Synthesis of Structure-Controlled Polyborosiloxanes and Investigation on Their Viscoelastic Response to Molecular Mass of Polydimethylsiloxane Triggered by Both Chemical and Physical Interactions

Sterically Hindered Organogels with Self-Healing, Impact Response, and High Damping Properties

Organogel materials are vital for impact or shock resistance because of their highly tailored dynamic properties. However, concurrently achieving excellent anti-impact and damping performances, high stability, and self-healing properties is challenging. Herein, a novel intelligent protective organogel (IPO) comprising a dynamic boronic ester containing poly(urethane-urea) as the network skeleton with a matching mesh size is synthesized, the network precisely entraps the hyperbranched fluid used as the bulky solvent via steric hindrance. The IPO exhibits self-healing ability, excellent impact responsiveness (a 1950-fold increase in flow stress under various impact speeds), and energy dissipation (the loss factor >0.8 from 10-4  to 104 Hz). The IPO maintains its dynamic mechanical properties during hot pressing and hydrolysis, exhibiting  high stability. Furthermore, the IPO exhibits omnibearing protection. When used as a protective coating, the IPO dissipates the impact force by 87% and 89% of control upon passive and active impact, respectively. When used as a shock pad, it attenuates 91% of the amplitude in the high-frequency vibrations. This study offers a novel perspective on the synthesis of tailored sterically hindered organogel and provides valuable insights into the development of next-generation intelligent protective materials that exhibit impact and vibration resistance.

Self-Healing and Shear-Stiffening Electrodes for Wearable Biopotential Sensing and Gesture Recognition

The achievement of flexible skin electrodes for dynamic monitoring of biopotential is one of the challenging issues in flexible electronics due to the interference of large acceleration and heavy sweat that influence the stability of skin-electrode interfaces. This work presents materials and techniques to achieve self-healing and shear-stiffening electrodes and an associated flexible system that can be used for multichannel biopotential measurement on the skin. The electrode that is based on a composite of silver (Ag) flakes, Ag nanowires, and polyborosiloxane offers an electrical conductivity of 9.71 × 104 S/m and a rheological characteristic that ensures stable and fully conformal contact with skin and easy removal under different shear rates. The electrode can maintain its conductivity even after being stretched by more than 60% and becomes self-healed after mechanical damage. The combination of the electrodes with a screen-printed multichannel flexible sensor allows stable monitoring of both static and dynamic electromyography signals, leading to the acquisition of high-quality multilead biopotential signals that can be readily extracted to yield gesture recognition results with over 97.42% accuracy. The conductive self-healing materials and flexible sensors may be utilized in various daily biopotential sensing applications, allowing highly stable dynamic measurement to facilitate artificial intelligence-enabled health condition diagnosis and human-computer interface.

Materials and Structural Designs toward Motion Artifact-Free Bioelectronics

Bioelectronics encompassing electronic components and circuits for accessing human information play a vital role in real-time and continuous monitoring of biophysiological signals of electrophysiology, mechanical physiology, and electrochemical physiology. However, mechanical noise, particularly motion artifacts, poses a significant challenge in accurately detecting and analyzing target signals. While software-based "postprocessing" methods and signal filtering techniques have been widely employed, challenges such as signal distortion, major requirement of accurate models for classification, power consumption, and data delay inevitably persist. This review presents an overview of noise reduction strategies in bioelectronics, focusing on reducing motion artifacts and improving the signal-to-noise ratio through hardware-based approaches such as "preprocessing". One of the main stress-avoiding strategies is reducing elastic mechanical energies applied to bioelectronics to prevent stress-induced motion artifacts. Various approaches including strain-compliance, strain-resistance, and stress-damping techniques using unique materials and structures have been explored. Future research should optimize materials and structure designs, establish stable processes and measurement methods, and develop techniques for selectively separating and processing overlapping noises. Ultimately, these advancements will contribute to the development of more reliable and effective bioelectronics for healthcare monitoring and diagnostics.

