Soft Composite Gels with High Toughness and Low Thermal Resistance through Lengthening Polymer Strands and Controlling Filler

Soft gels with high toughness have drawn tremendous attention recently due to their potential applications in flexible electronic fields. The miniaturization and high-power density of electronic devices require soft gels with both high toughness and low thermal resistance; however, it is difficult to achieve these properties simultaneously. Herein, a simple design strategy is reported for constructing soft (high stretchability of 6.91 and low Young's modulus of 340 kPa), tough (4741.48 J m⁻²) and thermal conductive (low thermal resistance of 0.14 cm² K W⁻¹, under 10 psi pressure) polydimethylsiloxane/aluminum composite gel. This is realized by precisely lengthening polymer strands between the chemical cross-linked points and controlling the aluminum content in the composite gels. The symbiosis of this combination involves: lengthening the polymer strands facilitates its unfolding to increase the softness and intrinsic toughness; the thermally conductive spherical aluminum enables low thermal resistance and increases the intrinsic toughness and stress dissipation. By utilizing this gel as a thermal interface material, effective heat dissipation is demonstrated in electronic devices operating under high-power conditions over numerous cycles. These results demonstrate the application potential of composite gels in meeting the performance maintenance and heat dissipation, which are needed for modern electronic devices.     

Rugged Soft Robots using Tough,Stretchable, and Self-Healable Adhesive Elastomers

Soft robots are susceptible to premature failure from physical damages incurred within dynamic environments. To address this, we report an elastomer with high toughness, room temperature self-healing, and strong adhesiveness, allowing both prevention of damages and recovery for soft robotics. By functionalizing polyurethane with hierarchical hydrogen bonds from ureido-4[1H]-pyrimidinone (UPy) and carboxyl groups, high toughness (74.85 MJ m⁻³), tensile strength (9.44 MPa), and strain (2340%) can be achieved. Furthermore, solvent-assisted self-healing at room temperature enables retention of high toughness (41.74 MJ m⁻³), tensile strength (5.57 MPa), and strain (1865%) within only 12 h. The elastomer possesses a high dielectric constant (≈9) that favors its utilization as a self-healing dielectric elastomer actuator (DEA) for soft robotics. Displaying high area strains of ≈31.4% and ≈19.3% after mechanical and electrical self-healing, respectively, the best performing self-healable DEA is achieved. With abundant hydrogen bonds, high adhesive strength without additional curing or heating is also realized. Having both actuation and adhesive properties, a “stick-on” strategy for the assembly of robust soft robots is realized, allowing soft robotic components to be easily reassembled or replaced upon severe damage. This study highlights the potential of soft robots with extreme ruggedness for different operating conditions.     

Hierarchical Interface Engineering for Advanced Nanocellulosic Hybrid Aerogels with High Compressibility and Multifunctionality

The hierarchical combination of mineral and biopolymer building blocks is advantageous for the notable properties of structural materials. Integrating silane and cellulose nanofibers into high-performance hybrid aerogels is promising yet remains challenging due to the unsatisfied interface connections. Here, an interfacial engineering strategy is introduced via freeze–drying-induced wetting and mineralization to reinforce the hierarchical porous cellulose network, resulting in mineral-coated nanocellulose hybrid aerogels in a simple and consecutive bottom-up assembly process. With optimized multiscale interfacial engineering between the stiff and soft components, the resulting cellulose-based hybrid aerogels are endowed with lightweight (>0.7 mg cm⁻³), superior enhanced mechanical compressibility (>99% strain) within a wide temperature range, as well as super-hydrophobicity (≈168°) and moisture stability under high humidity (95% relative humidity). Benefiting from these superior characters, the multifunctional hybrid aerogels as effective oil/water absorbents with excellent recyclability, thermal insulators in extreme conditions, and sensitive strain sensors are demonstrated. This assembly approach with optimized interfacial features is scalable and efficient, affording high-performance cellulose-based aerogels for various applications.     

