Natural rubber(NR)is a crucial elastic material used for damping and sealing applications in the nuclear industry,but its mechanical stability under radiation remains inadequate.Current efforts to improve radiation re...Natural rubber(NR)is a crucial elastic material used for damping and sealing applications in the nuclear industry,but its mechanical stability under radiation remains inadequate.Current efforts to improve radiation resistance rely on the addition of antiradiation agents,however,the effects of the components and microstructures of NR itself on radiation resistance remain unclear.In this study,we compared the composition and structure differences of four typical commercially used NR materials and investigated their effects on gamma radiation resistance.Furthermore,we examined the impact of non-rubber components(NRC)in NR on radiation resistance using deproteinized and dephosphorylated NR model samples.Our results revealed that NRC,such as proteins and phospholipids can enhance the strength of natural rubber before radiation exposure.However,after the removal of NRC,the samples exhibited improved mechanical stability under irradiation.Additionally,the ash content in NR could also influence the radiation resistance,as metal ions may react with the active centers produced by radiation,thereby enhancing the radiation resistance of the rubber.This work identifies the effect of non-rubber components in NR on radiation resistance and may serve as a reference for screening and developing radiation-resistant NR materials.展开更多
Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an...Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an asymmetric alicyclic structure adjacent to aromatic disulfide was tactfully introduced into the backbone of polyurethane(PU)elastomer.Specifically,such elastomer(PU-HPS)was fabricated by polycondensing polytetramethylene ether glycol(PTMEG),isophorone diisocyanate(IPDI)and p-hydroxydiphenyl disulfide(HPS)via one-pot method.The molecular mobility and phase morphology of PU-HPS can be tuned by adjusting the HPS content.Consequently,the dynamic exchange of hydrogen and disulfide bonds in the hard segment domains can also be tailored.The optimized sample manifests outstanding tensile strength(46.4 MPa),high toughness(109.1 MJ/m^(3)),high self-healing efficiency after fracture(90.3%),complete scratch recovery(100%)and good puncture resistance.Therefore,this work provides a facile strategy for developing robust self-healing polymers.展开更多
Natural rubber (NR) is widely used in various fields including aerospace, military industry and transportation due to its superior elasticity and comprehensive mechanical properties. Nonetheless, the commercial NR pre...Natural rubber (NR) is widely used in various fields including aerospace, military industry and transportation due to its superior elasticity and comprehensive mechanical properties. Nonetheless, the commercial NR prepared by different methods usually exhibits different mechanical properties, primarily due to variations in processing conditions during the conversion from latex to bulk rubber material. Consequently, this poses challenges in scientific research and industrial production of NR. In order to assess the properties of various commercially available NR and identify key structural and compositional components, this study systematically compares and analyzes four representative NR raw materials: air dried sheet (ADS), ribbed smoked sheets (RSS), constant viscidity NR (CV), and whole field latex rubber (WF). The investigation focuses on evaluating their static mechanical behavior, SIC behavior, wear resistance, and fatigue resistance. The findings indicate that protein and gel content exhibit a crucial influence on the NR properties. These constituents contribute to the formation of a high-crosslinking density region, generating a heterogeneous network structure within the rubber. This structure amplifies strains during deformation, leading to earlier and stronger strain-induced crystallization (SIC). Among the four commercial NR brands, RSS demonstrates superior overall mechanical and dynamic properties owing to its high protein and gel content. This study serves as a valuable reference for comprehending the differences in properties among various commercial NR, thereby offering guidance for the actual processing and selection of NR.展开更多
It remains a challenge to use a simple approach to fabricate a multi-shape memory material with high mechanical performances.Here,we report a triple crosslinking design to construct a multi-shape memory epoxy vitrimer...It remains a challenge to use a simple approach to fabricate a multi-shape memory material with high mechanical performances.Here,we report a triple crosslinking design to construct a multi-shape memory epoxy vitrimer(MSMEV),which exhibits high mechanical properties,multi-shape memory property and malleability.The triple crosslinking network is formed by reacting diglycidyl ether of bisphenol F(DGEBF)with 4-aminophenyl disulfide,γ-aminopropyltriethoxysilane(APTS)and poly(propylene glycol)bis(2-aminopropyl ether)(D2000).The triple crosslinking manifests triple functions:the disulfide bonds and the silyl ether linkages enable malleability of the epoxy network;the silyl ether linkages impart the network with high heterogeneity and broaden the glass transition region,leading to multi-shape memory property;a small amount of D2000 increases the modulus difference between the glassy and rubbery states,thereby improving the shape fixity ratio.Meanwhile,the high crosslinking density and rigid structure provide the MSMEV with high tensile strength and Young’s modulus.Moreover,integrating carbon fibers and MSMEV results in shape memory composites.The superior mechanical properties of the composites and the recyclability of carbon fiber derived from the dissolvability of MSMEV make the composites hold great promise as structural materials in varied applications.展开更多
