High Degree Of Crosslinking Research Articles

A novel rapid fabrication method and in-situ densification mechanism for ceramic matrix composite

The extensive application of ceramic matrix composites has always been limited due to the long-period and expensive process. Hence, this research introduces a rapid manufacturing method named as ViSfP-TiCOP (High Viscosity Solvent-free Precursor Combined Elemental Titanium Controlled Pyrolysis). The solvent-free precursor possesses high viscosity (30 °C, 106 mPa S) and wide molecular weight distribution (Mz/Mw = 3.3), accomplishing stable loading of inorganic fillers. Simultaneously, the elementary titanium and ZrB2, as the active and inert filler, are dopped into the precursor to control the pyrolysis. The ViSfP-TiCOP technique offers a rapid method to manufacture CMCs under pressureless and low pyrolysis temperature conditions (1200 °C). Comparing to the addition of ZrB2, the precursor with titanium provides an exceptional ceramic yield of 87 wt%, leading a notable enhancement in the rate of densification. This high densification efficiency is attributed to an in-situ titanium gas-phase reaction, besides with the high degree of cross-linking and low volatile of precursor. After undergoing three cycles of impregnation-pyrolysis, the porosity of C/SiBCN–Ti was discovered to be below 10 vol%, whereas that of C/SiBCN-25 wt%ZrB2 still remained as high as 20.91 vol%. The ViSfP-TiCOP technology can provide guidance for low-cost and rapid preparation of CMCs.

Molecular dynamics simulations of the micro mechanism of functionalized SiO2 nanoparticles and carbon nanotubes modified epoxy resin adhesives

AbstractThe bonding interface of carbon‐fiber‐reinforced polymer (CFRP)‐reinforced steel structure is a weak part, and nanomaterial‐modified adhesives are expected to improve its comprehensive performance. This paper investigates the micro‐modification mechanisms of nanomaterials on epoxy resin adhesives using molecular dynamics simulation method. It explores how the functionalized nano SiO2 and carbon nanotubes affects the thermal and mechanical properties of the epoxy resin adhesive. The models established using Materials Studio software include the pure epoxy resin adhesive model (EP) with varying degrees of crosslinking, the functionalized nano‐SiO2‐modified epoxy resin adhesive model (EP + SiO2/OH), the single‐walled carbon nanotube‐modified epoxy resin adhesive model (EP + SWNT), and the synergistic enhancements model of the epoxy resin adhesive with nano‐SiO2 and carbon nanotubes (EP + SWNT + SiO2/OH). Based on the aforementioned models, the Forcite module is used to calculate the free volume, glass transition temperature and mechanical properties of the adhesive. The results show that the degree of crosslinking effects significantly the mechanical performance of epoxy resin adhesive. A high degree of crosslinking restricts the movement of the molecular chain, enhancing the strength of the epoxy resin adhesive. Furthermore, the trend of the mechanical and thermal properties of the four models remains constant with the rise of temperature, and the properties decrease most significantly in the range of the glass transition temperature. Moreover, the epoxy resin adhesive doped with nanomaterials exhibits varying degrees of enhancement in mechanical and thermal properties. The epoxy resin adhesive reinforced with functionalized nano‐SiO2 and carbon nanotubes exhibits better properties compared to those with a single nanomaterial.Highlights The micro‐modification mechanism is revealed for nanomaterial modified epoxy resin adhesive. The degree of crosslinking effects significantly the mechanical performance of epoxy resin adhesive. The epoxy resin adhesive doped with nanomaterials exhibits varying degrees of enhancement in mechanical and thermal properties.

Diffusion-Regulated Interfacial Polymerization of Hierarchically Microporous Polyamide Membranes for Permselective Gas Separations.

