共查询到20条相似文献，搜索用时 31 毫秒
1.
Different polymers can be combined to yield a wide variety of composite materials: layered sheets and films, homogeneous and heterogeneous blends, interpenetrating polymer networks, bicomponent fibers, and others. Some properties of a multipolymer material are roughly additive, but synergistic interactions can yield properties and performances superior to those of the individual constituents. Consequently, the use of polymers in combination is a rapidly growing component of polymer materials technology. 相似文献
2.
Weissmüller J Viswanath RN Kramer D Zimmer P Würschum R Gleiter H 《Science (New York, N.Y.)》2003,300(5617):312-315
Dimension changes on the order of 0.1% or above in response to an applied voltage have been reported for many types of materials, including ceramics, polymers, and carbon nanostructures, but not, so far, for metals. We show that reversible strain amplitudes comparable to those of commercial piezoceramics can be induced in metals by introducing a continuous network of nanometer-sized pores with a high surface area and by controlling the surface electronic charge density through an applied potential relative to an electrolyte impregnating the pores. 相似文献
3.
High-resolution inelastic neutron scattering was used to identify major sources of low-frequency vibrations in zeolite crystals. Dispersed and nondispersed modes were found, both of which are prominent in the early stages of compressive amorphization but decline dramatically in strength once a glass of conventional density is created. By identifying the dispersed modes with the characteristic vibrations of the various secondary building units of zeolitic structures, the Boson peak, a characteristic of the glassy state, can be attributed to vibrations within connected rings of many different sizes. The nondispersed phonon features in zeolites, retained in the amorphized glass, were also replicated in silica. These modes are librational in origin and are responsible for destabilizing the microporous crystalline structure, for converting the resulting glass from a low- to a high-density phase, and for the associated changes in network topology that affect the Boson peak. 相似文献
4.
Surface-responsive materials 总被引：1，自引：0，他引：1
Russell TP 《Science (New York, N.Y.)》2002,297(5583):964-967
Synthetic polymers offer a wealth of opportunities to design responsive materials triggered by external stimuli. Changing the length, chemical composition, architecture, and topology of the chains allows response mechanisms and rates to be easily manipulated; and devices based on the entropy of the chains, surface energies, and specific segmental interactions can readily be made. Although numerous applications exist, intriguing possibilities are emerging that have tremendous potential to further developments in surface-responsive materials. 相似文献
5.
Miaudet P Derré A Maugey M Zakri C Piccione PM Inoubli R Poulin P 《Science (New York, N.Y.)》2007,318(5854):1294-1296
Shape-memory polymers can revert to their original shape when they are reheated. The stress generated by shape recovery is a growing function of the energy absorbed during deformation at a high temperature; thus, high energy to failure is a necessary condition for strong shape-memory materials. We report on the properties of composite nanotube fibers that exhibit this particular feature. We observed that these composites can generate a stress upon shape recovery up to two orders of magnitude greater than that generated by conventional polymers. In addition, the nanoparticles induce a broadening of the glass transition and a temperature memory with a peak of recovery stress at the temperature of their initial deformation. 相似文献
6.
Supramolecular polymers can be random and entangled coils with the mechanical properties of plastics and elastomers, but with great capacity for processability, recycling, and self-healing due to their reversible monomer-to-polymer transitions. At the other extreme, supramolecular polymers can be formed by self-assembly among designed subunits to yield shape-persistent and highly ordered filaments. The use of strong and directional interactions among molecular subunits can achieve not only rich dynamic behavior but also high degrees of internal order that are not known in ordinary polymers. They can resemble, for example, the ordered and dynamic one-dimensional supramolecular assemblies of the cell cytoskeleton and possess useful biological and electronic functions. 相似文献
7.
Chen X Dam MA Ono K Mal A Shen H Nutt SR Sheran K Wudl F 《Science (New York, N.Y.)》2002,295(5560):1698-1702
We have developed a transparent organic polymeric material that can repeatedly mend or "re-mend" itself under mild conditions. The material is a tough solid at room temperature and below with mechanical properties equaling those of commercial epoxy resins. At temperatures above 120 degrees C, approximately 30% (as determined by solid-state nuclear magnetic resonance spectroscopy) of "intermonomer" linkages disconnect but then reconnect upon cooling, This process is fully reversible and can be used to restore a fractured part of the polymer multiple times, and it does not require additional ingredients such as a catalyst, additional monomer, or special surface treatment of the fractured interface. 相似文献
8.
