Simultaneous Improvement on Strength, Modulus, and Elongation of Carbon Nanotube Films Functionalized by Hyperbranched Polymers

Amino-ended hyperbranched polyamide-cross-linked conducting polymer hydrogels with enhanced performance for wearable electronics

Strain sensors are essential for accurately capturing intricate motions across various applications. However, achieving both high mechanical strength and stability in strain sensors remains challenging. Herein, we present a novel and high-performance strain sensor using an amino-ended hyperbranched polyamide (HBPN) as a cross-linker to construct a strong and tough conducting polymer hydrogel composed of polyvinyl alcohol (PVA) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The terminal amino groups in HBPN create non-covalent cross-links within the network, resulting in a robust structure. Notably, the unique hyperbranched topology of HBPN significantly enhances the hydrogel's properties, providing superior strength and toughness compared to its non-hyperbranched counterparts. Specifically, the distinctive macromolecular structure and abundant hydrogen bonding in the HBPN-PVA-PEDOT:PSS conducting polymer hydrogel result in exceptional toughness (991.53 kJ m-3), which is five times higher than that of the PVA-PEDOT:PSS hydrogel without HBPN. Additionally, the HBPN cross-linker enhances the sensitivity of the conducting polymer hydrogel, making it more responsive than linear analogs when used as a strain sensor. The resulting sensors adapt dynamically to human motion, demonstrating excellent detection capabilities. This work showcases a promising approach for developing cost-effective, sustainable, flexible, and high-performance wearable devices.

Pre-Endcapping of Hyperbranched Polymers toward Intrinsically Stretchable Semiconductors with Good Ductility and Carrier Mobility

The advancement of semiconducting polymers stands as a pivotal milestone in the quest to realize wearable electronics. Nonetheless, endowing semiconductor polymers with stretchability without compromising their carrier mobility remains a formidable challenge. This study proposes a "pre-endcapping" strategy for synthesizing hyperbranched semiconducting polymers (HBSPs), aiming to achieve the balance between carrier mobility and stretchability for organic electronics. The findings unveil that the aggregates formed by the endcapped hyperbranched network structure not only ensure efficient charge transport but also demonstrate superior tensile resistance. In comparison to linear conjugated polymers, HBSPs exhibit substantially larger crack onset strains and notably diminished tensile moduli. It is evident that the HBSPs surpass their linear counterparts in terms of both their semiconducting and mechanical properties. Among HBSPs, HBSP-72h-2.5 stands out as the preeminent candidate within the field of inherently stretchable semiconducting polymers, maintaining 93% of its initial mobility even when subjected to 100% strain (1.41 ± 0.206 cm2 V-1 s-1). Furthermore, thin film devices of HBSP-72h-2.5 remain stable after undergoing repeated stretching and releasing cycles. Notably, the mobilities are independent of the stretching directions, showing isotropic charge transport behavior. The preliminary study makes this "pre-endcapping" strategy a potential candidate for the future design of organic materials for flexible electronic devices.

Ultrastrong and High-Tough Thermoset Epoxy Resins from Hyperbranched Topological Structure and Subnanoscaled Free Volume

The strength and toughness of thermoset epoxy resins are generally mutually exclusive, as are the high performance and rapid recyclability. Experimentally determined mechanical strength values are usually much lower than their theoretical values. The preparation of thermoset epoxy resins with high modulus, high toughness, ultrastrong strength, and highly efficient recyclability is still a challenge. Here, novel hyperbranched epoxy resins (Bn, n = 6, 12, 24) with imide structures by a thiol-ene click reaction. Bn shows an excellent comprehensive function in simultaneously improving the strength, modulus, toughness, low-temperature resistance, and degradability of diglycidyl ether of bisphenol-A (DGEBA). All the mechanical properties first increase and then decrease with minimization of the free volume properties. The improvement is attributable to uniform molecular holes or free volume by a molecular mixture of linear and hyperbranched topological structures. The precise measurement and controllability of the molecular free volume properties of epoxy resins is first discovered, as well as the imide structure degradation of crosslinked epoxy resins. The two conflicts are successfully resolved between strength and toughness and between high performance during service and high efficiency during degradation. These findings provide a route for designing ultrastrong, tough, and recyclable thermoset epoxy resins.