Interfacial polymerization has emerged as a robust method for fabricating task-specific polyamide (PA) membranes. However, the limited microporosity of highly cross-linked PA membranes constrains their effectiveness in gas separation applications. Herein, we introduce an ionic liquid (IL)-regulated interfacial polymerization process to fabricate polyamide nanofilms incorporating kinked tetrakis (4-aminophenyl) methane monomers. In situ ultraviolet-visible spectroscopy demonstrates that the diffusion of 1,3,5-benzenetricarbonyl trichloride (TMC) toward the interface increases with the IL/H2O ratio, leading to the formation of a more compact membrane with a higher cross-linking degree. The PA-TAM7/3-60 min membrane exhibits a CO2 permeance of 29.8 GPU and a CO2/CH4 selectivity of 109, exceeding the 2008 Robeson upper bond. Additionally, the highly cross-linked structure imparts the membranes with notable plasticization resistance. Mixed-gas tests (CO2/CH4 = 50/50, v/v) reveal that the PA-TAM7/3-60 min membrane experiences only a 2% reduction in CO2 permeance and a 10% decrease in CO2/CH4 selectivity at a CO2 partial pressure of 300 PSIG, compared to its performance at 30 PSIG. The ease of tuning membrane structure and gas separation performance, along with its excellent plasticization resistance, underscores the potential of these PA membranes for task-specific gas separations.

Pre-Coordination Induced Further Deamination to Create Inter-Chain Cross-Linking in Carbon Nitride for Enhanced Photocatalytic H2O2 Production.

Creating cross-linking to establish efficient inter-chain charge-transfer channels in carbon nitride represents a promising strategy for enhancing its photocatalytic capabilities. Molten salt-assisted calcining has emerged as a method for preparing cross-linked carbon nitrides. However, the precise influence of molten salts on the molecular structure of carbon nitride remains to be fully elucidated. Herein, we develop a KCl guided cross-linking reaction to preliminarily reveal the formation mechanism of cross-linking. The cross-linking reaction is initiated by the pre-coordination of amino groups with K+. Subsequent heating at high temperature converts the amino groups into chlorines. Then, dechlorination leads to the formation of cross-linking. Thus, this cross-linking reaction can be accurately described as a pre-coordination-induced, two-step deamination reaction. The pre-coordination step plays a pivotal role in the cross-linking process. Sufficient pre-coordination results in a relatively high cross-linking degree of the as-prepared CNK-2. Consequently, CNK-2 demonstrates a significantly enhanced photocatalytic H2O2 production, with a generation rate of 682 μmol L-1 h-1, about 59 times that of traditional carbon nitride.

Lactiplantibacillus plantarum ACCC 11095 microencapsulated by lotus seeds cross-linked resistant starch: Survival under simulated gastrointestinal conditions and its structural changes

Under simulated gastrointestinal digestion, we investigated the protective and releasing effects of lotus seed cross-linked resistant starch (LSCS) with low, medium, and high cross-linking degree toward Lactiplantibacillus plantarum ACCC 11095 and associated structural changes. Probiotic microcapsules (PM) made of high crosslinking starch showed better encapsulation rates (48.81%) and released 6.26 log CFU/g of viable bacteria after digestion, which helped colonize and exert probiotic effects in the intestinal tract. Scanning electron microscopy and Fourier Transform Infrared spectroscopy confirmed better high crosslinking starch protection for probiotic bacteria. This was closely related to PM embedded materials. Correlation analysis showed that agglomeration between high crosslinking starch starch granules in PM was significantly enhanced, and amorphous zones were hydrolyzed to a lesser extent, providing better Lactiplantibacillus plantarum ACCC 11095 protection. Thus, high crosslinking starch demonstrated potential as an oral probiotic carrier in terms of cost, suitability for functional foods, and commercialization potential.

