Controlling Spatiotemporal Mechanics of Supramolecular Hydrogel Networks with Highly Branched Cucurbit[8]uril Polyrotaxanes

Attempts to rationally tune the macroscopic mechanical performance of supramolecular hydrogel networks through noncovalent molecular interactions have led to a wide variety of supramolecular materials with desirable functions. While the viscoelastic properties are dominated by temporal hierarchy (crosslinking kinetics), direct mechanistic studies on spatiotemporal control of supramolecular hydrogel networks, based on host–guest chemistry, have not yet been established. Here, supramolecular hydrogel networks assembled from highly branched cucurbit[8]uril‐threaded polyrotaxanes (HBP‐CB[8]) and naphthyl‐functionalized hydroxyethyl cellulose (HECNp) are reported, exploiting the CB[8] host–guest complexation. Mechanically locking CB[8] host molecules onto a highly branched hydrophilic polymer backbone, through selective binary complexation with viologen derivatives, dramatically increases the solubility of CB[8]. Additionally, the branched architecture enables tuning of material dynamics of the supramolecular hydrogel networks via both topological (spatial hierarchy) and kinetic (temporal hierarchy) control. Relationship between macroscopic properties (time‐ and temperature‐dependent rheological properties, thermal stability, and reversibility), spatiotemporal hierarchy, and chain dynamics of the highly branched polyrotaxane hydrogel networks is investigated in detail. Such kind of tuning of material mechanics through spatiotemporal hierarchy improves our understanding of the challenging relationship between design of supramolecular polymeric materials and their complex viscoelasticity, and also highlights a facile strategy to engineer dynamic supramolecular materials.     

Mechanomorphogenic Films Formed via Interfacial Assembly of Fluorinated Amino Acids

Nature has evolved several elegant strategies to organize inert building blocks into adaptive supramolecular structures. Favored among these is interfacial self-assembly, where the unique environment of liquid–liquid junctions provides structural, kinetic, thermodynamic, and chemical properties that are distinct from the bulk solution. Here, antithetical fluorous–water interfaces are exploited to guide the assembly of non-canonical fluorinated amino acids into crystalline mechanomorphogenic films. That is, the nanoscale order imparted by this strategy yields self-healing materials that can alter their macro-morphology depending on exogenous mechanical stimuli. Additionally, like natural biomolecules, organofluorine amino acid films respond to changes in environmental ionic strength, pH, and temperature to adopt varied secondary and tertiary states. Complementary biophysical and biochemical studies are used to develop a model of amino acid packing to rationalize this bioresponsive behavior. Finally, these films show selective permeability, capturing fluorous compounds while allowing the free diffusion of water. These unique capabilities are leveraged in an exemplary application of the technology to extract perfluoroalkyl substances from contaminated water samples rapidly. Continued exploration of these materials will advance the understanding of how interface-templated and fluorine-driven assembly phenomenon a can be co-utilized to design adaptive molecular networks and living matter.     

Biomimetic Materials with Multiple Protective Functionalities

Natural tissues possess superior material properties such as self‐healing, mechanical robustness, and mechanical gradients that allow organisms to adapt and survive in dangerous environments. Although highly desired, imparting synthetic materials with these biomimetic protective features remains a challenge. Here, the versatile dimethylglyoxime–urethane (DOU) moiety is used to create a multifunctional polyurethane (DOU‐PU). The reactivities of DOU including reversible dissociation, metal coordination, photolysis enabled self‐healing, high strength and toughness, mechanical gradient formation, and spatially controlled functionalization. By incorporating DOU, a multifunctional protective film is produced with superior resistance to mechanical damage, rapid room temperature self‐healing, and anti‐counterfeiting features. This super biomimetic film is expected to be very useful for the protection of various types of valuable objects such as electronics, diplomas, currency, and automobiles.     

Permanently Mechanically Adjustable Photothermal Catalytic Spontaneous Double Cross-Linking Network Enables Durable and Stretchable Plant Skin-Like Materials

In cellulose-based plastics, as a type of thermoplastic and thermosetting materials, the excellent balance of mechanical strength and ductility poses a large challenge. To tackle this problem, a novel approach is devised to introduce reversible non-covalent ester cross-linking into dynamic covalent hydrogen-bonded polymer networks. However, the formation of ester bonds typically requires excess reactants and dehydrating agents, which is energy-intensive, environmentally harmful, and costly. To address these concerns, inspired by polyester-rich plant bark, a supramolecular composite material is developed. It can be dissolved and regenerated using a binary solvent system (choline hexanoate/choline chloride-oxalic acid). In water, this supramolecular composite material underwent self-healing and ester exchange reactions to form double-cross-linked networks, interfaced with photo-thermal catalysis promoting the reaction due to its high photo-thermal conversion efficiency (86.7%) and water evaporation rate (1.38 kg m⁻² h⁻¹). This enables the rapid and repeatable construction of durable and stretchable biomaterials. The mechanical properties of the supramolecular plastic can be adjusted by solar photo-thermal conditions of the synthesis environment. These materials exhibit high performance in solar water evaporation and have self-healing properties and are degradable, recyclable, and capable of eliminating their own adhesions.     