Ultra-High Toughness Fibers Using Controlled Disorder of Assembled Aramid Nanofibers

Assembling nanoscale building blocks with reduced defects has emerged as a promising approach to exploit nanomaterials in the fabrication of simultaneously strong and tough architectures at larger scales. Aramid nanofibers (ANFs), a type of organic nanobuilding block, have been spotlighted due to their superior mechanical properties and thermal stability. However, no breakthrough research has been conducted on the high mechanical properties of a structure composed of ANFs. Here, assembling ANFs into macroscale fiber using a simultaneous protonation and wet-spinning process is studied to reduce defects and control disorder. The ANF-assembled fibers consist of hierarchically aligned nanofibers that behave as a defective law structure, making it possible to reach a Young's modulus of 53.15 ± 8.98 GPa, a tensile strength of 1,353.64 ± 92.98 MPa, and toughness of 128.66 ± 14.13 MJ m⁻³. Compared to commercial aramid fibers, the fibers exhibit ≈1.6 times greater toughness while also providing specific energy to break as 93 J g⁻¹. Furthermore, this shows recyclability of the ANF assembly by retaining ≈94% of the initial mechanical properties. This study demonstrates a facile process to produce high stiffness and strength fibers composed of ANFs that possess significantly greater toughness than commercial synthetic fibers.     

In Situ Synthesis of Mechanically Robust,Transparent Nanofiber-Reinforced Hydrogels for Highly Sensitive Multiple Sensing

Hydrogels that are both highly conductive and mechanically robust have demonstrated great potential in various applications ranging from healthcare to soft robotics; however, the creation of such materials remains an enormous challenge. This study presents an in situ synthesis strategy for developing bioinspired chemically integrated silica-nanofiber-reinforced hydrogels (SFRHs) with robust mechanical and electronic performance. The strategy is to synthesize soft hydrogel matrices from acrylamide monomers in the presence of well-dispersed silica nanofibers and vinyl silane, which generates homogenous SFRHs with innovative interfacial chemical bonds. The resultant SFRHs exhibit excellent mechanical properties including high mechanical strength of 0.3 MPa at a fracture strain of 1400%, high Young's modulus of 0.11 MPa (comparable to human skin), and superelasticity over 1000 tensile cycles without plastic deformation, while maintaining high transmittance (≥83%). In parallel, the SFRHs show enhanced ionic conductivity (3.93 S m⁻¹) and can monitor multiple stimuli (stretching, compressing, and bending) with high sensitivity (gauge factor of 2.67) and ultra-durability (10 000 cycles). This work may shed light on the design and development of tough and stretchable hydrogels for various applications.     

Quantification of Temperature-Dependent Charge Separation and Recombination Dynamics in Non-Fullerene Organic Photovoltaics

Transient optical spectroscopy is used to quantify the temperature-dependence of charge separation and recombination dynamics in P3TEA:SF-PDI₂ and PM6:Y6, two non-fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF-PDI₂, a free charge generation rate constant of ≈2.4 × 10¹⁰ s⁻¹ is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 10¹⁰ s⁻¹ is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor-acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate.     

Quantitative Determination of Charge Transport Interface at Vertically Phase Separated Soluble Acene/Polymer Blends

Interfacial structure is critical for optimizing the electrical properties of organic field-effect transistors. In this study, the interfacial structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/polymer blends are nondestructively determined by the complementary neutron and X-ray reflectivity. The TIPS-pentacene/deuterated poly(methylmethacrylate) (d-PMMA) blends exhibit a vertically phase-separated structure with a molecularly sharp interface (interfacial roughness ≈5 Å), whereas the TIPS-pentacene/d-polystyrene (d-PS) blend intermix near the interface. Ultrahigh molecular weight d-PMMA leads to the formation of surface-segregated hexagonal spherulites of TIPS-pentacene owing to the thermodynamic factors (e.g., surface/interface energy, polarity, and viscosity) of the blending materials. The well-developed hexagonal spherulites of TIPS-pentacene on molecularly sharp d-PMMA interface result in higher field-effect mobility as compared to the dendritic crystals from d-PS blends because of the higher perfectness, coverage, and interfacial roughness of the TIPS-pentacene crystals. The approach used in this study facilitates the understanding of the charge transport mechanism at the phase-separated interfaces in soluble acene/polymer blends.     

