层状仿生高分子纳米复合材料

自然界中,鲍鱼壳具有有机-无机多级次层状结构以及大量的复合界面作用,力学性能优异。这一独特的层状结构主要由霰石碳酸钙片层构成,并通过体积分数约为5%的生物高分子在层间进行粘合。受鲍鱼壳这一微观结构的启发,我们利用不同的基元材料如纳米蒙脱土、碳纳米管以及氧化石墨烯等构筑仿鲍鱼壳层状结构,并结合多种界面设计,实现不同界面、不同基元材料之间的协同作用,得到了力学性能优异的高分子纳米复合材料。仿生高分子纳米复合材料的成功制备,为今后的研究提供了崭新的思路,拓宽了高分子纳米复合材料的应用前景。     

Biomimetic approach to forming chitin/aragonite composites

Biomimetic materials which display the complexity of biominerals like nacre are synthetically difficult to prepare. The formation of chitin/calcium carbonate composites, where CaCO(3) is present as aragonite, was achieved via reacetylation of preformed chitosan scaffolds followed by the combination of presoaking of chitin templates with mineral solutions in the presence of poly(acrylic acid). The as-synthesised composites are comprised of well-ordered ribbons of aragonite crystals held within an organic matrix, mimicking the structure of nacre.     

Photoacoustic FTIR spectroscopic study of undisturbed nacre from red abalone

In this work, photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy has been utilized to study interfacial interactions of undisturbed nacre and nacre powder from red abalone shell. The spectra of both undisturbed nacre and nacre powder showed characteristic bands of aragonite and proteins. Although nacre powder and undisturbed nacre are chemically identical, PA-FTIR spectrum of undisturbed nacre is found to be significantly different from that of nacre powder. A broad and strong band is observed at around 1485 cm(-1) in nacre powder. The intensity of this band is notably reduced in undisturbed nacre. This result is explained on the basis of interfacial interactions between aragonite platelets and acidic proteins. It is also observed that band at around 1788 cm(-1) originates from three overlapping bands 1797, 1787 and 1778 cm(-1). The band at around 1787 cm(-1) is assigned to CO stretching of carboxylate groups of acidic proteins. The other two bands at 1797 and 1778 cm(-1), originate from aragonite and have been assigned to combination bands, nu(3)+nu(4a) and nu(3)+nu(4b), respectively. For the study of stratification in undisturbed nacre, PA-FTIR spectra have been collected in step scan mode. The variation in spectra with depth can be attributed to changes in conformation of proteins as well as interfacial interactions.     

Scanning electron microscopy methods for studying interfacial interaction in polymer blends

The scanning electron microscopy method in combination with the selective etching technique for polymer blends have been used to evaluate interfacial interaction in natural rubber and low density polyethylene blends. The morphology of the polymer blends, studied under externally applied strain, has been investigated to understand the role of interface adhesion between natural rubber and polyethylene phases, for two separate crosslinking systems, i.e. sulphur and peroxide.

Externally induced strain which facilitates phase separation in sulphur cured blends by initiating cracks at the interface; peroxide curing prevents separating out of the polyethylene phase from the natural rubber matrix. In the latter case, induced stress is distributed predominantly by developing fine flaw paths in the rubber matrix.

The method which has been developed for natural rubber and polyethylene blend systems may be used to evaluate the degree of interfacial adhesion between the dispersed phase and the dispersion medium for other kinds of polymer-polymer, polymer-filler as well as polymer-fibre composites.     

贝壳珍珠层及其仿生材料的研究进展

贝壳珍珠层是一种天然的有机-无机层状复合材料, 其独特的多尺度、多级次“砖-泥”组装结构赋予其优异的机械性能. 受贝壳珍珠层启发, 人们已利用不同方法制备了一系列仿生高强超韧层状复合材料, 这些材料在航空航天、军事、民用工程及机械等领域表现出广阔的应用前景. 本文就贝壳珍珠层的结构及增韧机制和近年来仿贝壳材料的制备方法及其研究进展进行了综述, 并提出一些看法和思考.     

