Mechanically Robust Research Articles

Dimerized Acceptors with Conjugate-Break Linker Enable Highly Efficient and Mechanically Robust Organic Solar Cells.

Designing new acceptors is critical for intrinsically stretchable organic solar cells (IS-OSCs) with high efficiency and mechanical robustness. However, nearly all stretchable polymer acceptors exhibit limited efficiency and high-performance small molecular acceptors are very brittle. In this regard, we select thienylene-alkane-thienylene (TAT) as the conjugate-break linker and synthesize four dimerized acceptors by the regulation of connecting sites and halogen substitutions. It is found that the connecting sites and halogen substitutions considerably impact the overall electronic structures, aggregation behaviors, and charge transport properties. Benefiting from the optimization of the molecular structure, the dimerized acceptor exhibits rational phase separation within the blend films, which significantly facilitates exciton dissociation while effectively suppressing charge recombination processes. Consequently, FDY-m-TAT-based rigid OSCs render the highest power conversion efficiency (PCE) of 18.07 % among reported acceptors containing conjugate-break linker. Most importantly, FDY-m-TAT-based IS-OSCs achieve high PCE (14.29 %) and remarkable stretchability (crack-onset strain [COS]=18.23 %), significantly surpassing Y6-based counterpart (PCE=12.80 % and COS=8.50 %). To sum up, these findings demonstrate that dimerized acceptors containing conjugate-break linkers have immense potential in developing highly efficient and mechanically robust OSCs.

Dielectric, transparent, thermally stable and mechanically robust bionanocomposite films based on chitosan and modified cellulose nanocrystals

AbstractThe growing demand for electronics necessitates the development of novel environmentally responsible materials. A potential approach involves incorporating renewable and sustainable materials with mechanical and electrical properties while ensuring environmentally friendly disposal. Herein, this study reports the dielectric properties of chitosan (CS) reinforced with cellulose nanocrystals (CN) extracted from post‐harvest tomato plant residue. The resulting bionanocomposite material demonstrated remarkable characteristics, including dielectricity, transparency, thermal stability, and mechanical robustness. Additionally, the effect of high‐loading fillers (5 and 10 wt %) on the final properties of the material is investigated, as well as the effect of surface functionality of the CNs. The results showed that both the high‐loading fillers and the surface functionality of the CNs had a significant impact on the properties of the nanocomposite material. The bionanocomposite materials produced in this study hold great potential as an eco‐friendly substitute for conventional electronic materials and beyond. Its dielectric, transparent, thermally stable, and mechanically robust properties render it well‐suited for diverse applications.Highlights The phosphorylated groups insured high Crl (%) and high interface between the filler and matrix. High interface and crystallinity enhanced the mechanical characteristics. Low crystallinity increases the dielectric constant, case of 5% CNS. Filler’ type can tailor and optimize the energy dissipation up to tan δ = 0.5 for 5% CNP. Detection of Warburg impedance proves the interface polarization presence.

Facile Preparation of Impalement Resistant, Mechanically Robust and Weather Resistant Photothermal Superhydrophobic Coatings for Anti-/De-icing.

Photothermal superhydrophobic coatings hold great promise in addressing the limitations of conventional superhydrophobic anti-icing coatings. However, developing such coatings with excellent impalement resistance, mechanical robustness and weather resistance remains a significant challenge. Here, we report facile preparation of robust photothermal superhydrophobic coatings with all the above advantages. The coatings were prepared by spraying a dispersion consisting of fluorinated silica nanoparticles, a silicone-modified polyester adhesive and photothermal carbon black nanoparticles onto Al alloy plates followed by thermal curing. Thermal curing caused migration of perfluorodecyl polysiloxane from within the coatings to the surface, effectively maintaining a low surface energy despite the presence of the adhesive. Therefore, combined with the hierarchical micro-/nanostructure, dense yet rough nanostructure, adhesion of the adhesive and chemically inert components, the coatings exhibited remarkable superhydrophobicity, impalement resistance, mechanical robustness and weather resistance. Furthermore, the coatings demonstrated excellent photothermal effect even in the -10 °C, 80 % relative humidity and weak sunlight (0.2 sun) environment. Consequently, the coatings showed excellent passive anti-icing and active de-icing performance. Moreover, the coatings have good generalizability and scalability. We are confident that this study will accelerate the practical implementation of photothermal superhydrophobic coatings.