Strong and Ultra-tough Ionic Hydrogel Based on Hyperbranched Macro-Cross-linker: Influence of Topological Structure on Properties

The application of hydrogels often suffers from their inherent limitation of poor mechanical properties. Here, a carboxyl-functionalized and acryloyl-terminated hyperbranched polycaprolactone (PCL) was synthesized and used as a macro-cross-linker to fabricate a super strong and ultra-tough ionic hydrogel. The terminal acryloyl groups of hyperbranched PCL are chemically incorporated into the network to form covalent cross-links, which contribute to robust networks. Meanwhile, the hydrophobic domains formed by the spontaneous aggregation of PCL chains and coordination bonds between Fe3+ and COO- groups serve as dynamic non-covalent cross-links, which enhance the energy dissipation ability. Especially, the influence of the hyperbranched topological structure of PCL on hydrogel properties has been well investigated, exhibiting superior strengthening and toughening effects compared to the linear one. Moreover, the hyperbranched PCL cross-linker also endowed the ionic hydrogel with higher sensitivity than the linear one when used as a strain sensor. As a result, this well-designed ionic hydrogel possesses high mechanical strength, superior toughness, and well ionic conductivity, exhibiting potential applications in the field of flexible strain sensors.

Building a flexible and applicable sodium ion full battery based on self-supporting large-scale CNT films intertwined with ultra-long cycling NiCo2S4

The major difficulties for the development of flexible energy storage batteries lie in the scalable manufacture of high-performance flexible electrodes with bending tolerance. In the present study, large-scale CNT films are prepared by a continuous production method and used to fabricate a self-supported flexible high-capacity conversion anode with ultra-long cycling life by the in situ growth of NiCo₂S₄ nanosheets tightly anchored on the CNTs. The CNTs produced via such a scalable method have interconnected porous channels, providing a large contact area between the active materials and electrolyte facilitating the electrochemical conversion reaction of NiCo₂S₄. An ultra-high rate capability is achieved in terms of a capacity of 280 mA h g^-1 at 20 A g^-1. The interlaced construction of NiCo₂S₄ nanosheets with CNTs and firm anchoring on the CNT film result in a remarkable ultra-long cyclability of the NiCo₂S₄/CNT electrode with a capacity retention rate of 96% after 7500 cycles. A flexible full battery device is further established with the NiCo₂S₄/CNT anode and Na₃V₂(PO₄)₃/CNT cathode with the sealed package of PDMS, exhibiting good cycling stability and mechanical durability under different bending states. The present work highlights a scalable flexible battery electrode material, and demonstrates its potential applications in flexible Na-ion batteries.

Closed-Loop Recycling of Both Resin and Fiber from High-Performance Thermoset Epoxy/Carbon Fiber Composites

Currently, only 5% of thermoset carbon fiber reinforced polymer composites (CFRPs) are recycled into lower-value secondary products. Highly efficient closed-loop recycling of both thermoset resin and carbon fiber is a major challenge. Here, we report a sustainable approach for the closed-loop recycling of the resin and fiber from CFRPs. Thiol-functionalized carbon fiber (TCF) obtained by functionalization with a thiol-ended hyperbranched polymer, and then an epoxy-ended degradable hyperbranched polymer (HT₃) are used to prepare HT₃/TCF composites, which show considerable acid resistance and mechanical performance. The cured composites are controllably depolymerized into monomers and oligomers with high recyclability (89%), which can be utilized to prepare HT₃ and the precursor of cross-linked HT₃. A total of 100% of the carbon fibers are recovered and reused to fabricate composites without deterioration of performance. The results provide a method for designing high-performance composites and a pathway for high efficiency closed-loop recycling.

Progress and Perspectives on Covalent-organic Frameworks (COFs) and Composites for Various Energy Applications

Covalent-organic frameworks (COFs), being a new member of the crystalline porous materials family, have emerged as important materials for energy storage/conversion/generation devices. They possess high surface areas, ordered micro/mesopores, designable structures and an ability to precisely control electro-active groups in their pores, which broaden their application window. Thanks to their low weight density, long range crystallinity, reticular nature and tunable synthesis approach towards two and three dimensional (2D and 3D) networks, they have been found suitable for a range of challenging electrochemical applications. Our review focuses on the progress made on the design, synthesis and structure of COFs and their composites for various energy applications, such as metal-ion batteries, supercapacitors, water-splitting and solar cells. Additionally, attempts have been made to correlate the structural and mechanistic characteristics of COFs with their applications.

