Switchable Materials Research Articles

High-performance color and fluorescence switching of cotton fabrics via light-induced proton transfer strategy of spiropyran sulfonate molecule

Light-responsive color-switching materials have garnered persistent interest recently due to their passive response to external stimuli and manifestation of notable visual color variations. Nonetheless, their development into high-end products has been hindered by unsatisfactory overall performance, characterized by challenges such as the inability to combine color contrast and retention time, poor repeatability, and reliance on a single coloring mode. Herein, we present a negative photochromic cotton fabric (NPCF) capable of real-time dual output of optical signals (color change or fluorescence emission), featuring high color contrast and resolution, excellent reversibility, and facile multicolor printing. These attributes stem from the utilization of a unique photoinduced proton transfer (PPT) strategy exhibited by the designed and synthesized spiropyran sulfonate molecule (MC-NO2). Guided by this strategy, NPCF demonstrates significant color changes and fluorescence switching in a real-time and highly reversible manner, leveraging the remote non-contact and non-destructive nature of visible light. Moreover, direct blending of MC-NO2 with commercially available water-soluble non-stimuli-responsive dyes enables customization of various photosensitive color systems for straightforward multi-color printing, aligning well with the environmental principles of green printing. This study serves as a valuable reference for the advancement and design of diverse high-performance, switchable materials suitable for the production of high-end products.

A Colored Temperature‐Adaptive Cloak for Year‐Round Building Energy Saving

AbstractAchieving year‐round energy savings in buildings holds great significance toward reaching carbon neutrality and sustainability. Switchable thermal‐management materials offer an energy‐free solution to dynamically regulating internal building temperatures, by passively emitting heat into cold outer space in summer, and absorbing heat from hot sunlight in winter. In addition to dynamic thermal regulation, color display is another pursuit for addressing aesthetic considerations; however, most current dynamically switchable materials lack color options, due to an optical conflict between adaptive solar reflection and selective visible absorption, limiting their wide adoption in aesthetic scenarios such as commercial exterior walls. Herein, a colored temperature‐adaptive cloak (CTAC) that achieves dynamically switchable thermal management in an energy‐neutral way without sacrificing year‐round vibrant color display is reported. This is realized by decoupling solar reflectivity modulation and color display through the choice of two individual constituent components, including thermochromic microcapsules, and fluorescent dyes. Moreover, compared to single‐mode samples with similar colors, the CTAC with dual modes stays 5.6–3.4 °C warmer during cold winter and 14.9–7.9 °C cooler during hot summer (peak solar irradiance: ≈735 and 1030 W m−2, respectively), exhibiting a remarkable potential to achieve year‐round building energy savings.

Battery electronification: intracell actuation and thermal management

Electrochemical batteries – essential to vehicle electrification and renewable energy storage – have ever-present reaction interfaces that require compromise among power, energy, lifetime, and safety. Here we report a chip-in-cell battery by integrating an ultrathin foil heater and a microswitch into the layer-by-layer architecture of a battery cell to harness intracell actuation and mutual thermal management between the heat-generating switch and heat-absorbing battery materials. The result is a two-terminal, drop-in ready battery with no bulky heat sinks or heavy wiring needed for an external high-power switch. We demonstrate rapid self-heating (∼ 60 °C min−1), low energy consumption (0.138% °C−1 of battery energy), and excellent durability (> 2000 cycles) of the greatly simplified chip-in-cell structure. The battery electronification platform unveiled here opens doors to include integrated-circuit chips inside energy storage cells for sensing, control, actuating, and wireless communications such that performance, lifetime, and safety of electrochemical energy storage devices can be internally regulated.