Strong and Ultra-Tough Supramolecular Hydrogel Enabled by Strain-Induced Microphase Separation

Architected hydrogels are widely used in biomedicine, soft robots, and flexible electronics while still possess big challenges in strong toughness, and shape modeling. Here, inspired with the universal hydrogen bonding interactions in biological systems, a strain-induced microphase separation path toward achieving the printable, tough supramolecular polymer hydrogels by hydrogen bond engineering is developed. Specifically, it subtly designs and fabricates the poly (N-acryloylsemicarbazide-co-acrylic acid) hydrogels with high hydrogen bond energy by phase conversion induced hydrogen bond reconstruction. The resultant hydrogels exhibited the unique strain-induced microphase separation behavior, resulting in the excellent strong toughness with, for example, an ultimate stress of 9.1 ± 0.3 MPa, strain levels of 1020 ± 126%, toughness of 33.7 ± 6.6 MJ m⁻³, and fracture energy of 171.1 ± 34.3 kJ m⁻². More importantly, the hydrogen bond engineered supramolecular hydrogels possess dynamic shape memory character, i.e shape fixing at low temperature while recovery after heating. As the proof of concept, the tailored hydrogel stents are readily manufactured by 3D printing, which showed good biocompatibility, load-bearing and drug elution, being beneficial for the biomedical applications. It is believed that the present 3D printing of the architected dynamic hydrogels with ultrahigh toughness can broaden their applications.     

A Floating Integrated Solar Micro-Evaporator for Self-Cleaning Desalination and Organic Degradation

Safe and clean freshwater harvesting from (organic-containing) saline or wastewater holds great potential for mitigating water scarcity and pollution, but remains challenging. Herein, a floating photothermal/catalytic-integrated interfacial micro-evaporator (g-C₃N₄@PANI/PS) is reported as a proof-of-concept multifunctional scavenger evaporator system (MSES) to achieve both solar-driven complete desalination and organic degradation. The spherical porous lightweight polystyrene core, incorporated with a black surface functional layer (g-C₃N₄@PANI), enables the hybrid micro-evaporator to naturally float and thereby collectively self-assemble under surface tension for interfacial evaporation, which achieves preeminent self-cleaning for complete salt/solute separation and efficient organic photodegradation under rotation. Remarkably, the floating micro-evaporator achieves a high solar-vapor conversion efficiency of ≈90% with high interfacial energy localization and provides abundant active photocatalytic sites on the interface, which is further enhanced by interfacial photothermal cooperation. High photo-driven degradation efficiencies of 99% for nonvolatile organic compounds (non-VOC) bisphenol A and 95% for VOC phenol in wastewater are achieved. An outdoor comprehensive solar water treatment test toward organic-containing high-salinity sewage verifies the feasibility of MSES for sustainable freshwater harvesting (1.3 kg m⁻² h⁻¹), downstream salt recovery, and organic degradation. This strategy may inspire an integrated solution of water scarcity, clean energy, and environmental pollution toward carbon neutrality.     

Strong,Compressible, and Ultrafast Self-Recovery Organogel with In Situ Electrical Conductivity Improvement

Coordination complexes are widely used to tune the mechanical behaviors of polymer materials, including tensile strength, stretchability, self-healing, and toughness. However, integrating multivalent functions into one material system via solely coordination complexes is challenging, even using combinations of metal ions and polymer ligands. Herein, a single-step process is described using silver-based coordination complexes as cross-linkers to enable high compressibility (>85%). The resultant organogel displays a high compressive strength (>1 MPa) with a low energy loss coefficient (<0.1 at 50% strain). Remarkably, it demonstrates an instant self-recovery at room temperature with a speed >1200 mm s⁻¹, potentially being utilized for designing high-frequency-responsive soft materials (>100 Hz). Importantly, in situ silver nanoparticles are formed, effectively endowing the organogel with high conductivity (550 S cm⁻¹). Given the synthetic simplification to achieve multi-valued properties in a single material system using metal-based coordination complexes, such organogels hold significant potential for wearable electronics, tissue-device interfaces, and soft robot applications.     