Johnson WL Kaltenboeck G Demetriou MD Schramm JP Liu X Samwer K Kim CP Hofmann DC 《Science (New York, N.Y.)》2011,332(6031):828-833
The development of metal alloys that form glasses at modest cooling rates has stimulated broad scientific and technological interest. However, intervening crystallization of the liquid in even the most robust bulk metallic glass-formers is orders of magnitude faster than in many common polymers and silicate glass-forming liquids. Crystallization limits experimental studies of the undercooled liquid and hampers efforts to plastically process metallic glasses. We have developed a method to rapidly and uniformly heat a metallic glass at rates of 10(6) kelvin per second to temperatures spanning the undercooled liquid region. Liquid properties are subsequently measured on millisecond time scales at previously inaccessible temperatures under near-adiabatic conditions. Rapid thermoplastic forming of the undercooled liquid into complex net shapes is implemented under rheological conditions typically used in molding of plastics. By operating in the millisecond regime, we are able to "beat" the intervening crystallization and successfully process even marginal glass-forming alloys with very limited stability against crystallization that are not processable by conventional heating. 相似文献
9.
Heavily ionizing particles create trails of damage as they move through materials. In both addition and condensation polymers these trails can be selectively dissolved so that the sites and the directions taken by the moving particles are revealed. These materials thus serve as simple detectors of heavily charged particles. 相似文献
10.
以淀粉型甘薯品种(系)为试材,采用RVA仪和相关性分析,研究比较了不同淀粉型甘薯品种的全粉糊化特性、各特征值之间的差异和相关性。结果表明,加与不加硝酸银甘薯全粉RVA谱特征值均具有明显的差异。不加AgNO3甘薯全粉的峰值黏度平均值为484.64RVU,品种间变异系数为58.64%,变幅为68.01~947.50RVU。谷值黏度以徐18最高,为583.00RVU。徐22的崩解值、终值黏度和回复值最小,分别为91.67、46.33和9.00RVU。加AgNO3后全粉的RVA谱特征值均显著提高。峰值黏度、谷值黏度、崩解值、终值黏度和回复值较不加硝酸银各特征值分别增加了1.67、3.94、0.51、4.29和5.29倍。此外,加与不加硝酸银各甘薯品种全粉RVA谱特征值之间均呈现一定的相关性。不加硝酸银全粉的峰值黏度与回复值呈显著正相关;不加硝酸银全粉谷值黏度和终值黏度、崩解值与回复值、终值黏度与回复值呈显著负相关。 相似文献
11.
综述了近几年来二氧化锆固定相的研究进展及在环境、无公害食品中的应用前景,指出:二氧化锆及改性二氧化锆基质填料是很有发展前途的高效液相色谱(HPLC)填料,此类填料既保留了硅胶基质固定相和有机聚合物固定相的优点,又克服了它们各自的缺陷。在环境监测方面如测定土壤、植物中农药残留量、多环芳烃等致癌物以及在生化药品制备及检测方面,尤其是在强碱性化合物测定上具有极大的优势。 相似文献
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13.
Measurements of the yield strength of SiO(2) glass to pressures as high as 81 gigapascals at room temperature show that the strength of amorphous silica decreases significantly as it is compressed to denser strctures with higher coordination. Above 27 gigapascals, as the silicon in amorphous SiO(2) is continuously transformed from fourfold to sixfold coordination, the strength of the glass decrases by more than an order of magnitude. These data confirm theoretical predictions that the mechanical properties of polymerized amorphous silicates are sensitive to pressure-induced structural transformations and suggest that the viscosity of silica-rich liquids decreases significantly at high pressures. Such a change in melt rheology could enhance the processes of chemical differentiation with depth in the Earth's mantle. 相似文献
14.
为了研究硅溶胶和聚磷酸铵（APP）复配后的阻燃性能,真空常压方法下分别用APP、硅溶胶以及两者复配后的阻燃剂浸渍辐射松木材,分析各改性材的增重、增容率以及热解燃烧性能,并用扫描电镜（SEM）分析改性后的残炭形貌。研究结果表明：氧指数由高到低是APP-硅溶胶、APP、硅溶胶和素材;由APP处理和APP-硅溶胶联合处理材的初始分解温度、最大失重率温度均提前,残炭率提高,硅溶胶处理材的初始分解温度和最大失重率与素材相近。经锥形量热测试结果显示：由APP处理和APP-硅溶胶联合处理材的热释放速率峰值分别比素材降低了232.8和150.3 kW·m-2,总释放热降低29.63和17.98 MJ·m-2,而由硅溶胶处理的效果不明显。与其他3种试材相比,硅溶胶处理材的COP最低,说明硅溶胶对CO的生成有抑制作用。处理材的火灾蔓延指数（FGI）均比素材降低;扫描电镜显示,经浸渍处理过的残炭结构更加致密,表面更加光滑。结果说明了硅溶胶的加入可以降低CO毒气的生成,APP的加入使木材的阻燃性达到了难燃级。 相似文献
15.