Mechanically Robust, Durable, and Multifunctional Hyper-Crosslinked Elastomer Based on Metal-Organic-Cluster Crosslinker: The Role of Topological Structure.

Polymer materials formed by conventional metal-ligand bonds have very low branch functionality, the crosslinker of such polymer usually consists of 2-4 polymer chains and a single metal ion. Thus, these materials are weak, soft, humidity-sensitive, and unable to withstand their shape under long-term service. In this work, a new hyperbranched metal-organic cluster (MOC) crosslinker containing up to 16 vinyl groups is prepared by a straightforward coordination reaction. Compared with the current typical synthesis of metal-organic cages (MOCs) or metal-organic-polyhedra (MOP) crosslinkers with complex operations and low yield, the preparation of the MOC is simple and gram-scale. Thus, MOC can serve as a high-connectivity crosslinker to construct hyper-crosslinked polymer networks. The as-prepared elastomer exhibits mechanical robustness, creep-resistance, and humidity-stability. Besides, the elastomer possesses self-healing and recyclability at mild condition as well as fluorescence stability. These impressive comprehensive properties are proven to originate from the hyper-crosslinked topological structure and microphase-separated morphology. The MOC-driven hyper-crosslinked elastomers provide a new solution for the construction of mechanically robust, durable, and multifunctional polymers.

Amorphous Cellulose Electrolyte for Long Life and Mechanically Robust Aqueous Structural Batteries

AbstractAqueous zinc (Zn)‐based structural batteries capable of both electrochemical energy storage and mechanical load‐bearing capabilities are attractive for next‐generation energy storage for future electric vehicles due to their eco‐friendliness, non‐toxic, and safe nature. However, parasitic free water activities plague aqueous Zn‐based batteries, detrimental to the electrochemical performance and longevity of the cell. Developing polymer gel electrolytes is a notable potential solution, but they usually have poor electrode interfacial interactions and inadequate mechanical properties. This article introduces a novel non‐fibrous highly amorphous cellulose polymer electrolyte “Cellyte” for aqueous structural Zn‐based batteries. Cellyte exhibits a high strength of ≈24 MPa and Young's modulus of ≈380 MPa, along with the ability to suppress parasitic water activity. The symmetric Zn||Cellyte||Zn cell therefore demonstrates excellent cycling stability of over ≈3000 h. Cellyte can also serve as the binder for the structural cathode material, creating a continuous polymer electrolyte–cathode interface, thereby increasing mechanical robustness and decreasing interfacial resistances of the battery, allowing the structural Zn||Cellyte||LMO‐CF battery to achieve high electrochemical performance with excellent cycling stability over 1200 h with ≈91.5% capacity retention. This provides a pathway to design mechanically robust, electrochemically performing, and safe structural batteries.

Design of Star‐Shaped Trimer Acceptors for High‐Performance (Efficiency > 19%), Photostable, and Mechanically Robust Organic Solar Cells

AbstractHigh power conversion efficiency (PCE), long‐term stability, and mechanical robustness are prerequisites for the commercial applications of organic solar cells (OSCs). In this study, a new star‐shaped trimer acceptor (TYT‐S) is developed and high‐performance OSCs with a PCE of 19.0%, high photo‐stability (t80% lifetime = 2600 h under 1‐sun illumination), and mechanical robustness with a crack‐onset strain (COS) of 21.6% are achieved. The isotropic molecular structure of TYT‐S affords efficient multi‐directional charge transport and high electron mobility. Furthermore, its amorphous structure prevents the formation of brittle crystal‐to‐crystal interfaces, significantly enhancing the mechanical properties of the OSC. As a result, the TYT‐S‐based OSCs demonstrate a significantly higher PCE (19.0%) and stretchability (COS = 21.6%) than the linear‐shaped trimer acceptor (TYT‐L)‐based OSCs (PCE = 17.5% and COS = 6.4%) and the small‐molecule acceptor (MYT)‐based OSCs (PCE = 16.5% and COS = 1.3%). In addition, the increased molecular size of TYT‐S, relative to that of MYT and dimer (DYT), suppresses the diffusion kinetics of the acceptor molecules, substantially improving the photostability of the OSCs. Finally, to effectively demonstrate the potential of TYT‐S, intrinsically stretchable (IS)‐OSCs are constructed. The TYT‐S‐based IS‐OSCs exhibit high device stretchability (strain at PCE80% = 31%) and PCE of 14.4%.

