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在室温下,聚乙烯纳米纤维拉伸后的热导率可比聚乙烯块体的热导率提高几十到数百倍.为了相对准确地考察该现象的微观机制,根据聚合物高分子链拉伸应变后系带分子形变的微观特征,从量子力学出发,在密度泛函理论(DFT)计算的基础上,用非平衡格林函数(NEGF)方法,对聚乙烯单链拉伸前、后的声子透射谱、热导及热导率进行了比较,讨论了聚乙烯单链拉伸应变下热输运性能变化的规律.计算表明:聚乙烯单链导热性能随拉伸应变的增加而单调减少.分析了先前分子动力学(MD)方法在计算模型上的不足之处,并对实验现象做出了合理解释.这对澄清高分子聚合物拉伸后热物理性能提升的微观机制有着积极的意义. 相似文献
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用小角X射线散射法对辐照聚乙烯在不同条件下拉伸及热处理后的长周期进行了研究。在室温拉伸时长周期减小,拉伸试样再热处理时,长周期又逐渐增加。这可用结晶的破坏以及重结晶来解释。 相似文献
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本文采用电子显微镜和小角X-射线散射(SAXS)技术研究了含有串晶结构(Shish—kebab)的高密度聚乙烯(HDPE)/超高分子量聚乙烯(UHMWPE)共混物高取向膜在单轴拉伸过程中的微结构变化.深入探讨了拉伸温度对聚乙烯在形变过程中微结构变化的影响.室温拉伸时,聚乙烯串晶结构主要发生了解结晶过程;高温(115℃)形变时,主要表现为折叠链片晶直接转变为伸展链纤维晶的应变诱导结晶过程. 相似文献
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采用拉伸分子动力学方法研究聚乙烯单链从一个强吸附表面被拉伸的动力学过程.当聚乙烯单链被拉伸时,从理想弹簧测量到的平均力与形变的曲线上出现了一个力的平台,这与实验结果非常一致.在研究这个平台力与拉伸速度的关系时发现,当速度v<0.001 nm/ps时,不随速度的变化而变化;当速度v>0.001 nm/ps时,随着拉伸速度的增加而迅速上升,这表明拉伸速度0.001 nm/ps是平衡态拉伸和非平衡态拉伸的临界点,并与链长无关.按顺序拉伸和释放这条链,观察到有趣的力回滞现象,并与实验结果进行了比较. 相似文献
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超拉伸聚乙烯的弹性模量和导热性能 总被引:8,自引:0,他引:8
为了揭示聚合物分子链伸展、取向的本征特性,发展了两个新的测量方法和实验装置,用于研究拉伸比高达200的超拉伸聚乙烯凝胶的弹性性能、传热性能和聚合物结构的关系.应用激光脉冲热致超声法给出材料拉伸方向和横向杨氏模量,应用激光脉冲光热辐射法给出拉伸方向,横向和厚度方向的导热系数.随拉伸比λ的增加,轴向杨氏模量急剧的增加,而横向的仅有少许减小.导热系数具有相似的特性.本文发现当λ=200时,这种拉伸取向聚乙烯的轴向模量可达钢的80%,而导热系数甚至可达2倍,直至成为热的良导体,这是由于在高拉伸比时形成了相当数量的伸展分子链构成的针状晶体———晶桥.本文提出晶桥作为短纤维分散相的取向聚合物的结构模型,对于超拉伸聚乙烯的上述特性可以进行统一描述和定量化分析,和实验结果很好符合. 相似文献
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讨论了超高分子量聚乙烯(UHMW-PE)的熔融一次拉伸和二次拉伸的晶体结构和力学性能.利用WAXD和SAXD测定了拉伸片的晶体取向因子和极图,晶粒尺寸,晶体畸变,长周期等晶体结构.用DSC和VES测定热性能和动态力学性能.应力-应变实验测定拉伸片的杨氏模量,断裂强度和伸长.这些实验结果说明UHMW-PE经二次拉伸能产生正交晶系的伸直链晶体.二次拉伸片由折叠链片晶和伸直链晶体两元结构组成.二次拉伸片的杨氏模量比一次拉伸片有大幅度提高.二次拉伸片的晶体结构和力学性能是在一次拉伸的基础上形成的. 相似文献
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分别以2种咪唑类室温离子液体为溶剂,通过简单的还原反应制备了碲(Te)一维纳米材料.利用X射线衍射(XRD)、透射电镜(TEM)和选区电子衍射(SAED)对样品进行了表征,并初步探讨了2种咪唑类室温离子液体对Te生长的影响.此外,实验中发现同时加入聚乙烯吡咯烷酮(PVP)和室温离子液体可以得到Te束状结构. 相似文献
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聚合所得初生聚乙烯的晶型伍青,张启兴,卢泽俭,王海华,欧阳巍,林尚安,张光华(中山大学高分子研究所,广州,510275)(中国科学院广州化学研究所)关键词聚乙烯,结晶,单斜晶,颗粒形态热力学稳定的聚乙烯晶型为正交晶系[1].当聚乙烯受一定应力作用时如... 相似文献
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Braga D Maini L Fagnano C Taddei P Chierotti MR Gobetto R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(4):1222-1230
The structural relationship between the two crystal forms of cinchomeronic acid (CA 3,4-dicarboxypyridine) has been investigated by single crystal X-ray diffraction, IR and Raman spectroscopy and solid state NMR spectroscopy, showing that the two polymorphs form a monotropic system, with the orthorhombic form I being the thermodynamically stable form, while the monoclinic form II is unstable. In both forms CA crystallizes as a zwitterion and decomposes before melting. The crystal structure and spectroscopic analysis indicate that the difference in stability can be ascribed to the strength of the hydrogen-bonding patterns established by the protonated N-atom and the carboxylic/carboxylate O-atoms. 相似文献