Compression and tensile properties of self-reinforced poly(ethylene terephthalate)-composites

Tensile and compression properties of self-reinforced poly(ethylene terephthalate) (SrPET) composites has been investigated. SrPET composites or all-polymer composites have improved mechanical properties compared to the bulk polymer but with maintained recyclability. In contrast to traditional carbon/glass fibre reinforced composites, SrPET composites are very ductile, resulting in high failure strains without softening or catastrophic failure. In tension, the SrPET composites behave linear elastically until the fibre-matrix interface fails, at which point the stiffness starts decreasing. As the material is further strained, strain hardening occurs and the specimen finally fails at a global strain above 10%. In compression, the composite initially fails through fibre yielding, and at higher strains through fibre bending. The stress-strain response is reminiscent of an elastic-perfectly plastic material with a high strain to failure (typically over 10%). This indicates that SrPET composites are not only candidates as semi-structural composites but also as highly efficient energy absorbing materials.     

Induction of Osseointegration by Nacre in Pigs

Nacre is a biomaterial that has shown osteoinductive and osteoconductive properties in vitro and in vivo. These properties make nacre a material of interest for inducing bone regeneration. However, information is very limited regarding the introduction of nacre to dental implant surgery for promoting osteogenesis. This study investigated the potential of nacre powder for peri-implant bone regeneration in a porcine model. Ninety-six dental implants were placed into the tibia of twelve male domestic pigs. The dental implants were coated with nacre powder from the giant oyster before implantation. Implantations without nacre powder were used as control groups. Euthanization took place at 2, 4 and 6 weeks after implantation, after which we measured bone-to-implant contact (BIC) and bone volume density (BVD) of the implanted bone samples using micro-computed tomography (micro-CT), and examined the histology of the surrounding bone using histological sections stained with Stevenel’s blue and Alizarin red S. The micro-CT analyses showed that the BIC of dental implantations with nacre powder were significantly higher than those without nacre powder, by 7.60%. BVD of implantations with nacre powder were significantly higher than those without nacre powder, by 12.48% to 13.66% in cortical bone, and by 3.37% to 6.11% in spongy bone. Histological study revealed more peri-implant bone regeneration toward the surface of the dental implants after implantation with nacre powder. This was consistent with the micro-CT results. This study demonstrates the feasibility of using nacre to promote peri-implant bone regeneration in dental implantation.     

Temperature effect during humid ageing on interfaces of glass and carbon fibers reinforced epoxy composites

Weight change behavior of fiber-reinforced polymer composites in humid and thermal environments appears to be a complex phenomena. The state of fiber/matrix interface is believed to influence the nature of diffusion modes. A significant weakening often appears at the interface during the hygrothermal ageing. It effects the moisture uptake kinetics and also the reduction of mechanical properties. The importance of temperature at the time of conditioning plays an important role in environmental degradation of such composite materials. An attempt has been made here to evaluate the deleterious effect of temperature on shear strength of carbon/epoxy and glass/epoxy composites during hygrothermal conditionings. Mechanical tests were conducted at room temperature to assess the effectiveness of the relaxation process in the nullification of environmentally-induced damage in the composites.     

模拟研究石墨烯/生物基尼龙复合材料的界面热阻

生物基尼龙(PA56)源于天然产物,具有优良的环保性能和广阔应用前景,有望替代传统的石油基尼龙材料.为了开发基于PA56的导热材料,利用分子动力学模拟研究方法探索了石墨烯/PA56复合材料界面热阻的影响因素.首先,利用实验测试商用PA56样品的玻璃化转变温度(Tg)和导热系数(Tc),验证了PA56模型的模拟参数.接着,通过设计和比较不同表面改性状态对石墨烯/PA56复合材料的界面热阻的影响规律,最后,为了降低界面改性的难度,设计了一种新型的二嵌段共聚物作为石墨烯/PA56复合体系的界面改性剂,研究了界面改性剂的结构对界面热阻的影响规律.研究结果对于实验研究制备生物基尼龙导热复合材料具有重要的参考价值.     

