Material Design Concept Research Articles

Strain energy density maximization principle for material design and the reflection in trans-scale continuum theory

Traditional efforts in the design of damage-tolerant structural materials were largely exercises in optimizing the combination of strength and ductility. However, the simultaneous consideration of these two conflicting mechanical indices, improving one inevitably sacrifices the other, makes the design extremely complex and difficult, due to the dilemma of choosing between them. Here, physically guided by the energy variational expression in trans-scale continuum mechanics theory, we propose a general mechanics principle for material design that involving only one index: towards strong and tough material the strain energy density limit (w) should be maximized, i.e., strain energy density maximization principle, referred to as wmax principle. It aims to guide the attainment of exceptional comprehensive mechanical properties, while circumventing the dual-index dilemma by employing a singular index w. Extensive experimental data analyses prove that (i) the maximum wmax always exists, at a critical dimension of characteristic microstructure dc,micro, and (ii) w can effectively index strength-ductility synergy and the wmax is conjugated with both high strength and high ductility, verifying the validity of wmax principle. The universality, practicality and downward compatibility are also examined. The dc,micro approaches twice the span of strain gradient region around internal boundary, suggesting that the microstructure state with wmax is the critical state with strongest strain gradient. Importantly, the w improvement as a function of the characteristic size of either microstructure or deformation field can be well captured by strain gradient theory, confirming the consistence between the wmax principle, experimental results and trans-scale continuum theories. This principle opens up a new design concept for advanced structural materials from the perspective of microstructure-w-mechanical properties relationship.

Design of Thermally Activated Delayed Fluorescence Materials: Transition from Carbonyl to Amide‐Based Acceptor

AbstractBenzophenone skeletons containing a carbonyl unit (O=C) have been widely used as electron acceptors in the thermally activated delayed fluorescence (TADF) materials. Herein, we present a novel molecular design concept for TADF materials by transitioning from a carbonyl to an amide (O=C−N) skeleton as the acceptor. The amide unit, compared to its carbonyl counterpart, offers a more stable electronic configuration. Leveraging this insight, we have developed a series of high‐performance TADF molecules based on benzoyl carbazole and carbazoline acceptors. These molecules exhibit exceptionally small singlet‐triplet energy gaps and pronounced aggregation‐enhanced emission properties, achieving photoluminescence quantum yields in neat films as high as 99 %. Consequently, these materials serve as efficient emitters in non‐doped organic light‐eimtting diodes (OLEDs), reaching a maximum quantum efficiency (EQEmax) of up to 26.0 %, significantly higher than the 17.0 % obtained with benzophenone acceptor‐based TADF molecules. Additionally, they have been used as TADF hosts in narrowband red fluorescent OLEDs, setting a record‐high EQEmax of 22.4 %.

Design of Thermally Activated Delayed Fluorescence Materials: Transition from Carbonyl to Amide-Based Acceptor.

Benzophenone skeletons containing a carbonyl unit (O=C) have been widely used as electron acceptors in the thermally activated delayed fluorescence (TADF) materials. Herein, we present a novel molecular design concept for TADF materials by transitioning from a carbonyl to an amide (O=C-N) skeleton as the acceptor. The amide unit, compared to its carbonyl counterpart, offers a more stable electronic configuration. Leveraging this insight, we have developed a series of high-performance TADF molecules based on benzoyl carbazole and carbazoline acceptors. These molecules exhibit exceptionally small singlet-triplet energy gaps and pronounced aggregation-enhanced emission properties, achieving photoluminescence quantum yields in neat films as high as 99 %. Consequently, these materials serve as efficient emitters in non-doped organic light-eimtting diodes (OLEDs), reaching a maximum quantum efficiency (EQEmax) of up to 26.0 %, significantly higher than the 17.0 % obtained with benzophenone acceptor-based TADF molecules. Additionally, they have been used as TADF hosts in narrowband red fluorescent OLEDs, setting a record-high EQEmax of 22.4 %.

Exploration of a New Class p-type Conducting Oxide Based on the Strong Correlation Effect

Transparent conducting oxides (TCOs) have been researched for several decades thus utilizing in many technology advances especially on display area. While such an advance p-type TCO entry is still rare compared to the n-type one as hindering the next generation oxide-based electronics. This article briefly introduces materials design concepts on typical TCOs, and a new approach to realize a high-performance p-type TCO based on strong electron correlation effect.