Reliability study of underfill/chip interface under accelerated temperature cycling (ATC) loading

Interface reliability issue has become a major concern in developing flip chip assembly. The CTE mismatch between different material layers may induce severe interface delamination reliability problem. In this study, multifunctional micro-moiré interferometry (M³I) system was utilized to study the interfacial response of flip chip assembly under accelerated thermal cycling (ATC) in the temperature range of −40 °C to 125 °C. This in-situ measurement provided good interpretation of interfacial behavior of delaminated flip chip assembly. Finite element analysis (FEA) was carried out by introducing viscoelastic properties of underfill material. The simulation results were found to be in good agreement with the experimental results. Interfacial fracture mechanics was used to quantify interfacial fracture toughness and mode mixity of the underfill/chip interface under the ATC loading. It was found that the interfacial toughness is not only relative to CTE mismatch but also a function of stiffness mismatch between chip/underfill.     

Trigger-Detachable Hydrogel Adhesives for Bioelectronic Interfaces

Recent electronics technology development has provided unprecedented opportunities for enabling implantable bioelectronics for long-term disease monitoring and treatment. Current electronics-tissue interfaces are characterized by weak physical interactions, suffering from potential interfacial failure or dislocation during long-term application. On the other hand, some new technologies can be used to achieve robust electronics-tissue interfaces; however, such technologies are limited by potential risks and the discomfort associated with postdetachment of the bioelectronics. Here, a hydrogel-based electronics-tissue interface based on the exploitation of dynamic interactions (such as boronate-diol complexation) that features an interfacial toughness over 400 J m⁻² is presented. Moreover, these hydrogel adhesion layers are also trigger-detachable by dissociating the dynamic complexes (i.e., addition of glucose). These hydrogel-based bioelectronic interfaces enable the in vivo recording of physiological signals (i.e., electromyograph, blood pressure, or pulse rates). Upon mild triggering, these bioelectronics can be easily detached without causing any damage, trauma, or discomfort to the skin, tissues, and organs. This kind of trigger-detachable hydrogel adhesives offer general applicability in bioelectronic interfaces, exhibiting promising utility in monitoring, modulating, and treating diseases where temporary monitoring of physiologic signals, interfacial robustness, and postremoval of bioelectronics are required.     

Barnacle Cement Proteins-Inspired Tough Hydrogels with Robust,Long-Lasting,and Repeatable Underwater Adhesion

The development of adhesives that can achieve robust and repeatable adhesion to various surfaces underwater is promising; however, this remains a major challenge primarily because the surface hydration layer weakens the interfacial molecular interactions. Herein, a strategy is proposed to develop tough hydrogels that are robust, reusable, and long-lasting for underwater adhesion. Hydrogels from cationic and aromatic monomers with an aromatic-rich composition inspired by the amino acid residuals in barnacle cement proteins are synthesized. The hydrogels are mechanically strong and tough (elastic modulus 0.35 MPa, fracture stress 1.0 MPa, and fracture strain 720%), owing to the interchain π–π and cation–π interactions. In water, the hydrogels firmly adhere to diverse surfaces through interfacial electrostatic and hydrophobic interactions (adhesion strength of 180 kPa), which allows for instant adhesion and reversibility (50 times). Moreover, the hydrogel shows long-lasting adhesion in water for months (100 days). Novel adhesive hydrogels may be useful in many applications, including underwater transfer, water-based devices, underwater repair, and underwater soft robots.     

Resident holes and electrons at organic/conductor and organic/organic interfaces: An electron paramagnetic resonance investigation

A number of organic/conductor and organic/organic interfaces have been examined by EPR spectroscopy to ascertain the areal concentration of organic ions at the interface. Organic hole transport materials such as NPB and TAPC at an interface with MoO_x are found to have areal concentrations on the order of 10¹⁴ cations per cm². C₆₀ at an interface with MoO_x creates ≈10¹³ cations per cm² depending on the roughness of the substrate. However, C₆₀ at an interface with Mg or Ag produces only about 4 × 10¹² anions per cm². Ion concentrations are generally in accord with the energy levels (adiabatic IP, EA etc) of the two materials at a given interface.     

