Time-dependent behavior of layered arches with viscoelastic interlayers

This work studies the time-dependent behavior of a layered arch adhesively bonded by viscoelastic interlayers. The deformation of the viscoelastic interlayer is represented by the Maxwell–Wiechert model. The constitutive relation in an interlayer is simplified through the quasi-elastic approximation approach. The mechanical property of an arch layer is described by the exact two-dimensional (2-D) elasticity theory in polar coordinates. The stress and displacement components in an arch layer, which strictly satisfy the simply supported boundary conditions, have been analytically derived out. The stresses and displacements are efficiently obtained by means of the recursive matrix method for the arch with any number of layers. The comparison study shows that the 2-D finite element solution has good agreement with the present one, while the solution based on the one-dimensional (1-D) Euler–Bernoulli theory has considerable error, especially for thick arches. The influences of geometrical and material parameters on the time-dependent behavior of the layered arch are analyzed in detail.     

Detwinning through migration of twin boundaries in nanotwinned Cu films under in situ ion irradiation

The mechanism of radiation-induced detwinning is different from that of deformation detwinning as the former is dominated by supersaturated radiation-induced defects while the latter is usually triggered by global stress. In situ Kr ion irradiation was performed to study the detwinning mechanism of nanotwinned Cu films with various twin thicknesses. Two types of incoherent twin boundaries (ITBs), so-called fixed ITBs and free ITBs, are characterized based on their structural features, and the difference in their migration behavior is investigated. It is observed that detwinning during radiation is attributed to the frequent migration of free ITBs, while the migration of fixed ITBs is absent. Statistics shows that the migration distance of free ITBs is thickness and dose dependent. Potential migration mechanisms are discussed.     

Distinguishable Detection of Ultraviolet,Visible, and Infrared Spectrum with High‐Responsivity Perovskite‐Based Flexible Photosensors

Distinguishable detection of the ultraviolet, visible, and infrared spectrum is promising and significant for the super visual system of artificial intelligences. However, it is challenging to provide a photosensor with such broad spectral response ability. In this work, the ultraviolet, visible, and infrared spectrum is distinguished by developing serial photosensors based on perovskite/carbon nanotube hybrids. Oraganolead halide perovskites (CH₃NH₃PbX₃) possess remarkable optoelectronic properties and tunable optical band gaps by changing the halogens, and integration with single‐walled carbon nanotubes can further improve their photoresponsivities. The CH₃NH₃PbCl₃‐based photosensor shows a responsivity up to 10⁵ A W^?1 to ultraviolet and no obvious response to visible light, which is superior to that of most ultraviolet sensors. The CH₃NH₃PbBr₃‐based photosensor exhibits a high responsivity to visible light. Serial devices of the two hybrid photosensors with comparable electric and sensory performances can distinguish the spectrum of ultraviolet, visible, and infrared even with varying light intensities. The photosensors also demonstrate excellent mechanical flexibility and bending stability. By taking full advantages of the oraganolead halide perovskites, this work provides flexible high‐responsivity photosensors specialized for ultraviolet, and gives a simple strategy for distinguishable detection of ultraviolet, visible, and infrared spectrum based on the serial flexible photosensors.     

Patterning of Discotic Liquid Crystals with Tunable Molecular Orientation for Electronic Applications

The large‐area formation of functional micropatterns with liquid crystals is of great significance for diversified applications in interdisciplinary fields. Meanwhile, the control of molecular alignment in the patterns is fundamental and prerequisite for the adequate exploitation of their photoelectric properties. However, it would be extremely complicated and challenging for discotic liquid crystals (DLCs) to achieve the goal, because they are insensitive to external fields and surface chemistry. Herein, a simple method of patterning and aligning DLCs on flat substrates is disclosed through precise control of the formation and dewetting of the capillary liquid bridges, within which the DLC molecules are confined. Large‐area uniform alignment occurs spontaneously due to directional shearing force when the solvent is slowly evaporated and programmable patterns could be directly generated on desired substrates. Moreover, the in‐plane column direction of DLCs is tunable by slightly tailoring their chemical structures which changes their self‐assembly behaviors in liquid bridges. The patterned DLCs show molecular orientation–dependent charge transport properties and are promising for templating self‐assembly of other materials. The study provides a facile method for manipulation of the macroscopic patterns and microscopic molecular orientation which opens up new opportunities for electronic applications of DLCs.     