Mechanically robust ultrathin nanofibrous films by using microfluidic-based continuous printing.

Ultrathin nanofibrous films with unique properties, such as controlled thickness, structures, and excellent mechanical robustness, play a vital role in flexible wearable devices, electronic skin, and rechargeable batteries. However, nanofibrous films are always facing limitations in their mechanical properties, even though they are strong when used as textiles, mainly owing to their structural shortcomings by using conventional fabrication methods. Herein, we present the fabrication of free-standing ultrathin nanofibrous films with good mechanical properties by using a microfluidic-based continuous printing strategy. Owing to the precisely controllable microfluidic flow in the micrometre-scale, the resulting aramid nanofibre (ANF) films can reach thicknesses as low as 140 ± 25 nm. Specifically, the tensile strength of such ultrathin ANF films is recorded at an impressive value of 667 ± 40 MPa, representing a 120% improvement compared to the films prepared by using casting method. Such excellent mechanical robustness comes from the double-sided protonation, which shows a symmetrically dense structure compared to the asymmetric structure of cast films. Furthermore, we demonstrate the continuous fabrication of thin regenerated cellulose nanofiber (RCNF) and cellulose diacetate (CDA) films using the microfluidic-based printing strategy. Both microfluidic-based films show significant enhancements in strength, with a 42% increase for RCNF and a 94% increase for CDA compared to their cast films. We envision that this microfluidic-based continuous printing strategy provides a promising pathway for the development of advanced ultrathin nanofibrous films towards practical applications.

Mechanically robust, self-reporting and healable polyurethane elastomers by incorporating symmetric/asymmetric chain extenders.

Self-healing elastomers usually show poor mechanical properties and environmental stability, and they cannot self-report mechanical/chemical damage. Herein, an innovative design strategy is reported that combines symmetric/asymmetric chain extenders to create large yet disordered hard domains within polyurethane (PU) elastomers, enabling the integration of mechanical robustness and self-reporting and self-healing capabilities to overcome both mechanical and chemical damage. Specifically, large yet disordered hard domains were created by governing the molar contents of asymmetric fluorescent 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) and symmetric 4-aminophenyl disulfide (APDS). Such a structural feature led to a small free-volume fraction, prominent strain-induced crystallization (SIC), and high energy of dissipation, enabling the PU elastomer to display outstanding mechanical strength (60.7 MPa) and toughness (177.9 MJ m-3). Meanwhile, the loose stacking of disordered hard domains imposed small restriction on network chains and imparted the network with high relaxation dynamics, leading to high healing efficiency (97.8%). More importantly, the fluorescence intensity was stimulus-responsive and thus the PU elastomer could self-report mechanical/chemical damage and healing processes. The PU elastomer also showed potential application prospects in information encoding and encryption. Furthermore, selecting polydimethylsiloxane as one of the soft segments could effectively endow the PU elastomer with intrinsic hydrophobicity. Therefore, this work provides valuable guidance for designing multi-functional materials with anti-counterfeiting, self-reporting, and healing properties as well as high mechanical properties and hydrophobicity.

Cycloaliphatic Quaternary Ammonium Functionalized Poly(oxindole biphenyl) Based Anion-Exchange Membranes for Water Electrolysis: Stability and Performance.

