Ultrafine ordered L1_(2)-Pt-Co-Mn ternary intermetallic nanoparticles as high-performance oxygen-reduction electrocatalysts for practical fuel cells

The long-range periodically ordered atomic structures in intermetallic nanoparticles(INPs)can significantly enhance both the electrocatalytic activity and electrochemical stability toward the oxygen reduction reaction(ORR)compared to the disordered atomic structures in ordinary solid-solution alloy NPs.Accordingly,through a facile and scalable synthetic method,a series of carbon-supported ultrafine Pt_3Co_(x)Mn_(1-x)ternary INPs are prepared in this work,which possess the"skin-like"ultrathin Pt shells,the ordered L1_(2) atomic structure,and the high-even dispersion on supports(L1_(2)-Pt_3Co_(x)Mn_(1-x)/~SPt INPs/C).Electrochemical results present that the composition-optimized L1_(2)-Pt_3Co_(0.7)Mn_(0.3)/~SPt INPs/C exhibits the highest electrocata lytic activity among the series,which are also much better than those of the pristine ultrafine Pt/C.Besides,it also has a greatly enhanced electrochemical stability.In addition,the effects of annealing temperature and time are further investigated.More importantly,such superior ORR electrocatalytic performance of L1_(2)-Pt_3Co_(0.7)Mn_(0.3)/~SPt INPs/C are also well demonstrated in practical fuel cells.Physicochemical characterization analyses further reveal the major origins of the greatly enhanced ORR electrocata lytic performance:the Pt-Co-Mn alloy-induced geometric and ligand effects as well as the extremely high L1_(2) atomic-ordering degree.This work not only successfully develops a highly active and stable ordered ternary intermetallic ORR electrocatalyst,but also elucidates the corresponding"structure-function"relationship,which can be further applied in designing other intermetallic(electro)catalysts.

In situ grown nanoscale platinum on carbon powder as catalyst layer in proton exchange membrane fuel cells(PEMFCs)

An extensive study has been conducted on the proton exchange membrane fuel cells （PEMFCs） with reducing Pt loading. This is commonly achieved by developing methods to increase the utilization of the platinum in the catalyst layer of the electrodes. In this paper, a novel process of the catalyst layers was introduced and investigated. A mixture of carbon powder and Nafion solution was sprayed on the glassy carbon electrode （GCE） to form a thin carbon layer. Then Pt particles were deposited on the surface by reducing hexachloroplatinic （IV） acid hexahydrate with methanoic acid. SEM images showed a continuous Pt gradient profile among the thickness direction of the catalytic layer by the novel method. The Pt nanowires grown are in the size of 3 nm （diameter） x l0 nm （length） by high solution TEM image. The novel catalyst layer was characterized by cyclic voltammetry （CV） and scanning electron microscope （SEM） as compared with commercial Pt/C black and Pt catalyst layer obtained from sputtering. The results showed that the platinum nanoparticles deposited on the carbon powder were highly utilized as they directly faced the gas diffusion layer and offered easy access to reactants （oxygen or hydrogen）.

Study on the Supply Efficiency of Rural Public Service in China Based on Three-stage DEA Model

Improving the supply efficiency of rural public service is an important way to solve the severe shortage of rural public service. In this article,we use three-stage DEA model to carry out empirical research of the supply efficiency of rural public service in 31 provinces and regions of China. The results show that if without control over exogenous environment variables and random brunt,the classic DEA method will overestimate the rural public service efficiency; after controlling the impact of the external environmental factors,the mean of supply efficiency of rural public service in 31 provinces and regions of China is 0. 697; the improved rural per capita income,population density,population size and the educational level of residents,is a significantly favorable factor for enhancing the supply efficiency of rural public service,while the increase in the proportion of fiscal spending on rural public service to GDP plays no significant role in improving the rural public service efficiency; according to their efficiency type,the provinces and regions should adopt some measures,such as improving the management level or expanding the supply scale,to improve the supply efficiency.