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Peter Müller Frank R. Fronczek Stacey J. Smith Teresa Mako Mindy Levine 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(2):199-203
A second, monoclinic, polymorph of the title compound, C14H8Cl2, has been found. In addition to the structure of this monoclinic form, the structure of the previously described orthorhombic form [Desvergne, Chekpo & Bouas‐Laurent (1978). J. Chem. Soc. Perkin Trans. 2, pp. 84–87; Benites, Maverick & Fronczek (1996). Acta Cryst. C 52 , 647–648] has been redetermined at low temperature and using modern methods. The low‐temperature structure of the orthorhombic form is of significantly higher quality than the previously published structure and additional details can be derived. A comparison of the crystal packing of the two forms with a focus on weak intermolecular C—H...Cl interactions shows the monoclinic structure to have one such interaction linking the molecules into infinite ribbons, while two crystallographically independent C—H...Cl interactions give rise to an interesting infinite three‐dimensional network in the orthorhombic crystal form. 相似文献
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P. C. Painter J. Runt M. M. Coleman I. R. Harrison 《Journal of Polymer Science.Polymer Physics》1978,16(7):1253-1260
A complex fine structure in the C? H stretching region of the infrared spectrum of deformed polyethylene single crystals is reported. The deformed crystals are shown to be transformed from the orthorhombic crystal form to a monoclinic structure. The previously deduced C2/m monoclinic structure does not account for the appearance of the new bands. An alternative but similar monoclinic structure is proposed. The symmetry of this structure is consistent with the Fermi resonance interactions required for the observation of these bands. 相似文献
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N. Erchak S. Belyakov I. Kalvinsh K. Pypowski E. Valbahs E. Lukevics 《Chemistry of Heterocyclic Compounds》2009,45(9):1137-1143
The compound 1-(N-morpholiniomethyl)spirobi(3-oxo-2,5-dioxa-1-silacyclopentan)ate crystallizes from aqueous solution of γ-butyrolactone
in the form of two crystal hydrate modifications: monoclinic (with D = 1.53 g/cm3, space group P 21/n) and triclinic (D = 1.45 g/cm3, space group P1-). For the monoclinic form, an X-ray structural study at -100°C has been performed. For both structures the coordination polyhedron
of the silicon atom is a trigonal bipyramid. In the crystal structures there are strong intermolecular hydrogen bonds of NH···O
and OH···O types. 相似文献
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Choudhury AR Islam K Kirchner MT Mehta G Guru Row TN 《Journal of the American Chemical Society》2004,126(39):12274-12275
Polymorphism in diphenyl ether has been identified during in situ crystallization via single-crystal X-ray diffraction. Only weak inter- and intramolecular C-H...pi interactions control the packing of the molecules in both crystal forms monoclinic centrosymmetric (P21/n) in form I and orthorhombic noncentrosymmetric (P212121) in form II. 相似文献