Biomimetic Carbon Nanotube Films with Gradient Structure and Locally Tunable Mechanical Property

Naturally existing materials often acquire unique functions by adopting a gradient structure with gradual change in their microstructure and related properties. Imparting such an elegant structural control into synthetic materials has been a grand challenge in the field. Here, the concept of gradient structure into macroscopic carbon nanotube (CNT) films is employed and the CNT arrangement from well‐aligned array to completely random distribution, in a continuous and smooth way, is changed. Gradient films with tailored aligned‐to‐random transition rate or multilevel hierarchical structures with repeated transition have been fabricated. Local deformation and mechanical properties are directly related to the arrangement of CNTs and can be tailored by Herman's orientation factor; in particular, the elastic modulus and stiffness span over several orders of magnitude from aligned to random regions within a single monolithic film. Controlled synthesis of macroscopic CNT gradient structures with tunable mechanical properties opens a potential route toward manufacturing biomimetic functional materials with locally optimized design.     

Defect‐Tolerant Nanocomposites through Bio‐Inspired Stiffness Modulation

A biologically inspired, multilayer laminate structural design is deployed into nanocomposite films of graphene oxide‐poly(methyl methacrylate) (GO‐PMMA). The resulting multilayer GO‐PMMA films show greatly enhanced mechanical properties compared to pure‐graphene‐oxide films, with up to 100% increases in stiffness and strength when optimized. Notably, a new morphology is observed at fracture surfaces: whereas pure‐graphene‐oxide films show clean fracture surfaces consistent with crack initiation and propagation perpendicular to the applied tensile load, the GO‐PMMA multilayer laminates show terracing consistent with crack stopping and deflection mechanisms. As a consequence, these macroscopic GO‐PMMA films become defect‐tolerant and can maintain their tensile strengths as their sample volumes increase. Linear elastic fracture analysis supports these observations by showing that the stiffness modulation introduced by including PMMA layers within a graphene oxide film can act to shield or deflect cracks, thereby delaying failure and allowing the material to access more of its inherent strength. Together, these data clearly demonstrate that desirable defect‐tolerant traits of structural biomaterials can indeed be incorporated into graphene‐ oxide‐based nanocomposites.     

Mechanical properties of thin-film materials evaluated from amplitude-dependent internal friction

A method is presented to evaluate the mechanical properties of thin-film materials from measurements of the amplitude-dependent internal friction. According to the constitutive equation, the internal friction in the film can be determined separately from measured damping of the film/substrate composite. The internal friction in aluminum films is dependent on the strain amplitude that is approximately two orders of magnitude higher than that for bulk aluminum. On the basis of the microplasticity theory, the amplitude-dependent internal friction in the film can be converted into the plastic strain as a function of effective stress on dislocation motion. The mechanical responses thus obtained for aluminum films show that the plastic strain of the order of 10⁻⁹ increases nonlinearly with increasing stress. These curves tend to shift to a higher stress with decreasing film thickness and also with decreasing temperature, both indicating a suppression of microplastic flow. The microflow stress at a constant level of the plastic strain varies inversely with the film thickness, provided the grain size is larger than the film thickness. The film thickness effect in the microplastic range can be well explained by the bowing of a dislocation segment whose ends are pinned at the film surface and at the film/substrate interface.     

Photoswitchable Liquid-to-Solid Transition of Azobenzene-Decorated Polysiloxanes

Having external control over fundamental properties of polymers, such as their physical state, is a crucial yet challenging design criterion for smart materials. Liquifying polymers through photochemical events has significantly advanced various research lines. However, the opposite process of solidifying a polymer that is intrinsically in a liquid state reversibly with light is unattained. Herein, the light-controlled liquid-to-solid transition of polysiloxanes is reported, which are decorated with a small number of azobenzene-functionalized ureidopyrimidinone (Azo-UPy) pendants. The UPy moieties toggle between intra- and intermolecular hydrogen bonding via trans→cis photoisomerization of the azobenzene. This transformation on the molecular level leads to the formation of strong supramolecular cross-links, which, in turn, results in the macroscopic solidification of the material. The photoswitching event enables the post-synthetic tailoring of the polymers’ mechanical properties, thus providing an alternative to the addition of plasticizers or hardeners. Moreover, the adhesion strength of the photochromic material increases by a factor of 6 upon exposure to UV light. In situ illumination during rheological measurements reveals the delicate interplay between wavelength dependent penetration depth and photoswitching efficiency. This conceptually new (de)bonding on demand strategy paves the way for creating light-responsive materials with exciting applications in temporal adhesion, recycling, lithography, and material processing.     