Although synthetic rubbers show continuously improved mechanical properties,natural rubber (NR) remains irreplaceable in the rubber family due to its superior mechanical properties.A mainstream viewpoint regarding the...Although synthetic rubbers show continuously improved mechanical properties,natural rubber (NR) remains irreplaceable in the rubber family due to its superior mechanical properties.A mainstream viewpoint regarding the superiority of NR is that NR possesses a natural network formed by linking the poly(cis-l,4-isoprene) chain terminals to protein and phospholipid aggregates;after vulcanization,the natural network additionally contributes to rubber mechanics by both increasing the network density and promoting the strain-induced crystallization (SIC) behavior.However,the reason why the natural network promotes SIC is still unclear;in particular,only using the increased network density cannot explain our finding that the NR shows smaller onset strain of SIC than Gel (the gel component of NR with higher network density) and even vulcanized NR.Herein,we point out that the inhomogeneous chain deformation is the alternative reason why SIC of NR takes place at smaller strain than that of Gel.More specifically,although the natural network is homogenous on the subchain length scale based on the proton double-quantum NMR results,it is essentially inhomogeneous on mesoscale (100 nm),as revealed by the small angle X-ray scattering analysis.This inhomogeneous network also leads to the mesoscale deformation inhomogeneity,as detected by the orientation of stearic acid (SA) probe,thus resulting in the smaller onset strain of SIC of NR.Based on the experimental results,a mesoscale model is proposed to qualitatively describe the crucial roles of inhomogeneous structure and deformation of natural network in NR?s mechanical properties,providing a clue from nature to guide the development of high-performance rubbers with controlled structures at mesoscale.展开更多
It remains a significant challenge to fabricate self-healing aerogels with excellent flame retardancy.Herein,we develop a class of biomass aerogels by electrostatically assembling chitosan(CS),phytic acid(PA),and itac...It remains a significant challenge to fabricate self-healing aerogels with excellent flame retardancy.Herein,we develop a class of biomass aerogels by electrostatically assembling chitosan(CS),phytic acid(PA),and itaconic acid(IA).The electrostatic interaction between CS and IA is weak and dynamic,so freeze-drying the solution of CS and IA enables the formation of continuous aerogel skeleton with self-healing ability and re-programmability;in comparison,the electrostatic interaction between CS and PA is strong and less dynamic,and thus mixing PA with CS in aqueous solution leads to fine precipitates of high flame retardancy due to the synergistic phosphorus-nitrogen effect.Integrating the continuous skeleton and the fine precipitates results in self-healing aerogles with UL-4 V-0 rating of flame retardancy aerogels and autoextinguishable feature.Interestingly,the aerogels after burning in flame for 30 s form a skin-core structure,and the carbonized skin protects the integrity of the aerogels and the self-healing ability of the internal parts.Therefore,this work provides a facile strategy to develop multifunctional aerogels which hold great promise for advanced applications.展开更多
Epoxy resins are a kind of universal thermosetting plastics,which are widely used as structural materials in various applications.Thus,it is necessary to understand the network structure of epoxy resins.However,it is ...Epoxy resins are a kind of universal thermosetting plastics,which are widely used as structural materials in various applications.Thus,it is necessary to understand the network structure of epoxy resins.However,it is challenging to reveal the network heterogeneity of epoxy resins due to the permanent covalent crosslinking.Here,we provide a novel strategy to characterize the network heterogeneity of epoxy resins by using the dynamic covalent bonds to replace the conventional covalent bonds.The dynamic covalent bonds can reorganize under heat stimulus and the network keeps a constant crosslinking density during topological rearrangement,making it convenience to study the heterogeneity of epoxy resins.Kohlrausch-Williams-Watts(KWW)stretched exponential function is used to fit the stress relaxation data,and the parametersβandσperm/σ0 extracted from KWW equation indicate the network becomes more homogenous with the stoichiometric ratio of epoxy groups and amines decreases from 1/1 to 1/1.5.This method proves that the side reaction between epoxy and hydroxyl is the main origin of the structural heterogeneity in epoxy resins compared to the secondary amines network.展开更多