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Keizo Miyasaka Kunio Makishima 《Journal of polymer science. Part A, Polymer chemistry》1967,5(12):3017-3027
A crystal transition was found in nylon 6 fibers from the γ-phase to α-phase on stretching in the chain direction. The γ-phase fiber prepared by iodine treatment was stretched under constant load and the crystal deformation was observed by an x-ray method. The critical stress for the transition was estimated as 4 × 103 kg./cm.2 at room temperature. For this crystal transition the following conditions must be satisfied: (1) extension of the γ-phase chain to untwist the chain around the amide groups, (2) translational mobility of the chain to change the stacking in the crystallite. At the critical stress, the chain in the crystal is extended to nearly the same length as that of α-phase. The translational movement occurs under stress higher than about 3 × 103 kg./cm.2, and the pseudohexagonal cell is deformed into a monoclinic form. However, the monoclinic crystallites present at a stress lower than the critical value estimated above are unstable and may be brought back to the original form by head treatment at 100°C. No crystal transition occurs at low temperature. 相似文献
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β-Trichosanthin, a type 1 ribosome-inactivating protein (RIP) isolated from the root tuber of Trichosanthe kirilowii Maxim, is an isoform of trichosanthin. Here we report its crystal- lization in two crystal forms using the hanging-drop vapor-diffusion method. The form A and form B crystals belong to the orthorhombic space group P212121 and monoclinic space group P21, respectively. X-ray data have been collected to 1.6 and 1.2 (A) resolution for form A and form B crystals, respectively, using a synchrotron source. 相似文献
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Hua Huang Polymer Research Institute Sichuan University Chengdu China School of chemistry Chemical Technology Shanghai Jiao Tong University Shanghai China 《高分子科学》2000,(4):363-367
A detailed study was performed on the crystal structures of pan-milled high-density polyethylene (HDPE) usingdifferential scanning calorimetry (DSC) and X-ray diffraction. The crystallinity of HDPE first decreased slightly, followed bya gradual increase with increasing milling times. Monoclinic crystals appeared after 4 cycles of milling. With increasingtimes of milling, the proportion of monoclinic crystals increased significantly while the proportion of orthorhombic crystalsdecreased gradually. With increasing times of milling, the crystallite size of orthorhombic form decreased greatly, while thesize of monoclinic crystallites kept almost constant during milling. 相似文献
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用SYNTEXP3/R3四圆衍射仪收集4-(2-吡啶偶氮)间苯二酚盐酸盐晶体的三维衍射数据。晶体属P21/c空间群,a=11.339Å,b=6.835Å,c=18.170Å,β=102.76°,Z=4。利用Patterson法及直接法测定了晶体结构。经位置坐标参数,各向异性温度因子及比例因子块矩阵最小二乘修正后,最后的R值为0.055。晶体结构分析结果表明:4-(2-吡啶偶氮)间苯二酚的分子内所有非氢原子共面并形成大的共轭体系。氯离子及二个结晶水与分子中的N,O形成氢键,起到桥联分子的作用。 相似文献