Synergistic Promotion of the Photocatalytic Preparation of Hydrogen Peroxide (H2 O2 ) from Oxygen by Benzoxazine and Si─O─Ti Bond

Hydrogen peroxide (H2 O2 ) is considered one of the most important chemical products and has a promising future in photocatalytic preparation, which is green, pollution-free, and hardly consumes any non-renewable energy. This study involves the preparation of benzoxazine with Si─O bonds via the Mannich reaction, followed by co-hydrolysis to produce photocatalysts containing benzoxazine with Si─O─Ti bonds. In this study, a benzoxazine photocatalyst with Si─O─Ti bonds is synthesized and characterized using fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The size and elemental distribution of the nanoparticles are confirmed by transmission electron microscopy and scanning electron microscopy. The photocatalytic synthesis of H2 O2 is tested using the titanium salt detection method, and the rate is found to be 7.28 µmol h-1 . Additionally, the catalyst exhibits good hydrolysis resistance and could be reused multiple times. The use of benzoxazine with Si─O─Ti bonds presents a promising experimental and theoretical foundation for the industrial production of H2 O2 through photocatalytic synthesis.

An Extreme-Environment-Resistant Self-Healing Anti-Icing Coating

Anti-icing coatings on outdoor infrastructures and transportations inevitably suffer from surface injuries, especially in extreme weather events (e.g., freezing weather or acid rain). The coating surface damage can result in anti-icing performance loss or even icing promotion. The development of anti-icing coatings that enables self-healing in extreme conditions is highly desired but still challenging. Herein, an extreme-environment-resistant self-healing anti-icing coating is developed by integrating fluorinated graphene (FG) into a supramolecular polymeric matrix. The coating exhibits both anti-icing and deicing performance (ice nucleation temperature is ≈-30.3 °C; ice shear strength is ≈48.7 kPa), mainly attributable to the hydrophobic FG and silicone-based supramolecular material. Notably, owing to the crosslinking polymeric network with various dynamic bonds, this coating can sustain anti-icing/deicing performance after autonomous self-healing under harsh conditions including low temperature (-20 °C), strong acid (pH = 0), and strong alkali (pH = 14) environments. This coating paves the way to meet the anti-icing demand in open air, especially for the infrastructures in polar regions or acid/alkali environments.

Ultrasensitive and Recyclable Multifunctional Superhydrophobic Sensor Membrane for Underwater Applications, Weather Monitoring, and Wastewater Treatment

Although flexible sensors have attracted considerable attention in emerging fields, including wearable electronics and soft robotics, their stability must be considered in practical applications, especially the effects of external factors on the sensing performance. Herein, a recyclable flexible sensor with superhydrophobicity and a highly sensitive strain response was developed by combining electrospinning and ultrasonication anchoring techniques. The constructed hierarchical network structure is composed of the fluorine-free superhydrophobic multiwalled carbon nanotubes and a porous elastomer membrane substrate reinforced by nanoparticles. The obtained sensor exhibited exceptional strain-sensing performance in terms of ultrahigh sensitivity (maximum gauge factor of 12 172.46), a fast response time of 80 ms, and excellent durability (10 000 cycles). Based on these outstanding merits, the strain sensor can detect various human motions without being interfered with by harsh environments. Moreover, superhydrophobic membranes can be combined with electronic devices for weather monitoring and underwater sensing. Noteworthily, damaged sensors can be quickly dissolved by a small amount of cyclohexane, enabling material recovery. The recyclable multifunctional membranes could reduce the potential pollution to the environment and show highly promising applications in complex environments.

