The friction at the liquid-solid interfaces is widely involved in various phenomena ranging from nanometer to micrometer scales. By the molecular dynamic(MD)simulation, the friction properties of liquid-solid interfac...The friction at the liquid-solid interfaces is widely involved in various phenomena ranging from nanometer to micrometer scales. By the molecular dynamic(MD)simulation, the friction properties of liquid-solid interfaces at the molecular level are calculated via the Green-Kubo relation. It is found that the system size will influence the value of the friction coefficient, especially for the solid surfaces with the larger polar charge. The value of the friction coefficient decreases with the increase in the system size and converges at large system sizes. The large polar charge will lead to a significant friction coefficient. However, the diffusion of water molecules on this surface is almost a constant, indicating that the diffusion coefficient seems to be independent of the system size and polar charge. This work provides insights for the selection of the system size in modeling the frictional properties of hydrophobic/hydrophilic surfaces.展开更多
We theoretically and experimentally show that,with water being adsorbed,the graphene oxide(GO)is converted to a spontaneously dynamic covalent material under ambient conditions,where the dominated epoxy and hydroxyl g...We theoretically and experimentally show that,with water being adsorbed,the graphene oxide(GO)is converted to a spontaneously dynamic covalent material under ambient conditions,where the dominated epoxy and hydroxyl groups are mediated by water molecules to spontaneously break/reform their C–O bonds to achieve dynamic oxygen migration.This dynamic material presents structural adaptivity for response to biomolecule adsorption.Both density functional theory calculations and ab initio molecular dynamics simulations demonstrate that this spontaneously dynamic characteristics is attributed to the adsorption of water molecules,which sharply reduces the barriers of these oxygen migration reactions on GO to the level less than or comparable to the hydrogen bonding energy in liquid water.展开更多
For the inadequate interlaminar strength of 2D carbon/carbon(C/C)composite,in-situ grown carbon nanotubes(CNTs)reinforcing strategy was put forward to strengthen the interlaminar matrix at the nanoscale and inhibit th...For the inadequate interlaminar strength of 2D carbon/carbon(C/C)composite,in-situ grown carbon nanotubes(CNTs)reinforcing strategy was put forward to strengthen the interlaminar matrix at the nanoscale and inhibit the interlaminar cracking.CNT morphology is an essential factor in influencing the enhancement effect.Herein,the influence of in-situ grown CNT morphology on the microstructure and mechanical properties of C/C composite was deeply studied.The radially-aligned straight CNTs could induce the formation of highly-ordered pyrolytic carbon(PyC),while PyC in randomly-distributed curved CNTs concentrated area exhibits an isotropic structure.Further,radially-aligned straight CNTs show better improvement on the flexural and shear strength of C/C composites.According to the fine structural characterization and finite element simulation,the influence mechanism of CNT morphology was revealed.CNT morphology can influence the stress distribution in the PyC protective layer,and compared with radially-aligned straight CNTs,randomly-distributed curved CNTs induce higher tensile stress in the PyC protective layer,which has a detrimental impact on the flexural and shear properties of C/C com-posite.This work provides novel insights into the effect of CNT morphology on the microstructure and mechanical properties of C/C composites,which gives a basis for the structural design and preparation of CNTs reinforced C/C composites.展开更多
Ce2[Zr_(1-x)(Mg_(1/3)Sb_(2/3))_(x)]_(3)(MoO_(4))_(9)(0.02≤x≤0.10)ceramics were prepared by the traditional solid-state method.A single phase,belonging to the space group of R3c,was detected by using X-ray diffractio...Ce2[Zr_(1-x)(Mg_(1/3)Sb_(2/3))_(x)]_(3)(MoO_(4))_(9)(0.02≤x≤0.10)ceramics were prepared by the traditional solid-state method.A single phase,belonging to the space group of R3c,was detected by using X-ray diffraction at the sintering temperatures ranging from 700 to 850℃.The microstructures of samples were examined by applying scanning electron microscopy(SEM).The crystal structure refinement of these samples was investigated in detail by performing the Rietveld refinement method.The intrinsic properties were calculated and explored via far-infrared reflectivity spectroscopy.The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by Phillips-van Vechten-Levine(P-V-L)theory.Ce_(2)[Zr_(0.94)(Mg_(1/3)Sb_(2/3))_(0.06)]_(3)(Mo0_(4))_(9)ceramics with excellent dielectric properties were sintered at 725℃for 6 h(εr=10.37,Q×f=71,748 GHz,andτf=-13.6 ppm/℃,εr is the dielectric constant,τf is the quality factor,and rf is the temperature coefficient of resonant frequency).展开更多
