A mesoscale study of thermal expansion behaviors of epoxy resin and carbon fiber/epoxy unidirectional composites based on periodic temperature and displacement boundary conditions

The thermal expansion behaviors of neat epoxy resin and carbon fiber/epoxy unidirectional (UD) composites were experimentally and numerically studied in this paper. The dynamic mechanical analysis (DMA), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and thermal conductivity measurement were used to measure the thermo-mechanical properties of epoxy resin at different temperatures. The dilatometer was used to measure the thermal strains and linear CTEs of neat epoxy resin and UD composites. In addition, a mesoscale finite element model based on the periodic temperature and displacement boundary conditions was presented to analyze the thermal expansion behaviors of UD composites. The resin-voids representative volume element (RVE) was used to calculate the thermo-mechanical properties of several kinds of resin-voids mixed matrix. From the results it can be found that the glass transition temperature of epoxy resin, porosity and fiber orientation angle have significant effects on the thermal expansion behaviors of UD composites. The mesoscale finite element analyses (FEA) have obvious advantages than various existing analysis models by comparing their predictive results. The distributions of thermal displacement, thermal stress and thermal strain were extracted between the carbon fiber, resin-voids mixed matrix and their interface, and also between the front and back surfaces of the loading direction, to further investigate thermal expansion structure effects of UD composites. This paper revealed that the mesoscale FEA based on periodic temperature and displacement boundary conditions can be also used for thermal expansion researches of other complex structure composites.     

Achieving full effective microwave absorption in X band by double-layered design of glass fiber epoxy composites containing MWCNTs and Fe3O4 NPs

The glass fiber epoxy composites containing MWCNTs and Fe₃O₄ NPs were manufactured by composites liquid molding process. The microwave absorbing properties of single-layered and double-layered glass fiber/MWCNTs/epoxy and glass fiber/Fe₃O₄ NPs/epoxy composites were evaluated. The reflection loss(RL) were calculated by the measured complex permittivity and permeability using waveguide method by vector network analyzer. Based on the mechanism analysis and deficiency of single-layer absorber, the double-layered composites were fabricated by using matching layer and absorbing layer to enhance the microwave absorption performance, which can be modulated by tailoring the electromagnetic parameters and thicknesses of each layer. The optimized microwave absorbing properties of double-layered composites with minimum RL of −45.7 dB and full X-band effective absorption can be achieved when the total thickness of the matching layer and absorbing layer is 1.8 mm, which can be attributed to synergistic effect of improved impedance matching characteristic and superior microwave attenuation characteristic of the absorbing layer. The combined utilization of dielectric loss and magnetic loss absorbent and their double-layered structure design shows great design flexibility and diversity and can be a promising candidate for designing high performance microwave absorbing materials.     

Mesoscale modeling of electrical percolation in fiber-filled systems

The research described in this paper primarily involves mesoscale simulations: dissipative particle dynamics (DPD) of packed assemblies of oriented fibers suspended in a viscous medium. Computer simulations have been performed in order to explore how the aspect ratio and degree of fiber alignment affect the critical volume fraction (percolation threshold) required to achieve electrical conductivity. The fiber network impedance was assessed using Monte Carlo simulations after establishing the structural arrangement with DPD. The predictions are compared with the predictions of classical percolation theory and found to be in close agreement. The approach is thus validated and can be extended to systems that cannot be tackled analytically; in particular, the work is motivated by long-standing interest in materials which display a complex percolation behavior.     

Grazing-incidence scattering—status and perspectives in soft matter and biophysics

Investigating lateral structures of surfaces and interfaces from the mesoscale down to atomic resolution is of growing interest to modify, functionalize, and understand the behavior of materials in soft matter and biophysics. Grazing-incidence scattering techniques have proven to be very powerful for such kind of studies. Using X-rays and neutrons also buried lateral structures can be accessed in a non-destructive way. The large probed sample area provides a high statistical relevance of the determined structure information, and complex sample environments in combination with in situ and in operando experiments provide the full potential for gaining deep insights in structure formation processes. In the brief review, we reflect on the current state of the art of grazing-incidence scattering techniques using X-rays and neutrons, fields of interest, and applications in soft matter and biophysics, resulting in challenges and providing a short outlook. Owing to the already available literature on X-ray–based techniques, we will set a slight emphasis on neutron-based techniques.     