Self-Healing and Electrical Properties of Viscoelastic Polymer-Carbon Blends

Self-healing polymer-carbon composites are seen as promising materials for future electronic devices, which must be able to restore not only their structural integrity but also electrical performance after cracking and wear. Despite multiple reports about self-healing conductive elements, there is a lack of a broad fundamental understanding of correlation between viscoelasticity of such composites, their electrical properties, and self-healing of their mechanical as well as electrical properties. Here we report thorough investigation of electromechanical properties of blends of carbon black as conductive filler and viscoelastic polymers (polydimethylsiloxanes and polyborosiloxane) with different relaxation times as matrices. We show that behavior of composites depends strongly on the viscoelastic properties of polymers. Low molecular polymer composite possesses high conductivity due to strong filler network formation, quick electrical and mechanical properties restoration, but for this we sacrifice the ability to flow and ductility at large deformation (material is brittle). In contrary, high relaxation time polymer composite behaves elastically on small time and flows at large time scale due to weak filler network and can heal. However, the electrical properties are worse than that of carbon and viscous polymer and degrade with time. This article is protected by copyright. All rights reserved.

All-Around Universal and Photoelastic Self-Healing Elastomer with High Toughness and Resilience

Ultimately soft electronics seek affordable and high mechanical performance universal self-healing materials that can autonomously heal in harsh environments within short times scales. As of now, such features are not found in a single material. Herein, interpenetrated elastomer network with bimodal chain length distribution showing rapid autonomous healing in universal conditions (<7200 s) with high efficiency (up to 97.6 ± 4.8%) is reported. The bimodal elastomer displays strain-induced photoelastic effect and reinforcement which is responsible for its remarkable mechanical robustness (≈5.5 MPa stress at break and toughness ≈30 MJ m-3 ). The entropy-driven elasticity allows an unprecedented shape recovery efficiency (100%) even after fracturing and 100% resiliency up to its stretching limit (≈2000% strain). The elastomers can be mechanically conditioned leading to a state where they recover their shape extremely quickly after removal of stress (nearly order of magnitude faster than pristine elastomers). As a proof of concept, universal self-healing mechanochromic strain sensor is developed capable of operating in various environmental conditions and of changing its photonic band gap under mechanical stress.

A Highly Stretchable, Self-Healing Elastomer with Rate Sensing Capability Based on a Dynamic Dual Network

Flexible sensing materials have attracted tremendous attention in recent years because of their potential applications in the fields of health monitoring, artificial intelligence, and so on. However, the preparation of rate sensing materials with self-healing performance is always a huge challenge. Herein, we first report the design and synthesis of a highly stretchable, recyclable, self-healing polysiloxane elastomer with rate sensing capability. The elastomer is composed of a dynamic dual network with boron/oxygen dative bonds and hydrogen bonds, which overcomes the structural instability of conventional solid-liquid materials. It exhibits certain adhesion, satisfactory mechanical robustness, and superior elongation at break (up to 1171%). After heating treatment at 80 °C for 2-4 h, the mechanical properties of damaged materials can be almost completely restored. Because of the "solid-liquid" property of the elastomer, it has irreplaceable functions which can sense different rates by resistance change after blending with multiwalled carbon nanotubes, principally in the range of 10 mm/min-150 mm/min. Especially, this rate sensing elastomer can be personalized by 3D printing at room temperature. This rate sensing strategy coupled with the introduction of dynamic dual-network structure is expected to help design advanced wearable devices for human rhythmic movement.

Study on Optimization of Damping Performance and Damping Temperature Range of Silicone Rubber by Polyborosiloxane Gel

Polyborosiloxane gel (PBS-gel) with shear hardening properties was prepared by cross-linking boric acid and hydroxyl-terminated polydimethylsiloxane through B-O-Si dynamic covalent bonding. The prepared PBS gel was mixed with methyl vinyl silicone rubber (MVQ), and a benzoyl peroxide (BPO) cross-linking agent was added to vulcanize the silicone rubber. At the same time, the gel molecules were co-vulcanizing with MVQ to produce molecular cross-linking. The effects of PBS-gel on the damping properties of silicone rubber were analyzed by dynamic rheological test, Fourier transform infrared spectroscopy and dynamic mechanical analysis. The results demonstrated that the damping performance of MVQ/PBS rubber is greatly improved and the rubber has a tanδ > 0.3 in the range of -25~125 °C. The shear-hardening gel is uniformly dispersed in the system, due to the combined action of covalent bonds and intermolecular forces, which act as an active molecular chain that can efficiently dissipate and transfer energy inside the silicone rubber.

