Ice Templating Research Articles

Simultaneous realization of efficient solar evaporation and electricity collection through dual regulation of chemical composition and pore channels

The solar-driven interfacial evaporation is a recently developed zero-energy technology for seawater desalination. However, the low evaporation rate poses a significant obstacle to its industrial application, and the collection of streaming potential formed during the evaporation process remains challenging. In this paper, we constructed a solar evaporator capable of simultaneously achieving efficient solar evaporation and electricity collection. Specifically, a double network structure hydrogel comprising polyvinyl alcohol (PVA) and TEMPO-oxidized cellulose nanoparticles nanofibers (TOCNFs) was fabricated using ice templating, with the addition of sodium lignosulfonate (SLS) to further modulate water distribution within the network. The incorporation of carbon nanotubes (CNTs) enabled the achievement of a PVA/TOCNFs/SLS (PTFS) gel-based solar evaporator. The strong electronegativity carried by the TOCNFs enhances the electrostatic repulsion in the PVA-TOCNFs network, thus improving the mechanical properties of PTFS evaporator. The introduction of SLS, which contains abundant sulfonate groups, provides certain antibacterial properties to PTFS evaporator. Due to the presence of numerous hydrophilic groups, both TOCNFs and SLS can form weak hydrogen bonds with water. Through the synergistic effect of TOCNFs and SLS, the latent heat of water in PTFS evaporator is reduced to 924 kJ kg−1, enabling an evaporation rate of 3.70 kg m−2h−1 under 1 sun irradiation. Owing to the smaller pore size relative to the Debye radius and the presence of electronegative functional groups within the pores of PTFS evaporators, an overlapping bilayer is formed when water flows through, resulting in an open-circuit voltage increase of up to 270 mV. The integration of high-efficiency solar evaporation with streaming potential collection presents a novel avenue for enhancing the utilization of solar energy.

Low-Cost Hyperelastic Fuller-Dome-Structured Nanocellulose Aerogels by Dual Templates for Personal Thermal Management.

It is critically important to maintain the body's thermal comfort for human beings in extremely cold environments. Cellulose nanofibers (CNF)-based aerogels represent a promising sustainable material for body's heat retention because of their renewability and low thermal conductivity. However, CNF-based aerogels often suffer high production costs due to expensive CNF, poor elasticity and/or unsatisfactory thermal insulation owing to improper microstructure design. Here, a facile dual-template strategy is reported to prepare a low-cost, hyperelastic, superhydrophobic Fuller-dome-structured CNF aerogel (CNF@PU) with low thermal conductivity. The combination of air template by foaming process and ice template enables the formation of a dome-like microstructure of CNF@PU aerogel, in which CNF serves as rope bars while inexpensive polyurethane (PU) acts as joints. The aerogel combines ultra-elasticity, low thermal conductivity (24mW m-1 K-1), and low costs. The as-prepared CNF@PU aerogel demonstrates much better heat retention than commercial thermal retention fillers (e.g., Flannelette and goose down), promising its great commercial potential for massively producing warming garments. This work provides a facile approach for creating high-performance aerogels with tailored microstructure for effective personal thermal management.

Hierarchical porous MXene film with diffusion path optimization for supercapacitor

MXenes have immense potential in electrochemical energy storage owing to their outstanding physicochemical properties such as their oxygen-containing groups that impart additional pseudocapacitance to acidic electrolytes. However, during electrode assembly, MXene nanosheets undergo restacking because of hydrogen bonding and van der Waals forces, which causes electrolyte ions to traverse long diffusion pathways between the long and narrow nanosheets. Exploiting the oxidative properties of Ti3C2Tx, a hierarchical porous MXene film with micro-, meso- and macroporous structures was successfully prepared using a simple hydrothermal oxidation and etching process to create micro- and mesoporous structures, followed by ice templating to prepare three-dimensional (3D) linked macroporous structures. Because these hierarchical pores have synergistic effects on electrochemical activity and electrolyte ion diffusion, the film attained a specific capacitance of 539F/g at a current density of 2 A/g when it was used as a supercapacitor electrode, which corresponds to one of the highest values reported for MXene-based electrodes. The film retained 83% of its specific capacitance when the current density was increased to 40 A/g, and exhibited excellent cycling stability. By using this multi-porous MXene design, synergistic improvement in ion diffusion was successfully realized and thus a new strategy to prepare high-performance supercapacitor electrode materials was developed.