Mechanically robust anion-exchange membranes (AEMs) with high conductivity and long-term alkali resistance are needed for water electrolysis application. In this work, aryl-ether free polyaromatics containing isatin moieties were prepared via super acid-catalyzed copolymerization, followed by functionalization with alkaline stable cyclic quaternary ammonium (QA) cationic groups, to afford high performance AEMs for application in water electrolysis. The incorporation of side functional cationic groups (pyrrolidinium and piperidinium) onto a polymer backbone via a flexible alkyl spacer aimed at conductivity and alkaline stability improvement. The effect of cation structure on the properties of prepared AEMs was thoroughly studied. Pyrrolidinium- and piperidinium-based AEMs showed similar electrolyte uptakes and no obvious phase separation, as revealed by SAXS and further supported by AFM and TEM data. In addition, these AEMs displayed high conductivity values (81. 5 and 120 mS cm-1 for pyrrolidinium- and piperidinium-based AEM, respectively, at 80 °C) and excellent alkaline stability after 1 month aging in 2M KOH at 80 °C. Especially, a pyrrolidinium-based AEM membrane preserved 87% of its initial conductivity value, while at the same time retaining its flexibility and mechanical robustness after storage in alkaline media (2M KOH) for 1 month at 80 °C. Based on 1H NMR data, the conductivity loss observed after the aging test is mainly related to the piperidinium degradation that took place, probably via ring-opening Hofmann elimination, alkyl spacer scission and nucleophilic substitution reactions as well. The synthesized AEMs were also tested in an alkaline water electrolysis cell. Piperidinium-based AEM showed superior performance compared to its pyrrolidinium analogue, owing to its higher conductivity as revealed by EIS data, further confirming the ex situ conductivity measurements.

Direct Synthesis of Polyimide Curly Nanofibrous Aerogels for High-Performance Thermal Insulation Under Extreme Temperature.

Maintaining human body temperature is one of the basic needs for living, which requires high-performance thermal insulation materials to prevent heat exchange with external environment. However, the most widely used fibrous thermal insulation materials always suffer from the heavy weight, weak mechanical property, and moderate capacity to suppress heat transfer, resulting in limited personal cold and thermal protection performance. Here, an ultralight, mechanically robust, and thermally insulating polyimide (PI) aerogel is directly synthesized via constructing 3D interlocked curly nanofibrous networks during electrospinning. Controlling the solution/water molecule interaction enables the rapid phase inversion of charged jets, while the multiple jets are ejected by regulating charge density of the fluids, thus synergistically allowing numerous curly nanofibers to interlock and cross-link with each other to form porous aerogel structure. The resulted PI aerogel integrates the ultralight property with density of 2.4mg cm-3, extreme temperature tolerance (mechanical robustness over -196 to 300 °C), and thermal insulation performance with ultralow thermal conductivity of 22.4mW m-1 K-1, providing an ideal candidate to keep human thermal comfort under extreme temperature. This work can provide a source of inspiration for the design and development of nanofibrous aerogels for various applications.

Color adjustable, mechanically robust, flame-retardant and weather-resistant TiO2/MMT/CNF hierarchical nanocomposite coatings toward intelligent fire cyclic warning and protection

Fire safety and protection are very important but still show a critical global challenge. Developing smart fire warning materials with combined passive flame retardancy and active fire alarm response is promising for reducing or avoiding serious fire disasters. Various nano-fillers (e.g., graphene oxide and MXene) based composite coatings have proven to be effective for monitoring critical fire risk of various combustible materials; however, they still show some shortages, for example, high cost, black color, poor weather resistance and complicated fabricating process. Here, we report a green, cost-effective and large-scale strategy for fabricating water-based 3D-titania/2D-montmorillonite/1D-celluose nanofiber (TiO2/MMT/CNF) hierarchical nanocomposite coatings with adjustable color, mechanical robustness, good flame retardancy, long-term weather resistance and sensitive fire cyclic alarming response. The formation of strong chemical bonding and hydrogen bonding interactions among polyethylene glycol molecules and multi-scale nano-fillers together with silane surface modification can produce good mechanical flexibility (folded crane), surface hydrophobicity (water contact angle of 152°) and exceptional flame resistance (good structure integrity after 120 s flame exposure). Notably, the optimized nanocomposite coatings exhibit ultrafast fire alarm response (<3.5 s) and stable fire cyclic alarming capability via the possible band transition of the TiO2 network under flame. Further, such color-adjustable nanocomposite coatings can be easily fabricated for large-scale production, and they show excellent stable flame retardancy and stable fire cyclic warning response even after more than one-year outdoor exposure. This work provides a promising and green fire-warning nanocomposite coatings with combined passive-active functionalities for fire warning and protection.