Factors Influencing the Supply Efficiency of Basic Public Service at County Level

In this paper,we use DEA-Tobit model to conduct empirical study on the governmental supply efficiency of public service in Chongqing's 38 counties and the influencing factors during the period 2008-2011.The results show that the supply efficiency of basic public service at county level is generally low,and there is significant regional differences and strong volatility;per capita GDP,population density and population size,and level of education of the residents,are significantly correlated with the supply efficiency of basic public service at county level,but traffic density,urbanization level,and the proportion of government spending on public service to total fiscal expenditure,have no significant effects on the efficiency of basic public service at county level.Based on this,we propose some policy recommendations for enhancing the level of local economic development and the level of education,and reasonably guiding the residents'agglomeration.

Designing an automated FAQ answering system for farmers based on hybrid strategies

Purpose: The purpose of this study is to develop an automated frequently asked question(FAQ) answering system for farmers. This paper presents an approach for calculating the similarity between Chinese sentences based on hybrid strategies.Design/methodology/approach: We analyzed the factors influencing the successful matching between a user's question and a question-answer(QA) pair in the FAQ database. Our approach is based on a combination of multiple factors. Experiments were conducted to test the performance of our method.Findings: Experiments show that this proposed method has higher accuracy. Compared with similarity calculation based on TF-IDF,the sentence surface forms and the semantic relations,the proposed method based on hybrid strategies has a superior performance in precision,recall and F-measure value.Research limitations: The FAQ answering system is only capable of meeting users' demand for text retrieval at present. In the future,the system needs to be improved to meet users' demand for retrieving images and videos.Practical implications: This FAQ answering system will help farmers utilize agricultural information resources more efficiently.Originality/value: We design the algorithms for calculating similarity of Chinese sentences based on hybrid strategies,which integrate the question surface similarity,the question semantic similarity and the question-answer similarity based on latent semantic analysis(LSA) to find answers to a user's question.

Modification and sequential treatment of EU-1 zeolite in mild alkali and alkaline-acid conditions

EU-1 zeolites were sequentially treated with low-concentration sodium carbonate(Na_2CO_3) and hydrochloric acid(HCl) solutions.The obtained samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),N_2 adsorption/desorption,temperature programmed desorption of NH_3(NH_3-TPD),solid state^(27)A1 nuclear magnetic resonance(^(27)A1 NMR),and the catalytic performances of the treated samples were tested in the xylene isomerization reaction.The results showed that the external surface area and mesoporous volume of the sample sequentially treated with 0.05 mol·L^(-1) Na_2CO_3 and 0.1 mol·L^(-1) HCl solutions reached73.9 m^2·g^(-1) and 0.162 cm^3·g^(-1),respectively.The catalytic performances of EU-1 zeolites were significantly improved,that the activity of the probe reaction increased from 23.03%to 23.61%and the selectivity increased from85.09%to 87.14%compared with those of parent sample.Furthermore,it was found that only amorphous silica and alumina species was dissolved during the post-treatment process,but the framework structure and the acidic properties of EU-1 zeolite remained intact.

PBO fibers/fluorine-containing liquid crystal compound modified cyanate ester wave-transparent laminated composites with excellent mechanical and flame retardance properties