Molecular heterostructured interlayer for fabrication of high-performance thin film composite reverse osmosis membranes

To solve the scarcity of fresh water, reverse osmosis (RO) technology for seawater desalination and wastewater reuse has been developed rapidly. However, the performance of RO is limited by poor selectivity towards certain harmful small molecule constituents (e.g., boron in seawater and N-nitrosodimethylamine in wastewater) and the permeability-selectivity trade-off. Herein, a metal polyphenol network interlayer including both hydrophobic zone and monomer adsorption zone is proposed to optimize interfacial polymerization (IP) process for fabrication of RO membrane. This heterogeneous characteristic is endowed by well-chosen phenol (i.e. TTSBI) and metal (Ni). The physicochemical properties of the substrate are also optimized. An ultra-selective RO membrane with thinner separation layer, higher crosslinking degree and larger surface area is obtained. The RO membranes exhibit separation performance beyond the upper selectivity limit for NaCl and hazardous small molecules. The membrane water permeance is 3.50 L m−2h−1bar−1while the NaCl rejection is 99.5 %. Meanwhile, the mechanism of the interlayer influencing IP process is investigated by combining molecular simulation and experimental methods. Our work provides a novel design direction of substrate used for fabricating RO membrane with outstanding performance.

Effect of active carbonyl-carboxyl ratio on dynamic Schiff base crosslinking and its modulation of high-performance oxidized starch-chitosan hydrogel by hot extrusion 3D printing

The quest to develop 3D starch-based printing hydrogels for the controlled release of active substances with excellent mechanical and printing properties has gained significant attention. This work introduced a facile method based on crosslinking via Schiff base reaction for preparing bicomponent hydrogels. The method involved the utilization of customizable oxidized starch (OS) and chitosan (CS), enabling superior printing performance through the precise control of various active carbonyl-carboxyl ratios (ACR, 2:1, 1:1, and 2:3, respectively) of OS. OS-CS hydrogel (OSC) with an ACR level of 2:1 (OS-2-y%CS) underwent rearrangement during printing environment, fostering increased Schiff base reaction with a higher crosslinking degree and robust high structural recovery (>95 %). However, with decreasing ACR levels (from 2:1 to 2:3), the printing performance and mechanical strength of printed OSC (POSC) declined due to lower Schiff base bonds and increased phase separation. Compared with printed OS, POS-2-2%CS exhibited a remarkable 1250.52 % increase in tensile strength and a substantial 2424.71 % boost in compressive strength, enhanced shape fidelity and notable self-healing properties. Moreover, POS-2-2%CS exhibited stable diffusive drug release, showing potential application in the pH-responsive release of active substances. Overall, controlling the active carbonyl-carboxyl ratios provided an efficient and manageable approach for preparing high-performance 3D-printed hydrogels.

Biodegradable Cassava Starch/Phosphorite/Citric Acid Based Hydrogel for Slow Release of Phosphorus: In Vitro Study.

Phosphorous (P) is one the most important elements in several biological cycles, and is a fundamental component of soil, plants and living organisms. P has a low mobility and is quickly adsorbed on clayey soils, limiting its availability and absorption by plants. Here, biodegradable hydrogels based on Cassava starch crosslinked with citric acid (CA) were made and loaded with KH2PO4 and phosphorite to promote the slow release of phosphorus, the storing of water, and the reduction in P requirements during fertilization operations. Crosslinking as a function of CA concentrations was investigated by ATR-FTIR and TGA. The water absorption capacity (WAC) and P release, under different humic acid concentration regimens, were studied by in vitro tests. It is concluded that hydrogel formed from 10% w/w of CA showed the lowest WAC because of a high crosslinking degree. Hydrogel containing 10% w/w of phosphorite was shown to be useful to encouraging the slow release of P, its release behavior being fitted to the Higuchi kinetics model. In addition, P release increased as humic acid contents were increased. These findings suggest that these hydrogels could be used for encouraging P slow release during crop production.

Preparation and properties of walnut cake-based wood adhesive with oxidation modification

Walnut cake has the potential for use in preparing wood adhesives because of its richness in protein and carbohydrate. In this work, walnut cakes were treated with sodium periodate or potassium permanganate and then were directly used as wood adhesives. Their bonding properties, curing performances, thermal properties, and chemical structures were compared. The results showed that: (1) The oxidation by KMnO4was non-selective. The reaction was very intense, accompanied by the great variability of oxidation degree and degradation degree, enormous viscosity of oxidation products, high coating difficulty, and low content of active aldehyde groups. (2) The oxidation by NaIO4 was selective; the reaction was mild and easy to control. More active aldehydes could be produced and the treatment was beneficial for constructing a spatial net structure of the adhesive. (3) Compared with oxidation of KMnO4, the walnut cake adhesive prepared by NaIO4 oxidation exhibited a more compact structure, a higher crosslinking degree, low curing temperature, and high thermal stability after curing; its bonding performances met the requirements for Class II plywood specified in GB/T 17657(2013).