Green, recyclable, mechanically robust, wet-adhesive and ionically conductive cellulose-based bioplastics enabled by supramolecular covalent hydrophobic eutectic networks

The development of novel cellulose-based bioplastics (CBPs) is highly desirable because CBPs are green, rationally use resources, and lead to a reduction in environmental pollution compared to alternative materials. However, incorporating high transparency, water resistance, mechanical robustness, wet-adhesion, ionic conductivity and recyclability into CBP remains a challenge. In this paper, novel CBPs with supramolecular covalent networks are fabricated by introducing polymerizable hydrophobic deep eutectic solvents (HDES) into ethylcellulose (EC) networks through in situ plasticization followed by a rapid photopolymerization process. The excellent molecular interfacial compatibility enables EC to be loaded with a high content of poly(HDES), while allowing high transparency (more than 90 %) of the prepared CBPs. Multiple intermolecular interactions provide CBPs with mechanical robustness, water resistance, and underwater adhesion, and CBPs can be readily recovered by the solvent in a closed loop. Moreover, CBPs possess inherent ionic conductivities, and using them as green substrates, personalized electroluminescent devices can be successfully constructed. The method proposed in this paper provides a new strategy for the preparation of multifunctional CBPs, which will greatly enrich their applications in self-adhesive materials, green flexible electronics and other package materials.

Mechanically Robust Cellulose-Based Piezoelectric Elastomer Formed by Slidable Polyrotaxane Cross-Linker.

Cellulose has great potential in the field of piezoelectricity owing to its high crystallinity; however, it exhibits low processability and poor mechanical robustness. In this study, to enhance the applicability of cellulose-based piezoelectric materials, a robust cellulose-based piezoelectric elastomer with excellent piezoelectric properties was developed by cross-linking cellulose with polyrotaxane (PR). The effects of cross-linking on the mechanical properties and crystalline structures of the resulting elastomers were investigated. The ferroelectric and piezoelectric properties were evaluated from their polarization hysteresis loops and voltage generation characteristics. eHPC25PR75 exhibited 2.7 times higher toughness (20.4 MJ m-3) than eHPC100 (7.57 MJ m-3). It also shows a power density 4.2 times higher (1.34 μW cm-2) than eHPC100 (0.321 μW cm-2). As a result, eHPC25PR75 demonstrated piezosensitivity to mechanical vibrations in a variety of devices that require mechanical robustness. These results can inform the design and development of high-performance piezoelectric devices.

Regulating Phase Separation Kinetics for High-Efficiency and Mechanically Robust All-Polymer Solar Cells.

All-polymer solar cells (all-PSCs) possess excellent operation stability and mechanical robustness than other types of organic solar cells, thereby attracting considerable attention for wearable flexible electron devices. However, the power conversion efficiencies (PCEs) of all-PSCs are still lagging behind those of small-molecule-acceptor-based systems owing to the limitation of photoactive materials and unsatisfactory blend morphology. In this work, a novel terpolymer, denoted as PBDB-TFCl (poly4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b″]dithiophene-1,3-bis(2-ethylhexyl)-5,7-di(thiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c″]dithiophene-4,8-dione-4,8-bis(4-chloro-5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene), is used as an electron donor coupled with a ternary strategy to optimize the performance of all-PSCs. The addition of PBDB-TCl unit deepens the highest occupied molecular orbital energy level, reducing voltage losses. Moreover, the introduction of the guest donor (D18-Cl) effectively regulates the phase-transition kinetics of PBDB-TFCl:D18-Cl:PY-IT during the film formation, leading to ideal size of aggregations and enhanced crystallinity. PBDB-TFCl:D18-Cl:PY-IT devices exhibit a PCE of 18.6% (certified as 18.3%), judged as the highest value so far obtained with all-PSCs. Besides, based on the ternary active layer, the manufactured 36 cm2 flexible modules exhibit a PCE of 15.1%. Meanwhile, the ternary PSCs exhibit superior photostability and mechanical stability. In summary, the proposed strategy, based on molecular design and the ternary strategy, allows optimization of the all-polymer blend morphology and improvement of the photovoltaic performance for stable large-scale flexible PSCs.