Advanced treatment and reuse of dye wastewater using thermo-irreversible on/off switch starch with disruption of dissolution/precipitation dynamic equilibrium

The development of irreversible on/off switching materials is a potential strategy for unidirectional capture and encapsulation of pollutants, preventing the pollutant leakage problem resulting from the reversible dissolution of flocculants. Herein, a thermo-irreversible on/off switch starch (TISS) is prepared through modifying starch by etherification grafting glycidyl phenyl ether and 2,4-bis(dimethylamino)-6-chloro-[1,3,5]-triazine. It breaks the dissolution/precipitation dynamic equilibrium across heating–cooling cycles by thermal-induced irreversible coil-to-globule self-assembly of polymer chains, resulting in a 50-fold decrease in polymer solubility. Particularly, TISS shows a superior double-locking effect on pollutants and flocculants through its unique irreversible conformation memory capability, leading to a high-quality reuse water. 99.9 % of reactive brilliant red dye and 97.9 % of TISS remain fixed within sludge flocs even after prolonged immersion in cold water at 24 °C for 60 days. Furthermore, direct recycling and reuse of dye-bath energy can be realized through the isothermal flocculation and dyeing method, showing a 75 % decrease in energy consumption after three cycles compared to traditional dyeing techniques. This work presents a novel approach to constructing an irreversible pollutant delivery system using thermo-irreversible on/off switch starch, addressing the problems of high energy dissipation and water quality fluctuations during wastewater treatment.

Compliance-free, analog RRAM devices based on SnOx

Brain-inspired resistive random-access memory (RRAM) technology is anticipated to outperform conventional flash memory technology due to its performance, high aerial density, low power consumption, and cost. For RRAM devices, metal oxides are exceedingly investigated as resistive switching (RS) materials. Among different oxides, tin oxide (SnOx) received minimal attention, although it possesses excellent electronic properties. Herein, we demonstrate compliance-free, analog resistive switching behavior with several stable states in Ti/Pt/SnOx/Pt RRAM devices. The compliance-free nature might be due to the high internal resistance of SnOx films. The resistance of the films was modulated by varying Ar/O2 ratio during the sputtering process. The I–V characteristics revealed a well-expressed high resistance state (HRS) and low resistance states (LRS) with bipolar memristive switching mechanism. By varying the pulse amplitude and width, different resistance states have been achieved, indicating the analog switching characteristics of the device. Furthermore, the devices show excellent retention for eleven states over 1000 s with an endurance of > 100 cycles.

Remarkable Second Harmonic Generation Response in (C5H6NO)+(CH3SO3)-: Unraveling the Role of Hydrogen Bond in Thermal Driven Nonlinear Optical Switch.

Heat-activated second harmonic generation (SHG) switching materials are gaining interest for their ability to switch between SHG on and off states, offering potential in optoelectronic applications. The novel nonlinear optical (NLO) switch, (C5H6NO)+(CH3SO3)- (4-hydroxypyridinium methylsulfonate, 4HPMS), is a near-room-temperature thermal driven material with a strong SHG response (3.3 × KDP), making it one of the most potent heat-stimulated NLO switches. It offers excellent contrast of 13 and a high laser-induced damage threshold (2.5 × KDP), with reversibility > 5 cycles. At 73 °C, 4HPMS transitions from the noncentrosymmetric Pna21 room temperature phase (RTP) to the centrosymmetric P21/c phase, caused by the rotation of the (C5H6NO)+ and (CH3SO3)- due to partially thermal breaking of intermolecular hydrogen bonds. The reverse phase change exhibits a large 50 °C thermal hysteresis. Density functional theory (DFT) calculations show that (C5H6NO)+ primarily dictates both the SHG coefficient (dij) and birefringence (▵n(Zeiss) = 0.216 vs ▵n(cal.) = 0.202 at 546 nm; Δn(Immersion) = 0.210 vs ▵n(cal.) = 0.198 at 589.3 nm), while the band gap (Eg) is influenced synergistically by (C5H6NO)+ and (CH3SO3)-. Additionally, 4HPMS-RTP also exhibits mechanochromism upon grinding as well as an aggregation-enhanced emission in a mixture of acetone and water.