Flexible Cationic Nanoparticles with Photosensitizer Cores for Multifunctional Biomedical Applications

One challenge for multimodal therapy is to develop appropriate multifunctional agents to meet the requirements of potential applications. Photodynamic therapy (PDT) is proven to be an effective way to treat cancers. Diverse polycations, such as ethylenediamine‐functionalized poly(glycidyl methacrylate) (PGED) with plentiful primary amines, secondary amines, and hydroxyl groups, demonstrate good gene transfection performances. Herein, a series of multifunctional cationic nanoparticles (PRP) consisting of photosensitizer cores and PGED shells are readily developed through simple dopamine‐involving processes for versatile bioapplications. A series of experiments demonstrates that PRP nanoparticles are able to effectively mediate gene delivery in different cell lines. PRP nanoparticles are further validated to possess remarkable capability of combined PDT and gene therapy for complementary tumor treatment. In addition, because of their high dispersities in biological matrix, the PRP nanoparticles can also be used for in vitro and in vivo imaging with minimal aggregation‐caused quenching. Therefore, such flexible nanoplatforms with photosensitizer cores and polycationic shells are very promising for multimodal tumor therapy with high efficacy.     

Crystallization‐Induced Emission Enhancement of a Deep‐Blue Luminescence Material with Tunable Mechano‐ and Thermochromism

Organic luminescent materials with the ability to reversibly switch the luminescence when subjected to external stimuli have attracted considerable interest in recent years. However, the examples of luminescent materials that exhibit multiresponsive properties are rarely reported. In this work, a new stimuli‐responsive dye P1 is designed and synthesized with two identical chromophores of naphthalimide, one at each side of an amidoamine‐based spacer. This amide‐rich molecule offers many possibilities for forming intra‐ and intermolecular hydrogen bond interactions. Particularly, P1 has an intrinsic property of cocrystallizing with methanol. Compared with the pristine P1 sample, the as‐prepared two‐component cocrystalline material displays an exceptive deep‐blue emission, which is extremely rare among naphthalimide‐based molecules in the solid state. Furthermore, the target material exhibits an obvious mechanochromic fluorescent behavior and a large spectral shift under force stimuli. On the other hand, the cocrystalline material shows an unusual “turn off” thermochromic luminescence accompanied by solvent evaporation. Moreover, using external stimuli to reversibly manipulate fluorescent quantum yields is rarely reported to date. The results demonstrate the feasibility of a new design strategy for solid‐state luminescence switching materials: the incorporation of solvents into organic compounds by cocrystallization to obtain a crystalline state luminescence system.     

A Two‐Stage Annealing Strategy for Crystallization Control of CH3NH3PbI3 Films toward Highly Reproducible Perovskite Solar Cells

The solvent‐engineering method is widely used to fabricate top‐performing perovskite solar cells, which, however, usually exhibit inferior reproducibility. Herein, a two‐stage annealing (TSA) strategy is demonstrated for processing of perovskite films, namely, annealing the intermediate phase at 60 °C for the first stage then at 100 °C for the second stage. Compared to conventional direct annealing temperature (DHA) at 100 °C, using this strategy, MAPbI₃ films become more controllable, leading to superior film uniformity and device reproducibility with the champion device efficiency reaching 19.8%. More specifically, the coefficient of variation of efficiency for 49 cells is reduced to 5.9%, compared to 9.8% for that using DHA. The TSA process is carefully studied using Fourier transform infrared spectroscopy, X‐ray diffraction, and UV–vis absorption spectroscopy. It is found that in comparison with DHA the formation of hydrogen bonding and crystallization of perovskite are much slower and can be better controlled when using TSA. The improvements in film uniformity and device reproducibility are attributed to: 1) controllable MAPbI₃ crystal growth stemming from the progressive formation of hydrogen bonding between methylammonium and halide; 2) suppression of intermediate phase film dewetting, which is believed to be due to its decreased mobility at the initial low‐temperature annealing stage.     

Natural Plant Materials as Dielectric Layer for Highly Sensitive Flexible Electronic Skin

Nature has long offered human beings with useful materials. Herein, plant materials including flowers and leaves have been directly used as the dielectric material in flexible capacitive electronic skin (e‐skin), which simply consists of a dried flower petal or leaf sandwiched by two flexible electrodes. The plant material is a 3D cell wall network which plays like a compressible metamaterial that elastically collapses upon pressing plus some specific surface structures, and thus the device can sensitively respond to pressure. The device works over a broad‐pressure range from 0.6 Pa to 115 kPa with a maximum sensitivity of 1.54 kPa^?1, and shows high stability over 5000 cyclic pressings or bends. The natural‐material‐based e‐skin has been applied in touch sensing, motion monitoring, gas flow detection, and the spatial distribution of pressure. As the foam‐like structure is ubiquitous in plants, a general strategy for a green, cost‐effective, and scalable approach to make flexible e‐skins is offered here.