In vitro degradation, swelling, and bioactivity performances of in situ forming injectable chitosan-matrixed hydrogels for bone regeneration and drug delivery.

Injectable, tissue mimetic, bioactive, and biodegradable hydrogels offer less invasive regeneration and repair of tissues. The monitoring swelling and in vitro degradation capacities of hydrogels are highly important for drug delivery and tissue regeneration processes. Bioactivity of bone tissue engineered constructs in terms of mineralized apatite formation capacity is also pivotal. We have previously reported in situ forming chitosan-based injectable hydrogels integrated with hydroxyapatite and heparin for bone regeneration, promoting angiogenesis. These hydrogels were functionalized by glycerol and pH to improve their mechano-structural properties. In the present study, functionalized hybrid hydrogels were investigated for their swelling, in vitro degradation, and bioactivity performances. Hydrogels have degraded gradually in phosphate-buffered saline (PBS) with and without lysozyme enzyme. The percentage weight loss of hydrogels and their morphological and chemical properties, and pH of media were analyzed. The swelling ratio of hydrogels (55%-68%(wt), 6 h of equilibrium) indicated a high degree of cross-linking, can be suitable for controlled drug release. Hydrogels have gradually degraded reaching to 60%-70% (wt%) in 42 days in the presence and absence of lysozyme, respectively. Simulated body fluid (SBF)-treated hydrogels containing hydroxyapatite-induced needle-like carbonated-apatite mineralization was further enhanced by heparin content significantly.

Effects of two types of corn starches on physicochemical and structural properties of red bean protein isolate acid-induced cold gels

A mixture of red bean protein isolate (RBPI) with common starch (CS) or waxy starch (WS) from corn was heated, and induced by glucono-δ-lactone (GDL) to form a RBPI-starch complex cold gel. The physicochemical and structural properties of these gels were also investigated. Compared with the RBPI gels, the complex gels with CS had higher gel strength, water retention, viscoelasticity, and deformation resistance, forming a denser and more continuous microstructure with a high degree of crosslinking and small pores. Compared with the RBPI-CS complex gels, the RBPI-WS complex gels exhibited higher water retention and stronger transformation ability of free water to immobilized water; however, they exhibited poor mechanical properties and microstructures. The difference in the physicochemical properties of the gels was mainly related to the change in the hydrophobic interactions between the two gel systems. In addition, protein structure modification affected the gelation properties of the RBPI-CS and RBPI-WS complexes. The RBPI-CS complex gel exhibited strong X-ray peaks and fluorescence quenching ability. The addition of CS promoted the flexibility of the secondary structure and tightness of the tertiary conformation of the protein in the complex gel, forming a stronger and more compact non-covalent gel structure. However, the protein in the RBPI-WS complex gel showed an ordered secondary structure and a loose tertiary conformation, which weakened the gel network.

Evaluation of cell‐laden three‐dimensional bioprinted polymer composite scaffolds based on synthesized photocrosslinkable poly(ethylene glycol) dimethacrylate with different molecular weights