Bisphenol A dicyanate ester resins modified by fluorine-containing liquid crystal compound(LCFE)are applied as polymer matrix(LCFE-BADCy),poly(p-phenylene-2,6-benzobisoxazole)(PBO)fibers as rein-forcements,and fluorine/adamantane PBO precursor(pre FABPBO)as interfacial compatibilizer to prepare the corresponding PBO fibers/FABPBO/LCFE-BADCy wave-transparent laminated composites.LCFE could improve the order degree of BADCy cured network,in favor of enhancing the wave-transparent perfor-mance,mechanical properties,and intrinsic thermal conductivity.The dielectric constant and dielectric loss of PBO fibers/FABPBO/LCFE-BADCy composites are highly temperature(25–200℃)and frequency(10^(4)–10^(7) Hz and 8.2–12.4 GHz)stable with the value of 2.49 and 0.003 under 10^(6) Hz at 25℃,and the corresponding wave transmission efficiency is 95.0%,higher than that of 92.5%for PBO fibers/BADCy com-posites.The interlamellar shear strength and flexural strength are respectively 50.7 MPa and 682.5 MPa,38.1%and 16.2%higher than those of PBO fibers/BADCy composites.Besides,the volume resistivity,breakdown voltage,heat resistance index,glass transition temperature,flame retardant grade,and ul-timate oxygen index of PBO fibers/FABPBO/LCFE-BADCy composites are respectively 5.3×10^(15)Ωcm,29.75 kV/mm,217.2℃,245.7℃,V-1 grade,and 33.6%,expected to be performed as a new generation of“lightweight/loading/wave-transparent”electromagnetic window materials in advanced military weapons and civil communication base station.

Branched Fluorine/Adamantane Interfacial Compatibilizer for PBO Fibers/Cyanate Ester Wave-Transparent Laminated Composites

Comprehensive Summary Branched fluorine/adamantane PBO precursor(preFABPBO),synthesized via random co-condensation between 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoro propane,1,3-adamantanedicarbonyl dichloride,and trimesoyl chloride,is performed as interfacial compatibilizer,bisphenol A dicyanate ester(BADCy)resin as polymer matrix,and poly(p-phenylene-2,6-benzobisoxazole)(PBO)fibers as reinforcements to prepare PBO fibers/FABPBO-BADCy wave-transparent laminated composites by high temperature molding.The mechanical properties,wave-transparent performances,and heat resistances of PBO fibers/BADCy composites are simultaneously improved by the addition of preFABPBO.The interlaminar shear strength(ILSS)and flexural strength of PBO fibers/FABPBO-BADCy composites are 48.9 and 665.3 MPa,respectively,increased by 33.2%and 13.3%compared to those of PBO fibers/BADCy composites(36.7 and 587.4 MPa).The dielectric constant and dielectric loss values at 106 Hz are 2.53 and 0.003,respectively,lower than those of PBO fibers/BADCy composites(3.06 and 0.006),and the corresponding wave transmission efficiency is 94.8%,which also presents excellent stability over the wide temperature(25-200℃)and frequency range(103-107 Hz and 8.2-12.4 GHz).Meanwhile,the heat resistance index and glass transition temperature are 229.9℃and 247.5℃,also better than those of PBO fibers/BADCy composites(229.6℃and 247.1℃).

The effect of catalyst layer design on catalyst utilization in PEMFC studied via stochastic reconstruction method

Catalyst utilization is an important determinant of proton exchange membrane fuel cell performance,and increasing the catalyst utilization is one of the most critical approaches to reducing the catalyst loading in PEMFC.4-phase stochastic reconstruction method based on the variable-resolution Quartet Structure Generation Set(QSGS)algorithm is utilized to elucidate the influence of different parameters of electrode preparation,including the porosity,the dispersion degree of carbon agglomerate,ionomer content,and carbon support size,on the catalyst utilization in the catalyst layer.It was found that there exist optimal values for the porosity,dispersion degree of carbon agglomerate,ionomer content,and carbon support sizes in CLs and any deviations from these optimal values would lead to transport issues of electron,proton and mass within CLs.Taking electron,proton and mass transport into consideration simultaneously,the optimal Pt utilization is 46.55%among 48 cases in this investigation,taken at the carbon support diameter of 40 nm,the porosity of 0.4,the agglomerate spatial density of 25μm^(−3) and I/C at 0.7.The selection of porosity,ultrasonic dispersion technique and ionomer content for conventional electrode preparation requires compromises on mass,electron and proton transport,leading to catalyst utilization in CLs hardly exceeding 50%.Therefore,the next generation of catalyst layer design and preparation technology is desired.