Metal Penetration and Grain Boundary in MoS2 Memristors

Abstract2D semiconductors have demonstrated outstanding switching performance in resistive random‐access memory (RRAM). Despite the proposed resistive switching (RS) mechanism involving the penetration of electrode metal atoms, direct observation of metal penetration in these van‐der‐Waals stacked 2D semiconductors remains absent. This study utilizes 2D molybdenum disulfide (MoS2) as the switching material, employing gold and multilayer graphene as electrodes. Through analysis of the switching characteristics of these RRAM devices, the pivotal role of grain boundaries and metal atoms is identify in achieving RS. High‐resolution transmission electron microscopy and energy‐dispersive X‐ray spectroscopy provide direct evidence of metal penetration into multilayer MoS2. This study offers valuable insights into the RS mechanism in memristors based on multilayer MoS2, providing guidance for designing and optimizing 2D material memristive devices.

Microstructural contribution to the magnetic anisotropy in Fe 1−x Ga x thin films: correlation between crystallographic texture and magnetic response

In this study, we present a systematic analysis of the relation between the structural properties and magnetic anisotropies of as-grown and heat-treated polycrystalline Fe 1−x Ga x (0.11 <x< 0.19) thin films deposited on glass and Si(100) substrates. The results show that the crystallographic texture of the films has a significant impact on the evolution of the magnetic anisotropies. The samples grown on glass do not exhibit a preferred texture while, for samples grown on Si(100), the appearance of a weak in-plane fourfold magnetic anisotropy is reported. Such anisotropy is enhanced and better defined in the heat treated samples. Via a phenomenological model we show that this anisotropy has a microstructural origin. These findings demonstrate the possibility of tuning magnetic anisotropies by growing on different substrates and/or performing thermal treatments, which in turn reinforces the possibility of developing smart magnetic switching materials for electronic applications.

Digital light processing based multimaterial 3D printing: challenges, solutions and perspectives

Abstract Multimaterial (MM) 3D printing shows great potential for application in metamaterials, flexible electronics, biomedical devices and robots, since it can seamlessly integrate distinctive materials into one printed structure. Among numerous MM 3D printing technologies, digital light processing (DLP) MM 3D printing is compatible with a wide range of materials from hydrogels to ceramics, and can print MM 3D structures with high resolution, high complexity and fast speed. This paper introduces the fundamental mechanisms of DLP 3D printing, and reviews the recent advances of DLP MM 3D printing technologies with emphasis on material switching methods and material contamination issues. It also summarizes a number of typical examples of DLP MM 3D printing systems developed in the past decade, and introduces their system structures, working principles, material switching methods, residual resin removal methods, printing steps, as well as the representative structures and applications. Finally, we provide perspectives on the directions of the further development of DLP MM 3D printing technology.

Three-State Dielectric Switching within a Narrow Temperature Range in Isopropylammonium Lead Iodide, a One-Dimensional Perovskite with Polar Phase.

The phenomenon of dielectric switching has garnered considerable attention due to its potential applications in electronic and photonic devices. Typically, hybrid organic-inorganic perovskites, HOIPs, exhibit a binary (low-high) dielectric state transition, which, while useful, represents only the tip of the iceberg in terms of functional relevance. One way to boost the versatility of applications is the discovery of materials capable of nonbinary switching schemes, such as three-state dielectric switching. The ideal candidate for that task would exhibit a trio of attributes: two reversible, first-order phase transitions across three distinct crystal phases, minimal thermal hysteresis, and pronounced, step-like variations in dielectric permittivity, with a substantial change in its real part. Here, we demonstrate a one-dimensional lead halide perovskite with the formula (CH3)2C(H)NH3)PbI3, abbreviated as ISOPrPbI3, that fulfills these criteria and demonstrates three-state dielectric switching within a narrow temperature range of ca. 45 K. Studies on ISOPrPbI3 also revealed the polar nature of the low-temperature phase III below 266 K through pyrocurrent experiments, and the noncentrosymmetric character of the intermediate phase II and low-temperature phase III is confirmed via second harmonic generation measurements. Additionally, luminescence studies of ISOPrPbI3 have demonstrated combined broadband and narrow emission properties. The introduction of ISOPrPbI3 as a three-state dielectric switch not only addresses the limitations posed by the wide thermal gap between dielectric states in previous materials but also opens new avenues for the development of nonbinary dielectric switchable materials.