石墨烯纤维材料的化学气相沉积生长方法

石墨烯纤维材料是以石墨烯为主要结构基元沿某一特定方向组装而成或由石墨烯包覆纤维状基元形成的宏观一维材料。根据组成基元的不同可将石墨烯纤维材料分为石墨烯纤维和石墨烯包覆复合纤维。石墨烯纤维材料在一维方向上充分发挥了石墨烯高强度、高导电、高导热等特点,在智能纤维与织物、柔性储能器件、便携式电子器件等领域具有广阔的应用前景。随着化学气相沉积(Chemical Vapor Deposition,CVD)制备石墨烯薄膜技术的发展,CVD技术也逐渐应用于石墨烯纤维材料的制备。利用CVD法制备石墨烯纤维可避免传统纺丝工艺中繁琐的氧化石墨烯(Graphene Oxide,GO)还原过程。同时,通过CVD法直接将石墨烯沉积至纤维表面可以保证石墨烯与纤维基底之间强的粘附作用,提高复合纤维的稳定性,同时可实现对石墨烯质量的有效调控。本文综述了石墨烯纤维材料的CVD制备方法,石墨烯纤维材料优异的力学、电学、光学性质及其在智能传感、光电器件、柔性电极等领域的应用,并展望了CVD法制备石墨烯纤维材料未来的发展方向。     

Molecular Motions in Polymer Matrix for Microenvironment Sensing

Polymer science entails the structural study at multi-levels from nano-to micro-and mesoscale,which is highly important to transfer or even amplify the molecular information to macroscopic materials.Multiple polymer structural transitions from lower-order to higher-order superstructures are normally involved to achieve selective,efficient and sophisticated functions.Therefore,in-situ visualization of these processes is highly important,not only for fundamental understanding the structural evolution,but also for the optimization of the process flow during the materials processing.Fluorescence imaging based on aggregation-induced emission(AIE)provides an ideal tool that offers a simple,accurate,and easy-readable method to fulfill the above requirements.Owing to the twisted propeller-like structure of AIE luminogens(AIEgens),they show high fluorescence sensitivity to the surrounding microenvironment(e.g.,viscosity,rigidity,and polarity)through intramolecular motions.In this short review,we summarize the recent applications of AIEgens to serve as“built-in”sensors to analyze the process of polymerization,microphase separation,glass/vitrification transition,polymer solvation,crystallization,etc.The perspective on the future application of AIE technology in polymer engineering,especially fiber materials,is also discussed.     

线性脂环族聚酰胺化学结构对其力学和光学性能的影响

以重复单元结构不同的3种线性脂环族聚酰胺(LATPA)材料为研究对象,通过核磁共振谱、红外光谱、热分析、X射线衍射等技术,研究了链结构单元的侧基、端基对材料聚集态结构的影响,并对比研究了不同聚集态结构材料的宏观力学性能和光学透明性差异,建立了链结构、聚集态结构与力学性能、光学性能的关系.研究发现,侧基带来的大空间位阻降...     

A polar corundum oxide displaying weak ferromagnetism at room temperature

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO(3) (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO(3) has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO(3).     

Higher-order organization by mesoscale self-assembly and transformation of hybrid nanostructures

The organization of nanostructures across extended length scales is a key challenge in the design of integrated materials with advanced functions. Current approaches tend to be based on physical methods, such as patterning, rather than the spontaneous chemical assembly and transformation of building blocks across multiple length scales. It should be possible to develop a chemistry of organized matter based on emergent processes in which time- and scale-dependent coupling of interactive components generate higher-order architectures with embedded structure. Herein we highlight how the interplay between aggregation and crystallization can give rise to mesoscale self-assembly and cooperative transformation and reorganization of hybrid inorganic-organic building blocks to produce single-crystal mosaics, nanoparticle arrays, and emergent nanostructures with complex form and hierarchy. We propose that similar mesoscale processes are also relevant to models of matrix-mediated nucleation in biomineralization.     