Construction of 3D modified hexagonal boron nitride thermal conductivity network by ice template method and research of high heat‐conducting coefficient of epoxy resin matrix composite material

Construction of <scp>3D</scp> modified <scp>hexagonal boron nitride</scp> thermal conductivity network by ice template method and research of high heat‐conducting coefficient of epoxy resin matrix composite material

A hydrophilic porous graphene aerogel electrode with a large specific surface area for high-performance all-aqueous thermally regenerative batteries

All-aqueous thermally regenerative batteries (ATRBs) have shown great potential in harvesting low-grade waste heat. In this study, a hydrophilic porous graphene aerogel (GA) electrode developed by an ice template was developed for ATRBs to enhance electricity generation. The physicochemical property of GA was analyzed by traditional characterization. The main functional group of GA was N–H, which offered ATRBs a high hydrophilic surface. As a result of the ice templates, the diameter of pores in GA was almost lower than 4 nm, which provided a high specific area and good wettability. In addition, density functional theory calculations were carried out to verify the superiority of good electrical conductivity and strong adsorption on the cupric ions. Therefore, ATRB with GA achieved a competitive performance (a peak power density of 432 W/m2), illustrating great potential in the future thermoelectricity conversion application.

Cellulose nano-dispersions enhanced by ultrasound assisted chemical modification drive osteoblast proliferation and differentiation in PVA/HA bone tissue engineering scaffolds

To develop a biological bone tissue scaffold with uniform pore size and good cell adhesion was both challenging and imperative. We prepared modified cellulose nanocrystals (CNCs) dispersants (K-PCNCs) by ultrasound-assisted alkylation modification. Subsequently, nano-hydroxyapatite (HC-K) was synthesized using K-PCNCs as a dispersant and composited with polyvinyl alcohol (PVA) to prepare the scaffold using the ice template method. The results showed that the water contact angle and degree of substitution (135°, 1.53) of the K-PCNCs were highest when the ultrasound power was 450 W and the time was 2 h. The dispersion of K-PCNCs prepared under this condition was optimal. SEM showed that the pore distribution of the composite scaffolds was more homogeneous than the PVA scaffold. The porosity, equilibrium swelling rate, and mechanical properties of the composite scaffolds increased and then decreased with the increase of HC-K content, and reached the maximum values (56.1 %, 807.7 %, and 0.085 ± 0.004 MPa) at 9 % (w/w) of HC-K content. Cell experiments confirmed scaffold has good cytocompatibility and mineralization capacity. The ALP activity reached 1.71 ± 0.25 (ALP activity/mg protein). In conclusion, the scaffolds we developed have good biocompatibility and mechanical properties and have great potential in promoting bone defect repair.

Thermally Conductive Polydimethylsiloxane-Based Composite with a Three-Dimensional Vertically Aligned Thermal Network Incorporating Hexagonal Boron Nitride Nanosheets and Nanodiamonds.

Thermal interface materials play a pivotal role in efficiently transferring heat from heating devices to thermal management components, thereby reducing the risk of component degradation due to overheating. In this study, we propose a strategy for enhancing the out-of-plane thermal conductivity (TC) of composite materials by fabricating a three-dimensional (3D) thermal network within a polydimethylsiloxane (PDMS) matrix. Specifically, the composite material was designed to incorporate a dense thermal network comprising hexagonal boron nitride nanosheets (BNNSs) and nanodiamonds (NDs). The fabrication process commenced with the preparation of BNNSs through liquid-phase exfoliation, followed by the creation of a 3D BNNSs-NDs/polyimide aerogel thermal framework using a unidirectional solidification ice templating method and subsequent heat treatment. Vacuum impregnation and curing were then employed to finalize the production of the 3D BNNSs-NDs/PDMS composite material. Characterization analyses indicated that the addition of NDs filled the voids between BNNSs, leading to the densification of the thermal framework pore walls and the establishment of additional thermal pathways. Impressively, with concentrations of BNNSs and NDs of 17.99 and 7.71 wt %, respectively, the out-of-plane TC of the 3D BNNSs-NDs/PDMS composite material reached 1.623 W m-1 K-1, marking notable enhancements of 754.21% and 256.70% compared to those of pure PDMS and composites prepared via direct blending with randomly distributed BNNSs and NDs, respectively. Furthermore, the 3D BNNSs-NDs thermal framework improved the compressive strength and the dimensional stability of the composite material. Finite element simulations additionally confirmed the synergistic improvement of the TC achieved through the combination of BNNSs and NDs, demonstrating that the 3D BNNSs-NDs/PDMS composite material displayed superior heat conduction and a greater density of thermal pathways compared to those of its counterparts, including 3D BNNSs/PDMS and 3D NDs/PDMS composite materials. In summary, this work presents a strategy for enhancing the out-of-plane TC of polymer-based composite materials by incorporating vertically aligned thermal networks.