Theoretical insight into the activity and selectivity in palladium/Ming-Phos-catalyzed three-component asymmetric synthesis of gem-diarylmethine silanes

Recently,a three-component coupling reaction for efficient construction of gem-diarylmethine silanes was developed,utilizing a Pd-Ming-Phos catalyst.To explore the underlying mechanism governing this intriguing reaction,we have conducted comprehensive density functional theory(DFT)computations(M06-L/SDD/6-311++G(d,p)/SMD//B3LYP-D3/lanl2dz/6-31G(d,p)).DFT calculations reveal that the oxidative addition of Ar Br to Pd(0)is the rate-determining step,and the carbenation process of Ph CHN_(2)to Pd(Ⅱ)is the enantioselectivity-determining step.Moreover,the Ming-Phos ligand exhibits a self-adaptive nature,allowing it to dynamically adapt its coordination patterns with the metal center in different elementary steps,thereby enhancing the overall reactivity.The enantioselectivity is determined by both the trans effect and the side-arm effect of the ligand.This mechanism nicely explains why TY-Phos with P-tBu_(2)instead of the Ming-Phos with P-Ph2results in poor reactivity and much reduced enantioselectivity.This study not only provides deeper insights into the functioning principles of Sad Phos ligands but also offers valuable guidance for future ligand modifications and optimizations.

A perspective on influences of cathode material degradation on oxygen transport resistance in low Pt PEMFC

A large-scale industrial application of proton exchange membrane fuel cells(PEMFCs)greatly depends on both substantial cost reduction and continuous durability enhancement.However,compared to effects of material degradation on apparent activity loss,little attention has been paid to influences on the phenomena of mass transport.In this review,influences of the degradation of key materials in membrane electrode assemblies(MEAs)on oxygen transport resistance in both cathode catalyst layers(CCLs)and gas diffusion layers(GDLs)are comprehensively explored,including carbon support,electrocatalyst,ionomer in CCLs as well as carbon material and hydrophobic polytetrafluoroethylene(PTFE)in GDLs.It is analyzed that carbon corrosion in CCLs will result in pore structure destruction and impact ionomer distribution,thus affecting both the bulk and local oxygen transport behavior.Considering the catalyst degradation,an eventual decrease in electrochemical active surface area(ECSA)definitely increases the local oxygen transport resistance since a decrease in active sites will lead to a longer oxygen transport path.It is also noted that problems concerning oxygen transport caused by the degradation of ionomer chemical structure in CCLs should not be ignored.Both cation contamination and chemical decomposition will change the structure of ionomer,thus worsening the local oxygen transport.Finally,it is found that the loss of carbon and PTFE in GDLs lead to a higher hydrophilicity,which is related to an occurrence of water flooding and increase in the oxygen transport resistance.

Block copolymer functionalized quartz fibers/cyanate ester wave-transparent laminated composites

A block copolymer of PDMS-b-PGMA is synthesized by polymerizing glycidyl methacrylate(GMA)via reversible addition-fragmentation chain transfer(RAFT)polymerization applying a polydimethylsiloxane(PDMS)based macro-RAFT agent,which is then performed to functionalize the quartz fibers(QFs@PDMS-b-PGMA)via a simple coating process.Finally,the QFs@PDMS-b-PGMA/bisphenol A dicyanate ester(BADCy)wave-transparent laminated composites are fabricated by high-temperature molding.Nuclear magnetic resonance(NMR)spectroscopy,Fourier transform infrared(FT-IR)spectroscopy and size ex-clusion chromatography(SEC)demonstrate the successful preparation of PDMS-b-PGMA with expected structure.When the molar mass and coating amount of PDMS-b-PGMA are respectively 8100 g/mol and 2.0 wt.%,QFs@PDMS-b-PGMA/BADCy wave-transparent laminated composites present optimal mechan-ical properties and wave-transparent performance.The interlaminar shear strength(ILSS)and flexural strength are 53.6 and 552.0 MPa,respectively.Meanwhile,the dielectric constant and dielectric loss val-ues are 2.61 and 0.0028 at 1 MHz(wave transmittance of 93.8%),showing good stability at different frequencies(102-106 Hz and 8.4-12.4 GHz)and temperatures(25-250℃).