Multipurpose nanomechanical testing machines revealing the size-dependent strength and high ductility of pure aluminium submicron films

The mechanical properties measurement of materials with submicron dimensions is extremely challenging, from the preparation and manipulation of specimens, to the application of small loads and extraction of accurate stresses and strains. A novel, versatile concept of micro and nano-machines to test films or beams with characteristic dimensions ranging between 10 and 1000 nm, allowing multiple loading configurations and geometries, is described. This new nanotesting method has been applied to thin, pure aluminium films. The yield strength linearly increases with the inverse of the film thickness, reaching 625 MPa for 150 nm thickness which is ten times larger than for macroscopic samples. The strain hardening rate is large, similar to what is measured with macroscopic specimens. Unexpectedly, large strains equal to about 75% have been measured before the initiation of a stable ductile failure mode. This nanomechanical laboratory involves thousands of micromachines built onto a single silicon wafer, providing a unique platform for investigating the elementary mechanisms of deformation and fracture in nanoscale metal, polymer or ceramic samples     

Comparative study of electrically conductive thick films with and without glass

An air-fireable, glass-free, electrically conductive thick-film material (96.6% Ag, 1.38% Cu, 0.28% Al, 0.35% Ti, and 1.39% Sn by weight) and a conventional glass-containing, electrically conductive thick-film materials (96.6% Ag and 3.4% glass frit by weight), both on alumina substrates, were studied by electrical, mechanical, thermal, and microscopic methods. The volume electrical resistivity of the glass-free thick film (2.5×10⁻⁶ Ω·cm, 30-μm thick) is lower than that of the glass-containing thick film (3.9×10⁻⁶ Ω·cm, 19-μm thick), with each film processed at its optimum firing temperature. The optimum firing temperature is 930°C and 850°C for glass-free and glass-containing thick films, respectively, as indicated by the criteria of low resistivity and high scratch resistance. The glass-free thick film has a higher scratch resistance than the glass-containing thick film, both fired at their respective optimum temperatures, suggesting that the former has higher bond strength to the alumina substrate. The formation process of the glass-free and glass-containing thick films is similar. The process involves solid-state diffusion of silver, which results in a silver network and grain boundaries. However, the sintering of silver particulates in the glass-containing thick film is enhanced by the viscous flow of glass.     

Supramolecular Surface Chemistry: Substrate‐Independent,Phosphate‐Driven Growth of Polyamine‐Based Multifunctional Thin Films

The ability to engineer surfaces at the supramolecular level by controlled integration of specific chemical units through substrate‐independent methodologies represents one of the new paradigms of contemporary materials science. Here, a method is reported to form multifunctional supramolecular coatings through simple dip‐coating of substrates in an aqueous solution of polyamine in the presence of phosphate anions. The chemical richness and versatility of polyamines are exploited as phosphate receptors to form thin functional films on a broad variety of substrates, ranging from metal to carbonaceous surfaces. It is shown that the simple derivatization of pendant amino groups of polyallylamine precursors with different chemical groups can endow films with predefined responsiveness or multiple functions—this translates into one‐pot and one‐step preparation of substrate‐adherent films displaying built‐in functions. It is believed that the flexibility, speed, and versatility with which this method provides such robust functional films make it very attractive for preparing samples of fundamental and technological interest.     

Mechano-Optical Sensors Fabricated with Multilayered Liquid Crystal Elastomers Exhibiting Tunable Deformation Recovery

Advances in tuning the mechanoresponsive behavior of liquid crystal elastomers have facilitated the development of next-generation applications such as reconfigurable photonic/electronic materials, energy-harvesting devices, and flexible sensors. However, the molecular-level control of mechanical responses remains difficult, with limited tunability achieved for recovery processes after stimulus removal. Herein, a design concept is proposed for facilely tuning the recovery of both the macroscopic deformation and molecular orientation change of liquid crystal elastomers using layered materials that exhibit the desired mechanoresponsive behavior. Changing the layering materials (a polydimethylsiloxane film with elastic response to a polymethylpenten film with plastic response) alters the relaxation time from <1 s to >6 months. To demonstrate this concept, highly sensitive, stretchable mechano-optical sensors with fast and ultraslow recovery times are developed that enable an applied strain to be quantitatively detected in real time or memorized with high spatial resolution, even with a conventional camera. This material design concept for arbitrarily controlling the recovery response can provide a platform for stimuli-responsive applications.     