Thin, Highly Ionic Conductive, and Mechanically Robust Frame‐Based Solid Electrolyte Membrane for All‐Solid‐State Li Batteries

AbstractA thin but robust solid electrolyte layer is crucial for realizing the theoretical energy density of all‐solid‐state batteries (ASSBs) beyond state‐of‐the‐art Li‐ion batteries (LIBs). This study proposes a simple but practical strategy for fabricating thin solid electrolyte membranes using 5‐µm perforated polyethylene separators with 35% open areas as the supporting component, which ensures mechanical robustness for commercial‐level cell assembly. The thickness of this frame‐based solid electrolyte (f‐SE) membrane can be reduced to ≈45 µm, even after coating the Li6PS5Cl (LPSCl) solid electrolyte composite. Despite a slightly lower ionic conductivity compared to that of thick LPSCl pellets, the f‐SE membranes show high conductance and low overpotential in Li||Li symmetric cells. Their incorporation into LiNi0.7Co0.15Mn0.15O2 full cells increases the reversible capacity and rate capability compared to those of cells with conventional LPSCl pellets. The f‐SE membrane cells exhibit excellent cycling stability over 250 cycles, while maintaining high‐capacity retention and Coulombic efficiency. Notably, the f‐SE membranes significantly increase the energy density of ASSBs (314 Wh kg−1), exceeding the values reported for sulfide‐based cells. These results highlight the crucial role of f‐SE membranes in improving the mechanical properties and energy density of ASSBs, thereby contributing to the development of next‐generation Li battery technologies.

Monolithic SOI through-wafer Knudsen pumps with mechanically robust Si channels

Knudsen pumps (KPs) generate gas flow using thermal transpiration in narrow channels with a longitudinal temperature gradient. With no moving parts, KPs offer long lifetime and are attractive for complex microfluidic systems. Although high performance was previously reported in microfabricated KPs that utilized suspended dielectric membranes to construct the pumping channels, this approach can limit the mechanical robustness and complicate the fabrication process. In this work, we present monolithically microfabricated KPs without using suspended membranes. These types of structures significantly improve the mechanical robustness, allow a wider process window, and simplify the microfabrication process. The pumping channels in this work are 14 µm in length, 1.2 × 200 µm2 in cross-section, vertically oriented, and with rigid silicon and dielectric sidewalls; the overall structures are easily manufacturable. This work primarily focuses on two core KP designs, which incorporate 4 and 6 parallel pumping channels in ≈ 11 and 17 mm2 footprints, respectively. The scaling capability is also investigated preliminarily in a design with 45 parallel pumping channels. The KPs were fabricated on a silicon-on-insulator wafer by a six-mask lithographic process with standard fabrication steps. This process eliminated the use of complicated trench refill, polish, and sacrificial dry etch steps that were required for the previously reported KPs with suspended membranes. At atmospheric pressure, the 4-channel KPs provided a blocking pressure of 620 Pa and maximum flow rate of 0.041 sccm through 0.001 mm2 channel area, using 2 W applied power. This maximum flow rate per unit channel area (sccm/mm2) is superior to that of the KPs with suspended membranes. For all the KP designs, the experimentally measured pumping performance well matched the modeling results, with <15 % discrepancy. The fabrication simplicity and reliability of the mechanically robust KPs can enable monolithic integration onto complex lab-on-a-chip systems.

Highly Conductive Robust Carbon Nanotube Networks for Strong Buckypapers and Transparent Electrodes

AbstractWhile individual single‐wall carbon nanotubes (SWCNTs) have remarkable strength and electrical conductivity, SWCNT networks fabricated from dispersions have inferior properties due to nanotube bundling, limiting the potential applications of SWCNT materials. Herein, a common dye molecule (purpurin) is used to exfoliate SWCNTs via noncovalent functionalization and to fabricate SWCNT materials by a simple solution‐based process. The advantageous noncovalent interactions result in efficient exfoliation and metallic SWCNT enrichment, affording SWCNT materials with high mechanical robustness and electrical conductivity. This method is used to prepare mechanically robust SWCNT films and flexible transparent conductive electrodes.