Flammability and thermal analysis of vertically oriented polyvinyl alcohol/DOPO derivative/MXene composite aerogel

The fabrication of ultralight high-performance flame-retardant composites significantly reduces fire risk for buildings. Flame retardation of porous polyvinyl alcohol (PVA) aerogels with directional arrangement is difficult. Herein, the polyvinyl alcohol/ 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative/two-dimensional (2D) MXene (PVA/DiDOPO/MXene) composite aerogel was prepared by ice template one-way freezing process. PVA-DiDOPO4 composite aerogel with an oriented porous structure reaches the V-1 level at the UL-94 test. Moreover, the peak heat release rate (pHRR) value of PVA-DiDOPO4 reduces to 452.26 (W/g) from 482.88 (W/g) of pure PVA. In addition, PVA/DiDOPO/MXene composite aerogel has improved thermal decomposition properties such as the maximum decomposition temperature (Tmax1) of the PVA-DiDOPO4 sample attains 319.92 °C from pure PVA of 302.90 °C. The design strategy of PVA combined 2D MXene nanosheet and DOPO derivatives construct oriented porous composite aerogel paves the way for the fabrication and customization of ultralight flame-retardant polymer composites, which can be expected to be applied in construction and reduce fire risk.

Boosting Zinc‐Ion Storage Capability in Longitudinally Aligned MXene Arrays with Microchannel Architecture

AbstractFlexible Zn2+ ion hybrid capacitors (ZHCs) will play a crucial role in developing next‐generation wearable products, which demand portability, durability, and environmental adaptability. To further meet these requirements, Ti3C2Tx MXene with exceptional conductivity and robust mechanical properties can be utilized as cathodes, except for challenges such as the dense stacking of Ti3C2Tx nanosheets. In this study, a novel MXene cathode architecture has been developed with the facilitation of an ice template, which creates longitudinally aligned Ti3C2Tx arrays with microchannels. The introduction of hydrochloric acid to the Ti3C2Tx slurry induces a crumpled morphology, increasing active sites and enhancing ion transport with expanded interlayer spacing. Interestingly, experimental results and COMSOL simulations verify that the cathode structure also has effective impacts on the Zn anode with a weakened ion concentration gradient and suppressed dendrite formation. Consequently, the ZHCs exhibit enhanced electrochemical performance with excellent rate performance and long‐term cycling stability (enduring over 50 000 cycles at 5 A g−1) and further deliver a reliable low‐temperature operation by applying an anti‐freezing electrolyte. Moreover, flexible ZHCs assembled with gel electrolytes demonstrate excellent flexibility, improved rate performance, and mechanical stability, making them well‐suited for flexible electronics that power flexible LED panels.

