molecular dynamics (TPMD) method is a recent addition to the list of rare-event simulation techniques for materials. Study of thermally-activated events that are rare at molecular dynamics (MD) timescales is possible with TPMD by employing a temperature program that raises the temperature in stages to a point where the transitions happen frequently. Analysis of the observed waiting time distribution yields a wealth of information including kinetic mechanisms in the material, their rate constants and Arrhenius parameters. The first part of this review covers the foundations of the TPMD method. Recent applications of TPMD are discussed to highlight its main advantages. These advantages offer the possibility for rapid construction of kinetic Monte Carlo (KMC) models of a chosen accuracy using TPMD. In this regards, the second part focuses on the latest developments on uncertainty measures for KMC models. The third part focuses on current challenges for the TPMD method and ways of resolving them.

Predictions of the mechanical response of polycrystalline metals and underlying microstructure evolution and deformation mechanisms are critically important for the manufacturing and design of metallic components, especially those made of new advanced metals that aim to outperform those in use today. In this review article, recent advancements in modeling deformation processing-microstructure evolution and in microstructure–property relationships of polycrystalline metals are covered. While some notable examples will use standard crystal plasticity models, such as self-consistent and Taylor-type models, the emphasis is placed on more advanced full-field models such as crystal plasticity finite elements and Green’s function-based models. These models allow for nonhomogeneity in the mechanical fields leading to greater insight and predictive capability at the mesoscale. Despite the strides made, it still remains a mesoscale modeling challenge to incorporate in the same model the role of influential microstructural features and the dynamics of underlying mechanisms. The article ends with recommendations for improvements in computational speed.

Solar steam generation is an efficient and green technology for desalination and drinking water purification, however, impeded by high cost, low efficiency, and complicated process. Black titania is expected to exhibit excellent solar steam performance due to its outstanding light absorption properties, chemical stability, low cost, and innocuity. Herein, we design a high absorbing and efficient solar steam generation system based on a black titania/graphene oxide nanocomposite film affixed to airlaid paper wrapped over the surface of expandable polyethylene foam; the system possesses several important criteria required for the ideal solar steam generator: wide-spectrum absorption, adequate water supply, reduced heat loss for localized water heating, and porous structure for steam flow. Remarkably, we realized a solar thermal conversion efficiency of 69.1% under illumination of 1 kW/m2 without solar concentration, and the device delivered remarkable cycle stability.

Cell morphology and relative density (ρrel) are two crucial intrinsic parameters controlling the mechanical properties of metal foams (MFs) and directly depend on their structure (closed/open-cell) and composition (affecting processing parameters). Here, we report on compressive studies of MFs of aluminum (Al) and 7075-T6 alloy processed via a customized route at strain rate, έ = 0.002 and 2.0 s−1. In both sets of MFs, the strength and apparent elastic modulus (E) monotonically increased with ρrel at both έ. At έ = 2.0 s−1, an increase in cell size (Cs) enhanced the strength of both sets of MFs, while at έ = 0.002 s−1, only the alloy foams showed strength increment. The densification strain (εd) of Al foams at έ = 0.002 s−1 monotonically decreased with increasing ρrel, whereas the alloy foams collapsed before the onset of densification. None of the MFs showed any particular trend of εd at έ = 2.0 s−1. The studies conclude that the mechanical properties of MFs with similar morphology, foam parameters, and processing route depend on έ and Cs. Absorption energy (W) and absorption efficiency (Im) of the two sets of MFs were also compared.

Combining density functional theory calculations and temperature programmed desorption (TPD) experiments, the adsorption behavior of various sulfur containing compounds, including C2H5SH, CH3SCH3, tetrahydrothiophene, thiophene, benzothiophene, dibenzothiophene, and their derivatives on the coordinately unsaturated sites of Mo27Sx model nanoparticles, are studied systematically. Sulfur molecules with aromaticity prefer flat adsorption than perpendicular adsorption. The adsorption of nonaromatic molecules is stronger than the perpendicular adsorption of aromatic molecules, but weaker than the flat adsorption of them. With gradual hydrogenation (HYD), the binding affinity in the perpendicular adsorption modes increases, while in flat adsorption modes it increases first, then decreases. Significant steric effects on the adsorption of dimethyldibenzothiophene were revealed in perpendicular adsorption modes. The steric effect, besides weakening adsorption, could also activate the S–C bonds through a compensation effect. Finally, by comparing the theoretical adsorption energies with the TPD results, we suggest that HYD and direct-desulfurization path may happen simultaneously, but on different active sites.