AbstractThis manuscript aims to three‐dimensional bioprint and evaluate new polymer composite scaffolds based on synthesized poly(ethylene glycol) dimethacrylate (PEGDMA) as well as methyl cellulose and gelatin. The PEGDMA was synthesized by a simple microwave‐assisted method using three distinct molecular weights (MWs) of poly(ethylene glycol) (PEG), 3, 6, and 12 kDa, and methacrylic anhydride. The percent functionalization of the PEGDMA was analyzed using the nuclear magnetic resonance spectrum, and the theoretical calculations indicated that over 50% of methacrylation was achieved in all samples, with the PEGDMA synthesized from 6 kDa PEG surpassing 66% methacrylation. These three PEGDMA‐based bioinks were investigated for their suitability for bioprinting scaffolds. It was observed that lower MW PEGDMA resulted in a higher degree of crosslinking, leading to more stable composite scaffolds. However, higher crosslinking degree did not support long‐term cell viability when encapsulated with cells. Higher MW PEGDMA showed higher cell viability over time though overall stability was lower. Synthesized PEGDMA with 6 kDa PEG showed both stability and long‐term cell viability after postprinting. Over 80% of cell viability was maintained for a 7‐day study period, showing potential use in tissue engineering applications as a cell delivery vehicle.

GO and surfactant assisted regulation of polyamide nanofiltration membranes for improved separation performance

Fabricating nanofiltration membranes with high water permeance and selectivity by tailoring the structure and morphology is crucial to efficient water purification. In this work, the fabrication of thin film nanocomposite (TFN) nanofiltration membranes by combining two methods, the surfactant-assembly interfacial polymerization (SARIP) and the addition of graphene oxide (GO) or ionic liquid functionalized graphene oxide (GO-IL) for the preparation of the selective PA layer on a novel porous substrate is reported. For the preparation of the porous substrate, mechanically robust, aromatic polyethers containing polar pyridine units (PDSPP) were chosen targeting to improved hydrophilicity and thus enhanced water permeability. The anionic sodium dodecyl sulfate (SDS) surfactant was used to regulate the interfacial polymerization thereby enabling the formation of dense PA layers with high cross-linking degree and consequently high salt rejections. On the other hand, the addition of GO/GO-IL nanosheets could impart hydrophilicity and antifouling properties. The novel porous PDSPP substrate was selected for the fabrication of TFN membranes due to its improved water permeability and superior salt rejection and increased hydrophilicity compared to commercial PSf substrate. The detailed study of the fabricated TFN membranes by ATR-FT-IR, SEM, AFM, XPS, contact angle measurements revealed the formation of polyamide selective layers with rougher surfaces, increased hydrophilicity and high cross-linking degrees (from 44 % to 94 %), resulted from the synergistic effect of SDS and GO incorporation. Moreover, the prepared TFN membranes exhibited high salt rejections while maintaining a moderate water permeability. In particular, the membrane containing the neat GO (TFNGO50) displayed excellent Na2SO4 and MgSO4 rejections (98.8 % and 99.5 %, respectively) while the NaCl rejection was 47.0 % and a water permeability value of 4.2 L m-2h−1 bar−1. The divalent salt rejections were among the highest values reported in the literature in comparison with commercial NF membranes and TFN membranes containing GO/functionalized GO. When GO-IL nanosheets were embedded in the PA layer, the water permeability was slightly improved while the salt rejections were significantly reduced compared to TFNGO50. Lastly, the incorporation of GO enhanced the anti-fouling properties of the prepared membranes due to increased hydrophilicity of the PA surface.

Structurally tuned polyamide membranes via the polyvinylpyrrolidone-modulated interfacial polymerization reaction for enhanced forward osmosis performance

Controllable interfacial polymerization (IP) reaction is an important strategy to fabricate high-performance polyamide (PA) thin-film composite (TFC) membranes. In this work, a new TFC membrane was successfully fabricated by incorporating polyvinylpyrrolidone (PVP) with different molecular weights (K15, K30 and K60) at different concentrations into the aqueous phase of IP process. Due to an increased solution viscosity and interaction between PVP and amine monomers, the lower diffusion rate of amine monomers resulted into a thin (the thinnest basal PA layer of approximately 30 nm) and smooth PA layer with a high crosslinking degree. Among, the optimum PVP K60–0.25 TFC membranes with the highest molecular weights and lower incorporating concentrations had a more positive effect on forward osmosis performance, which presented a pure water flux of 11.2 L m−2 h−1, 25 % higher, and a specific salt flux of 0.04 g L−1, 43 % lower than the original membrane. Our work provides a low-cost and simple approach to obtain high-performance TFC membrane with an improved trade-off effect, and helps to deeply understand the role played by additives in PA layer modulation.