Optimising printing fidelity of the single-nozzle based multimaterial direct ink writing for 3D food printing

ABSTRACT Single-nozzle based multimaterial direct ink writing enables voxel-based fabrication with superior printing efficiency than multi-nozzle protocol. This is attractive for food 3D printing process where efficiency matters for its application. However, for single-nozzle based process, the presence of residual material in the shared channel can affect its printing fidelity. In this study, we propose a path planning algorithm that can address this issue by incorporating (i) advance distance to compensate the extrusion delay when switching materials, and (ii) in-process printhead motion adjustments to stabilise the extrusion process. Our approach demonstrated a substantial improvement in printing fidelity, where the switching point offset was reduced to ±0.5 mm. Similarly, the unstable extrusion behaviours (bulging and necking) during switching materials were suppressed, where the printing fidelity was improved by 27 ± 5% (bulging) and 19 ± 3% (necking) respectively. Additionally, we provide an open-source slicing programme that empowers users to implement the above two algorithms.

Bioinspired on-off switchable multi-level responsiveness for ultralong fire-warning, super-sensitive solvent/humidity and light-driven behaviors

The prospects of endowing the omnipresent hazardous substances with sensitive, safe, and stable life-like behaviors poses significant for the development of on–off switchable smart materials. Herewith, based on material-structural synergistic design, a multi-level responsiveness smart structures (VBGO) inspired by phospholipid biomolecules is self-assembled through asymmetric swelling and smart supramolecular nano-structures. Due to the outstanding sensitive of fire-warning nano-hybrid of functionalized cyclodextrin-graphene and highly stable substrate of vermiculite, the designed VBGO exhibits the high-sensitively fire alarm time (only 0.17 s) and super-along sustained fire alarm time (up to 249 s). Moreover, the VBGO displays significant increment in thermal stability and film-forming properties. Besides, given the asymmetrical and self-assembled smart structures, the VBGO exhibits the unique fast responses in their surrounding environments like fire, heat, light, humidity, and solvent vapor. Additionally, the on–off switchable mechanisms of fire-warning responsiveness, solvent-/humidity-/light-driven, shape memory and environmental awareness are presented systematically. This work introduces a sensitive, safe, and stable approach to designing multi-level responsive smart materials by modifying fire-warning bioinspired structures.

Resistive Memristors Using Robust Electropolymerized Porous Organic Polymer Films as Switchable Materials.

Porous organic polymers (POPs) with inherent porosity, tunable pore environment, and semiconductive property are ideally suitable for application in various advanced semiconductor-related devices. However, owing to the lack of processability, POPs are usually prepared in powder forms, which limits their application in advanced devices. Herein, we demonstrate an example of information storage application of POPs with film form prepared by an electrochemical method. The growth process of the electropolymerized films in accordance with the Volmer-Weber model was proposed by observation of atomic force microscopy. Given the mechanism of the electron transfer system, we verified and mainly emphasized the importance of porosity and interfacial properties of porous polymer films for memristor. As expected, the as-fabricated memristors exhibit good performance on low turn-on voltage (0.65 ± 0.10 V), reliable data storage, and high on/off current ratio (104). This work offers inspiration for applying POPs in the form of electropolymerized films in various advanced semiconductor-related devices.

Superconducting heat switch made from a transition metal

High sensitivity astrophysics detectors such as transition edge sensor (TES) bolometers or microwave kinetic inductance detectors (MKIDs) require sub-Kelvin operating temperatures for observing low energy photons in infrared and x-ray ranges. Continuous Adiabatic Demagnetization Refrigerators (CADRs) are presently the state of the art solution for providing cooling to these detectors below as low as 50 mK. The CADR shuttles heat through a series of paramagnetic stages from a 50 mK heat load to a 1-6+ K heat sink, using heat switches between stages to “switch” between thermal isolation and thermal communication. A superconducting heat switch is required between the two lowest temperature stages and is considered a critical system component as it determines recycling time and cooling power of the lowest temperature stage. A figure of merit for this technology is the “switching ratio”: the ratio of the thermal conductivity in the on and off states. This ratio is a function of temperature, fixed material properties, and the purity and anneal state of the metal. Lead is most commonly used in this type of thermal switch because it is readily available as a high purity material. However, an analysis of the material properties of other superconducting material suggests that transition metals such as tantalum and vanadium could achieve a significantly higher switching ratio – as high as 5-10 times that of lead. Increasing the switching ratio could allow for shorter recycling times and reduce the parasitic load on the lowest temperature stage. This work discusses relevant properties of various potential heat switch material and compares predicted performance in the CADR against the presently used lead switch.