Exploration of the oxygen transport behavior in non-precious metal catalyst-based cathode catalyst layer for proton exchange membrane fuel cells

High cost has undoubtedly become the biggest obstacle to the commercialization of proton exchange membrane fuel cells(PEMFCs),in which Pt-based catalysts employed in the cathodic catalyst layer(CCL)account for the major portion of the cost.Although nonprecious metal catalysts(NPMCs)show appreciable activity and stability in the oxygen reduction reaction(ORR),the performance of fuel cells based on NPMCs remains unsatisfactory compared to those using Pt-based CCL.Therefore,most studies on NPMC-based fuel cells focus on developing highly active catalysts rather than facilitating oxygen transport.In this work,the oxygen transport behavior in CCLs based on highly active Fe-N-C catalysts is comprehensively explored through the elaborate design of two types of membrane electrode structures,one containing low-Pt-based CCL and NPMCbased dummy catalyst layer(DCL)and the other containing only the NPMC-based CCL.Using Zn-N-C based DCLs of different thickness,the bulk oxygen transport resistance at the unit thickness in NPMC-based CCL was quantified via the limiting current method combined with linear fitting analysis.Then,the local and bulk resistances in NPMC-based CCLs were quantified via the limiting current method and scanning electron microscopy,respectively.Results show that the ratios of local and bulk oxygen transport resistances in NPMCbased CCL are 80%and 20%,respectively,and that an enhancement of local oxygen transport is critical to greatly improve the performance of NPMC-based PEMFCs.Furthermore,the activity of active sites per unit in NPMCbased CCLs was determined to be lower than that in the Pt-based CCL,thus explaining worse cell performance of NPMC-based membrane electrode assemblys(MEAs).It is believed that the development of NPMC-based PEMFCs should proceed not only through the design of catalysts with higher activity but also through the improvement of oxygen transport in the CCL.

Half‑Power Prediction and Its Application on the Energy Management Strategy for Fuel Cell City Bus

The fuel cell hybrid powertrain is a potential power supply system for fuel cell vehicles.The underlying problem is that the fuel cell vehicles encounter exhaustive hydrogen consumption.To effectively manage hydrogen consumption,the aim is to propose fuel cell city bus power and control system.The underlying idea is to determine the target power of fuel cell through simulation study on fuel cell and battery energy management strategy and road test verifications.A half-power prediction energy management strategy is implemented to predict the target power of the fuel cell in the current time step based on the demand power of the vehicle and the state of charge(SOC)of the battery in the previous time steps.This offers better understanding of the correlation between fuel cell power and vehicle drive cycle for enabling effective power supply management.The research results show that the half-power prediction energy management strategy effectively reduces the hydrogen consumption of the vehicle by 7.1%and the number of battery cycle by 6.0%,compared to the stepped manage-ment strategy of battery SOC.When applied to a 12-m fuel cell city bus—F12,specially designed and manufactured for the Winter Olympic Games in 2022—the fuel economy of 3.7 kg/100 km is achieved in urban road conditions.This study lays a foundation for providing the powertrain configuration and energy management strategy of fuel cell city bus.

MiR-29b suppresses the proliferation and migration of osteosarcoma cells by targeting CDK6