Cyclodextrin Nano-Assemblies Enabled Robust,Highly Stretchable,and Healable Elastomers with Dynamic Physical Network

Artificial materials with biomimic self-healing ability are fascinating, however, the balance between mechanical properties and self-healing performance is always a challenge. Here, a robust, highly stretchable self-healing elastomer with dynamic reversible multi-networks based on polyurethane matrix and cyclodextrin-assembled nanosheets is proposed. The introduction of cyclodextrin nano-assemblies with abundant surface hydroxyl groups not only forms multiple interfacial hydrogen bonding but also enables a strain-induced reversible crystalline physical network owing to the special nanoconfined effect. The formation and dissociation of a dynamic crystalline physical network under stretching–releasing cycles skillfully balance the contradiction between mechanical robustness and self-healing ability. The resulting nanocomposites exhibit ultra-robust tensile strength (40.5 MPa), super toughness (274.7 MJ m⁻³), high stretchability (1696%), and desired healing efficiency (95.5%), which can lift a weight ≈ 100 000 times their own weight. This study provides a new approach to the development of mechanically robust self-healing materials for engineering applications such as artificial muscles and healable robots.     

Block Copolymer-Based Supramolecular Ionogels for Accurate On-Skin Motion Monitoring

Interest in wearable and stretchable on-skin motion sensors has grown rapidly in recent years. To expand their applicability, the sensing element must accurately detect external stimuli; however, weak adhesiveness of the sensor to a target object has been a major challenge in developing such practical and versatile devices. In this study, freestanding, stretchable, and self-adhesive ionogel conductors are demonstrated which are composed of an associating polymer network and ionic liquid that enable conformal contact between the sensor and skin even during dynamic movement. The network of ionogel is formed by noncovalent association of two diblock copolymers, where phase-separated micellar clusters are interconnected via hydrogen bonds between corona blocks. The resulting ionogels exhibit superior adhesive characteristics, including a very high lift-off force of 93.3 N m⁻¹, as well as excellent elasticity (strain at break ≈ 720%), toughness ( ≈ 2479 kJ m⁻³), thermal stability ( ≈ 150  ° C), and high ionic conductivity ( ≈ 17.8 mS cm⁻¹ at 150  ° C). These adhesive ionogels are successfully applied to stretchable on-skin strain sensors as sensing elements. The resulting devices accurately monitor the movement of body parts such as the wrist, finger, ankle, and neck while maintaining intimate contact with the skin, which was not previously possible with conventional non-adhesive ionogels.     

Passivation of Interfacial States for GaAs- and InGaAs/InP-Based Regrown Nanostructures

The interfacial charge density of regrown structures was studied for several␣different material systems: GaAs, InGaAs/InP, and InAlAs-InGaAs superlattice structures on InP. The particular application of interest is in the␣fabrication of nanoscale devices. Such structures require a very low density of interfacial charge at their exposed surfaces in order to avoid Fermi-level pinning and subsequent lateral carrier depletion across the structure. (110)-Oriented samples, mimicking the exposed sidewalls of nano-etched structures, were plasma-etched using a variety of gas-phase chemistries. The interfacial charge density at regrown interfaces was studied using capacitance–voltage (CV) and electrochemical CV techniques after in situ and ex situ pretreatments and epitaxial regrowth. The minimum interfacial charge densities obtained for these material systems were <10¹¹ cm⁻². Preferential regrowth around etched nanopillars was demonstrated for InP-based structures.     