Mollusk shell nacre ultrastructure correlates with environmental temperature and pressure

Nacre, or mother-of-pearl, the tough, iridescent biomineral lining the inner side of some mollusk shells, has alternating biogenic aragonite (calcium carbonate, CaCO(3)) tablet layers and organic sheets. Nacre has been common in the shells of mollusks since the Ordovician (450 million years ago) and is abundant and well-preserved in the fossil record, e.g., in ammonites. Therefore, if any measurable physical aspect of the nacre structure was correlated with environmental temperatures, one could obtain a structural paleothermometer of ancient climates. Using X-ray absorption near-edge structure (XANES) spectroscopy, Photoelectron emission spectromicroscopy (PEEM), and X-ray linear dichroism we acquired polarization-dependent imaging contrast (PIC) maps of pristine nacre in cross-section. The new PIC-map data reveal that the nacre ultrastructure (nacre tablet width, thickness, and angle spread) is species-specific in at least eight mollusk species from completely different environments: Nautilus pompilius, Haliotis iris, Haliotis rufescens, Bathymodiolus azoricus, Atrina rigida, Lasmigona complanata, Pinctada margaritifera, and Mytilus californianus. Nacre species-specificity is interpreted as a result of adaptation to diverging environments. We found strong correlation between nacre crystal misorientations and environmental temperature, further supported by secondary ion mass spectrometry measurements of in situ δ(18)O in the nacre of one shell. This has far-reaching implications: nacre texture may be used as a paleothermometer of ancient climate, spanning 450 million years of Earth's history.     

Layer-by-layer assembly of nacre-like nanostructured composites with antimicrobial properties

In a recent report, we have presented the layer-by-layer (LBL) assembly of a biomimetic nanostructured composite from Na(+)-montmorillonite clay nanosheets and poly(diallylmethylammonium chloride) (Tang, Z.; Kotov, N.; Magonov, S.; Ozturk, B. Nat. Mater. 2003, 2, 413). The structure, deformation mechanism, and mechanical properties of the material are very similar to those of natural nacre and lamellar bones. This fact prompts further investigation of these composites as potential bone implants. LBL assembly affords preparation of multifunctional composites, and here we demonstrate that not only mechanical strength, but also antibacterial activity, can be introduced in these implantable materials by alternating clay layers with starch-stabilized silver nanoparticles. The resulting composite showed excellent structural stability with no detectable levels of silver lost over a 1 month period. Evaluation of the antibacterial properties showed almost complete growth inhibition of E. coli over an 18 h period. The amount of silver eluted from the LBL composite over a 1 month period was determined to be only 0.5-3.0 microg/L. This concentration of silver did not prevent the growth of the mammalian tissue cultures. The LBL composite has shown biocompatibility with the human osteoblast cell line.     

Effects of Graphene Nanoplatelets on Mechanical and Fire Performance of Flax Polypropylene Composites with Intumescent Flame Retardant

The integration of intumescent flame-retardant (IFR) additives in natural fiber-based polymer composites enhances the fire-retardant properties, but it generally has a detrimental effect on the mechanical properties, such as tensile and flexural strengths. In this work, the feasibility of graphene as a reinforcement additive and as an effective synergist for IFR-based flax-polypropylene (PP) composites was investigated. Noticeable improvements in tensile and flexural properties were achieved with the addition of graphene nanoplatelets (GNP) in the composites. Furthermore, better char-forming ability of GNP in combination with IFR was observed, suppressing HRR curves and thus, lowering the total heat release (THR). Thermogravimetric analysis (TGA) detected a reduction in the decomposition rate due to strong interfacial bonding between GNP and PP, whereas the maximum decomposition rate was observed to occur at a higher temperature. The saturation point for the IFR additive along with GNP has also been highlighted in this study. A safe and effective method of graphene encapsulation within PP using the fume-hood set-up was achieved. Finally, the effect of flame retardant on the flax–PP composite has been simulated using Fire Dynamics Simulator.     