Osteosarcoma is the most common primary sarcoma of bone, and it is a leading cause of cancer death among adolescents and young adults. However, the molecular mechanism underlying osteosarcoma carcinogenesis remains poorly understood. Recently, cyclin-dependent kinase 6 （CDK6） was identified as an important onco- gene. We found that CDK6 protein level, rather than CDK6 mRNA level, is much higher in osteosarcoma tissues than in normal adjacent tissues, which indicates a post-transcriptional mechanism involved in CDK6 regulation in osteosarcoma. MiRNAs are small non- coding RNAs that repress gene expression at the post- transcriptional level and have widely been shown to play important roles in many human cancers. In this study, we investigated the role of miR-29b as a novel regulator of CDK6 using bioinformatics methods. We demon- strated that CDK6 can be downregulated by miR-29b via binding to the 3＇-UTR region in osteosarcoma cells. Furthermore, we identified an inverse correlation between miR-29b and CDK6 protein levels in osteosar- coma tissues. Finally, we examined the function of miR- 29b-driven repression of CDK6 expression in osteosarcoma cells. The results revealed that miR-29b acts as a tumor suppressor of osteosarcoma by targeting CDK6 in the proliferation and migration processes. Taken together, our results highlight an important role for miR-29b in the regulation of CDK6 in osteosarcoma and may open new avenues for future osteosarcoma therapies.

Lightweight and robust rGO/sugarcane derived hybrid carbon foams with outstanding EMI shielding performance

Increasingly severe electromagnetic pollution is now in urgent need of materials with lightweight,excellent flame retardancy,and outstanding electromagnetic interference shielding effectiveness(EMI SE).Renewable source-derived carbon foams and graphene have attracted extensive attention due to their 3D porous structure and remarkable electrical conductivity().In this work,annealed sugarcane(ASC)was prepared by removal of lignin from sugarcane via hydrothermal reaction,followed by annealing treatment.Then graphene oxide(GO)was filled by vacuum-assisted impregnation process and thermally annealed to obtain the ASC/reduced graphene oxide(rGO)hybrid foams.When the loading of rGO is 17 wt.%,the ASC/rGO hybrid foam(density,of 0.047 g/cm^3)exhibits the optimal of 6.0 S/cm,EMI SE of 53 dB,specific SE(SSE=SE/)/thickness(t)of 3830 dB·cm^2/g,and compressive strength of 1.33 MPa,which is 76%,36%,13%and 6%higher than those of ASC,respectively.Moreover,ASC/rGO presents excellent flame retardancy,thermal stability,and heat insulation,which remains constant under burning on an alcohol lamp and presents low thermal conductivity of 115.19 mW(m·K),close to the requirement for heat insulation.Synergistic effect of ASC and rGO not only significantly increase of ASC/rGO,but fully utilizes the capability of ASC and rGO to attenuate electromagnetic waves by virtue of unique porous structures and abundant interfaces.Such kind of lightweight EMI materials with excellent mechanical property,shielding performance,flame retardancy,and heat insulation is expected to tackle the key scientific and technical bottleneck problems of EMI materials,and will greatly expand the application of carbon nanomaterials in the field of aerospace industry.

Random copolymer membrane coated PBO fibers with significantly improved interfacial adhesion for PBO fibers/cyanate ester composites

Poly(p-phenylene-2,6-benzobisoxazole)(PBO) fibers possess excellent dielectric, mechanical properties and heat resistance. However, the surface of PBO fibers is smooth and highly chemical inert, resulting in poor interfacial compatibility to polymer matrix, which severely limits its wider application in high-performance fiber-reinforced resin matrix composites. In this work, random copolymers(P(S-co-BCB-co-MMA)) containing benzocyclobutene in the side-chain were synthesized by reversible addition-fragmentation chain transfer(RAFT) polymerization, which were then utilized to form dense random copolymer membrane on the surface of PBO fibers by thermally cross-linking at 250 °C(PBO@P fibers). Four kinds of synthesized P(S-co-BCB-co-MMA) with different number-average molar mass(Mn) were well controlled and possessed narrow dispersity.When the Mnwas 32300, the surface roughness of PBO@P fibers was increased from 11 nm(PBO fibers) to 39 nm. In addition, PBO@P fibers presented the optimal interfacial compatibility with bisphenol A cyanate(BADCy) resins. And the single fiber pull-out strength of PBO@P fibers/BADCy micro-composites was 4.5 MPa, increasing by 45.2% in comparison with that of PBO fibers/BADCy micro-composites(3.1 MPa). Meantime, PBO@P fibers still retained excellent tensile strength(about 5.1 GPa). Overall, this work illustrates a simple and efficient surface functionalization method, which would provide a strong theoretical basis and technical support for controlling the surface structure & chemistry of inert substrates.