Hybrid Materials from Ultrahigh‐Inorganic‐Content Mineral Plastic Hydrogels: Arbitrarily Shapeable,Strong, and Tough

Natural mineralized structural materials such as nacre and bone possess a unique hierarchical structure comprising both hard and soft phases, which can achieve the perfect balance between mechanical strength and shape controllability. Nevertheless, it remains a great challenge to control the complex and predesigned shapes of artificial organic–inorganic hybrid materials at ambient conditions. Inspired by the plasticity of polymer‐induced liquid precursor phases that can penetrate and solidify in porous organic frameworks for biomineral formation, here a mineral plastic hydrogel is shown with ultrahigh silica content (≈95 wt%) that can be similarly hybridized into a porous delignified wood scaffold, and the resultant composite hydrogels can be manually made into arbitrary shapes. Subsequent air drying well preserves the designed shapes and produces fire‐retardant, ultrastrong, and tough structural organic–inorganic hybrids. The proposed mineral plastic hydrogel strategy opens an easy and eco‐friendly way for fabricating bioinspired structural materials that compromise both precise shape control and high mechanical strength.     

Light-Responsive Programmable Shape-Memory Soft Actuator Based on Liquid Crystalline Polymer/Polyurethane Network

Liquid crystalline polymers (LCPs), especially liquid crystalline elastomers (LCEs) can generate ultrahigh shape change amplitude but has lower mechanical strength. Although some attempts have been tried to improve the mechanical performance of LCE, there are still limitations including complicated fabrication and high actuation temperature. Here, a versatile method is reported to fabricate light-driven actuator by covalently cross-linking polyurethane (PU) into LCP networks (PULCN). This new scheme is distinct from the previous interpenetrating network strategy, the hydrogen bonds and covalent bonds are used in this study to improve the miscibility of non-liquid-crystalline PU and LCP materials and enhance the stability of the composite system. This material not only possesses the shape memory properties of PU but shows shape-changing behavior of LCPs. With a shrinkage ratio of 20% at the phase transition temperature, the prepared materials reached a maximum mechanical strength of 20 MPa, higher than conventional LCP. Meanwhile, the resulting film shows diverse and programmable initial shapes by constructing crosslinking density gradient across the thickness of the film. By integration of PULCN with near-infrared light-responsive polydopamine, local and sequential light control is achieved. This study may provide a new route for the fabrication of programmable and mechanically robust light-driven soft actuator.     

钢基板厚膜环形电位器的研制

传统的陶瓷基板厚膜环形电位器不能承受高过载。选用不锈钢板作为基板材料,被覆绝缘介质,在其上印制厚膜电路,然后烧结,制作了钢基板厚膜环型电位器。该电位器经过温度循环、抗过载、机械强度和动态射击试验,结果表明:被覆绝缘介质不锈钢基板厚膜环型电位器具有过载值高(18000~20000g)、动态电阻装定精度高(误差小于1%)等优点,满足高过载使用要求。     

Ultrastrong Hierarchical Porous Materials via Colloidal Assembly and Oxidation of Metal Particles

Porous materials are useful as lightweight structures, bone substitutes, and thermal insulators, but exhibit poor mechanical properties compared to their dense counterparts. Biological materials such as bone and bamboo are able to circumvent this trade‐off between porosity and mechanical performance by combining pores at multiple length scales. Inspired by these biological architectures, a manufacturing platform that allows for the fabrication of Al₂O₃ foams and Al₂O₃/Al composites with hierarchical porosity and enhanced mechanical properties is developed. Macroscale pores are formed through the assembly of aluminum particles around templating air bubbles in wet foams, whereas the thermal oxidation of the metal particles above 800 °C generates porosity at the micrometer scale. After elucidating the mechanism of pore formation under different sintering conditions at the microscale, the mechanical performance of the resulting hierarchical foams using compression experiments and finite element simulations is evaluated. Porous materials manufactured via this simple approach are found to reach unparalleled mechanical properties with near‐zero sintering shrinkage and minimum loss in mechanical strength. The ability to produce macroscopic objects with ultrahigh strength at porosities up to 95% makes this an attractive manufacturing technology for the fabrication of high‐performance lightweight structures or advanced thermal and acoustic insulators.     