Fabrication of novel 316L stainless steel scaffolds by combining freeze-casting and 3D-printed gyroid templating techniques

Porous metals have been widely investigated as bioimplants to repair cancellous bone defects. Nevertheless, how to endure extreme stress and strike a balance between load-bearing performance, elastic modulus, and permeability are important issues. Freeze-casting is a novel technique for manufacturing micro-scale open-cellular lamellar porous materials. However, the pore size is relatively small because of the inherent constraints of the ice template. On the other hand, the scaffold with gyroid pore structures has been proven to have higher permeability due to its larger and smoother channels. To combine the advantages of both porous structures, the present study aims to develop dual-scale 316L stainless steel (316L SS) porous structures by incorporating the 3D-printed gyroid templates into the freeze-casting to further improve the lightweight, specific strength, energy absorption, and permeability of the porous structures. The results showed that macro-scale gyroid channels were successfully built into the micro-scale open-cellular lamellar porous scaffolds. The porosity of dual-scale scaffolds was 70.1 %–74.4 %, which was higher than that of 53.1 %–66.5 % in the single-scale scaffolds. The elastic moduli of the single-scale scaffolds were higher than that of the dual-scale scaffolds; both were within the range of human cancellous bone, demonstrating their mechanical compatibility. Furthermore, the dual-scale scaffolds presented a prominent rise in permeability compared to the single-scale scaffolds. Notably, the permeability of the 3G series scaffolds was comparable to human cancellous bone. In summary, the hierarchical 316L SS scaffolds with controllable macro-scale gyroid channels exhibit great potential for biomedical applications.

Ti3C2Tx MXene/Graphene hybrid frameworks for constructing thermally conductive phase change composites with solar-thermal conversion ability

Application of three-dimensional (3D) carbon framework in phase change material (PCM) has aroused a tremendous interest. However, implementing a high alignment carbon framework with low interfacial thermal resistance (ITR) remain challenging. Herein, we demonstrated a synergetic effect strategy by Ti3C2Tx MXene and graphene nanoplate (GNP) to achieve a 3D thermally conductive framework with high alignment skeleton and low filler-to-filler ITR. Typically, the 3D anisotropic carbon framework is fabricated by unidirectional ice template freezing cellulose nanofibers (CNF)/GNP solution with the assistance of MXene. The abundant functional groups of MXene and the similar layered structure promote the dispersion stability of GNP in CNF aqueous solution, resulting in the significant improvement in GNP alignment and the filler-to-filler ITR. Therefore, the final phase change composites obtained by impregnating polyethylene glycol (PEG) into the framework achieves a satisfactory thermal conductivity (TC) of up to 3.49 W/m K at only 6.25 vol% filler loading. Combining the solar-thermal conversion ability of graphene and MXene, the PCM reveals a rapid energy conversion, transfer and storage capability. More importantly, the phase change enthalpy of the PCM can be as high as 164.3 J/g, with little change even after 50 heating-cooling cycles, and the existence of carbon framework can effectively prevent the leakage phenomenon in solid-liquid conversion process, ensuring its shape stability.

Bridging biomimetic and bioenergetics scaffold: Cellulose-graphene oxide-arginine functionalized aerogel for stem cell-mediated cartilage repair

The avascular nature of cartilage tissue limits inherent regenerative capacity to counter any damage and this has become a substantial burden to the health of individuals. As a result, there is a high demand to repair and regenerate cartilage. Existing tissue engineering approaches for cartilage regeneration typically produce either microporous or nano-fibrous scaffolds lacking the desired biological outcome due to lack of biomimetic dual architecture of microporous construct with nano-fibrous interconnected structures like the native cartilage. Most of these scaffolds also fail to suppress ROS generation and provide sustained bioenergetics to cells, resulting in the loss of metabolic activity under avascular microenvironment of cartilage. A dual architecture microporous construct with nano-fibrous interconnected network of cellulose aerogel reinforced with arginine-coated graphene oxide (CNF-GO-Arg aerogel) was developed for cartilage regeneration. The designed dual-architectured CNF-GO-Arg aerogel using dual ice templating assembly demonstrates 80 % strain recovery ability under compression. The release of Arginine from CNF-GO-Arg aerogel supported 41 % reduction in intracellular ROS activity and promoted chondrogenic differentiation of hMSCs by shifting mitochondrial bioenergetics towards oxidative phosphorylation indicated by JC-1 dye staining. Overall developed CNF-GO-Arg aerogel provided multifunctionality via biomimetic morphology, cellular bioenergetics, and suppressed ROS generation to address the need for regeneration of cartilage.