Polymer matrix wave-transparent composites:A review

With the rapid development of electronic information technology,antenna systems in the fields of aviation,aerospace,transportation,and 5 G communication services are becoming more and more intensive and accurate.Polymer matrix wave-transparent composites with lightweight,low dielectric constant(∈)and dielectric loss tangent(tanδ),high temperature resistance,and excellent mechanical properties are urgently needed in order to ensure high-fidelity transmission of electromagnetic wave and protect antenna systems from external interference.This review introduces the wave transmission mechanism,key compositions(polymer matrix&reinforced fibers),and several typical testing methods for dielectric properties of polymer matrix wave-transparent composites,mainly elaborates the latest research progress and achievements of polymer matrix wave-transparent composites from polymer matrix,reinforced fibers and their surface functionalization methods,and presents the key scientific and technical problems that need to be solved urgently in the application of polymer matrix wave-transparent composites in the antenna systems.Finally,the future development trends and application prospects of the polymer matrix wave-transparent composites are also proposed.

Intrinsic high thermal conductive liquid crystal epoxy film simultaneously combining with excellent intrinsic self-healing performance

One kind of side chain liquid crystal epoxy(S-LCE) based on biphenyl mesomorphic unit is synthesized from 2,2-bis(hydroxymethyl)propionic acid,4-phenyl phenol,and epichlorohydrin.And the intrinsic thermal conductive liquid crystal epoxy film(LCEF) simultaneously combining with intrinsic self-healing performance is then prepared via thiol-epoxide nucleophilic ring-opening reaction and coating method.1 H NMR and FTIR show that S-LCE and LCEF have been successfully prepared.S-LCE presents nematic liquid crystal from room temperature to 160℃.LCEF maintains nematic liquid crystal performance and shows highly intrinsic thermal conductivity & excellent self-healing performance.Thermal conductivity coefficient(λ)values in vertical direction(λ⊥)and parallel direction(λ‖)of LCEF are 0.33 and 1.25 W/mK,re spectively,much higher than that of general bisphenol A epoxy resin(E-51,λ⊥ of 0.19 W/mK and λ‖ of0.65 W/mK).Tensile strength of LCEF is 10.6 MPa,which can maintain at 90.6 % and 61.3 % after one and four cycles of self-healing behavior,respectively.In addition,LCEF presents a wide service temperature range(-9.8-251℃) and good thermal stability(THRI of 148.5℃).Simultaneously,LCEF has good transparency,flexibility,and tailorability,expected to be utilized in the fields of flexible electronic devices and intelligent structures.

高强度、超疏水聚对苯撑苯并二噁唑纳米透波复合纸

聚对苯撑苯并二噁唑纳米透波复合纸在航空/航天、交通运输和5G通讯等领域具有广阔的应用前景.然而,透波复合纸内的聚对苯撑苯并二噁唑纳米纤维(PNF)间的相互作用力较低,且表面疏水性较差使其难以服役暴雨、冰雪、盐雾等恶劣自然环境.基于此,本文通过引入铁离子在PNF间构建金属配位键,并采用溶胶-凝胶薄膜转化法制备高强度聚对苯撑苯并二噁唑纳米透波复合纸,再将聚四氟乙烯(PTFE)颗粒喷涂到表面,经热处理得到双层结构的PTFE-P/PNF纳米透波复合纸.基于金属配位键的作用以及PTFE颗粒的引入,PTFE-P/PNF纳米透波复合纸具有卓越的拉伸强度(271.6 MPa)、优异的超疏水(与水的接触角为151o)和自清洁性能.此时,PTFE-P/PNF纳米透波复合具有出色的透波性能,当电磁波从透波复合纸两侧入射时,其透波率均>95%.这种兼具高强度、超疏水和自清洁的透波复合纸在雷达天线罩、电磁窗等领域有着巨大的应用潜能.