Stabilization of TiO<Subscript>2</Subscript>–Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films on a glass fiber material by introduction of silica into the matrix

The TiO₂–Co₃O₄–SiO₂ oxide system supported on glass fiber was synthesized and studied. The oxide layers attached to the glass fiber surface have a porous structure. Characteristics of thin-film coatings on the glass fiber substrate (oxide layer phase composition and adhesion to the glass fiber surface) depend on the silica concentration. The obtained materials are catalytically active towards the exhaustive oxidation of propane.     

Tuning the architecture of mesostructures by electrodeposition

When the dimension of materials decreases to mesoscale, their properties can change dramatically, depending on the boundary conditions imposed by the sample architecture including geometry, morphology, and hierarchical structures. Here we show that electrodeposition, a method for reducing materials from a solution onto a substrate, can provide a versatile pathway to tailor the architecture of mesostructures. Novel lead (Pb) structures ranging from nanowires, mesoparticles with octahedral, decahedral, and icosahedral shapes to porous nanowires, multipods, nanobrushes, and even snowflake-shaped structures were synthesized through systematically exploring electrodeposition parameters including reduction potentials, solution concentration, starting materials, supporting electrolytes, and surfactants.     

利用二氧化钛静电纺丝和透明质酸甲基丙烯酸酯构筑用于细胞培养的纤维凝胶结构

通过观察生物体内骨的电镜图片,发现骨表面具有丰富的纤维微纳结构,在此观测的启发下,本实验设计将二氧化钛表面生物活性化的同时构筑这种纤维微纳结构,模仿骨表面。考虑到二氧化钛具有光催化性,且具有生物无毒性,本实验采用"自上而下"的一步法,在紫外光照的条件下,将二氧化钛静电纺丝与透明质酸衍生物在光照条件下通过双键稳定地连接起来。傅立叶-红外光谱分析表明实验成功地在二氧化钛静电纺丝表面嫁接上透明质酸分子。通过荧光和扫描电镜分析表明,间充质干细胞可以很好地在二氧化钛静电纺丝和透明质酸的复合结构上生长。这种构筑复合结构表面的方法,生物活化了二氧化钛纺丝的表面,同时模仿骨表面获得了微纳纤维拓扑结构。此外,可以将二氧化钛静电纺丝纺在不同种类的材料表面,从而在不同材料表面简便地得到可用于细胞培养的纤维表面结构,对于未来可实际应用的移植材料研发具有很好的借鉴意义。     

典型高分子纤维发展回顾与未来展望

高分子纤维作为发展国民经济的基础材料、国防军工的战略材料、新兴产业的前沿材料,其产品内涵与应用领域正在不断拓展.本文首先简要介绍了国内外高分子纤维材料的发展简史,其依次经历了天然纤维、人造纤维、合成纤维(差别化、功能化、高性能等纤维)等发展阶段.其次,结合本课题组相关工作重点阐述了通用型聚酯纤维、高性能聚苯硫醚纤维以及生物质聚乳酸纤维等典型高分子纤维材料的研究进展,包括发展历程、制备方法、性能优化、应用领域等内容.最后,展望了高分子纤维材料的发展趋势,我们认为基于材料、信息、生物、机械等学科交叉融合与技术突破,具有多材料、多结构、多功能的绿色、超性能、智能纤维材料将成为未来发展方向.     

偶联剂对玻璃纤维/环氧树脂基复合材料介电性能的影响

偶联剂对玻璃纤维／环氧树脂基复合材料介电性能的影响陈平刘胜平张明艳（哈尔滨理工大学电工材料系哈尔滨１５００４０）关键词环氧树脂基复合材料，介电性能，偶联剂，浸润性玻璃纤维／环氧树脂基复合材料（ＧＦＲＰ）具有优异的电气和力学性能．然而孔隙的存在强烈地...     