Viscoelasticity describes the ability of a material to possess both elasticity and viscosity. Viscoelastic materials, such as rubbers, possess a limited operational temperature range (for example, for silicone rubber it is -55° to 300°C), above which the material breaks down and below which the material undergoes a glass transition and hardens. We created a viscoelastic material composed from a random network of long interconnected carbon nanotubes that exhibited an operational temperature range from -196° to 1000°C. The storage and loss moduli, frequency stability, reversible deformation level, and fatigue resistance were invariant from -140° to 600°C. We interpret that the thermal stability stems from energy dissipation through the zipping and unzipping of carbon nanotubes at contacts. 相似文献
16.
Strukelj M Papadimitrakopoulos F Miller TM Rothberg LJ 《Science (New York, N.Y.)》1995,267(5206):1969-1972
Operating lifetime is the main problem that complicates the use of polymeric light-emitting diodes (LEDs). A class of electron transport (ET) polymers [poly(aryl acrylate) and poly(aryl ether)s] is reported in which moieties with high electron affinities are covalently attached to stable polymer backbones. Devices based on poly(p-phenylenevinylene) (PPV) prepared with these materials exhibited a 30-fold improvement in stability and, in one case, dramatically lower (10 volts versus about 30 volts) operating voltage relative to those having conventional ET layers. The current-carrying capacity of indium tin oxide-PPV-polymeric ET layer-aluminum LEDs was also increased by a factor of 30. These improvements lead to an enhancement in power efficiency of nearly an order of magnitude. Choosing polymers with high glass transition temperatures increases device lifetime. 相似文献
17.
Lines ME 《Science (New York, N.Y.)》1984,226(4675):663-668
Today's fiber-optic communications systems are fused-silica-based fibers for which signals require reamplification every 30 kilometers. Repeaterless long-haul (transcontinental and transoceanic) links can only be envisaged if a new fiber material with intrinsic power losses significantly lower than those of silica can be identified and developed. This article reviews the development of silica-based systems, details the physical mechanisms which produce signal attenuation in fiber materials in general, and identifies that class of materials from which ultralow loss glasses are most likely to be developed in the future. 相似文献
18.
Liphardt M Goonesekera A Jones BE Ducharme S Takacs JM Zhang L 《Science (New York, N.Y.)》1994,263(5145):367-369
Photorefractive materials can form "instant" holograms without time-consuming development steps. Their potential applications include image processing, optical data storage, and correction of image distortion, but the cost of crystal growth and preparation has been a primary impediment to commercial application. Polymers, on the other hand, are low in cost and readily fabricated in a variety of forms. Photorefractive polymers were constructed with performance that matched or exceeded the performance of available photorefractive crystals. The largest observed two-beam energy coupling gain coefficient for the polymers was 56 per centimeter. 相似文献
19.
The atomic-scale dynamics of the glass-to-liquid transition are, in general, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected just above the glass transition of K(2)Si(4)O(9) at temperatures as high as 583 degrees C are presented. Rates of exchange for silicon among silicate species, which involves Si-O bond breaking, have been measured and are shown to be closely related in time scale to those defined by viscosity. Thus, even at viscosities as high as 10(10) pascal seconds, local bond breaking (in contrast to the cooperative motion of large clusters) is of major importance in the control of macroscopic flow and diffusion. 相似文献
20.
Stable zeolites that have larger pore apertures and a three-dimensional pore topology are of interest because they could be used to adsorb larger molecules, particularly for application in oil refining. Several large-pore zeolitic materials with channels formed by openings of more than 12 rings are known, but all of them have a one-dimensional channel system that limits their use in catalysis. We report the synthesis and some characterizations of IM-12, a thermally stable germanium-containing zeolite that contains the first two-dimensional channel system with extra-large pores formed by 14- and 12-ring channels. 相似文献