Bacterial Blocking and Repair of Intestinal Defects With Well-Alighed Lamellar MXene/Polyvinyl Alcohol Hydrogels Prepared by Bidirectional Freezing Method

To explore the bacterial blocking effect of oriented multilayer MXene/polyvinyl alcohol (PVA) nanocomposite hydrogels and their effect on the repair of intestinal defects. MXene/PVA nanocomposite hydrogels were prepared using the traditional freezing method and the bidirectional freezing ice template method. The structures of the different hydrogels were observed using scanning electron microscopy (SEM) and micro-CT reconstruction. The rheological properties of the hydrogels were measured using a dynamic rheometer, and their mechanical properties were assessed using a universal testing machine. The burst pressure of the hydrogels was determined through burst experiments, and bacterial colony growth was observed by the osmosis method to assess the bacteria blocking ability of the hydrogels in vitro. A rat model of cecal perforation was established, and the hydrogels were used for intestinal repair. Gram staining was performed to observe in vivo the bacterial blocking ability of the hydrogels, HE staining was performed to observe the intestinal inflammation, and CD31 and CD68 immunofluorescence staining and proliferating cell nuclear antigen (PCNA) staining were performed to observe the repair effect of the hydrogels on intestinal defects. SEM and micro-CT reconstruction revealed that the hydrogel prepared by the traditional freezing method exhibited a random porous structure, while the hydrogel prepared by the bidirectional freezing method showed an oriented multilayer structure. Rheological and tensile tests indicated that the oriented hydrogel had superior mechanical properties, and the burst pressure of the oriented multilayer hydrogel was as high as 27 kPa, significantly higher than that of the non-oriented hydrogel (P<0.001). Bacterial colony growth was observed by the osmosis method and it was found that, compared with the non-oriented hydrogel, the oriented multilayer hydrogel could effectively prevent the infiltration of Escherichia coli and Staphylococcus aureus in vitro. Gram staining results showed that the oriented multilayer hydrogel could effectively block intestinal bacteria from entering the abdominal cavity in vivo. HE staining results showed that the oriented multilayer hydrogel could effectively reduce intestinal inflammation in vivo. CD31 and CD68 immunofluorescence staining and PCNA staining results showed that the oriented multilayer hydrogel had a repairing effect on intestinal defects in vivo. The oriented multilayer hydrogel prepared by bidirectional freezing effectively prevents bacterial infiltration and reduces intestinal inflammation.

Multi‐Interfacial Heterostructure Design of Carbon Fiber/Silicone Rubber‐Oriented Composites for Microwave Absorption and Thermal Management

AbstractIn order to ensure the operation and longevity of electronic devices, the design of multifunctional composites integrating microwave absorption (MA) and thermal conduction has become the key to solving the problem. However, the superior MA properties and thermal conductivity are usually incompatible in the blend system. In this study, a modified carbon fiber/silicone rubber‐oriented structure is designed based on the multiscale design concept of heterostructures with multiple interfaces. The forward deposition‐reverse growth mechanism is utilized at the microscopic level to construct multi‐interfacial heterogeneous structures on the surface of 1D carbon fibers (CFs). The magneto‐electric coupling network of the multi‐interfacial heterostructure induces interfacial polarization and enhances MA properties and heat transfer. Subsequently, the structural design of the modified CFs is carried out on a macroscopic scale using the ice template method. The directionally aligned modified CFs/silicone rubber aerogel composites are obtained by backfilling with silicone rubber (SR). The samples achieved an effective absorption bandwidth of 4.41 GHz and a maximum reflection loss of −42.29 dB with ultra‐thin thickness (1.3 mm). The thermal conductivity of the sample is improved to 200% compared to pure silicone rubber. The composites with directional alignment have promising applications in lightweight and flexible electronic packaging.