SnO2 aerogels were successfully synthesized by using SnCl4, ammonium hydroxide (AH), formamide, propylene oxide, and tetraethoxysilane as tin source, reaction promoter, drying control chemical additive (DCCA), gel accelerator, and surface modifier, respectively, via the sol–gel method, combined with subsequent ambient pressure drying of sol–gel. The results of Fourier transform infrared spectroscopy proved that the CH3CH2OSi-bond was transferred to SnO2 gel. A contact angle measuring instrument was utilized for the study of hydrophicity and hydrophobicity of SnO2 aerogels, and the complete porous skeleton structure of SnO2 aerogels was confirmed by field emission scanning electron microscopy (FESEM) and nitrogen adsorption–desorption analyzer, denoting AH allowed SnO2 aerogels to shape more macropores. Based on the thermal resistance tester, it showed that the SnO2 aerogels had low thermal conductivity. The biggest specific surface area and lowest thermal conductivity of SnO2 aerogels were 447.26 m2/g and 0.0717 K/(m•K), respectively.

Biomimicry is a desirable quality of tissue engineering scaffolds. While most of the scaffolds reported in the literature contain a single pore size or porosity, the native biological tissues such as cartilage and skin have a layered architecture with zone-specific pore size and mechanical properties. Thus, there is a need for functionally graded scaffolds (FGS). EHD-jet 3D printing is a high-resolution process and a variety of polymer solutions can be processed into 3D porous scaffolds at ease, overcoming the limitations of other 3D printing methods (SLS, stereolithography, and FDM) in terms of resolution and limited material choice. In this paper, a novel proof of concept study on fabrication of porous polycaprolactone-based FGS by using EHD-jet 3D printing technology is presented. Organomorphic scaffolds, multiculture systems, interfacial tissue engineering, and in vitro cancer metastasis models are some of the futuristic applications of these polymeric FGS.

As an important member of semiconducting transition metal oxides, MoO2 nanomaterials have many advantages in optical and electrical applications. However, MoO2 itself has no significant photocatalytic performance possibly because of its inferior conductivity and strong recombination of photogenerated electron–hole pairs. Here, we propose a facile, one-step pyrolysis method to prepare a novel C fibers@MoO2 nanoparticles core–shell composite, where the oxidative MoO2 nanoparticles in situ grew on the surface of conducting C fibers. Due to the compositing of MoO2 and C fibers, during photocatalysis tests, the recombination of photogenerated electron–hole pairs was effectively inhibited, and the lifetime of the photogenerated carries was efficiently prolonged, finally significantly improving the solar-driven photocatalytic activity on degrading various organic and inorganic pollutants in water, such as methylene blue, rhodamine B, phenol, and potassium dichromate, showing the great potential for environmental remediation by degrading toxic industrial chemicals in waste water under sunlight. Moreover, the composite presented good stability in composition and structure during the repeated use and long-term storage. In addition, this one-step growth method is an easy-to-handle, environmentally friendly, and low-cost synthesis method for large-scale production.

The microstructure evolution of high nitrogen austenitic steel wires under various annealing times and drawing temperatures was carefully characterized. Special attention was paid to the widely distributed twins and the nanoprecipitates at twin boundaries (TBs) in high nitrogen stainless steels (HNSSs). The results of microhardness indicated that the traditional Hall–Petch (H–P) equation, which only took the role of grain boundaries into account, was unsuitable. A new H–P equation that connected grain size, twin density, precipitates at TBs, and microhardness in HNSS was established for the first time and showed to be in good agreement with the experimental results. By analyzing the strained regions near TBs, a model describing the precipitation of nano-M23C6 carbides on coherent twin boundaries and incoherent twin boundaries was proposed. In addition, the influence mechanism of the nano-M23C6 at TBs on microhardness was discussed.

Here we report a facile and mild synthesis of the sulfonated graphene (PSS-RGO) catalysts by in situ polymerization of sodium p-styrenesulfonate. Graphene sheets can be used as the flat backbones to graft abundant sulfonate groups on both sides. The PSS-RGO catalysts were characterized by 1H Nuclear Magnetic Resonance (1H NMR), energy dispersive spectrometer, Raman spectroscopy, X-ray photoelectron spectroscopy, and so on. The catalytic properties of the PSS-RGO catalysts for the hydrolysis of ethyl acetate and the esterification of acetic acid with ethanol were evaluated, showing that the as-made PSS-RGO catalysts were active for both probe reactions. The possible deactivation mechanism involved in the surface catalysis of the graphene-based acid catalysts has been addressed.