3D Printable, Highly Stretchable, Superior Stable Ionogels Based on Poly(ionic liquid) with Hyperbranched Polymers as Macro-cross-linkers for High-Performance Strain Sensors

Stretchable ionogels have recently emerged as promising soft and safe ionic conductive materials for use in wearable and stretchable electrochemical devices. However, the complex preparation process and insufficient thermomechanical stability greatly limit the precise rapid fabrication and application of stretchable ionogels. Here, we report an in situ 3D printing method for fabricating high-performance single network chemical ionogels as advanced strain sensors. The ionogels consist of a special cross-linking network constructed by poly(ionic liquid) and hyperbranched polymer (macro-cross-linkers) that exhibits high stretchability (>1000%), superior room-temperature ionic conductivity (up to 5.8 mS/cm), and excellent thermomechanical stability (-75 to 250 °C). The strain sensors based on ionogels have a low response time (200 ms), high sensitivity with temperature independence, long-term durability (2000 cycles), and excellent temperature tolerance (-60 to 250 °C) and can be used as human motion sensors. This work provides a new strategy to design highly stretchable and superior stable electronic devices.

Efficient Synthesis of Folate-Conjugated Hollow Polymeric Capsules for Accurate Drug Delivery to Cancer Cells

This study presents an efficient and systematic approach to synthesize bioapplicable porous hollow polymeric capsules (HPCs). The hydroxyl-functionalized nanoporous polymers with hollow capsular shapes could be generated via the moderate Friedel-Crafts reaction without using any hard or soft template. The numerous primitive hydroxyl groups on these HPCs were further converted to carboxyl groups. Owing to the abundance of highly branched carboxyl groups on the surface of the HPCs, biomolecules [such as folic acid (FA)] could be covalently decorated on these organic capsules (FA-HPCs) for drug delivery applications. The intrinsic hollow porosities and specific targeting agent offered a maximum drug encapsulation efficiency of up to 86% and drug release of up to 50% in 30 h in an acidic environment. The in vitro studies against cancer cells demonstrated that FA-HPCs exhibited a more efficient cellular uptake and intracellular doxorubicin release than bare HPCs. This efficient approach to fabricate carbonyl-functionalized hollow organic capsules may open avenues for a new type of morphological-controlled nanoporous polymers for various potential bioengineering applications.

Fabrication of Transparent UV-Cured Coatings with Allyl-Terminated Hyperbranched Polycarbosilanes and Thiol Silicone Resins

To improve thermal stability and hardness of UV-cured materials, a series of UV-cured solvent-free coatings were prepared from allyl-terminated hyperbranched polycarbosilanes and thiol silicone resins. The silicone coatings prepared have pencil hardness of 4-9 H, water absorption no more than 0.04 wt %, and transmittance higher than 94%. The temperature for the coatings' starting thermal decomposition is higher than 236 °C; especially, that of the coating prepared with G1 is as high as 371.1 °C. The UV-cured coatings in this work exhibit much higher pencil hardness than and superior thermal stability to those reported previously.

UV-Cured Coatings Prepared with Sulfhydryl-Terminated Branched Polyurethane and Allyl-Terminated Hyperbranched Polycarbosilane

The conventional polyurethane (PU) coatings have poor heat resistance, which will undergo severe pyrolysis when the temperature exceeds 200 °C. To overcome the shortcoming of conventional PU coatings, an ultraviolet (UV)-cured solvent-free hyperbranched polycarbosilane modified PU coatings was prepared by sulfhydryl-terminated polyurethane and allyl-terminated hyperbranched polycarbosilane. The initial decomposition temperature (Td5%) of the UV-cured coating ranges from 258 to 268 °C, which is obviously higher than those of the conventional PU coatings reported. The coating shows fairly low water absorption in the range of 0.6–1.36 wt% and exhibits grade 1, grade 2 and grade 3 adhesion to glass, tin plate and aluminum sheet, respectively.