Multifunctional Natural and Synthetic Melanin for Bioelectronic Applications: A Review.

Emerging material interest in bioelectronic applications has highlighted natural melanin and its derivatives as promising alternatives to conventional synthetic conductors. These materials, traditionally noted for their adhesive, antioxidant, biocompatible, and biodegradable properties, have barely been used as conductors due to their extremely low electrical activities. However, recent studies have demonstrated good conductive properties in melanin materials that promote electronic-ionic hybrid charge transfer, attributed to the formation of an extended conjugated backbone. This review examines the multifunctional properties of melanin materials, focusing on their chemical and electrochemical synthesis and their resulting structure-property-function relationship. The wide range of bioelectronic applications will also be presented to highlight their importance and potential to expand into new design concepts for high-performance electronic functional materials. The review concludes by addressing the current challenges in utilizing melanin for biodegradable bioelectronics, providing a perspective on future developments.

Fast fabrication of a hierarchical nanostructured multifunctional ferromagnet.

Materials with multifunctionality affect society enormously. However, the inability to surmount multiple functionality trade-offs limits the discovery of next-generation multifunctional materials. Departing from conventional alloying design philosophy, we present a hierarchical nanostructure (HNS) strategy to simultaneously break multiple performance trade-offs in a material. Using a praseodymium-cobalt (PrCo5) ferromagnet as a proof of concept, the resulting HNS outperforms contemporary high-temperature ferromagnets with a 50 to 138% increase in electrical resistivity while achieving their highest energy density. Our strategy also enables an exceptional thermal stability of coercivity (-0.148%/°C)-a key characteristic for device accuracy and reliability-surpassing that of existing commercial rare-earth magnets. The multifunctionality stems from the deliberately introduced nanohierarchical structure, which activates multiple micromechanisms to resist domain wall movement and electron transport, offering an advanced design concept for multifunctional materials.

Liquid metal in prohibiting polysulfides shuttling in metal sulfides anode for sodium-ion batteries

Metal sulfides are a class of promising anode materials for sodium-ion batteries (SIBs) owing to their high theoretical specific capacity. Nevertheless, the reactant products (polysulfides) could dissolve into electrolyte, shuttle across separator, and react with sodium anode, leading to severe capacity loss and safety concerns. Herein, for the first time, gallium (Ga)-based liquid metal (LM) alloy is incorporated with MoS2 nanosheets to work as an anode in SIBs. The electron-rich, ultrahigh electrical conductivity, and self-healing properties of LM endow the heterostructured MoS2-LM with highly improved conductivity and electrode integrity. Moreover, LM is demonstrated to have excellent capability for the adsorption of polysulfides (e.g., Na2S, Na2S6, and S8) and subsequent catalytic conversion of Na2S. Consequently, the MoS2-LM electrode exhibits superior ion diffusion kinetics and long cycling performance in SIBs and even in lithium/potassium-ion battery (LIB/PIB) systems, far better than those electrodes with conventional binders (polyvinylidene difluoride (PVDF) and sodium carboxymethyl cellulose (CMC)). This work provides a unique material design concept based on Ga-based liquid metal alloy for metal sulfide anodes in rechargeable battery systems and beyond.

Theoretical and experimental investigation of Al3+ ion-suppressed phase-separation structures in rare-earth-doped high-phosphorus silica glasses.

Rare-earth-doped silica-based composite glasses (Re-SCGs) are widely used as high-quality laser gain media in defense, aerospace, energy, power, and medical applications. The variable regional chemical environments of Re-SCGs can induce new photoluminescence properties of rare-earth ions but can cause the selective aggregation of rare-earth ions, limiting the application of Re-SCGs in the field of high-power lasers. Here, topological engineering is proposed to adjust the degree of cross-linking of phase-separation network chains in Re-SCGs. A combination of experimental and theoretical characterization techniques suggested that the selective aggregation of rare-earth ions originates from the formation of phase-separated structures in glasses. The decomposition of nanoscale phase separation structures to the sub-nanometer scale, enabled by incorporating Al3+ ions, not only maintains the high luminescence efficiency of rare earth ions but also increases light transmittance and reduces light scattering. Furthermore, our investigation encompassed the exploration of the inhibitory mechanism of Al3+ ions on phase-separation structures, as well as their influence on the spectral characteristics of Re-SCGs. This work provides a new design concept for composite glass materials doped with rare-earth ions and could broaden their application in the field of high-power lasers.