Reprogrammed metabolism is a hallmark of cancer. Glioblastoma（GBM） tumor cells predominantly utilize aerobic glycolysis for the biogenesis of energy and intermediate nutrients. However, in GBM, the clinical signific...Reprogrammed metabolism is a hallmark of cancer. Glioblastoma（GBM） tumor cells predominantly utilize aerobic glycolysis for the biogenesis of energy and intermediate nutrients. However, in GBM, the clinical significance of glycolysis and its underlying relations with the molecular features such as IDH1 mutation and subtype have not been elucidated yet. Herein, based on glioma datasets including TCGA（The Cancer Genome Atlas）, REMBRANDT（Repository for Molecular Brain Neoplasia Data） and GSE16011 we established a glycolytic gene expression signature score（GGESS） by incorporating ten glycolytic genes. Then we performed survival analyses and investigated the correlations between GGESS and IDH1 mutation as well as the molecular subtypes in GBMs. The results showed that GGESS independently predicted unfavorable prognosis and poor response to chemotherapy of GBM patients. Notably, GGESS was high in GBMs of mesenchymal subtype but low in IDH1-mutant GBMs. Furthermore, we found that the promoter regions of tumor-promoting glycolytic genes were hypermethylated in IDH1-mutant GBMs.Finally, we found that high GGESS also predicted poor prognosis and poor response to chemotherapy when investigating IDH1-wild type GBM patients only. Collectively, glycolysis represented by GGESS predicts unfavorable clinical outcome of GBM patients and is closely associated with mesenchymal subtype and IDH1 mutation in GBMs.展开更多
There have been significant interests in recent years for incorporating dynamic bonds into polymer materials for achieving multiple functionalities,such as self-healing,recycling,stimuli-responsiveness,and so on.Never...There have been significant interests in recent years for incorporating dynamic bonds into polymer materials for achieving multiple functionalities,such as self-healing,recycling,stimuli-responsiveness,and so on.Nevertheless,the impact of dynamic bonds on the polymer dynamics is actually less explored.In this study,we investigate a self-healing solid-liquid elastomer(SLE),which is a dual-crosslinked network made by coupling a permanently crosslinked polydimethylsiloxane(PDMS)network with polyborosiloxane(PBS)via abundant dynamic boron/oxygen dative bonds.Proton double-quantum(DQ)NMR reveals that the crosslinking degree is reduced while the structural heterogeneity of network is enhanced with increasing PBS content,i.e.,increasing the content of dynamic boron/oxygen dative bonds.Rheological experiments clearly reveal two chain relaxation modes in the SLE samples with a characteristic relaxation time of around 2.1 s and 11.8 s,corresponding to the relaxation of coupled PBS and PDMS chains,respectively.The master curves obtained from variable-temperature frequency-dependent rheological experiments also reveal enhanced heterogeneity of chain relaxation with increasing PBS content.Finally,the impact of boron/oxygen dative bonds on the Rouse dynamics is further revealed by fast-field-cycling(FFC)NMR experiments,where the spinlattice relaxation rate(R_(1))of all SLE samples follows the same power law of R_(1)(ω)∝ω^(-0.33).Nevertheless,the incorporation of PBS did slightly increase the energy barrier of Rouse dynamics.Our study well demonstrates a combined use of rheology and solid-state NMR spectroscopy can provide piercing insights into the interplay of crosslinking structures and dynamics of polymer materials.展开更多
Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure...Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure remains an academic challenge.Herein,by employing graphene oxide(GO)as the aerogel skeleton and utilizing poly(vinyl alcohol)(PVA)to regulate the ice crystal growth,we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method.We demonstrate that due to the hydrogen bond formed between PVA and water molecules,resulting in the initial crystallization temperature being reduced from-12.60℃(GO/PVA-0.01)to-16.21℃(GO/PVA-0.1).Meanwhile,the strong hydrogen bond between PVA and GO limits the diffusion of water molecules,thereby inhibiting the growth of ice crystals,decreasing the pore size of the GO/PVA aerogel from 9.96 nm(GO/PVA-0.01)to 7.19 nm(GO/PVA-0.3),and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13MPa.Overall,the finding of this study can be extended to other aerogel precursors,and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.展开更多
Semi-interpenetrating(semi-IPN)hydrogels formed by the continuous interpenetration of cross-linked polymer network and linear non-crosslinked polymer with multifunctionality are widely used in biomedical and other fie...Semi-interpenetrating(semi-IPN)hydrogels formed by the continuous interpenetration of cross-linked polymer network and linear non-crosslinked polymer with multifunctionality are widely used in biomedical and other fields.However,the negative impact of linear polymer on the homogeneity of the cross-linked network often leads to a decrease in the mechanical properties of semi-IPN hydrogels and severely limits their applications.Herein,a bioinspired hydrogen-bonding induced phase separation strategy is presented to construct the tough semi-IPN polyvinylpyrrolidone/polyacrylamide hydrogels(named PVP/PAM hydrogels),including the linear polymer polyvinylpyrrolidone(PVP)and cross-linked polyacrylamide(PAM)network.The resultant PVPx/PAM hydrogels exhibit unique phase separation induced by the hydrogen bonding between PVP and PAM and affected by the amount of substance of PVP.Meanwhile,the phase separation of PVPx/PAM hydrogels results in excellent mechanical properties with a strain of 2590%,tensile strength of 0.28 MPa and toughness of 2.17 MJ/m^(3).More importantly,the hydrogen bonding between PVP and PAM firstly disrupts to dissipate energy under external forces,so the PVPx/PAM hydrogels exhibit good self-recovery properties and outperform chemically cross-linked PAM hydrogels in impact resistance and damping applications.It is believed that the PVPx/PAM hydrogels with hydrogen-bonding induced phase separation possess more potential application prospects.展开更多
