Construction of all-organic low dielectric polyimide hybrids via synergistic effect between covalent organic framework and cross-linking structure

Polyimide(PI)is a promising electronic packaging material,but it remains challenging to obtain an all-organic PI hybrid film with decreased dielectric constant and loss without modifying the monomer.Herein,a series of allorganic PI hybrid films were successfully prepared by introducing the covalent organic framework(COF),which could induce the formation of the cross-linking structure in the PI matrix.Due to the synergistic effects of the COF fillers and the cross-linking structure,the PI/COF hybrid film containing 2 wt%COF exhibited the lowest dielectric constant of 2.72 and the lowest dielectric loss(tanδ)of 0.0077 at 1 MHz.It is attributed to the intrinsic low dielectric constant of COF and a large number of mesopores within the PI.Besides,the cross-linking network of PI prevents the molecular chains from stacking and improves the fraction of free volume(FFV).The molecular dynamics simulation results are well consistent with the dielectric properties data.Furthermore,the PI/COF hybrid film with 5 wt%COF showed a significant enhancement in breakdown strength,which increased to 412.8 kV/mm as compared with pure PI.In addition,the PI/COF hybrid film achieve to reduce the dielectric constant and thermal expansion coefficient(CTE).It also exhibited excellent thermal,hydrophobicity,and mechanical performance.The all-organic PI/COF hybrid films have great commercial potential as next-generation electronic packaging materials.

Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature. Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method. Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes. In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time. And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test. As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking. From the results of the 1H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution. Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.

Preparation of Controllable Cross-Linking Polyethylene Foaming Materials and Their Properties

In order to prepare the polyethylene materials with controlling properties,we developed two kinds of controllable cross-linking polyethylene foaming system.2,5-dimethyl-2,5-bis (tert-butyl peroxy) hexane was used as cross-linking agent and TEMPO as cross-linking inhibitor,azodicarbonamide (AC) was used as foaming agent and citric acid as foaming promoter.The density,expansion ratio,cellular structure and mechanical property of these two kinds of controllable materials were studied.Experimental results show that,properties of these two kinds of materials appear similar trend:cellular size and expansion ratio are enlarged with the amount of cross-linking inhibitor or foaming promoter increasing,while density and mechanical strength appear decreasing trend.Through comparing those two material systems’ properties,cross-linking polyethelene foaming system with citric acid as foaming promoter has better properties.

Cross-Linked Hollow Graphitic Carbon as Low-Cost and High-Performance Anode for Potassium Ion Batteries

Large-scale and low-cost preparation of carbon-based potassium anode with long life and high capacity is one of the footstones for the development of potassium ion batteries(PIBs).Herein,a low-cost carbon-based material,cross-linked hollow graphitic carbon(HGC),is large scale synthesized to apply for PIBs anode.Its hollow structure can afford sufficient space to overcome the damage caused by the volume expansion of graphitic carbon(GC).While the cross-linked structure forms a compact interconnection network that allows electrons to rapid transfer between different GC frameworks.Electrochemical measurements demonstrated that the HGC anode exhibited low charge/discharge plateau(about 0.25 V and 0.1 V)and excellent specific capacity as high as 298 m A h g^(-1)at the current density of 50 m A g^(-1).And more important,after 200 cycles the capacity of HGC anode still shows 269 m A h g^(-1)(the decay rate of per cycle is only 0.048%).Meanwhile,the use of commercial traditional electrolyte(KPF_(6))and cheap raw materials that provide new hope for trying and realizing the large-scale production of PIBs based on carbon anode materials.

Preparation and characterization of genipin-cross-linked chitosan microparticles by water-in-oil emulsion solvent diffusion method

Chitosan (CS) microparticles with and without cross-linking were prepared by a water-in-oil emulsion solvent diffusion method without any surfactants. Aqueous CS solution and ethyl ace- tate were used as water and oil phases, respectively. Genipin was used as a cross-linker. Influ- ences of genipin ratios and cross-linking times on CS microparticle characteristics were investigated. Non-cross-linked and cross-linked CS microparticles were spherical in shape and rough in surface. Microparticle matrices showed porous structures. Surface roughness, mean par- ticle sizes and bulk density of CS microparticles increased and their dissolutions in acetic acid solution decreased when genipin ratio and cross- linking time increased.