Versatile Neuromorphic Modulation and Biosensing based on N-type Small-molecule Organic Mixed Ionic-Electronic Conductors.

The ion/chemical-based modulation feature of organic mixed ionic-electronic conductors (OMIECs) are critical to advancing next generation bio-integrated neuromorphic hardware. Despite achievements with polymeric OMIECs in organic electrochemical neuronal synapse (OENS). However, small molecule OMIECs based OENS has not yet been realized. Here, for the first time, we demonstrate an effective materials design concept of combining n-type fused all-acceptor small molecule OMIECs with subtle side chain optimization that enables robustly and flexibly modulating versatile synaptic behavior and sensing neurotransmitter in solid or aqueous electrolyte, operating in accumulation modes. By judicious tuning the ending side chains, the linear oligoether and butyl chain derivative gNR-Bu exhibits higher recognition accuracy for a model artificial neural network (ANN) simulation, higher steady conductance states and more outstanding ambient stability, which is superior to the state-of-art n-type OMIECs based OENS. These superior artificial synapse characteristics of gNR-Bu can be attributed to its higher crystallinity with stronger ion bonding capacities. More impressively, we unprecedentedly realized n-type small-molecule OMIECs based OENS as a neuromorphic biosensor enabling to respond synaptic communication signals of dopamine even at sub-μM level in aqueous electrolyte. This work may open a new path of small-molecule ion-electron conductors for next-generation ANN and bioelectronics.

Versatile Neuromorphic Modulation and Biosensing based on N‐type Small‐molecule Organic Mixed Ionic‐Electronic Conductors

AbstractThe ion/chemical‐based modulation feature of organic mixed ionic‐electronic conductors (OMIECs) are critical to advancing next generation bio‐integrated neuromorphic hardware. Despite achievements with polymeric OMIECs in organic electrochemical neuronal synapse (OENS). However, small molecule OMIECs based OENS has not yet been realized. Here, for the first time, we demonstrate an effective materials design concept of combining n‐type fused all‐acceptor small molecule OMIECs with subtle side chain optimization that enables robustly and flexibly modulating versatile synaptic behavior and sensing neurotransmitter in solid or aqueous electrolyte, operating in accumulation modes. By judicious tuning the ending side chains, the linear oligoether and butyl chain derivative gNR‐Bu exhibits higher recognition accuracy for a model artificial neural network (ANN) simulation, higher steady conductance states and more outstanding ambient stability, which is superior to the state‐of‐art n‐type OMIECs based OENS. These superior artificial synapse characteristics of gNR‐Bu can be attributed to its higher crystallinity with stronger ion bonding capacities. More impressively, we unprecedentedly realized n‐type small‐molecule OMIECs based OENS as a neuromorphic biosensor enabling to respond synaptic communication signals of dopamine even at sub‐μM level in aqueous electrolyte. This work may open a new path of small‐molecule ion‐electron conductors for next‐generation ANN and bioelectronics.

Self-Assembled and Multilayer-Overlapped ESM-PDA@rGO Nanofilm-Based Flexible Wearable Sensor for Real-Time Body Temperature Monitoring.