Electrochemical Ethanol Oxidation using RuO2‐Based Catalysts: Suppressing OER and Tailored Switching between Water Oxidation and Ethanol Oxidation

AbstractFor an efficient hydrogen production, electrochemical ethanol oxidation is a great alternative to the oxygen evolution reaction (OER) due to the generation of value‐added products. In this electrosynthetic contribution, the properties of ethanol oxidation are investigated with regard to the influence of pH, temperature and potential using RuO2‐based catalysts. Results show acetic acid as main reaction product with yields of up to 29 % and Faraday efficiencies of ≥71 %. Increasing the potential marginally from 1.40 V vs. RHE to 1.45 V vs. RHE promoted parasitic OER and, therefore, yield (≥10 %) and Faraday efficiency (≥56 %) of the organic products decreased. Doping RuO2 electrodes with TiO2 shows promising results in suppressing OER during ethanol oxidation. Additionally, the catalyst allows moderate OER potentials in water electrolysis, making the catalyst a switchable material.

Atomic Layer Deposition Films for Resistive Random‐Access Memories

AbstractResistive random‐access memory (RRAM) stands out as a promising memory technology due to its ease of operation, high speed, affordability, exceptional stability, and potential to enable smaller memory devices with sizes under 10 nm. This has drawn significant attention, with atomic layer deposition (ALD) emerging as an ideal technology to tackle the challenges of nanoscale fabrication in the micro‐ and nanomanufacturing industry. ALD offers technological advantages such as functional multiple‐layer stacking, doping capabilities, and incorporating oxygen reservoirs or reactive layers. These factors contribute to achieving more intriguing, stable, and reliable nonvolatile resistance switching behaviors in RRAM. Specifically, ALD greatly benefits RRAM, that relies on the valence change mechanism, where high‐k transition metal oxides are commonly used as switching materials, and precise control over oxygen vacancies is achievable. This review provides a comprehensive overview of ALD films used in RRAM, delves into resistive switching properties and microscopic mechanisms in binary and ternary oxides and nitrides, and explores the impact of ALD‐prepared electrodes. Furthermore, the current status and future prospects of ALD‐based RRAM are highlighted, which is poised to catalyze further advancements in the fields of information storage and neural networks.

Polar Crystals Using Molecular Chirality: Pseudosymmetric Crystallization toward Polarization Switching Materials.

Polar compounds with switchable polarization properties are applicable in various devices such as ferroelectric memory and pyroelectric sensors. However, a strategy to prepare polar compounds has not been established. We report a rational synthesis of a polar CoGa crystal using chiral cth ligands (SS-cth and RR-cth, cth = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Both the original homo metal Co crystal and Ga crystal exhibit a centrosymmetric isostructure, where the dipole moment of metal complexes with the SS-cth ligand and those with the RR-cth ligand are canceled out. To obtain a polar compound, the Co valence tautomeric complex with SS-cth in the homo metal Co crystal is replaced with the Ga complex with SS-cth by mixing Co valence tautomeric complexes with RR-cth and Ga complexes with SS-cth. The CoGa crystal exhibits polarization switching between the pseudononpolar state at a low temperature and the polar state at a high temperature because only Co complexes exhibit changes in electric dipole moment due to metal-to-ligand charge transfer. Following the same strategy, the polarization-switchable CoZn complex was synthesized. The CoZn crystal exhibits polarization switching between the polar state at a low temperature and the pseudononpolar state at a high temperature, which is the opposite temperature dependence to that of the CoGa crystal. These results revealed that the polar crystal can be synthesized by design, using a chiral ligand. Moreover, our method allows for the control of temperature-dependent polarization changes, which contrasts with typical ferroelectric compounds, in which the polar ferroelectric phase typically occurs at low temperatures.