Highly Stretchable and Self-Healing "Solid-Liquid" Elastomer with Strain-Rate Sensing Capability

To mimic the velocity-sensitive ability of the human skin, we fabricate a class of "solid-liquid" elastomers (SLEs) by interpenetrating polyborosiloxane (PBS) with polydimethylsiloxane (PDMS). PBS forms a dynamic network through boron/oxygen dative bonds, while PDMS is covalently cross-linked to form a permanent network. The permanent network affords a scaffold for the dynamic network, endowing SLEs with high elasticity and structural stability, thereby overcoming the inherent drawbacks such as fluidity and irreversible deformation of conventional solid-liquid materials. Meanwhile, the dissociation and association of the dynamic network is time-dependent. Thus, the modulus of SLEs varies with strain rates, and if the SLEs contain carbon nanotubes, their electric conductivity is also responsive to strain rates. This property can be utilized to fabricate skin-like sensors with the ability to distinguish different contact velocities. Moreover, the dynamic network can dissipate energy and be repaired, leading to the high stretchability and self-healing performance of SLEs.

Boric Acid as a Coupling Agent for Preparation of Phenolic Resin Containing Boron and Silicon with Enhanced Char Yield

In this study, an innovative, facile, and low-cost method is developed to prepare phenolic resin (PR) containing boron and silicon (BSiPR). BSiPR is synthesized by a solvent-free, one-pot method using boric acid as the coupling agent instead of silane, and methyltriethoxysilane as the silicon source. The results show that boron and silicon elements are introduced into PR via BOC and BOSi structures. The char yield of the resulting resin at 800 °C is improved to 76%. The reasons for higher char yield are investigated. The formation of BOC can reduce the content of phenolic hydroxyl, which helps to decrease the weight loss. B₂ O₃ is also formed at 400 °C, and it can prevent the release of carbon oxides. Moreover, thermally stable BOSi and SiO structures remain stable during the pyrolysis. In addition, the mechanical and ablative properties of fiber-reinforced composites are also enhanced.

Vapor-Liquid Sol-Gel Approach to Fabricating Highly Durable and Robust Superhydrophobic Polydimethylsiloxane@Silica Surface on Polyester Textile for Oil-Water Separation

Large-scale fabrication of superhydrophobic surfaces with excellent durability by simple techniques has been of considerable interest for its urgent practical application in oil-water separation in recent years. Herein, we proposed a facile vapor-liquid sol-gel approach to fabricating highly durable and robust superhydrophobic polydimethylsiloxane@silica surfaces on the cross-structure polyester textiles. Scanning electron microscopy and Fourier transform infrared spectroscopy demonstrated that the silica generated from the hydrolysis-condensation of tetraethyl orthosilicate (TEOS) gradually aggregated at microscale driven by the extreme nonpolar dihydroxyl-terminated polydimethylsiloxane (PDMS(OH)). This led to construction of hierarchical roughness and micronano structures of the superhydrophobic textile surface. The as-fabricated superhydrophobic textile possessed outstanding durability in deionized water, various solvents, strong acid/base solutions, and boiling/ice water. Remarkably, the polyester textile still retained great water repellency and even after ultrasonic treatment for 18 h, 96 laundering cycles, and 600 abrasion cycles, exhibiting excellent mechanical robustness. Importantly, the superhydrophobic polyester textile was further applied for oil-water separation as absorption materials and/or filter pipes, presenting high separation efficiency and great reusability. Our method to construct superhydrophobic textiles is simple but highly efficient; no special equipment, chemicals, or atmosphere is required. Additionally, no fluorinated slianes and organic solvents are involved, which is very beneficial for environment safety and protection. Our findings conceivably stand out as a new tool to fabricate organic-inorganic superhydrophobic surfaces with strong durability and robustness for practical applications in oil spill accidents and industrial sewage emission.