Recastable assemblies of carbon dots into mechanically robust macroscopic materials

Assembly of nanoparticles into macroscopic materials with mechanical robustness, green processability, and recastable ability is an important and challenging task in materials science and nanotechnology. As an emerging nanoparticle with superior properties, macroscopic materials assembled from carbon dots will inherit their properties and further offer collective properties; however, macroscopic materials assembled from carbon dots solely remain unexplored. Here we report macroscopic films assembled from carbon dots modified by ureido pyrimidinone. These films show tunable fluorescence inherited from carbon dots. More importantly, these films exhibit collective properties including self-healing, re-castability, and superior mechanical properties, with Young’s modulus over 490 MPa and breaking strength over 30 MPa. The macroscopic films maintain original mechanical properties after several cycles of recasting. Through scratch healing and welding experiments, these films show good self-healing properties under mild conditions. Moreover, the molecular dynamics simulation reveals that the interplay of interparticle and intraparticle hydrogen bonding controls mechanical properties of macroscopic films. Notably, these films are processed into diverse shapes by an eco-friendly hydrosetting method. The methodology and results in this work shed light on the exploration of functional macroscopic materials assembled from nanoparticles and will accelerate innovative developments of nanomaterials in practical applications.

Fully flexible and mechanically robust tactile sensors containing core–shell structured fibrous piezoelectric mat as sensitive layer

Tactile sensors based on poly(vinylidene fluoride) (PVDF) are widely investigated, but their flexibility and mechanical robustness are limited due to the poor elasticity of PVDF. Herein, fully flexible and mechanically robust tactile sensors with a sandwich-like structure are fabricated by introducing a core–shell structured fibrous piezoelectric mat between two fibrous TPU/AgNWs (TPU: thermoplastic polyurethane, AgNWs: silver nanowires) flexible electrodes. The piezoelectric mat works as the sensitive layer, in which TPU is designed as the elastic skeleton in the core of fibers to enhance the mechanical properties while PVDF is wrapped on TPU fiber as a piezoelectric component. The core–shell structured TPU/PVDF mat has achieved improved elasticity and stretchability and excellent piezoelectric effects are demonstrated (sensitivity: 95.8 mV N−1). Because of the flexibility of both sensitive layer and electrodes, the tactile sensors have achieved an elongation of 300 %, excellent elasticity, a sensitivity of 20.3 mV N−1 and stable sensing in more than 2,000 cycles. Interestingly, such tactile sensors also exhibit outstanding mechanical robustness and have the ability to properly respond to mechanical stimuli in deformed states. Various pressures generated in daily life (e.g., hand slapping, feather brushing, joint bending, blowing, vocal cord vibration and writing) are successfully monitored utilizing such tactile sensors. Overall, this work has provided a new clue to regulate the flexibility and mechanically robustness of tactile sensors.

Mechanically robust, flexible hybrid tactile sensor with microstructured sensitive composites for human-cyber-physical systems

Advances in human-cyber-physical system (HCPS) requires multiple and multimodal sensory network to address the challenge of human-machine relationships, posing substantial potential for human health monitoring and human-centric smart manufacturing. However, combining electrical sensitivity and mechanical robustness of flexible sensors with simple device structure is still challenging. This work presents a flexible porous bimodal pressure sensor (PBPS) by fabricating 3D microstructured sensitive porous carbon-nanotubes composites (PCNC). The multi-layered PBPS can offer the ability to switch between piezoresistive and piezocapacitive sensing modes without altering the device structure, enhancing mechanical stability of device under loading/unloading cycles. This versatility allows for the detection of hardness discrimination, grabbing sensing, and dynamic human physiological signal recognition, which possess superior pressure sensing performances with a high sensitivity (0.1059 kPa−1 in piezoresistive mode, 0.2054 kPa−1 in capacitive mode), wide measuring range (0–25 kPa), rapid response time (<130 ms in piezoresistive mode, <55 ms in piezocapacitive mode), and long-term durability (>3000 cycles). Furthermore, we proposed a mechanical constitutive model to elucidate the sensing mechanism of microstructured PCNC by 3D micro-CT based modeling and experimental data. Finally, we employed multiple PBPSs as sensing elements to real-time monitor 3D printing manufacturing stress, structure assembling stress, and human physiology signals in HCPS, indicating the potential applications of PBPS ranging from monitoring human health to facilitating intelligent manufacturing.