When ultrafine-grained (UFG) samples are deformed plastically, it is necessary to consider the role of grain boundaries even at the micrometer scale in sample size. We report here the occurrence of intensive grain boundary sliding (GBS) at room temperature in micro-pillars of a UFG aluminum alloy having an unusually high strain rate sensitivity. A consequence of this GBS is that the intermittent flow with detrimental strain avalanches characterizing micro-sized conventional crystals is not present in UFG materials, thereby illustrating a potential for effectively applying these UFG materials in micro-devices.

A simple and facile stereolithography 3D printing technique was utilized to fabricate piezoelectric photopolymer-based polyvinylidene fluoride (PVDF) blends. Different process variables, such as solvent (N,N-dimethylformamide, DMF) to PVDF ratio and PVDF solution to photopolymer resin (PR) ratio, were engineered to enhance the dispersion of the PVDF into the PR so as to achieve the maximum piezoelectric coupling coefficient. Our results demonstrate that a ratio of 1:10 (PVDF:DMF) and 2 wt%-PVDF/PR was optimal for the best dissolution of the PVDF, 3D printability, and piezoelectric properties. Under these conditions, the blend generated ±0.121 nA under 80 N dynamic loading excitation. We believe that the findings of this work would promote many further studies on the mass production of flexible piezoelectric polymer blends with higher quality finished surface and design flexibility.

Doping is a potent and often used strategy to modify properties of active electrode materials in advanced electrochemical batteries. There are several factors by which doping changes properties critically affecting battery performance, most notably the voltage, capacity, rate capability, and stability. These factors have to do specifically with changes in structure, band gap and band structure, and structural instability induced by doping. We review our recent modeling works on the effects of doping of active electrode materials, notably for prospective materials for organic and post-lithium (Na ion, Mg ion) batteries, as well as present new results, to build a coherent view on the use of n- and p-doping to modulate Li, Na, and Mg storage properties, most notably voltage. Specifically, we clearly point out effects due to electronic structure and those due to strain (structural instability), which clears some confusion about the effects of n- versus p-doping and facilitates rational rather than ad hoc design of doped materials.

Human mesenchymal stem cells (MSCs) are the most intensely studied and clinically used adult stem cell type. Conventional long-term cultivation of MSCs as a monolayer is known to result in a reduction of their functionality and viability. In addition, large volumes of cell culture medium are required to obtain cell quantities needed for their clinical use. In this proof of concept study, we cultivated human MSCs within a three-dimensional nanofibrillar cellulose (NFC) hydrogel. We show that NFC is biocompatible with human MSCs, and represents a feasible approach to upscaling of their culture.

Materials design and discovery can be represented as selecting the optimal structure from a space of candidates that optimizes a target property. Since the number of candidates can be exponentially proportional to the structure determination variables, the optimal structure must be obtained efficiently. Recently, inspired by its success in the Go computer game, several approaches have applied Monte Carlo tree search (MCTS) to solve optimization problems in natural sciences including materials science. In this paper, we briefly reviewed applications of MCTS in materials design and discovery, and analyzed its future potential.

Robust superhydrophobic surfaces can improve the performance of various applications. Considerable research has focused on developing superhydrophobic surfaces, but in these studies, superhydrophobicity was attained using polymeric materials, which deteriorate under harsh environments. Recently, it has been shown that rare-earth oxide ceramics are hydrophobic and since they are ceramics, they withstand harsh environments including high temperature. Here we fabricate a superhydrophobic surface by texturing a ceria pellet using laser ablation. We demonstrate water repellency by showing an impinging water droplet bouncing off the surface. This study extends the possibility of producing robust superhydrophobic ceramics using accessible techniques for industrial applications.

Regarding the significance of cement paste in construction materials, the present paper aims to use nanoindentation to measure and map mechanical properties of hardened cement pastes. The mechanical properties of involved phases were extracted from grid nanoindentation on the cement paste. The results suggested that nanoindentation can be used as a tool to measure and map mechanical properties of hardened cement pastes, and can identify the phases, including outer product, inner product, calcium hydroxide (or interface of residual cement clinker), and residual cement clinker.