There is an urgent need for wearable sensors that continuously monitor human physiological conditions in real time. Herein, an ESM-PDA@rGO-based flexible wearable temperature sensor was successfully constructed by integrating an eggshell membrane (ESM) with reduced graphene oxide (rGO) through dopamine (DA) polymerization. Depending on the "bridge effect" of diversified polydopamine (PDA) chains, on the one hand, a staggered arrangement of PDA-rGO frameworks and a lot of conductive pathways were produced and acted as an active layer. On the other hand, PDA-rGO frameworks were linked with ESM by PDA chains as a flexible sensing nanofilm. As a result, these mechanical merits of the ESM-PDA@rGO exhibited a 1.8-fold increase in Young' s modulus and 1.4-fold increase in tensile strength. Thereby, the conformability and performance of the temperature sensor were greatly enhanced, showing excellent sensitivity (-2.23%/°C), good linearity (R2 = 0.979), as well as stability. Especially, the flexible sensing nanofilm is evolved from the staggered arrangement of PDA-rGO frameworks, which endows it with rapid response (only 4-8 s), high resolution (0.1 °C), as well as excellent long-term durability (10 weeks). More importantly, the temperature sensor demonstrates insensitivity to bending deformation, ensuring reliable wearing stability. The sensor allows for online, real-time monitoring of human body temperature, encompassing both core (forehead, temple, cochlea, and exhale gas) and shell (palm and back of the hand, fingertip, and instep) temperatures. Particularly, it can accurately assess minor changes in peripheral body temperature before and after exercise, and it is capable of mapping daily patterns of body temperatures. The developed temperature sensor will provide us new materials design concepts and holds considerable promise in the fields of e-skin, disease surveillance, prediction, and diagnose.

High performance photodegradation resistant PVA@TiO2/carboxyl-PES self-healing reactive ultrafiltration membrane

The occurrence of ultrafiltration (UF) membrane fouling frequently hampers the sustainable advancement of UF technology. Reactive self-cleaning UF membranes can effectively alleviate the problem of membrane fouling. Nevertheless, the self-cleaning process may accelerate membrane aging. Addressing these concerns, we present an innovative design concept for composite self-healing materials based on self-cleaning UF membranes. To begin, TiO2 nanoparticles were incorporated into the polymer molecular structure via molecular design, resulting in the synthesis of TiO2/carboxyl-polyether sulfone (PES) hybrid materials. Subsequently, the nonsolvent-induced phase inversion technique was employed to prepare a novel of UF membrane. Lastly, a polyvinyl alcohol (PVA) hydrogel coating was applied to the hybrid UF membrane surface to create PVA@TiO2/carboxyl-PES self-healing reactive UF membranes. By establishing a covalent bond, the TiO2 nanoparticles were effectively and uniformly dispersed within the UF membrane, leading to exceptional self-cleaning properties. Furthermore, the water-absorbing and swelling properties of PVA hydrogel, along with its capacity to form hydrogen bonds with water molecules, resulted in UF membranes with improved hydrophilicity and active self-healing abilities. The results demonstrated that the water contact angle of PVA@5%TiO2/carboxyl-PES UF membrane was 43.1°. Following a 1-h exposure to simulated solar exposure, the water flux recovery ratio increased from 48.16% to 81.03%. Moreover, even after undergoing five cycles of 12-h simulated sunlight exposure, the UF membranes exhibited a consistent retention rate of over 97%, thus fully demonstrating their exceptional self-cleaning, antifouling, and self-healing capabilities. We anticipate that the self-healing reactive UF membrane system will serve as a pioneering and comprehensive solution for the self-cleaning antifouling challenges encountered in UF membranes while also effectively mitigating the aging effects of reactive UF membranes.

Structural Regulation of Photocatalyst to Optimize Hydroxyl Radical Production Pathways for Highly Efficient Photocatalytic Oxidation.

Ring-opening of phenol in wastewater is the pivotal step in photocatalytic degradation. The highly selective generation of catalytical active species (•OH) to facilitate this process presents a significant scientific challenge. Therefore, a novel approach for designing photocatalysts with single-atom containment in metal-covalent organic frameworks (M-COFs) is proposed. The selection of imine-linked COFs containing abundant N and O-chelate sites provides a solid foundation for anchoring metal atom. These dispersed metal atom possess rapid accumulation and transfer capabilities for photogenerated electrons, while the periodic π-conjugated structure in 2D-COFs establishes an effective platform. Additionally, the Lewis acid properties of imine bonds in COFs can enhance the adsorption capacity toward gases with Lewis base properties, such as O2 and N2 . It is demonstrated that the Pd2+ @Tp-TAPT, designed based on this concept, exhibits efficient oxygen adsorption and follows the reaction pathway of O2 →•O2 - →H2 O2 →•OH with high selectivity, thereby achieving completely degradation of refractory phenol through photocatalysis within 10 min. It is anticipated that the selective generation of catalytic active species via advanced material design concepts will serve as a significant reference for achieving precise material catalysis in the future.