Polyamide reverse osmosis membrane compaction and relaxation: Mechanisms and implications for desalination performance

This work investigates the compaction and relaxation behavior of composite reverse osmosis (RO) polyamide (PA) selective layers, utilizing non-equilibrium molecular dynamic (NEMD) simulations and well-controlled permeation experiments. Composite PA-RO membranes are prepared by interfacial polymerization of para and meta diamine monomer blends to achieve different PA film crosslinking degrees (CD). Wet-testing results suggest that “tighter” (higher CD) composite RO membranes undergo 65 % less compaction and recover 17 % more of their initial permeability (termed “relaxation”) when the pressure is relieved compared to lower CD PA layers. NEMD simulations provide a visual and quantitative characterization of PA layer's free volume changes in operando. NEMD simulations also corroborate experimental findings and elucidate the viscoelastic properties of the PA layer that govern compaction and relaxation behavior. The mechanisms of compaction under water permeation derived from NEMD simulations further support the notion of viscous flow of water through interconnected free volume elements (i.e., “pores”) within crosslinked PA films.

Boosting Molecular Cross-Linking in a Phenolic Resin for Spherical Hard Carbon with Enriched Closed Pores toward Enhanced Sodium Storage Ability.

Phenolic resin (PF) is considered a promising precursor of hard carbon (HC) for advanced-performance anodes in sodium-ion batteries (SIBs) because of its facile designability and high residual carbon yield. However, understanding how the structure of PF precursors influences sodium storage in their derived HC remains a significant challenge. Herein, the microstructure of HC is controlled by the degree of cross-linking of resorcinol-benzaldehyde (RB) resin. We reveal that robust molecular cross-linking in RB resin induced by hydrothermal treatment promotes closed-pore formation in the derived HC. The mechanism is devised for the decomposition of a highly cross-linked RB three-dimensional network into randomly stacked short-range graphitic microcrystals during high-temperature carbonization, contributing to the abundant closed pores in the derived HC. In addition, the high cross-linking degree of RB resin endows its derived HC with a small-sized spherical morphology and large interlayer spacing, which improves the rate performance of HC. Consequently, the optimized hydrothermal treatment HC anode shows a higher specific capacity of 372.7 mAh g-1 and better rate performance than the HC anode without hydrothermal treatment (276.0 mAh g-1). This strategy can provide feasible molecular cross-linking engineering for the development of closed pores in PF-based HC toward enhanced sodium storage.

Transglutaminase-crosslinked cold-set pea protein isolate gels modified by pH shifting: Properties, structure and formation mechanisms

The poor gelation properties of pea protein isolate (PPI) limit their use in food industries. In the present study, PPI was modified by pH-shifting combined with heat treatment, followed by cold-set gelation of PPI gels induced by transglutaminase. Both pH 2–3 and pH 10–12 promoted the unfolding of PPI molecules and the transformation of secondary structures from ordered to disordered. In particular, PPI molecules with pH 12-shifting tended to expand and unfold, which resulted in the exposure of internal active groups and improvement in surface hydrophobicity. Accordingly, after the addition of 50 U/g transglutaminase, PPI gels with pH 12-shifting and heating treatment exhibited homogeneous and dense gel network with high cross-linking degree (88.12 ± 1.80%) and water holding capacity (92.13 ± 2.40%), since pH 12-shifting and heating treatment promoted the conversion of random coils and β-turns to β-folds and α-helices in PPI gels. However, with pH 10 and 11-shifting, the PPI molecules was partially unfolded and the PPI gels had a high non-network protein content, resulting in low-strength gel networks of PPI gels with rough and loose microstructures and a low WHC. These results showed that TGase-crosslinked cold-set PPI gels after pH 12-shifting and heat treatment could promote the formation of homogeneous and dense gel network structure, so that improved the PPI gelation properties, which had great potential to be used as gelling agents or nutraceutical delivery systems for thermal sensitive bioactive compounds in food and non-food fields.