Elastomeric vitrimers with covalent adaptable networks are promising candidates to overcome the intrinsic drawbacks of conventional covalently-crosslinked elastomers;however, most elastomeric vitrimers show poor mecha...Elastomeric vitrimers with covalent adaptable networks are promising candidates to overcome the intrinsic drawbacks of conventional covalently-crosslinked elastomers;however, most elastomeric vitrimers show poor mechanical properties and require the addition of exogenous catalysts. Herein, we fabricate a catalyst-free and mechanically robust elastomeric vitrimer by constructing a segregated structure of sodium alginate (SA) in the continuous matrix of epoxidized natural rubber (ENR), and further crosslinking the composite by exchangeable hydroxyl ester bonds at the ENR-SA interfaces. The manufacturing process of the elastomeric vitrimer is facile and environmentally friendly without hazardous solvents or exogenous catalysts, as the abundant hydroxyl groups of the segregated SA phase can act as catalyst to activate the crosslinking reaction and promote the dynamic transesterification reaction. Interestingly, the segregated SA structure bears most of the load owing to its high modulus and small deformability, and thus ruptures preferentially upon deformation, leading to efficient energy dissipation.Moreover, the periodic stiffness fluctuation between rigid segregated SA phase and soft ENR matrix is beneficial to the crack-resisting. As a result,the elastomeric vitrimer manifests exceptional combination of catalyst-free, defect-tolerance, high tensile strength and toughness. In addition,the elastomeric vitrimer also exhibits multi-shape memory behavior which may further broaden its applications.展开更多
Recently,numerous mechanically robust synthetic hydrogels have been created.However,unlike natural loading-bearing materials such as cartilages and muscles,most hydrogels have inherently contradictory requirements,obs...Recently,numerous mechanically robust synthetic hydrogels have been created.However,unlike natural loading-bearing materials such as cartilages and muscles,most hydrogels have inherently contradictory requirements,obstructing the design of hydrogels with characteristics of robustness and rapid self-recoverability.Herein,we present a facile strategy for constructing mechanically robust and rapidly self-recoverable hydrogels.The linear poly(acrylamide-co-itaconic acid)chains crosslink via coordination bonds and minimal chemical crosslinkers to form the hydrogel network.Such design endows the coordination interactions to be asymmetrically distributed.Under deformation,the coordination interactions exhibit a reversible dissociation-and-reorganization property,demonstrating a new mechanism for energy dissipation and stress redistribution.Thus,the hydrogels possess tensile strength up to 12.5 MPa and toughness up to 28.2 MJ/m3.Moreover,the inherent dynamic nature of the coordination bonds imparts these hydrogels with stretch rate-and temperature-dependent mechanical behavior as well as excellent self-recovery performance.The method employed in this study is universal and is applicable to other polymers with load-bearing yet rapid recovery conditions.This study will facilitate diverse applications of most metallosupramolecular hydrogels.展开更多
Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,ho...Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,however,the investigation of the superconductivity intertwined with other or-ders are scarce.Investigating the pseudogap in atomic layers of MDCs may help to understand the superconducting mechanism for these true two dimensional(2D)superconducting systemns.Herein we report a pseudogap opening in the tunneling spectra of thin layers of SnSe2 epitaxially grown on highly oriented pyrolytic graphite(HOPG)with scanning tunneling microscopy/spectroscopy(STM/STS).A significant V-shaped pseudogap was observed to open near the Fermi level(Er)in the sTS.And at elevated temperatures,the gap gradually evolves to a shallow dip.Our experimental observations provide direct evidence of a pseudogap state in the electron-doped SnSe2 atomic layers on the HOPG surface,which may stimulate further exploration of the mechanism of superconductivity at 2D limit in MDCs.展开更多
基金supported by the Natural Science Foundation of Sichuan Province(No.2024NSFSC0173)the National Natural Science Foundation of China(Nos.5240030820,52173058 and 52403072)National Key R&D Program of China(No.2022YFD2301202)。
文摘Natural rubber(NR)is a crucial elastic material used for damping and sealing applications in the nuclear industry,but its mechanical stability under radiation remains inadequate.Current efforts to improve radiation resistance rely on the addition of antiradiation agents,however,the effects of the components and microstructures of NR itself on radiation resistance remain unclear.In this study,we compared the composition and structure differences of four typical commercially used NR materials and investigated their effects on gamma radiation resistance.Furthermore,we examined the impact of non-rubber components(NRC)in NR on radiation resistance using deproteinized and dephosphorylated NR model samples.Our results revealed that NRC,such as proteins and phospholipids can enhance the strength of natural rubber before radiation exposure.However,after the removal of NRC,the samples exhibited improved mechanical stability under irradiation.Additionally,the ash content in NR could also influence the radiation resistance,as metal ions may react with the active centers produced by radiation,thereby enhancing the radiation resistance of the rubber.This work identifies the effect of non-rubber components in NR on radiation resistance and may serve as a reference for screening and developing radiation-resistant NR materials.