等离子接枝处理的CF/PAA复合材料层间剪切强度及其形貌研究

采用等离子技术对碳纤维(CF)进行接枝芳基乙炔(PAA)处理,研究了影响CF／PAA复合材料层间剪切强度(ILSS)的因素。结果表明,经等离子接枝PAA处理后,复合材料的ILSS有了很大提高。SEM显示经接枝处理后CF和PAA树脂之间的界面结合紧密,改善了复合材料的界面结合性能。     

Layered nanocomposites inspired by the structure and mechanical properties of nacre

Nacre (mother-of-pearl), made of inorganic and organic constituents (95 vol% aragonite calcium carbonate (CaCO(3)) platelets and 5 vol% elastic biopolymers), possesses a unique combination of remarkable strength and toughness, which is compatible for conventional high performance materials. The excellent mechanical properties are related to its hierarchical structure and precisely designed organic-inorganic interface. The rational design of aragonite platelet strength, aspect ratio of aragonite platelets, and interface strength ensures that the strength of nacre is maximized under platelet pull-out failure mode. At the same time, the synergy of strain hardening mechanisms acting over multiple scales results in platelets sliding on one another, and thus maximizes the energy dissipation of viscoplastic biopolymers. The excellent integrated mechanical properties with hierarchical structure have inspired chemists and materials scientists to develop biomimetic strategies for artificial nacre materials. This critical review presents a broad overview of the state-of-the-art work on the preparation of layered organic-inorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies. Discussion is focused on the effect of the layered structure, interface, and component loading on strength and toughness of nacre-mimic layered nanocomposites (148 references).     

电子背散射衍射法研究马氏珠母贝珍珠层中文石择优取向

贝壳珍珠层中的文石相对于在自然环境中生长的文石来说具有更优异的力学性能,这种力学性能取决于其独特的晶体排布方式。通过电子背散射衍射(EBSD)技术获得了马氏珠母贝中不同文石的结晶学取向信息,结果表明珍珠层中文石晶体的c轴均垂直于珍珠层层面,而a、b轴在平行珍珠层方向上具有两级取向畴结构:在初级畴结构内,相邻畴绕c轴偏转,导致不同畴之间a轴或b轴的取向差约64°。在次级畴结构内,文石板片围绕c轴偏转,导致不同畴之间a轴或b轴取向差在10°或20°左右。这种畴结构为我们认识珍珠层中文石的生长机理提供了有益线索。     

Electrochemical codeposited polypyrrole–tungsten oxide composite materials with wide potential windows

The three-dimensional morphology has sufficient interface contact and can be in favor of the electronic transport process. In this work, the demand for high-performance electrodes such as energy storage devices has been designed. Polypyrrole and tungsten oxide composite materials (PPy-WO₃) have been synthesized by cyclic voltammetry (CV) technology at −0.6 to 0.9 V versus saturated calomel electrode (SCE) for 20 cycles. The PPy-WO₃^{20 mV/s}, PPy-WO₃^{60 mV/s}, and PPy-WO₃^{120 mV/s} electrodes have been prepared by CV technology at sweep rates of 20, 60, and 120 mV/s. The influences of scan rate on morphologies and charge storage properties of the composites are discussed. Among them, a three-dimensional flake structure for PPy-WO₃^{20 mV/s} with a size of up to several micrometers was synthesized. PPy-WO₃^{20 mV/s} composites as electrode materials exhibit a wide charge storage potential window of 1.4 V (between −0.9 and 0.5 V vs. SCE) and a specific capacitance of 145.13 F/g at 1 mA/cm². Moreover, the long-term stability of PPy-WO₃^{20 mV/s} and PPy has been investigated in 5 M LiCl aqueous electrolyte. The stability of the materials can be improved by inorganic and organic composites.     