Lightweight, high-strength and fireproof borax-crosslinked graphene/hydroxyethyl cellulose hybrid aerogels fabricated via ice template method

In recent years, there has been a growing interest in fireproof nanomaterials due to their broad applications in fire-safety and environmental preservation. In this study, one kind of lightweight fireproof hybrid aerogel with low thermal conductivity (0.039 W/m•K) was prepared through a facile ice template method, where the graphene nanosheets and hydroxyethyl cellulose (HEC) are combined with borax crosslinkers. It was found that this aerogel can be not only recyclable and repairable, but also possesses excellent compressive strength and stiffness, owing to the interfacial van der Waals adsorption, ionic crosslinking and hydrogen bonding interactions. Remarkably, it has excellent flame retardancy performance (an extremely low peak heat release rate (PHRR) was measured to be 37.44 kW/m2, reduced by 88.6 % comparing to that of graphene/HEC aerogel). To further explore the fire resistance mechanism of this aerogel, the molecular dynamics simulation was performed. It reveals that the borax can effectively wrap and hinder the graphene and HEC molecules from decomposition. Besides, the borax can compact graphene and HEC closer, thereby further isolating heat and oxygen, realizing the fireproof property. This study offers valuable insights for designing advanced fireproof nanomaterials and applications in shipbuilding or construction.

Preparation of three dimensional boron nitride-aluminum oxide dual thermal network resin-based composite materials and their performance study

With the gradual miniaturization and integration of electronic devices, the design and development of new high thermal conductivity polymer-based composite materials are crucial for enhancing the performance of modern electronic devices. In this study, three-dimensional boron nitride (3D-BN) aerogels with vertically aligned structures were prepared using the ice templating method, serving as the primary thermal conductive network. Subsequently, aluminum oxide (Al2O3)/epoxy resin (EP) nanofluids were infiltrated into the aerogel’s air pores using vacuum impregnation. The Al2O3 particles in contact with each other formed the secondary thermal conductive network. Thus, a 3D BN-Al2O3/EP composite material with a dual thermal conductive network structure was successfully fabricated. The composite material exhibited a high thermal conductivity coefficient of 1.077 Wm−1K−1 when loaded with 17.67 wt% BN and 26.23 wt% Al2O3, representing a 496 % increase compared to pure EP and a 211 % increase compared to 3D-BN/EP composite materials. Furthermore, this composite material demonstrated excellent thermal stability and mechanical properties. This work provides a new direction for designing novel polymer-based composite materials with low filler loading and high thermal conductivity performance.

Dual-crosslinked reduced graphene oxide/polyimide aerogels possessing regulable superelasticity, fatigue resistance, and rigidity for thermal insulation and flame retardant protection in harsh conditions

Polyimide (PI) aerogels have various applications in aerospace, national defense, military industry, and rail transit equipment. This paper reports a series of ultra-lightweight, high elasticity, high strength, low thermal conductivity, and high flame retardant rGO/PI nanocomposite aerogels prepared by the ice templating method. The effects of freezing processes (unidirectional freezing and random freezing), chemical composition, and environmental temperature (−196–200 °C) on the morphology, mechanical, and thermal properties of the aerogels were systematically studied. The results indicated that unidirectional aerogels exhibit anisotropic mechanical properties and thermal performance. Compression in the horizontal direction showed high elasticity, high fatigue resistance, and superior thermal insulation. Meanwhile, in the vertical direction, it demonstrated high strength (PI-G-9 reaching 14 MPa). After 10,000 cycles of compression in the horizontal direction (at 50 % strain), the unidirectional PI-G-5 aerogel still retains 90.32 % height retention, and 78.5 % stress retention, and exhibited a low stable energy loss coefficient (22.11 %). It also possessed a low thermal conductivity (32.8 mW m−1 K−1) and demonstrated good thermal insulation performance by sustaining at 200 °C for 30 min. Interestingly, the elasticity of the aerogels was enhanced with decreasing temperatures, achieving a height recovery rate of up to 100 % when compressed in liquid nitrogen. More importantly, the rGO/PI aerogels could be utilized over a wide temperature range (−196–200 °C) and had a high limiting oxygen index (LOI) ranging from 43.3 to 48.1 %. Therefore, this work may provide a viable approach for designing thermal insulation and flame-retardant protective materials with excellent mechanical properties that are suitable for harsh environments.