In Part I, equal channel angular extrusion (ECAE) was demonstrated as a novel, simple-shear deformation process for producing bulk forms of the low ductility Fe–Co–2V (Hiperco 50A®) soft ferromagnetic alloy with refined grain sizes. Microstructures and mechanical properties were discussed. In this Part II contribution, the crystallographic textures and quasi-static magnetic properties of ECAE-processed Hiperco were characterized. The textures were of a simple-shear character defined by partial {110} and 〈111〉 fibers inclined relative to the extrusion direction, in agreement with the expectations for simple-shear deformation textures of BCC metals. These textures were observed throughout all processing conditions and only slightly reduced in intensity by subsequent recrystallization heat treatments. Characterization of the magnetic properties revealed a lower coercivity and higher permeability for ECAE-processed Hiperco specimens relative to the conventionally processed and annealed Hiperco bar. The effects of the resultant microstructure and texture on the coercivity and permeability magnetic properties are discussed.

This research introduces a novel single-step approach to improve the absorbency under load (AUL) of agricultural superabsorbent polymers (SAPs) made of acrylamide. Crosslinked (acrylamide–potassium acrylate–acrylic acid) terpolymers were successfully prepared and modified via a transamidation (amide exchange) reaction. The surface of the polymer particles was treated using polyamine modifiers (i.e., diethylenetriamine and polyethyleneimine) in the presence or absence of AlCl3 as a catalyst. The modification reaction was confirmed via spectral, morphological, and rheological studies. The process variables including time and temperature, the modifier type and amount, and the catalyst concentration were found to affect the polymer swelling properties. The swelling capacity of the control and treated SAPs were determined in deionized water and saline. The AUL in saline, as a key swelling property of SAPs, was also determined. The AUL of the PEI-treated samples (19.82–24.8 g/g) was higher than those of the control (17.7 g/g) and the DETA-treated SAPs (18.3–23.5 g/g). In conclusion, the transamidation effectively improved the AUL of the terpolymer superabsorbents by about 25%.

The growth of Ag on ZnO was modeled using a reactive force field potential and a combination of molecular dynamics and adaptive kinetic Monte Carlo (AKMC) simulations. An adaptive lattice-based AKMC model is described as a method of extending timescales and length scales that can be simulated. Reusing previously found transitions to reduce computational time is discussed for both the lattice and off-lattice AKMC approaches. With these methods, growth of over 1 monolayer’s worth of Ag is simulated corresponding to a real deposition time of up to 0.1 s. The results show that the deposited silver aggregates on the surface through mainly single atom moves with few concerted motions. Initially silver adatoms do not agglomerate and the energy barriers for silver dimers to form are larger than for them to break apart. The first layer of silver grows as a series of connected regions rather than forming well-defined centro-symmetric islands.

Induced pluripotent stem cells (iPSCs) offer the possibility to accelerate tissue reconstruction through cell differentiation. The use of iPSCs in bone tissue engineering is promoted by next generation scaffolds which guide bone tissue repair and provide specific cues and molecular recognition to enhance differentiation as well as the bone forming ability of these cells. However, bone tissue repair faces additional challenges such as requirement for a consequent bone vasculature and exhaustion of stem cells in the aging adults. In this context, iPSC reprogramming seems to be unaffected by age and they have better pro-angiogenic potential as well as proliferation rate. The benefits of iPSCs using polymeric scaffolds include access to humanized in vitro models, triggering bone tissue reconstruction through a supply of bone cells via differentiation, compensating mesenchymal stem cells age-related deficiencies in osteodegenerative diseases, and enhancing angiogenesis.