电子背散射衍射法研究马氏珠母贝珍珠层中文石择优取向

贝壳珍珠层中的文石相对于在自然环境中生长的文石来说具有更优异的力学性能,这种力学性能取决于其独特的晶体排布方式。通过电子背散射衍射（EBSD）技术获得了马氏珠母贝中不同文石的结晶学取向信息,结果表明珍珠层中文石晶体的c轴均垂直于珍珠层层面,而a、b轴在平行珍珠层方向上具有两级取向畴结构：在初级畴结构内,相邻畴绕c轴偏转,导致不同畴之间a轴或b轴的取向差约64°。在次级畴结构内,文石板片围绕c轴偏转,导致不同畴之间a轴或b轴取向差在10°或20°左右。这种畴结构为我们认识珍珠层中文石的生长机理提供了有益线索。     

Electrical properties of conductive polymer composites prepared by an innovational method

<正>An innovational method that poly(styrene-co-maleic anhydride)(SMA),a compatibilizer of immiscible nylon6/polystyrene(PA6/PS) blends,was first reacted with carbon black(CB) and then blended with PA6/PS,has been employed to prepare the PA6/PS/(SMA-CB) composites of which CB localized at the interface.In PA6/PS/CB blends,CB was found to preferentially localize in the PA6 phase.However,in the PA6/PS/(SMA-CB) blends,it was found that CB particles can be induced by SMA to localize at the interface.The electrical porperties of PA6/PS/(SMA-CB) composites were investigated.The results showed that the composites exhibited distinct triple percolation behavior,i.e.the percolation is governed by the percolation of CB in SMA phase,the continuity of SMA-CB at the interface and the continuity of PA6/PS interface.The percolation threshold of PA6/PS/(SMA-CB) was only 0.15 wt%,which is much lower than that of PA6/PS/CB.Moreover,the PTC(positive temperature coefficient) intensity of PA6/PS/(SMA-CB) composites was stronger than that of PA6/PS/CB and the negative temperature coefficient(NTC) effect was eliminated.The electrical properties of PA6/PS/(SMA-CB) were explained in terms of its special interface morphology:SMA and CB localize at interphase to form the conductive pathways.     

Nanostructured Composites with Layered Morphology: Structure and Properties

Using different microscopic techniques, we investigate the morphology and the micro-deformation processes in two entirely different classes of polymer based composites: natural biocomposites and synthetic polymer composites. The emphasis has been put on the comparison of the micromechanical properties of those composite materials. In the natural layered composites exemplified by human cortical bone, analogous to the synthetic glassy polymers, craze-like deformation zones were formed. A strong dependence of deformation mechanisms (such as transition from formation of single crazes to multiple crazing behaviour) on the layer dimension was observed in the layered composites made up of different amorphous polymers.     

Nanocellulose reinforced as green agent in polymer matrix composites applications

Owing to their abundance, high strength and stiffness, and low weight and biodegradability, nanocellulose (NC) is regarded as a promising candidate for the preparation of green composites. The high reinforcing effect assigned to the mechanical percolation phenomenon of NC is due to the stiff continuous networks of cellulosic nanoparticles linked via hydrogen bonding. Compared to nanocrystalline cellulose, NC fibers result in more significant improvement to the modulus, stiffness, and strength as aspect ratio NC fiber is higher compared to NC crystal. Indeed, in the case of biopolymer composites, the reinforcement effect of NC is attributed to the NC‐polymer interactions and the reinforcing effect occurring through effective stress transfer at the NC‐polymer interface. The NC‐reinforced composites tend to become more brittle as the concentration of the reinforcing particles increase up to the saturated level, due to the reduction in surface adhesion between filler and matrix. Due to its promising mechanical and structural stability, NC composites have been used widely in many industrial applications such as food packaging, electronic applications, and tissue engineering.