Biomimetic Supertough and Strong Biodegradable Polymeric Materials with Improved Thermal Properties and Excellent UV‐Blocking Performance

The preparation of biodegradable polymeric materials with both great strength and toughness remains a huge challenge. The natural spider silk exhibits a combined super high tensile strength and high fracture toughness (150–190 J g^?1), attributing to the hierarchically assembled nanophase separation and the densely organized sacrificial hydrogen bonds confined in the nanoscale granules. Herein, inspired by natural spider silk, a facile strategy is reported for the preparation of nanostructured biomimetic polymeric material by incorporating biomass‐derived lignosulfonic acid (LA) as interspersed nanoparticles into a biodegradable poly(vinyl alcohol) (PVA) matrix. The fabricated PVA/LA nanocomposite film exhibits the world's highest toughness of 172 (±5) J g^?1 among the PVA materials, as well as a powerful tensile strength of 98.2 MPa and a large breaking strain of 282%. The outstanding performance is attributed to the strain‐induced scattering of LA nanoparticles in the PVA matrix and the strong intermolecular sacrificial hydrogen bonds confined in the interphase. Moreover, after introducing the easily available green biomass LA, the prepared biomimetic polymer films show excellent ultraviolet‐blocking performance and good thermal stability. As both PVA and LA are biodegradable, this work presents an innovative design strategy for fully biodegradable robust polymeric materials with integrated strength and toughness.     

Multiscale simulation of aluminum thin films for the design of highly-reliable MEMS devices

A multiscale simulation methodology is presented to predict the macroscopic mechanical properties of aluminum thin films with a columnar grain structure from the morphology at microscopic scale. The elasto–plastic characteristics of the thin films are calculated as a function of the grain size, temperature, and strain rate by taking into account creep phenomena. The simulated data are validated by experimental stress–strain curves measured by dedicated microstructures in conjunction with a nanoindentation test equipment.     

Design and Optimization of Gradient Interface of Ba0.4In0.4Co4Sb12/Bi2Te2.7Se0.3 Thermoelectric Materials

A series of Ba_0.4In_0.4Co₄Sb₁₂/Bi₂Te_2.7Se_0.3 (FS/BT) thermoelectric (TE) materials were fabricated by a two-step spark plasma sintering method. The samples contained various numbers of gradient layers between FS and BT as follows: one gradient layer (1GL) with FS/BT volume ratio of 5:5, three GLs with ratios of 3:7, 5:5, and 7:3 (denoted as 3GLs-I with 3:7?C5:5?C7:3), 3GLs-II with 7:3?C5:5?C3:7, 5GLs-I with 3:7?C4:6?C5:5?C6:4?C7:3, and 5GLs-II with 2:8?C3:7?C5:5?C7:3?C8:2. The interfacial structure and mechanical properties of the FS/BT TE materials were investigated in this work. In FS/BT TE materials with no GLs, a large number of macroscopic cracks occurred on the FS bulk material side. It was discovered that designing and optimizing GLs between the FS and BT bulk materials could effectively relax the thermal stress induced by the large difference in coefficient of thermal expansion, eliminating the macroscopic cracks and resulting in a remarkable enhancement of the interfacial mechanical properties of the FS/BT TE materials. The flexural strength of the FS/BT TE material with 1GL reached 9.67?MPa, increased by 85% compared with that of the FS/BT TE material with no GLs. The present work indicates that increasing the BT content in the GL near to the FS bulk material side is an effective method to completely eliminate macroscopic cracking. The optimized gradient interface of the FS/BT TE material was 3GLs-II with FS/BT volume ratios of 3:7?C5:5?C7:3. The highest flexural strength reached 12.76?MPa, representing a 144% increase.     

Producing a Room Temperature Phosphorescent Film from Natural Wood Using a Top-Down Approach

Producing mechanic robust and sustainable room temperature phosphorescent (RTP) films in a convenient manner is a fundamental requirement but remains challenging. Here, an efficient “top-down” method for processing natural wood into RTP films is developed. Specifically, natural wood is partially delignified to increase its processability in the first step. After that, the treated wood is converted to W-film with a tensile strength of 273.6 MPa via mechanical pressing. The lignin units are well confined by cellulose in the W-film, triggering RTP emission with a lifetime of ≈241.9 ms. Additionally, the W-film exhibits good processability and energy transfer properties with Rhodamine B (RhB). Therefore, a series of multifunctional afterglow 2D and 3D RTP materials are constructed using W-film as a building block. This research is expected to result in a convenient and sustainable method for the preparation of RTP films.