A simple method to increase both strength and toughness of carbon/carbon(C/C) composites is presented.This method is based on the heat treatment of the pre-deposited thin carbon coating, leading to the formation of mo...A simple method to increase both strength and toughness of carbon/carbon(C/C) composites is presented.This method is based on the heat treatment of the pre-deposited thin carbon coating, leading to the formation of more orderly pyrolytic carbon(PyC) as a functional interlayer between fiber and matrix that could optimize the interfacial sliding strength in C/C composites. Effects of such a heat-treated PyC layers on the microstructure, tensile strength and fracture behavior of unidirectional C/C composites were investigated. Results showed that although the in-situ fiber strength was deteriorated after the introduction of interfacial layer, tensile strength of the specimen was greatly improved by 38.5% compared with pure C/C composites without any treatment. The interfacial sliding stress sharply decreased, which was interpreted from finite element analysis and verified by Raman spectra. Therefore, the fracture behavior was changed from brittle fracture to multiple-matrix cracking induced non-linear mechanical behavior.Finally, the ultimate strength can be predicted by different models according to the interfacial sliding stress. Our research would provide a meaningful way to improve both strength and toughness of C/C composites.展开更多
Lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1 D carbon nanotubes(C...Lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1 D carbon nanotubes(CNT)and carbon nanofibers(CNF)with 2 D edge-rich graphene(ERG)are used to form a lightweight,flexible CNT-ERG-CNF hybrid foam.This foam was fabricated through a self-sacrificial templating chemical vapor deposition process,where nanocarbons bond through covalent bonding,forming a hierarchical 3 D hybridized carbon nanostructure.Multistage conductive networks and heterogeneous interfaces were constructed using edge-rich nanocarbons to increase the induced currents and interfacial polarization which makes great contributions to achieve high absorption electromagnetic shielding effectiveness(SEA).The CNT-ERG-CNF hybrid foam exhibits EMI shielding effectiveness(SE)exceeding55.4 dB in the X-band while the specific SE(SSE,SE divided by mass density)achieves 9200 dB cm^(3)g^(-1),which surpasses that of nearly all other carbon-based composite materials.Furthermore,the structural stability and durability of the flexible CNT-ERG-CNF hybrid foams is examined by measuring EMI SE after 10000 times cyclic bending.Remarkably,this work not only provides a new idea for preparing hierarchical carbon materials for a wide range of applications,but presents some fundamental insights for achieving higher absorption losses in EMI shielding materials.展开更多
As modern electronics are developed towards miniaturisation,high-degree integration and intelligentisation,a large amount of heat will be generated during the operation of devices.How to efficiently remove needless he...As modern electronics are developed towards miniaturisation,high-degree integration and intelligentisation,a large amount of heat will be generated during the operation of devices.How to efficiently remove needless heat is becoming more and more crucial for the lifetime and performance of electronic devices.Many efforts have been made to improve the thermal conductivity of polymer composites,which is an important component of electronics.Herein,the authors report on preparation of boron nitride micosphere/epoxy composites.The cross-plane thermal conductivity of the resultant composites is up to 1.03 Wm‒1K‒1.This is attributed to the thermally conductive network formed by the peeled hexagonal boron nitride flakes.Thanks to the superior thermal stability of boron nitride micosphere,the boron nitride micosphere/epoxy composite shows a decreased coefficient of thermal expansion(53.47 ppm/K)and an increased glass transition temperature(147.2℃)compared with the pure epoxy resin.In addition,the boron nitride micosphere/epoxy composite exhibits a lower dielectric constant compared with that of the hexagonal boron nitride/epoxy composite.This strategy can potentially pave the way for the design and fabrication of materials with high cross-plane thermal conductivity and lower dielectric properties.展开更多
基金the National Natural Science Foundation of China(Nos.11605151,11675138,and 11422542)the Special Program for Applied Research on Super Computation of the NSFCGuangdong Joint Fund(the second phase)。