Fabrication of anisotropic porous silica monoliths by means of magnetically controlled phase separation in sol-gel processes

Sol-gel accompanied by phase separation is an established method for the preparation of porous silica monoliths with well-defined macroporosity, which find numerous applications. In this work, we demonstrate how the addition of (superpara)magnetic nanocolloids as templates to a system undergoing a sol-gel transition with phase separation leads to the creation of monoliths with a strongly anisotropic structure. It is known that magnetic nanocolloids respond to the application of an external magnetic field by self-assembling into columnar structures. The application of a magnetic field during the chemically driven spinodal decomposition induced by the sol-gel transition allows one to break the symmetry of the system and promote the growth of elongated needle-like silica domains incorporating the magnetic nanocolloids, aligned in the direction of the field. It is found that this microstructure imparts a strong mechanical anisotropy to the materials, with a ratio between the Young's modulus values measured in a direction parallel and perpendicular to the one of the field as high as 150, and an overall smaller average macropores size as compared to isotropic monoliths. The microstructure and properties of the porous monoliths can be controlled by changing both the system composition and the strength of the applied magnetic field. Our monoliths represent the first example of materials prepared by magnetically controlling a phase transition occurring via spinodal decomposition.     

高分子金属络合物的性能及应用进展

介绍了高分子金属络合物的种类及合成。综述了高分子金属络合物不同于低分子络合物的催化性能、电学性能、光学性能和磁性 ,以及高分子金属络合物作为催化剂、光学材料、电学材料等方面的应用进展。     

Imitational modeling of residual stresses in materials employed for the repair of structural steels

Results of the calculations of residual stresses of composites based on polymer binder and glass fiber, which are used in the repair of metal structures of machines, by imitational modeling have been considered. Imitational modeling has been carried out using a special program that enables one to calculate required parameters with a very high rate after choosing initial data from preformed number sets. It has been determined that the modulus of glass plastics has the most sizeable effect on residual stresses.     

Disorder engineering in transition metal dichalcogenides toward efficient high current density reduction electrocatalysts

In this perspective, we highlight the importance of nanoscale disorder and mesoscale morphology to enhance the activity and tune the selectivity of group VI transition metal dichalcogenide electrocatalysts toward two paramount reductions reactions as H₂ evolution reaction and CO₂ reduction. The strategy we propose takes advantage of the metastable nanoscale atomic arrangement of highly disordered and amorphous materials, to overcome the limits of the typical transition metal dichalcogenide crystalline catalysts. For the H₂ evolution reaction, going beyond the creation of point defects in crystalline structures in favor of fully amorphous organizations not only increases the per-site activity and active surface area but also improves the conductivity and the reaction kinetics. In addition, the incorporation of nanoscale disorder promotes the formation of complex products in CO₂ reduction through reaction pathways inaccessible on other sites. On the other hand, the mesoscale architecture of the catalyst controls mass transport in both the liquid and gas phase, as well as determines the real-world performance of catalysts. We suggest that by exploiting disordered nanoscale organization and controlled mesoscale features, the performances can be drastically improved to reach the state-of-art metallic electrocatalysts.     

Structural defects in periodic and quasicrystalline binary nanocrystal superlattices

Binary nanocrystal superlattices (BNSLs) emerge as an important class of man-made materials where components and functionalities can be added, tuned, or combined in a predictable manner. These amazingly complex structures spontaneously self-assemble from colloidal solutions containing binary mixtures of functional (semiconducting, magnetic, plasmonic, etc.) nanocrystals. Further developments of the BNSL-based materials require a deep understanding and control over BNSL formation and structural perfection. Like any solid, BNSL can contain different kinds of structural defects. It is well-known that defects can have a tremendous effect on the material's behavior. Defect engineering is used to modify and improve many of the mechanical, electrical, magnetic, and optical properties of conventional solids. In this work, we provide the first systematic analysis of structural defects in various BNSL structures. We used BNSLs as a platform for studying structural defects in both periodic (crystalline) and aperiodic (quasicrystalline) lattices, as well as for direct imaging of the interfaces between crystalline and quasicrystalline domains. Such direct observation of local imperfections in complex multicomponent lattices provides a unique insight into the fundamental aspects of crystal formation.     

Strain of 2D materials via substrate engineering

Two-dimensional(2D) materials have received extensive attention in the fields of electronics, optoelectronics, and magnetic devices attributed to their unique electronic structures and physical properties. The application of strain is a simple and effective strategy to change the lattice structure of 2D materials thus modulating their physical properties, which further facilitate their applications in carrier mobility transistor, magnetic sensor, single-photon emitter etc. In this short review, ...