We study the temperature dependence of thermoelectric transport properties of four FeSb2 nanocomposite samples with different grain sizes. The comparison of the single crystals and nanocomposites of varying grain sizes indicates the presence of substantial phonon drag effects in this system contributing to a large Seebeck coefficient at low temperature. As the grain size decreases, the increased phonon scattering at the grain boundaries leads to a suppression of the phonon-drag effect, resulting in a much smaller peak value of the Seebeck coefficient in the nanostructured bulk materials. As a consequence, the ZT values are not improved significantly even though the thermal conductivity is drastically reduced.

Large volume fractions of Mn–Ni–Si (MNS) precipitates formed in irradiated light water reactor pressure vessel (RPV) steels cause severe hardening and embrittlement at high neutron fluence. A new equilibrium thermodynamic model was developed based on the CALculation of PHAse Diagrams (CALPHAD) method using both commercial (TCAL2) and specially assembled databases to predict precipitation of these phases. Good agreement between the model predictions and experimental data suggest that equilibrium thermodynamic models provide a basis to predict terminal MNS precipitation over wider range of alloy compositions and temperatures, and can also serve as a foundation for kinetic modeling of precipitate evolution.

Two-step, solar-driven thermochemical fuel production offers the potential of efficient conversion of solar energy into dispatchable chemical fuel. Success relies on the availability of materials that readily undergo redox reactions in response to changes in environmental conditions. Those with a low enthalpy of reduction can typically be reduced at moderate temperatures, important for practical operation. However, easy reducibility has often been accompanied by surprisingly poor fuel production kinetics. Using the La1−x Sr x MnO3 series of perovskites as an example, we show that poor fuel production rates are a direct consequence of the diminished enthalpy. Thus, material development efforts will need to balance the countering thermodynamic influences of reduction enthalpy on fuel production capacity and fuel production rate.

Nanotechnology has been considered as a promising strategy for diagnosis and treatment of various diseases. However, the stability and circulation times of the conventional nano-carriers, such as liposomes and micelles, are still unsatisfied. Perfluorocarbons (PFCs) are biologic inert synthetic materials, which are highly hydrophobic and have a tendency to self-aggregation. Additionally, PFCs themselves can act as 19F magnetic resonance imaging agents and oxygen carriers. Thus, the construction of the fluorinated carriers will not only improve the stability of the carriers, but also endow them with additional functions. Here we review the recent advances of PFC-based nanosystems for diagnosis and treatment of diseases.

Recent discovery of ferroelectricity in doped HfO2 has reignited research interest in the ferroelectric field-effect transistor (FeFET) as emerging embedded nonvolatile memory with the potential for neuro-inspired computing. This paper reviews two major aspects for its application in neuro-inspired computing: ferroelectric devices as multilevel synaptic devices and the circuit primitive design with FeFET for in-memory computing. First, the authors survey representative FeFET-based synaptic devices. Then, the authors introduce 2T-1FeFET synaptic cell design that improves its in situ training accuracy to approach software baseline. Then, the authors introduce the FeFET drain–erase scheme for array-level operations, which makes the in situ training feasible for FeFET-based hardware accelerator. Finally, the authors give an outlook on the future 3D-integrated 2T-1FeFET design.

We demonstrate here the design, synthesis and characterization of two new chlorinated polymers, P(NDI2HD–T2Cl2) and P(NDI2OD–T2Cl2) based on N,N′-difunctionalized naphthalene diimide (NDI) and 3,3′-dichloro-2,2′-bithiophene (T2Cl2) moieties. Our results indicate that organic thin-film transistors (OTFTs) based on these new chlorinated polymers exhibit electron mobilities approaching 0.1 cm2V−1s−1 (I on:I off ~ 106–107), with far less ambipolarity due to their lower highest occupied molecular orbital energies, and they are more stable under deleterious high-humidity conditions (RH ~ 60%) and upon submersion in water, compared with those fabricated with the parent non-chlorinated polymers. In addition, OTFTs fabricated with the new chlorinated polymers exhibit excellent operational stabilities with <3% degradations upon bias-stress test.