Vanadium oxide nanospheres encapsulated in N-doped carbon nanofibers with morphology and defect dual-engineering toward advanced aqueous zinc-ion batteries

Vanadium-based electrodes are regarded as attractive cathode materials in aqueous zinc ion batteries (ZIBs) caused by their high capacity and unique layered structure. However, it is extremely challenging to acquire high electrochemical performance owing to the limited electronic conductivity, sluggish ion kinetics, and severe volume expansion during the insertion/extraction process of Zn2+. Herein, a series of V2O3 nanospheres embedded N-doped carbon nanofiber structures with various V2O3 spherical morphologies (solid, core–shell, hollow) have been designed for the first time by an electrospinning technique followed thermal treatments. The N-doped carbon nanofibers not only improve the electrical conductivity and the structural stability, but also provides encapsulating shells to prevent the vanadium dissolution and aggregation of V2O3 particles. Furthermore, the varied morphological structures of V2O3 with abundant oxygen vacancies can alleviate the volume change and increase the Zn2+ pathway. Besides, the phase transition between V2O3 and ZnXV2O5−m·nH2O in the cycling was also certified. As a result, the as-obtained composite delivers excellent long-term cycle stability and enhanced rate performance for coin cells, which is also confirmed through density functional theory (DFT) calculations. Even assembled into flexible ZIBs, the sample still exhibits superior electrochemical performance, which may afford new design concept for flexible cathode materials of ZIBs.

Effective Scald Wound Functional Recovery Patch Achieved by Molecularly Intertwined Electrical and Chemical Message in Self-Adhesive Assemblies.

Bioactive materials that communicate with bio-tissues via simultaneous chemical and electrical information promise an advanced medical treatment strategy. Rational design of simultaneous chemically and electrically active materials is still challenging. In this study, we develop a bioactive wound healing patch that enables functional recovery of scald skin wounds by integrating electrically and chemically active units at the molecular level. The patch should be used with massages for 10 min daily during the recovery process. This healing patch consists of a closely intertwined piezoelectric poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) film and a self-adhesive poly(N,N-dimethylacrylamide) (PDMAA) hydrogel layer, which permits itself to adhere on skin wounds reversibly. Frequency-dependent electrical and chemical dose delivery is achieved in response to mechanical stimuli via the electrical-chemical crosstalk within the healing patch. Animal scald experiments show that the patch can effectively guide the functional recovery of grade I and shallow grade II scald wounds, promoting proper collagen deposition and hair follicle, blood vessel, and gland regeneration. Integrating electrically and chemically active units at the molecular level in treatment devices provides a new design concept for tissue engineering and medical treatment materials.

Material Design Concepts and Gas Separation Mechanism of CO2 Selective Polyether-Based Multiblock Copolymers.

Aliphatic polyethers have been widely explored as membrane materials for the separation of CO2 from other gases, e.g., N2 , H2 , CH4, O2 etc. The polymeric membranes having aliphatic polyether segments, especially poly(ethylene oxide) segments, allow faster permeation of CO2 compared to the light gases due to the affinity of the polar ether oxygen and quadrupolar CO2 . Rational macromolecular design is the key to control the permeation of gases through these membrane materials. In this regard, multiblock copolymers having short amorphous polyether segments have been extensively investigated. A large number of tailor made polymers have been reported to get the best combination of permeability and selectivity. Material design concepts and structure-property relationships of these membrane materials in terms of CO2 separation performance are thoroughly discussed in this review.