文摘The friction at the liquid-solid interfaces is widely involved in various phenomena ranging from nanometer to micrometer scales. By the molecular dynamic(MD)simulation, the friction properties of liquid-solid interfaces at the molecular level are calculated via the Green-Kubo relation. It is found that the system size will influence the value of the friction coefficient, especially for the solid surfaces with the larger polar charge. The value of the friction coefficient decreases with the increase in the system size and converges at large system sizes. The large polar charge will lead to a significant friction coefficient. However, the diffusion of water molecules on this surface is almost a constant, indicating that the diffusion coefficient seems to be independent of the system size and polar charge. This work provides insights for the selection of the system size in modeling the frictional properties of hydrophobic/hydrophilic surfaces.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11675138,11705160,11605151,U1832150,U1932123 and 11974366)the National Science Fund for Outstanding Young Scholars(Grant No.11722548)+4 种基金the Key Research Program of Chinese Academy of Sciences(Grant No.QYZDJ-SSW-SLH053)the Fundamental Research Funds for the Central Universitiesthe Special Program for Applied Research on Supercomputation of the NSFC-Guangdong Joint Fund(the second stage)Supercomputer Center of CASthe BL01B Beamline of NFPS at SSRF。
文摘We theoretically and experimentally show that,with water being adsorbed,the graphene oxide(GO)is converted to a spontaneously dynamic covalent material under ambient conditions,where the dominated epoxy and hydroxyl groups are mediated by water molecules to spontaneously break/reform their C–O bonds to achieve dynamic oxygen migration.This dynamic material presents structural adaptivity for response to biomolecule adsorption.Both density functional theory calculations and ab initio molecular dynamics simulations demonstrate that this spontaneously dynamic characteristics is attributed to the adsorption of water molecules,which sharply reduces the barriers of these oxygen migration reactions on GO to the level less than or comparable to the hydrogen bonding energy in liquid water.
基金supported by National Natural Science Foundation of China(52293371,52222204,52202047,52172103,52072304)Natural Science Basic Research Plan in Shaanxi(2022JC-25,2022JQ-324)+4 种基金the Key R&D Program of Shaanxi Provence(2019ZDLGY04-02)China Postdoctoral Science Foundation(2021M702659)Young Talent Fund of Association for Science and Technology in Shaanxi,China(20220435)State Key Laboratory of Advanced Technology for Materials Synthesis and Processing(Wuhan University of Technology)(2023-KF-25)Project supported by the Research Fund of the State Key Laboratory of Solidification Processing(NPU),China(2023-BJ-03).
文摘For the inadequate interlaminar strength of 2D carbon/carbon(C/C)composite,in-situ grown carbon nanotubes(CNTs)reinforcing strategy was put forward to strengthen the interlaminar matrix at the nanoscale and inhibit the interlaminar cracking.CNT morphology is an essential factor in influencing the enhancement effect.Herein,the influence of in-situ grown CNT morphology on the microstructure and mechanical properties of C/C composite was deeply studied.The radially-aligned straight CNTs could induce the formation of highly-ordered pyrolytic carbon(PyC),while PyC in randomly-distributed curved CNTs concentrated area exhibits an isotropic structure.Further,radially-aligned straight CNTs show better improvement on the flexural and shear strength of C/C composites.According to the fine structural characterization and finite element simulation,the influence mechanism of CNT morphology was revealed.CNT morphology can influence the stress distribution in the PyC protective layer,and compared with radially-aligned straight CNTs,randomly-distributed curved CNTs induce higher tensile stress in the PyC protective layer,which has a detrimental impact on the flexural and shear properties of C/C com-posite.This work provides novel insights into the effect of CNT morphology on the microstructure and mechanical properties of C/C composites,which gives a basis for the structural design and preparation of CNTs reinforced C/C composites.
基金supported by the National Natural Science Foundation(No.51972143).
文摘Ce2[Zr_(1-x)(Mg_(1/3)Sb_(2/3))_(x)]_(3)(MoO_(4))_(9)(0.02≤x≤0.10)ceramics were prepared by the traditional solid-state method.A single phase,belonging to the space group of R3c,was detected by using X-ray diffraction at the sintering temperatures ranging from 700 to 850℃.The microstructures of samples were examined by applying scanning electron microscopy(SEM).The crystal structure refinement of these samples was investigated in detail by performing the Rietveld refinement method.The intrinsic properties were calculated and explored via far-infrared reflectivity spectroscopy.The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by Phillips-van Vechten-Levine(P-V-L)theory.Ce_(2)[Zr_(0.94)(Mg_(1/3)Sb_(2/3))_(0.06)]_(3)(Mo0_(4))_(9)ceramics with excellent dielectric properties were sintered at 725℃for 6 h(εr=10.37,Q×f=71,748 GHz,andτf=-13.6 ppm/℃,εr is the dielectric constant,τf is the quality factor,and rf is the temperature coefficient of resonant frequency).