基金supported by the National Natural Science Foundation of China(No.51873110)the Foundation of Guangdong Provincial Key Laboratory of Natural Rubber Processing and Key Laboratory of Carb on Fiber and Functio nal Polymers(Beijing University of Chemical Technology),Ministry of Educati on.
文摘Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an asymmetric alicyclic structure adjacent to aromatic disulfide was tactfully introduced into the backbone of polyurethane(PU)elastomer.Specifically,such elastomer(PU-HPS)was fabricated by polycondensing polytetramethylene ether glycol(PTMEG),isophorone diisocyanate(IPDI)and p-hydroxydiphenyl disulfide(HPS)via one-pot method.The molecular mobility and phase morphology of PU-HPS can be tuned by adjusting the HPS content.Consequently,the dynamic exchange of hydrogen and disulfide bonds in the hard segment domains can also be tailored.The optimized sample manifests outstanding tensile strength(46.4 MPa),high toughness(109.1 MJ/m^(3)),high self-healing efficiency after fracture(90.3%),complete scratch recovery(100%)and good puncture resistance.Therefore,this work provides a facile strategy for developing robust self-healing polymers.
基金supported by Research and Development Program in key area of Guangdong Province(No.2020B020217001)the National Natural Science Foundation of China(No.52173058)National Key R&D Program of China(No.2022YFD2301202).
文摘Natural rubber (NR) is widely used in various fields including aerospace, military industry and transportation due to its superior elasticity and comprehensive mechanical properties. Nonetheless, the commercial NR prepared by different methods usually exhibits different mechanical properties, primarily due to variations in processing conditions during the conversion from latex to bulk rubber material. Consequently, this poses challenges in scientific research and industrial production of NR. In order to assess the properties of various commercially available NR and identify key structural and compositional components, this study systematically compares and analyzes four representative NR raw materials: air dried sheet (ADS), ribbed smoked sheets (RSS), constant viscidity NR (CV), and whole field latex rubber (WF). The investigation focuses on evaluating their static mechanical behavior, SIC behavior, wear resistance, and fatigue resistance. The findings indicate that protein and gel content exhibit a crucial influence on the NR properties. These constituents contribute to the formation of a high-crosslinking density region, generating a heterogeneous network structure within the rubber. This structure amplifies strains during deformation, leading to earlier and stronger strain-induced crystallization (SIC). Among the four commercial NR brands, RSS demonstrates superior overall mechanical and dynamic properties owing to its high protein and gel content. This study serves as a valuable reference for comprehending the differences in properties among various commercial NR, thereby offering guidance for the actual processing and selection of NR.
基金by the State Key Scientific Special Project of China(No.2016ZX05017-002)the National Natural Science Foundation of China(No.51873110).
文摘It remains a challenge to use a simple approach to fabricate a multi-shape memory material with high mechanical performances.Here,we report a triple crosslinking design to construct a multi-shape memory epoxy vitrimer(MSMEV),which exhibits high mechanical properties,multi-shape memory property and malleability.The triple crosslinking network is formed by reacting diglycidyl ether of bisphenol F(DGEBF)with 4-aminophenyl disulfide,γ-aminopropyltriethoxysilane(APTS)and poly(propylene glycol)bis(2-aminopropyl ether)(D2000).The triple crosslinking manifests triple functions:the disulfide bonds and the silyl ether linkages enable malleability of the epoxy network;the silyl ether linkages impart the network with high heterogeneity and broaden the glass transition region,leading to multi-shape memory property;a small amount of D2000 increases the modulus difference between the glassy and rubbery states,thereby improving the shape fixity ratio.Meanwhile,the high crosslinking density and rigid structure provide the MSMEV with high tensile strength and Young’s modulus.Moreover,integrating carbon fibers and MSMEV results in shape memory composites.The superior mechanical properties of the composites and the recyclability of carbon fiber derived from the dissolvability of MSMEV make the composites hold great promise as structural materials in varied applications.