Deciphering In-vivo Cross-linking Mass Spectrometry Data for Dynamic Protein Structure Analysis

Protein structure and protein-protein interactions(PPIs)are crucial for regulating cellular activities required for cell viability and homeostasis.Chemical cross-linking coupled with mass spectrometry(CXMS)has become a versatile tool providing insights into both protein structure with distance restraints and protein-protein interactions with interface sites.Cross-links as the most information-rich data in a CXMS experiment are responsible for the structural model validation and integrative modeling with high throughput and sensitivity.In this work,ensemble refinement of the existing protein structure against the in-vivo cross-linking distance restraints was performed for dynamic protein structure modeling and protein interaction binding interface building in the intracellular environment.These results indicate great potential of in-vivo CXMS data for providing a molecular basis of protein structural dynamics exploration and function performance.

The Influence of Pore Structures and Degree of Cross-Linking on Catalytic Properties of Aminomethyl Polystyrene Resin Supported Dendritic Copper Complexes

1 Introduction Immobilization of homogeneous catalysts onto polymer supports through covalent attachment has received wide attention because these materials offer advantage features of heterogeneous catalysis to homogeneous systems.The polymer-supported catalysts enhance their thermal stability,selectivity,recyclability and easy separation from reaction products leading to the operationally flexible[1-2].Such behaviour prompted us to know the effect of pore structures of polymer supporters on catalytic ...

Preparation and characterization of cross-linked β-cyclodextrin polymer/Fe_3O_4 composite nanoparticles with core-shell structures

Cross-linkedβ-cyclodextrin polymer/Fe3O4 composite nanoparticles with core-shell structures were prepared via cross linking reaction on the surface of carboxymethylβ-cyclodextrin（CM-β-CD） modified Fe3O4 nanoparticles inβ-cyclodextrin alkaline solution by using epichlorohydrin as crosslinking agent.The morphology,structure and magnetic properties of the prepared composite nanoparticles were investigated by transmission electron microscopy（TEM）,Fourier transform infrared（FTIR） spectrometry,X-ray diffraction（XRD） measurement,thermogravimetric analysis（TGA） and Vibrating sample magnetometry （VSM）,respectively.

聚丙烯酸镁/丙烯酸钠双交联水凝胶的制备及性能研究

以丙烯酸镁(MgA)和丙烯酸钠(SA)为单体、N,N'-亚甲基双丙烯酰胺(MBA)为共价交联剂,通过溶液聚合方法制备了系列聚丙烯酸镁/丙烯酸钠(PAMgA/x-PASA)双交联水凝胶,并测试分析了共聚水凝胶材料的结构、吸水特性和力学性能。结果表明,MBA作用下丙烯酸镁和丙烯酸钠形成了双交联结构的共聚水凝胶,显著提高了丙烯酸盐水凝胶的吸水溶胀比、保水性和重复吸水能力。当SA质量分数为20%时,水凝胶的吸水溶胀比达550%,较单一离子交联的聚丙烯酸镁提高近4倍;12 h干燥后的保水率约60%;而多次干燥-吸水溶胀以后,水凝胶的吸水溶胀比仍高达300%。此外,丙烯酸钠和MBA的加入对水凝胶的拉伸强度影响不大,但显著提高了材料的断裂伸长率,可从395%提高到690%。

ABS回料/SB/DMMT复合材料的结构与性能

制备了苯乙烯-丁二烯塑料(SB)/双改性蒙脱土(DMMT)杂化物,并以其增韧增强丙烯腈-丁二烯-苯乙烯塑料(ABS)回料,研究了ABS回料/SB/DMMT复合材料的结构与性能。结果表明,随着SB/DMMT(70/30)杂化物用量的增加,复合材料的缺口冲击强度、拉伸强度和弯曲强度呈先增加后降低的趋势,在杂化物用量为10份时达到最大值,其力学性能和热稳定性明显高于ABS回料。透射电子显微镜和X射线衍射仪的测试结果显示,ABS回料/SB/DMMT复合材料属于插层结构与剥离结构共存的纳米复合材料。

Highly integrated sulfur cathodes with strong sulfur/high-strength binder interactions enabling durable high-loading lithium-sulfur batteries

The development of high-sulfur-loading Li-S batteries is a key prerequisite for their commercial applications.This requires to surmount the huge polarization,severe polysulfide shuttling and drastic volume change caused by electrode thickening.High-strength polar binders are ideal for constructing robust and long-life high-loading sulfur cathodes but show very weak interfacial interaction with non-polar sulfur materials.To address this issue,this work devises a highly integrated sulfur@polydopamine/highstrength binder composite cathodes,targeting long-lasting and high-sulfur-loading Li-S batteries.The super-adhesion polydopamine(PD)can form a uniform nano-coating over the graphene/sulfur(G-S)surface and provide strong affinity to the cross-linked polyacrylamide(c-PAM)binder,thus tightly integrating sulfur with the binder network and greatly boosting the overall mechanical strength/conductivity of the electrode.Moreover,the PD coating and c-PAM binder rich in polar groups can form two effective blockades against the effusion of soluble polysulfides.As such,the 4.5 mg cm−2 sulfur-loaded G-S@PD-c-PAM cathode achieves a capacity of 480 mAh g−1 after 300 cycles at 1 C,while maintaining a capacity of 396 mAh g−1 after 50 cycles at 0.2 C when the sulfur loading rises to 9.1 mg cm−2.This work provides a system-wide concept for constructing high-loading sulfur cathodes through integrated structural design.