基金supported by the National Natural Science Foundation of China (U1435202, 51432008, 51502242)the "111" Project (Grant No. B08040)the Research Fund of State Key Laboratory of Solidification Processing (NWPU), China (Grant No. 142-TZ-2016)
文摘A simple method to increase both strength and toughness of carbon/carbon(C/C) composites is presented.This method is based on the heat treatment of the pre-deposited thin carbon coating, leading to the formation of more orderly pyrolytic carbon(PyC) as a functional interlayer between fiber and matrix that could optimize the interfacial sliding strength in C/C composites. Effects of such a heat-treated PyC layers on the microstructure, tensile strength and fracture behavior of unidirectional C/C composites were investigated. Results showed that although the in-situ fiber strength was deteriorated after the introduction of interfacial layer, tensile strength of the specimen was greatly improved by 38.5% compared with pure C/C composites without any treatment. The interfacial sliding stress sharply decreased, which was interpreted from finite element analysis and verified by Raman spectra. Therefore, the fracture behavior was changed from brittle fracture to multiple-matrix cracking induced non-linear mechanical behavior.Finally, the ultimate strength can be predicted by different models according to the interfacial sliding stress. Our research would provide a meaningful way to improve both strength and toughness of C/C composites.
基金financial supports of this work by National Natural Science Foundation of China(51821091,51872234)Natural Science Basic Research Plan in Shaanxi(No.2020JQ-154)。
文摘Lightweight,flexible,ultrahigh-performance electromagnetic-interfe rence(EMI)shielding materials are urgently required in the areas of aircraft/aerospace,portable and wearable electronics.Herein,1 D carbon nanotubes(CNT)and carbon nanofibers(CNF)with 2 D edge-rich graphene(ERG)are used to form a lightweight,flexible CNT-ERG-CNF hybrid foam.This foam was fabricated through a self-sacrificial templating chemical vapor deposition process,where nanocarbons bond through covalent bonding,forming a hierarchical 3 D hybridized carbon nanostructure.Multistage conductive networks and heterogeneous interfaces were constructed using edge-rich nanocarbons to increase the induced currents and interfacial polarization which makes great contributions to achieve high absorption electromagnetic shielding effectiveness(SEA).The CNT-ERG-CNF hybrid foam exhibits EMI shielding effectiveness(SE)exceeding55.4 dB in the X-band while the specific SE(SSE,SE divided by mass density)achieves 9200 dB cm^(3)g^(-1),which surpasses that of nearly all other carbon-based composite materials.Furthermore,the structural stability and durability of the flexible CNT-ERG-CNF hybrid foams is examined by measuring EMI SE after 10000 times cyclic bending.Remarkably,this work not only provides a new idea for preparing hierarchical carbon materials for a wide range of applications,but presents some fundamental insights for achieving higher absorption losses in EMI shielding materials.
基金The authors acknowledge the financial support from National Natural Science Foundation of China(no.51603226)the National Key R&D Project from Minister of Science and Technology of China(2016YFA0202702)Shenzhen Fundamental Research Program(JCYJ20150831154213681).
文摘As modern electronics are developed towards miniaturisation,high-degree integration and intelligentisation,a large amount of heat will be generated during the operation of devices.How to efficiently remove needless heat is becoming more and more crucial for the lifetime and performance of electronic devices.Many efforts have been made to improve the thermal conductivity of polymer composites,which is an important component of electronics.Herein,the authors report on preparation of boron nitride micosphere/epoxy composites.The cross-plane thermal conductivity of the resultant composites is up to 1.03 Wm‒1K‒1.This is attributed to the thermally conductive network formed by the peeled hexagonal boron nitride flakes.Thanks to the superior thermal stability of boron nitride micosphere,the boron nitride micosphere/epoxy composite shows a decreased coefficient of thermal expansion(53.47 ppm/K)and an increased glass transition temperature(147.2℃)compared with the pure epoxy resin.In addition,the boron nitride micosphere/epoxy composite exhibits a lower dielectric constant compared with that of the hexagonal boron nitride/epoxy composite.This strategy can potentially pave the way for the design and fabrication of materials with high cross-plane thermal conductivity and lower dielectric properties.