Compressible Hydrogels with Stabilized Chirality from Thermoresponsive Helical Dendronized Poly(phenylacetylene)s

AbstractFabrication of chiral hydrogels from thermoresponsive helical dendronized phenylacetylene copolymers (PPAs) carrying three‐fold dendritic oligoethylene glycols (OEGs) is reported. Three different temperatures, i.e. below or above cloud point temperatures (Tcps) of the copolymers, and under freezing condition, were utilized, affording thermoresponsive hydrogels with different morphologies and mechanical properties. At room temperature, transparent hydrogels were obtained through crosslinking among different copolymer chains. Differently, opaque hydrogels with much improved mechanical properties were formed at elevated temperatures through crosslinking from the thermally dehydrated and collapsed copolymer aggregates, leading to heterogeneity for the hydrogels with highly porous morphology. While crosslinking at freezing temperature synergistically through ice templating, these amphiphilic dendronized copolymers formed hydrogels with highly porous lamellar structures, which exhibited remarkable compressible properties as human articular cartilage with excellent fatigue resistance. Amphiphilicity of the dendronized copolymers played a pivotal role in modulating the network formation during the gelation, as well as morphology and mechanical performance of the resulting hydrogels. Through crosslinking, these dendronized copolymers featured with typical dynamic helical conformations were transformed into hydrogels with unprecedently stabilized helicities due to the restrained chain mobilities in the three‐dimensional networks.

Compressible Hydrogels with Stabilized Chirality from Thermoresponsive Helical Dendronized Poly(phenylacetylene)s.

Fabrication of chiral hydrogels from thermoresponsive helical dendronized phenylacetylene copolymers (PPAs) carrying three-fold dendritic oligoethylene glycols (OEGs) is reported. Three different temperatures, i.e. below or above cloud point temperatures (Tcps) of the copolymers, and under freezing condition, were utilized, affording thermoresponsive hydrogels with different morphologies and mechanical properties. At room temperature, transparent hydrogels were obtained through crosslinking among different copolymer chains. Differently, opaque hydrogels with much improved mechanical properties were formed at elevated temperatures through crosslinking from the thermally dehydrated and collapsed copolymer aggregates, leading to heterogeneity for the hydrogels with highly porous morphology. While crosslinking at freezing temperature synergistically through ice templating, these amphiphilic dendronized copolymers formed hydrogels with highly porous lamellar structures, which exhibited remarkable compressible properties as human articular cartilage with excellent fatigue resistance. Amphiphilicity of the dendronized copolymers played a pivotal role in modulating the network formation during the gelation, as well as morphology and mechanical performance of the resulting hydrogels. Through crosslinking, these dendronized copolymers featured with typical dynamic helical conformations were transformed into hydrogels with unprecedently stabilized helicities due to the restrained chain mobilities in the three-dimensional networks.

3D vertical ultra-sodiophilic leaf-vein-like MXene/Sn@CNF array of structured sodium enabling high-rate and long-life sodium metal batteries

Uncontrolled Na dendrite growth and infinite volume change during cycling have greatly impeded the practical application of Na metal anode for high-energy-density batteries. To address these two issues simultaneously, a 3D vertical ultra-sodiophilic leaf-vein-like MXene/Sn@CNF array (VL-MXene/Sn@CNF) aerogel, integrated by 1D Sn@CNF and 2D MXene, was prepared by an ingenious hydrogen bonding self-assembly and unidirectional ice template method. The low-tortuosity and ultra-sodiophilic vertical array facilitates uniform and rapid Na+ transport along the ordered interspaces, achieving a negligible nucleation overpotential of 1.0 mV. Furthermore, experimental results and theoretical calculations revealed a unique bidirectional growth mode of Na, in which vertical leaf-vein-like lamellae and bridging fibers guided Na to be densely deposited along the vertical and horizontal directions, respectively. Benefitting from the ultra-sodiophilic vertical array of structured Na, the designed material exhibits an endurance of 1000 cycles for asymmetric cell at 3.0 mA cm−2 and 3.0 mAh cm−2, and the symmetrical cell delivers an ultra-long lifespan of 6000 h at 1.0 mA cm−2 and 3.0 mAh cm−2 with a high depth of discharge up to 50 %. Remarkably, at the high current of 15 C, the full cell based on NaTi2(PO4)3 cathode and Na@VL-MXene/Sn@CNF anode can deliver a reversible capacity of 88.94 mAh g−1 after 9200 cycles with an ultralow 0.0016 % capacity decay per cycle, which represents the most impressive full cell performance so far.