基金financially supported by the National Natural Science Foundation of China (No. 51333003)Special Fund for Agro-scientific Research in the Public Interest (No. 201403066-1)
文摘Although synthetic rubbers show continuously improved mechanical properties,natural rubber (NR) remains irreplaceable in the rubber family due to its superior mechanical properties.A mainstream viewpoint regarding the superiority of NR is that NR possesses a natural network formed by linking the poly(cis-l,4-isoprene) chain terminals to protein and phospholipid aggregates;after vulcanization,the natural network additionally contributes to rubber mechanics by both increasing the network density and promoting the strain-induced crystallization (SIC) behavior.However,the reason why the natural network promotes SIC is still unclear;in particular,only using the increased network density cannot explain our finding that the NR shows smaller onset strain of SIC than Gel (the gel component of NR with higher network density) and even vulcanized NR.Herein,we point out that the inhomogeneous chain deformation is the alternative reason why SIC of NR takes place at smaller strain than that of Gel.More specifically,although the natural network is homogenous on the subchain length scale based on the proton double-quantum NMR results,it is essentially inhomogeneous on mesoscale (100 nm),as revealed by the small angle X-ray scattering analysis.This inhomogeneous network also leads to the mesoscale deformation inhomogeneity,as detected by the orientation of stearic acid (SA) probe,thus resulting in the smaller onset strain of SIC of NR.Based on the experimental results,a mesoscale model is proposed to qualitatively describe the crucial roles of inhomogeneous structure and deformation of natural network in NR?s mechanical properties,providing a clue from nature to guide the development of high-performance rubbers with controlled structures at mesoscale.
基金supported by the National Natural Science Foundation of China(Nos.51873133 and 51873110)the Opening Project of State Key Laboratory of Polymer Materials Engineering(Sichuan University)(No.sklpme2018-4-33 and sklpme2019-4-32)Chengdu Science and Technology Bureau(No.2019-YF05-01319-SN).
文摘It remains a significant challenge to fabricate self-healing aerogels with excellent flame retardancy.Herein,we develop a class of biomass aerogels by electrostatically assembling chitosan(CS),phytic acid(PA),and itaconic acid(IA).The electrostatic interaction between CS and IA is weak and dynamic,so freeze-drying the solution of CS and IA enables the formation of continuous aerogel skeleton with self-healing ability and re-programmability;in comparison,the electrostatic interaction between CS and PA is strong and less dynamic,and thus mixing PA with CS in aqueous solution leads to fine precipitates of high flame retardancy due to the synergistic phosphorus-nitrogen effect.Integrating the continuous skeleton and the fine precipitates results in self-healing aerogles with UL-4 V-0 rating of flame retardancy aerogels and autoextinguishable feature.Interestingly,the aerogels after burning in flame for 30 s form a skin-core structure,and the carbonized skin protects the integrity of the aerogels and the self-healing ability of the internal parts.Therefore,this work provides a facile strategy to develop multifunctional aerogels which hold great promise for advanced applications.
基金financially supported by the National Natural Science Foundation of China(No.51873110)Sichuan Science and Technology Program(No.2021JDJQ0018)State Key Laboratory of Polymer Materials Engineering。
文摘Epoxy resins are a kind of universal thermosetting plastics,which are widely used as structural materials in various applications.Thus,it is necessary to understand the network structure of epoxy resins.However,it is challenging to reveal the network heterogeneity of epoxy resins due to the permanent covalent crosslinking.Here,we provide a novel strategy to characterize the network heterogeneity of epoxy resins by using the dynamic covalent bonds to replace the conventional covalent bonds.The dynamic covalent bonds can reorganize under heat stimulus and the network keeps a constant crosslinking density during topological rearrangement,making it convenience to study the heterogeneity of epoxy resins.Kohlrausch-Williams-Watts(KWW)stretched exponential function is used to fit the stress relaxation data,and the parametersβandσperm/σ0 extracted from KWW equation indicate the network becomes more homogenous with the stoichiometric ratio of epoxy groups and amines decreases from 1/1 to 1/1.5.This method proves that the side reaction between epoxy and hydroxyl is the main origin of the structural heterogeneity in epoxy resins compared to the secondary amines network.