A Bioinspired Polymer-Based Composite Displaying Both Strong Adhesion and Anisotropic Thermal Conductivity

The integration and functionality of high-power electronic architectures or devices require a high strength and good heat flow at the interface. However, simultaneously improving the interfacial bonding and phonon transport of polymers is challenging because of the tradeoff between the cross-linked flexible chains and high-quality crystalline structure. Here, a copolymer, poly(dopamine methacrylate-co-hydroxyethyl methacrylate [P(DMA-HEMA)] is designed and synthesized, inspired by the snail and mussel adhesion. The copolymer achievs a high surface adhesion up to 6.38 MPa owing to the synergistic effects of hydrogen bonds and mechanical interlocking. When the copolymer is introduced into vertically aligned carbon nanotubes (VACNTs), the catechol groups in P(DMA-HEMA) formed strong bonding with the nanotubes through π-π interactions at the interface. As a result, the P(DMA-HEMA)/VACNTs composite shows a high through-plane thermal conductivity (21.46 W m⁻¹ K⁻¹), an in-plane thermal conductivity that is 3.5 times higher than that of pristine VACNTs, and an extremely low thermal contact resistance (20.27 K mm² W⁻¹). Furthermore, the composite forms weld-free high-strength connections between two pieces of various metals to bridge directional thermal pathways. It also exhibits excellent interfacial heat transfer capability and high reliability even under zero-pressure conditions.     

Glassy/Ceramic Li2TiO3/LixByOz Analogous “Solid Electrolyte Interphase” to Boost 4.5 V LiCoO2 in Sulfide-Based All-Solid-State Batteries

Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) are the widely recognized approach toward high safety owing to excellent ionic conductivity and nonflammable nature of solid-state electrolytes (SSEs). However, narrow potential window of SSEs brings about serious interfacial parasitic reactions, resulting in fast degradation of the battery. Herein, a glassy/ceramic analogous solid electrolyte interface (SEI) is constructed on LiCoO₂ (LCO) to enhance interfacial stability between LCO and the Li₁₀GeP₂S₁₂ (LGPS) SSEs. In which, ceramic Li₂TiO₃ guarantees good mechanical toughness of analogous SEI, while glassy LixByOz reinforces the coverage to avoid parasitic reactions. Analogous SEI endows ASSLIBs with excellent cycling and rate performance under an upper charge voltage of 4.3 V with 82.3% capacity retention after 300 cycles at 0.2 C. When pushing charge voltage to 4.5 V, analogous SEI also enables desirable performance with an initial capacity of 172.7 mAh g⁻¹ and long lifespan of 200 cycles at 0.2 C. Both experiments and theoretical computation reveal excellent stability between analogous SEI and LGPS, which endows ASSLIBs with small polarization and improved performance. This work provides an insight on glassy/ceramic analogous SEI strategy to boost the interfacial stability of ASSLIBs.     

Inheritable Organic-Inorganic Hybrid Interfaces with π–d Electron Coupling for Robust Electrocatalytic Hydrogen Evolution at High-Current-Densities

Rational heterointerface engineering is crucial for superior and robust hydrogen evolution reaction (HER). Herein, a delicate organic-inorganic hybrid heterojunction based on the assembly of oxalate with polyaniline (PANI) for HER at high-current-densities is envisioned. Strong π–d electron coupling is achieved between the delocalized π electrons of PANI and the localized d electrons of oxalate metal sites. The CoC₂O₄ nanosheets are grown on nickel foam (NF) with Ni²⁺ ions substitution by the precursor etching. By virtue of the synergy of hetero ions and π–d electron coupling, metal sites obtain sufficient exposure and electronic structure optimization. Surprisingly, the phase transition of oxalate during HER in the alkaline environment does not weaken the π–d electronic coupling of the organic-inorganic hybrid interfaces. Inheritable interfacial electron interaction provides a reliable guarantee for robust stability at high-current-densities while endowing the hybrid materials with extremely low overpotentials. As expected, post-phase reconstructed Co_0.59Ni_0.41(OH)₂@PANI/NF displays impressive HER activity, with a low overpotential of 43 mV@−10 mA cm⁻² and robust stability at −1000 mA cm⁻² for 30 h in the alkaline environment. This study sheds light on the rational heterostructure interface design and promotes the architecture of an impressive electrocatalysts system.