Hematite films deposited by plasma-enhanced chemical vapor deposition of iron pentacarbonyl [Fe(CO)5] in an oxygen plasma were modified by postdeposition (i) oxygen plasma treatment and (ii) short annealing treatments to reduce the defects and to modify the (sub)surface states and consequently the photoelectrochemical properties. The oxygen plasma treatment resulted in the increase of particle size and augmented surface roughening by densification of grains. Moreover, it induced saturated surface states with reactive oxygen species (O−, OH−), evident in the X-ray photoelectron spectroscopy (XPS). Under standard illumination (1.5 AM; 100 mW/cm2; 150 W xenon lamp), when compared to the pristine hematite coating (0.696 mA/cm2 at 1.23 V versus RHE and 0.74 Vonset) the oxygen plasma-treated films showed severe deterioration in photocurrent density of 0.035 mA/cm2 and an anodic shift in the onset potential (1.10 Vonset) due to oxygen rich surface. In a second set of experiments, the oxygen plasma-treated hematite films were briefly annealed (10 min at 750 °C) and the signals of Fe 2p and O 1s recovered to higher binding energies, indicating the formation of oxygen vacancies. In addition, a superior photocurrent density value of max. 1.306 mA/cm2 at 1.23 V versus RHE to that of the pristine hematite photoanode with 0.74 Vonset was obtained. Transient absorption spectroscopy further elucidated that the oxygen plasma-induced electron trap states acting as recombination centers that are unfavorable for photoelectrochemical activity. The alteration in Fe:O stoichiometry and thus photocurrent density are corroborated by determination of water oxidation rates in annealed (7.1 s−1) and oxygen plasma treated (2.5 s−1) samples.

Bistable Auxetic Metamaterials (BAMs) are a class of monolithic perforated periodic structures with negative Poisson’s ratio. Under tension, a BAM can expand and reach a second state of equilibrium through a globally large shape transformation that is ensured by the flexibility of its elastomeric base material. However, if made from a rigid polymer, or metal, BAM ceases to function due to the inevitable rupture of its ligaments. The goal of this work is to extend the unique functionality of the original kirigami architecture of BAM to a rigid solid base material. We use experiments and numerical simulations to assess performance, bistability, and durability of rigid BAMs at 10,000 cycles. Geometric maps are presented to elucidate the role of the main descriptors of the BAM architecture. The proposed design enables the realization of BAM from a large palette of materials, including elastic-perfectly plastic materials and potentially brittle materials.

The protective effect of poly(methylmethacrylate) (PMMA) cover layers against the degradation of π-conjugated polymers by ozone and photo-oxidation, respectively, has been investigated by UV/Vis spectroscopy. The PMMA films were cast from solution at thicknesses between 20 and 100 nm on top of films of poly(3-hexylthiophene) and poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene]. PMMA layers of more than 65 nm in thickness reduce the oxidation rate of the π-conjugated polymers under 15 ppm of ozone in the dark by more than three orders of magnitude, whereas photo-oxidation rates under dry and humid air remain unaffected. The PMMA cover layers are hardly affected by ambient ozone over thousands of hours. Calculations of ozone and oxygen fluxes through the PMMA films reveal that ozonation rates are limited by the diffusion of ozone, whereas photo-oxidation rates are not limited by the diffusion of oxygen, due to the much larger pressure gradient of the latter.

Three-dimensional nitrogen-doped graphene frameworks (3DNGFs) hold great promise in the application of supercapacitors for the advantages of superior conductivity, well-connected porous structure, and additional N-containing active sites for charge storage. Nevertheless, the developed techniques for preparing 3DNGFs always suffer from the drawbacks of high cost or complex processes for large-scale application. Herein, a new and cost-effective method has been developed to massively prepare monolithic 3DNGFs by a simple and scalable electrochemical oxidation process. Benefiting from the enhanced electrical conductivity, the increase in the pore volume for fast diffusion increased the electrode–electrolyte contact area and additional active sites resulting from the incorporation of nitrogen species, the 3DNGFs showed a high specific capacitance of 2250.3 mF/cm2 at 4 mA/cm2, with good rate capability. Furthermore, this 3DNGFs electrode also owns an excellent long-term cycling stability that can retain more than 97.5% of its original capacitance after 10,000 cycles.

AlMg alloys have widespread industrial applications. Grain refinement techniques have been frequently used to achieve high strength in these alloys. Here, we report on the fabrication of epitaxial co-sputtered AlMg thin films with high-density growth twins. The microstructure evolution with varying Mg composition has been characterized. Nanoindentation and in-situ micropillar compression tests show that the strength of AlMg alloys increases with increasing Mg composition. The flow stress of epitaxial nanotwinned Al–10 at.% Mg thin film exceeds 800 MPa. The modified Hall–Petch plots incorporating the solid solution strengthening effect suggest that, compared to high angle grain boundaries, incoherent twin boundaries are equivalent barriers to the transmission of dislocations in nanotwinned AlMg alloys.