Phase-change materials (PCMs) have important applications in optical and electronic storage devices. Ge2Sb2Te5 (GST) is a prototypical phase-change material (PCM) employed in state-of-the-art storage-class memories. In this work, we investigate crystallization of GST at temperatures 600–800 K by ab initio molecular dynamics. We consider large models containing 900 atoms, which enable us to investigate finite-size effects by comparison with smaller models. We use the metadynamics method to accelerate the formation of a large nucleus and then study the growth of the nucleus by unbiased simulations. The calculated crystal growth speed and its temperature-dependent behavior are in line with recent experimental work.

Lithium (Li) dendrite formation in Li-metal batteries (LMBs) remains a key obstacle preventing LMBs from their widespread application. This study focuses on the role of the stress field in the Li electrodeposits formation and growth. Coupled electrochemical and mechanical phase-field model (PFM) is used to investigate electrodeposited Li evolution under different conditions. The PFM results, using both the anisotropic elastic properties of Li and the random delivery of Li-ions through the solid electrolyte interface, show a significant local stress development indicating a direct correlation between the stress field and the origin of the undesired Li filaments initiation.

The great properties of the paramagnetic nitrogen-vacancy (NV) color center in diamond predestine it for nanoscale sensor applications; however, these properties are often compromised when NV centers reside near diamond surface for sensing. Here we show in a mini review that first-principles calculations can characterize diamond surfaces and predict the ideal surface terminators to host NV sensors. We discuss technical issues on the modeling of NV centers close to diamond surfaces, and results on the most employed diamond (100) and the most promising (111) surfaces with various terminators involving hydrogen, oxygen, fluorine, and nitrogen are presented.

We report on the ability to switch an optical material composed of a polymer stabilized cholesteric liquid crystal (polymer stabilized cholesteric texture, PSCT) between stable transparent (reflective) and scattering modes. The degree of scattering is controllable with the strength of the applied electric field. The mechanism for bistable switching of the PSCT is distinguished from prior examinations by employing electromechanical displacement of a stabilizing polymer network. The stable transparent (reflective) or scattering modes are induced with a variety of driving schemes employing both alternating and direct current fields. The relative degree of scattering can be varied to allow for grayscale control potentially useful in smart window and display applications.

Gelatin/poly(epichlorohydrin-co-ethylene oxide) [GL : PECO] composites are synthesized in a one-step process by the incorporation of elastic PECO and diclofenac. [GL : PECO] fibers are prepared by Forcespinning®. GL : PECO fibers are capable of diclofenac, by conjugation via a labile amide linkage. Fourier transform infrared spectroscopy (FTIR) results confirmed the chemical reactions and hydrogen bonds between gelatin, PECO, and diclofenac. Diclofenac drug release from GL : PECO fibers are measured for 15 days and prolonged drug release is observed. The cell viability is studied with NIH/3T3 and excellent results are observed. The sustained drug release and cytotoxicity results reveal that GL : PECO fibers could be promising substitutes for skin tissue engineering, wound healing, and drug delivery.

High-aspect-ratio (HAR) pillar arrays offer large surface area, well-defined surface topography, and large mechanical compliance. In this Prospective, we showcase micro- and nanopillar array systems that exploit the responsiveness and/or harness the mechanical instabilities for myriad surface-mediated applications, including tunable wetting, adhesion, optical properties, and actuation. In each application, we start with biological examples with HAR pillar structures, and discuss strategies to fabricate responsive HAR polymer pillar structures. We then discuss approaches to tune the surface topography, such as via bending, tilting, expansion or contraction, and collapsing of the pillars, and the resulting change of surface and optical properties, and their dynamic actuation. In each system, we discuss the controllability and recoverability of pillar deformation.

Biomineralization is a natural concept to alter the mechanical properties of soft matter. Mimicking this concept became desirable with a resulting great variety of approaches toward realizing functional hybrid materials. Vapor-phase infiltration (VPI), a solvent-free approach, is complementary to solution-based processes and often provides hybrid materials with a different chemical nature. This article overviews the evolution of VPI from a curiosity-driven alternative way to mimic biomineralization toward its application in functional materials design. Even though still in infancy, the rapidly growing interest shows promise for upcoming innovative applications of VPI in a great variety of research and development directions.