A breathable and sweat-absorbing pressure sensor based on PDMS gradient foam to achieve high sensitivity and wide detection range

Various designs of porous structures have been introduced to enhance the sensitivity of resistive pressure sensors. However, this method often comes at the cost of narrowing down the measurement range, limiting its use to low-pressure detection. This study proposes a soft pressure sensor with two-layer gradient foam structure. By finely adjusting the porosity and cross-linking degree of the PDMS, we aim to enhance the sensitivity without compromising the range of the sensor. Testing results demonstrate that the sensitivity of the gradient foam increases with a higher porosity, and the measurement range expands with a higher cross-linking degree. The soft sensor with the PDMS gradient stiffness foam (PGSF) achieves a sensitivity of 0.202 kPa−1 in the range of 0–40 kPa, 0.067 kPa−1 in the range of 40–210 kPa and 0.020 kPa−1 in the range of 210–850 kPa. Furthermore, the sensor exhibits a minimum detection limit of 50 Pa and demonstrates excellent stability (withstanding over 8000 testing cycles), breathability and sweat absorption. Additionally, we conducted motion detection, health monitoring and pressure mapping tests to showcase the potential applications of our proposed soft sensor in these fields.

The crosslinking sites and molecular conformation of gelatin hydrogel modified by transglutaminase

This work aimed to investigate the covalent crosslinking sites induced by transglutaminase (TGase, EC 2.3.2.13) in gelatin hydrogel and their impact on the gelatin molecular conformation. LC-MS/MS results demonstrated that Lys644 and Gln1351 of α1 chain and Gln19 of α2 chain were the main sites. The results of molecular dynamic (MD) simulation indicated that at the moderate degree of covalent crosslinking (13.55%), Radius of gyration (Rg) values decreased from 11.5 to 10.0 nm at 4 °C and led to a more compact structure, therefore enhancing structural tightness and gel strength. As the degree of crosslinking rose, the number of crosslinking sites gradually increased, with a predominant distribution in the C-terminal pro-peptide of gelatin chain. At the high crosslinking degree (37.48%), Rg value decreased at 100 °C and gelatin chains were connected through a “head to tail” linkage configuration, resulting in a significant reduction in the triple helix-like structure. The structure maintained the gel-forming ability at high temperature while lowering the aggregation energy of water molecules from −2.359 × 105 to −2.455 × 105 kJ/mol, leading to thermal irreversibility of gelatin hydrogel.

Modulating the graphitic domains of hard carbons via tuning resin crosslinking degree to achieve high rate and stable sodium storage

Sodium-ion batteries (SIBs) are regarded as an outstanding alternative to lithium-ion batteries (LIBs) due to abundant sodium sources and their similar chemistry. As a most promising anode of SIBs, hard carbons (HCs) receive extensive attention because of their low potential and low cost, but their rational design for commercial SIBs is restricted by their variable and complicated microstructure, which is analogous to that of graphite in LIBs. Herein, a series of controllable HC materials derived from 3-aminophenol formaldehyde resin (AFR) were designed and fabricated. We discover that the optimized HC features expanded graphite regions, highly developed nanopores, and reduced defect content, contributing to the enhanced Na+ storage. This optimization is achieved by adjusting the resin crosslinking degree of the precursor. Specifically, a resin precursor with a higher crosslinking degree can produce HC with a larger interlayer distance, relatively higher crystallinity, and a lower specific surface area. Encouragingly, the as-optimized AFR-HC electrode manifests superior electrochemical performance in the aspect of high capacity (383 mAh·g-1 at 0.05 A·g-1), better rate capability (140 mAh·g-1 at 20 A·g-1), and high initial coulombic efficiency (82%) than other contrast samples. Moreover, the as-constructed full cell coupled with a Na3V2(PO4)3 cathode shows an energy density of 250 Wh·kg-1. Together with the simple synthesis, cost-efficiency of the precursors and superior electrochemical performance, AFR-HCs are promising for the commercial application.