Dual Enhancement of Phosphorescence and Circularly Polarized Luminescence through Entropically Driven Self‐Assembly of a Platinum(II) Complex

AbstractAddressing the dual enhancement of circular polarization (glum) and luminescence quantum yield (QY) in circularly polarized luminescence (CPL) systems poses a significant challenge. In this study, we present an innovative strategy utilizing the entropically driven self‐assembly of amphiphilic phosphorescent platinum(II) complexes (L−Pt) with tetraethylene glycol chains, resulting in unique temperature dependencies. The entropically driven self‐assembly of L−Pt leads to a synergistic improvement in phosphorescence emission efficiency (QY was amplified from 15 % at 25 °C to 53 % at 60 °C) and chirality, both in the ground state and the excited state (glum value has been magnified from 0.04×10−2 to 0.06) with increasing temperature. Notably, we observed reversible modulation of phosphorescence and chirality observed over at least 10 cycles through successive heating and cooling, highlighting the intelligent control of luminescence and chiroptical properties by regulating intermolecular interactions among neighboring L−Pt molecules. Importantly, the QY and glum of the L−Pt assembly in solid state were measured as 69 % and 0.16 respectively, representing relatively high values compared to most self‐assembled CPL systems. This study marks the pioneering demonstration of dual thermo‐enhancement of phosphorescence and CPL and provides valuable insights into the thermal effects on high‐temperature and switchable CPL materials.

Dual Enhancement of Phosphorescence and Circularly Polarized Luminescence through Entropically Driven Self-Assembly of a Platinum(II) Complex.

Addressing the dual enhancement of circular polarization (glum) and luminescence quantum yield (QY) in circularly polarized luminescence (CPL) systems poses a significant challenge. In this study, we present an innovative strategy utilizing the entropically driven self-assembly of amphiphilic phosphorescent platinum(II) complexes (L-Pt) with tetraethylene glycol chains, resulting in unique temperature dependencies. The entropically driven self-assembly of L-Pt leads to a synergistic improvement in phosphorescence emission efficiency (QY was amplified from 15 % at 25 °C to 53 % at 60 °C) and chirality, both in the ground state and the excited state (glum value has been magnified from 0.04×10-2 to 0.06) with increasing temperature. Notably, we observed reversible modulation of phosphorescence and chirality observed over at least 10 cycles through successive heating and cooling, highlighting the intelligent control of luminescence and chiroptical properties by regulating intermolecular interactions among neighboring L-Pt molecules. Importantly, the QY and glum of the L-Pt assembly in solid state were measured as 69 % and 0.16 respectively, representing relatively high values compared to most self-assembled CPL systems. This study marks the pioneering demonstration of dual thermo-enhancement of phosphorescence and CPL and provides valuable insights into the thermal effects on high-temperature and switchable CPL materials.

CogniFiber: Harnessing Biocompatible and Biodegradable 1D Collagen Nanofibers for Sustainable Nonvolatile Memory and Synaptic Learning Applications.

Here, resistive switching (RS) devices are fabricated using naturally abundant, nontoxic, biocompatible, and biodegradable biomaterials. For this purpose, 1D chitosan nanofibers (NFs), collagen NFs, and chitosan-collagen NFs are synthesized by using an electrospinning technique. Among different NFs, the collagen-NFs-based device shows promising RS characteristics. In particular, the optimized Ag/collagen NFs/fluorine-doped tin oxide RS device shows a voltage-tunable analog memory behavior and good nonvolatile memory properties. Moreover, it can also mimic various biological synaptic learning properties and can be used for pattern classification applications with the help of the spiking neural network. The time series analysis technique is employed to model and predict the switching variations of the RS device. Moreover, the collagen NFs have shown good cytotoxicity and anticancer properties, suggesting excellent biocompatibility as a switching layer. The biocompatibility of collagen NFs is explored with the help of NRK-52E (Normal Rat Kidney cell line) and MCF-7 (Michigan Cancer Foundation-7 cancer cell line). Additionally, the biodegradability of the device is evaluated through a physical transient test. This work provides a vital step toward developing a biocompatible and biodegradable switching material for sustainable nonvolatile memory and neuromorphic computing applications.