Semi-interpenetrating network anion exchange membranes based on quaternized polyvinyl alcohol/poly(diallyldimethylammonium chloride)

The semi-interpenetrating network anion exchange membranes(AEMs)based on quaternized polyvinyl alcohol(QPVA)and poly(-diallyldimethylammonium chloride)(PDDA)are synthesized.The chemical cross-linking structure is formed between hydroxyl groups of QPVA and aldehyde groups of glutaraldehyde(GA),which makes PDDA more stable embed in the QPVA matrix and also improves the mechanical properties and dimensional stability of AEMs.Due to the phase separation phenomenon of AEMs swelling in water,a microporous structure may be formed in the membrane,which reduces the transmission resistance of hydroxide ions and provides a larger space for the transfer of hydroxide ions,thus improving the conductivity.The ring structure of PDDA is introduced as a cationic group to transfer hydroxide ions,and shields the nucleophilic attack of the hydroxide ions through the steric hindrance effect,which improves alkaline stability.The hydroxide conductivity of semi-interpenetrating network membrane(QPVA/PDDA0.5-GA)is 36.5 mS cm^(-1) at 60℃.And the membrane of QPVA/PDDA0.5-GA exhibits excellent mechanical property with maximum tensile strength of 19.6 MPa.After immersing into hot 3 mol L^(-1) NaOH solutions at 60℃ for 300 h,the OHconductivity remains 78%of its initial value.The semi-interpenetrating network AEMs with microporous structure exhibit good ionic conductivity,mechanical strength and alkaline durability.

Ultra-thick,dense dual-encapsulated Sb anode architecture with conductively elastic networks promises potassium-ion batteries with high areal and volumetric capacities

Ultra-thick,dense alloy-type anodes are promising for achieving large areal and volumetric performance in potassium-ion batteries(PIBs),but severe volume expansion as well as sluggish ion and electron diffusion kinetics heavily impede their widespread application.Herein,we design highly dense(3.1 g cm^(-3))Ti_(3)C_(2)T_(x) MXene and graphene dual-encapsulated nano-Sb monolith architectures(HD-Sb@Ti_(3)C_(2)T_(x)-G)with high-conductivity elastic networks(1560 S m^(-1))and compact dually encapsulated structures,which exhibit a large volumetric capacity of 1780.2 mAh cm^(-3)(gravimetric capacity:565.0 mAh g^(-1)),a long-term stable lifespan of 500 cycles with 82%retention,and a large areal capacity of 8.6 mAh cm^(-2)(loading:31 mg cm^(-2))in PIBs.Using ex-situ SEM,in-situ TEM,kinetic investigations,and theoretical calculations,we reveal that the excellent areal and volumetric performance mechanism stems from the three dimensional(3D)high-conductivity elastic networks and the dualencapsulated Sb architecture of Ti_(3)C_(2)T_(x) and graphene;these effectively mitigate against volume expansion and the pulverization of Sb,offering good electrolyte penetration and rapid ionic/electronic transmission.Ti_(3)C_(2)T_(x) also decreases the Kþdiffusion energy barrier,and the ultra-thick compact electrode ensures volumetric and areal performance.These findings provide a feasible strategy for fabricating ultra-thick,dense alloy-type electrodes to achieve high areal and volumetric capacity energy storage via highly-dense,dual-encapsulated architectures with conductive elastic networks.

竞争与规划双线驱动:我国西部高校博士学位点结构布局的优化策略

优化学位点布局是对教育公平性问题的回应,是强化西部地区人才自我供给支撑新时代西部大开发的重要途径。多维度分析表明:我国博士点布局区域失衡问题严重,西部地区供需矛盾突出,制约了高层次创新人才自我供给能力的提升。以"质量优先"为导向的竞争型审核机制在调节博士点结构布局方面具有一定的局限性,以此提出以"质量与结构并重"为导向的"竞争+规划"双线驱动的博士点审核机制优化策略,从宏观、中观和微观层面针对性地调节博士点布局失衡问题,为西部地区高校博士点"补短板"提供解决路径。