Design and Preparation of Flexible Graphene/Nonwoven Composites with Simultaneous Broadband Absorption and Stable Properties

As the world moves into the 21st century, the complex electromagnetic wave environment is receiving widespread attention due to its impact on human health, suggesting the critical importance of wearable absorbing materials. In this paper, graphene nonwoven (RGO/NW) composites were prepared by diffusely distributing graphene sheets in a polypropylene three-dimensional framework through Hummers' method. Moreover, based on the Jaumann structural material design concept, the RGO/NW composite was designed as a multilayer microwave absorber, with self-recovery capability. It achieves effective absorption (reflection loss of -10 dB) in the 2~18 GHz electromagnetic wave frequency domain, exhibiting a larger bandwidth than that reported in the literature for absorbers of equivalent thickness. In addition, the rationally designed three-layer sample has an electromagnetic wave absorption of over 97% (reflection loss of -15 dB) of the bandwidth over 14 GHz. In addition, due to the physical and chemical stability of graphene and the deformation recovery ability of nonwoven fabric, the absorber also shows good deformation recovery ability and stable absorption performance. This broadband absorption and extreme environmental adaptability make this flexible absorber promising for various applications, especially for personnel wearable devices.

Membranes for Osmotic Power Generation by Reverse Electrodialysis

In recent years, the utilization of the selective ion transport through porous membranes for osmotic power generation (blue energy) has received a lot of attention. The principal of power generation using the porous membranes is same as that of conventional reverse electrodialysis (RED), but nonporous ion exchange membranes are conventionally used for RED. The ion transport mechanisms through the porous and nonporous membranes are considerably different. Unlike the conventional nonporous membranes, the ion transport through the porous membranes is largely dictated by the principles of nanofluidics. This owes to the fact that the osmotic power generation via selective ion transport through porous membranes is often referred to as nanofluidic reverse electrodialysis (NRED) or nanopore-based power generation (NPG). While RED using nonporous membranes has already been implemented on a pilot-plant scale, the progress of NRED/NPG has so far been limited in the development of small-scale, novel, porous membrane materials. The aim of this review is to provide an overview of the membrane design concepts of nanofluidic porous membranes for NPG/NRED. A brief description of material design concepts of conventional nonporous membranes for RED is provided as well.

Efficient implementation of kilogram-scale, high-capacity and long-life Si-C/TiO2 anodes

High-performance silicon-carbon (Si-C) anodes have drawn extensive attention for next-generation high-energy lithium-ion batteries (LIBs). However, it is challenging to develop an easily scalable but effective strategy for fabricating Si-C composites to address the issues of low tap density, low initial coulombic efficiency (ICE), and poor interfacial compatibility. Here, a scalable method has been developed to fabricate kilogram-scale graphite-Si-C/TiO2 composites (GSCT) consisted of Si nanoparticles tightly fixed on the micron-graphite skeleton covered with a thin C/TiO2 layer via liquid-phase self-assembly combined with mechanical fusion and solid-phase sintering treatment. Benefiting from the structural and compositional merits, the as-obtained GSCT-c anode can deliver high ICE values of 80-83% and the tap density of 0.82 g cm−3, and achieve a high reversible capacity of 919.8 mAh g−1 even for 900 cycles at 800 mA g−1, outperforming many reported Si-C anodes. Substantial experimental characterizations and electrochemical investigations clearly unveil that the interface compatibility and structure stabilization mechanism induced by trace TiO2 incorporation and carbon coating, accounting for high-capacity and stable cycling performance. Furthermore, the assembled pouch full cells of GSCT-c||NCM622 delivered stable cycling performance and high energy density of 288.4 Wh kg−1, offering valuable material design concepts for further development in Si-C based anodes.

Designing strong, fast, high-performance hydrogel actuators.

Hydrogel actuators displaying programmable shape transformations are particularly attractive for integration into future soft robotics with safe human-machine interactions. However, these materials are still in their infancy, and many significant challenges remain presenting impediments to their practical implementation, including poor mechanical properties, slow actuation speed and limited actuation performance. In this review, we discuss the recent advances in hydrogel designs to address these critical limitations. First, the material design concepts to improve mechanical properties of hydrogel actuators will be introduced. Examples are also included to highlight strategies to realize fast actuation speed. In addition, recent progress about creating strong and fast hydrogel actuators are sumarized. Finally, a discussion of different methods to realize high values in several aspects of actuation performance metrics for this class of materials is provided. The advances and challenges discussed in this highlight could provide useful guidelines for rational design to manipulate the properties of hydrogel actuators toward widespread real-world applications.