基金supported by grants from the China National Science and Technology Major Project (2016YFA0101203)
文摘Reprogrammed metabolism is a hallmark of cancer. Glioblastoma（GBM） tumor cells predominantly utilize aerobic glycolysis for the biogenesis of energy and intermediate nutrients. However, in GBM, the clinical significance of glycolysis and its underlying relations with the molecular features such as IDH1 mutation and subtype have not been elucidated yet. Herein, based on glioma datasets including TCGA（The Cancer Genome Atlas）, REMBRANDT（Repository for Molecular Brain Neoplasia Data） and GSE16011 we established a glycolytic gene expression signature score（GGESS） by incorporating ten glycolytic genes. Then we performed survival analyses and investigated the correlations between GGESS and IDH1 mutation as well as the molecular subtypes in GBMs. The results showed that GGESS independently predicted unfavorable prognosis and poor response to chemotherapy of GBM patients. Notably, GGESS was high in GBMs of mesenchymal subtype but low in IDH1-mutant GBMs. Furthermore, we found that the promoter regions of tumor-promoting glycolytic genes were hypermethylated in IDH1-mutant GBMs.Finally, we found that high GGESS also predicted poor prognosis and poor response to chemotherapy when investigating IDH1-wild type GBM patients only. Collectively, glycolysis represented by GGESS predicts unfavorable clinical outcome of GBM patients and is closely associated with mesenchymal subtype and IDH1 mutation in GBMs.
基金the financial supports by the R&D program of Guangzhou(No.202102020941)the National Natural Science Foundation of China(Nos.21973031 and 22173046)the Natural Science Foundation of Guangdong Province,China(No.2019A1515011140)。
文摘There have been significant interests in recent years for incorporating dynamic bonds into polymer materials for achieving multiple functionalities,such as self-healing,recycling,stimuli-responsiveness,and so on.Nevertheless,the impact of dynamic bonds on the polymer dynamics is actually less explored.In this study,we investigate a self-healing solid-liquid elastomer(SLE),which is a dual-crosslinked network made by coupling a permanently crosslinked polydimethylsiloxane(PDMS)network with polyborosiloxane(PBS)via abundant dynamic boron/oxygen dative bonds.Proton double-quantum(DQ)NMR reveals that the crosslinking degree is reduced while the structural heterogeneity of network is enhanced with increasing PBS content,i.e.,increasing the content of dynamic boron/oxygen dative bonds.Rheological experiments clearly reveal two chain relaxation modes in the SLE samples with a characteristic relaxation time of around 2.1 s and 11.8 s,corresponding to the relaxation of coupled PBS and PDMS chains,respectively.The master curves obtained from variable-temperature frequency-dependent rheological experiments also reveal enhanced heterogeneity of chain relaxation with increasing PBS content.Finally,the impact of boron/oxygen dative bonds on the Rouse dynamics is further revealed by fast-field-cycling(FFC)NMR experiments,where the spinlattice relaxation rate(R_(1))of all SLE samples follows the same power law of R_(1)(ω)∝ω^(-0.33).Nevertheless,the incorporation of PBS did slightly increase the energy barrier of Rouse dynamics.Our study well demonstrates a combined use of rheology and solid-state NMR spectroscopy can provide piercing insights into the interplay of crosslinking structures and dynamics of polymer materials.
基金financially supported by the National Natural Science Foundation of China(No.51873133)。
文摘Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure remains an academic challenge.Herein,by employing graphene oxide(GO)as the aerogel skeleton and utilizing poly(vinyl alcohol)(PVA)to regulate the ice crystal growth,we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method.We demonstrate that due to the hydrogen bond formed between PVA and water molecules,resulting in the initial crystallization temperature being reduced from-12.60℃(GO/PVA-0.01)to-16.21℃(GO/PVA-0.1).Meanwhile,the strong hydrogen bond between PVA and GO limits the diffusion of water molecules,thereby inhibiting the growth of ice crystals,decreasing the pore size of the GO/PVA aerogel from 9.96 nm(GO/PVA-0.01)to 7.19 nm(GO/PVA-0.3),and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13MPa.Overall,the finding of this study can be extended to other aerogel precursors,and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.
基金This work was financially supported by the National Natural Science Foundation of China(No.52273210).
文摘Semi-interpenetrating(semi-IPN)hydrogels formed by the continuous interpenetration of cross-linked polymer network and linear non-crosslinked polymer with multifunctionality are widely used in biomedical and other fields.However,the negative impact of linear polymer on the homogeneity of the cross-linked network often leads to a decrease in the mechanical properties of semi-IPN hydrogels and severely limits their applications.Herein,a bioinspired hydrogen-bonding induced phase separation strategy is presented to construct the tough semi-IPN polyvinylpyrrolidone/polyacrylamide hydrogels(named PVP/PAM hydrogels),including the linear polymer polyvinylpyrrolidone(PVP)and cross-linked polyacrylamide(PAM)network.The resultant PVPx/PAM hydrogels exhibit unique phase separation induced by the hydrogen bonding between PVP and PAM and affected by the amount of substance of PVP.Meanwhile,the phase separation of PVPx/PAM hydrogels results in excellent mechanical properties with a strain of 2590%,tensile strength of 0.28 MPa and toughness of 2.17 MJ/m^(3).More importantly,the hydrogen bonding between PVP and PAM firstly disrupts to dissipate energy under external forces,so the PVPx/PAM hydrogels exhibit good self-recovery properties and outperform chemically cross-linked PAM hydrogels in impact resistance and damping applications.It is believed that the PVPx/PAM hydrogels with hydrogen-bonding induced phase separation possess more potential application prospects.
基金financially supported by the National Natural Science Foundation of China (Nos. 51873110 and 51790501)State Key Laboratory of Polymer Materials Engineering (No. sklpme2019-2-14)the Fundamental Research Funds for Central Universities。
文摘Elastomeric vitrimers with covalent adaptable networks are promising candidates to overcome the intrinsic drawbacks of conventional covalently-crosslinked elastomers;however, most elastomeric vitrimers show poor mechanical properties and require the addition of exogenous catalysts. Herein, we fabricate a catalyst-free and mechanically robust elastomeric vitrimer by constructing a segregated structure of sodium alginate (SA) in the continuous matrix of epoxidized natural rubber (ENR), and further crosslinking the composite by exchangeable hydroxyl ester bonds at the ENR-SA interfaces. The manufacturing process of the elastomeric vitrimer is facile and environmentally friendly without hazardous solvents or exogenous catalysts, as the abundant hydroxyl groups of the segregated SA phase can act as catalyst to activate the crosslinking reaction and promote the dynamic transesterification reaction. Interestingly, the segregated SA structure bears most of the load owing to its high modulus and small deformability, and thus ruptures preferentially upon deformation, leading to efficient energy dissipation.Moreover, the periodic stiffness fluctuation between rigid segregated SA phase and soft ENR matrix is beneficial to the crack-resisting. As a result,the elastomeric vitrimer manifests exceptional combination of catalyst-free, defect-tolerance, high tensile strength and toughness. In addition,the elastomeric vitrimer also exhibits multi-shape memory behavior which may further broaden its applications.
基金National Natural Science Foundation of China(No.51873110).
文摘Recently,numerous mechanically robust synthetic hydrogels have been created.However,unlike natural loading-bearing materials such as cartilages and muscles,most hydrogels have inherently contradictory requirements,obstructing the design of hydrogels with characteristics of robustness and rapid self-recoverability.Herein,we present a facile strategy for constructing mechanically robust and rapidly self-recoverable hydrogels.The linear poly(acrylamide-co-itaconic acid)chains crosslink via coordination bonds and minimal chemical crosslinkers to form the hydrogel network.Such design endows the coordination interactions to be asymmetrically distributed.Under deformation,the coordination interactions exhibit a reversible dissociation-and-reorganization property,demonstrating a new mechanism for energy dissipation and stress redistribution.Thus,the hydrogels possess tensile strength up to 12.5 MPa and toughness up to 28.2 MJ/m3.Moreover,the inherent dynamic nature of the coordination bonds imparts these hydrogels with stretch rate-and temperature-dependent mechanical behavior as well as excellent self-recovery performance.The method employed in this study is universal and is applicable to other polymers with load-bearing yet rapid recovery conditions.This study will facilitate diverse applications of most metallosupramolecular hydrogels.
基金We thank Prof.Tao Wu for helpful discus.sion.This work was supported by the National Key R&D Program of China(Grant Nos.2016YFA0200603 and 2017YFA0205004)the"Strategic Priority Research Program"of CAS(Grant No.XDB01020100)+2 种基金the National Natural Science Foundation of China(Grant Nos.91321309,21421063,and 21473174)the Funda-mental Research Funds for the Central Science Advances Universi-ties(Nos.WK2060190027 and WK2060190084)A.Z.acknowledges a fellowship from the Youth Innovation Promotion Association of CAS(No.2011322)。
文摘Superconducting metal dichalcogenides(MDCs)present several similarities to the other layered SI1-perconductors like cuprates.The superconductivity in atomically thin MDCs has been demonstrated by recent experiments,however,the investigation of the superconductivity intertwined with other or-ders are scarce.Investigating the pseudogap in atomic layers of MDCs may help to understand the superconducting mechanism for these true two dimensional(2D)superconducting systemns.Herein we report a pseudogap opening in the tunneling spectra of thin layers of SnSe2 epitaxially grown on highly oriented pyrolytic graphite(HOPG)with scanning tunneling microscopy/spectroscopy(STM/STS).A significant V-shaped pseudogap was observed to open near the Fermi level(Er)in the sTS.And at elevated temperatures,the gap gradually evolves to a shallow dip.Our experimental observations provide direct evidence of a pseudogap state in the electron-doped SnSe2 atomic layers on the HOPG surface,which may stimulate further exploration of the mechanism of superconductivity at 2D limit in MDCs.
