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71.
发现某些含二维液晶基元的热致液晶高分子容易产生反向壁织构与含有高强度有错点(│S│大于1)的向列态纹影织构。这类液晶高分子的织构与形态学特点与含一维棒状液晶基元的其他液晶高分子不同。  相似文献   
72.
设计并合成了4个对称联苯双酯类液晶化合物,化合物结构通过红外和核磁表征,它们的介晶性通过差示扫描量热仪(DSC),X射线衍射仪(XRD)和热台偏光显微镜(POM)进行了研究.并测定了4,4'-3,3',5,5'-四甲基联苯-二(4-甲基苯甲酸酯)(Ⅲa)的单晶结构,结果显示:晶体属于单斜晶系,P21/c空间群,晶胞参数为a=18.525(3)(A),b=12.196(2)(A),c=12.195(2)(A),β=97.142(2)°,V=2733.7(9)(A)3,Z=4,Dc=1.163 Mg/m3,R=0.0521,Rw=0.1161.化合物均为热致型互变液晶,并讨论了氧原子、不饱和端基和端基链长对介晶性的影响.  相似文献   
73.
应用X射线衍射、偏光显微镜及电子显微镜研究了胆甾液晶与甲基丙烯酸甲酯(MMA)─甲基丙烯酸丁酯(BMA)无规共聚物共混体系的形态结构。研究了体系的结晶态及液晶态的行为和共聚物含量及组成对光学织构的影响。  相似文献   
74.
Poly[4-(4-hydroxyphenoxy) benzoic acid] was prepared by the bulk polycondensation of 4-(4-acetoxyphenoxy) benzoic acid. Polycondensation was conducted at 350°C for 3 h under a reduced pressure of 0.1 mmHg and gave a polymer with X?n of 255. The polymer was characterized by elemental analysis, IR spectroscopy, differential scanning calorimetry, and wide-angle X-ray measurement. The crystal/nematic and nematic/isotropic phase transition temperatures of polymer, which depend on the molecular weight, were observed at about 300°C and 410°C, respectively. The polymers with low molecular weights showed nematic textures above 300°C. This nematic/isotropic phase transition temperature is lower than that of poly (4-hydroxybenzoic acid). This thermal behavior of polymer comes from ether units, which increase the flexibility (the rotation or torsion of skeletal bonds) of the polymer chain. © 1994 John Wiley & Sons, Inc.  相似文献   
75.
76.
In developing physical theories, analogical reasoning has been found to be very powerful, as attested by a number of important historical examples. An analogy between two apparently different phenomena, once established, allows one to transfer information and bring new concepts from one phenomenon to the other. Here, we discuss an important analogy between two widely different physical problems, namely, the Jahn–Teller distortion in molecular physics and the Rashba spin splitting in condensed matter physics. By exploring their conceptual and mathematical features and by searching for the counterparts between them, we examine the orbital texture in Jahn–Teller systems, as the counterpart of the spin texture of the Rashba physics, and put forward a possible way of experimentally detecting the orbital texture. Finally, we discuss the analogy by comparing the coexistence of linear Rashba + Dresselhaus effects and Jahn–Teller problems for specific symmetries, which allow for nontrivial spin and orbital textures, respectively.  相似文献   
77.
以季戊四醇为中心,4-(正烷基酰氧基)-4′-苯甲酰氧基苯甲酸为液晶臂,经酯化反应合成一种芳香酯类星型四臂液晶化合物。通过元素分析、红外光谱、核磁共振谱测试技术对其分子结构进行表征。采用差示扫描量热、偏光显微分析、X射线衍射分析等测试技术对其液晶相行为进行研究。结果表明,随着端基柔性链的加长,tm、ti、tic及tc呈降低趋势,它们在液晶态时均呈现破碎焦锥及焦锥织构,属互变近晶相液晶,液晶区间较宽。其中升温时D1~D4的tm和ti值分别为92.3、80.6、68.3、51.1和159.2、145.1、127.5、109.8℃,液晶范围△t1在66.9~58.7℃之间,降温时的tic和tc值分别为138.6、127.4、111.6、99.1和57.1、52.6、42.0、31.8℃,液晶范围△t2在81.5~67.3℃之间。  相似文献   
78.
Investigations of a commercial NiMo/Al2O3 hydrodesulfurization (HDS) catalyst are directed towards optimization of the activation procedure of HDS catalyst concerning active phase formation and thermal stability. Structural and textural data obtained with XRD, IR-FTIR, XPS and LTNA reveal that the optimal temperature for the formation of active species on the catalyst surface and an appropriate pore structure is 300°C.  相似文献   
79.
通过改变侧链中柔性间隔基的长度,合成了一系列含有两个手性中心的侧链液晶(甲基)丙烯酸酯类聚合物.红外、核磁和GPC表征各中间体、单体及聚合物的结构和分子量.通过DSC和热台偏光显微镜系统地研究了单体和聚合物的液晶态织构.结果表明,含有六个碳的柔性间隔基的丙烯酸酯类聚合物表现为近晶SA和手性近晶SC^*液晶相.  相似文献   
80.
李安华  赵睿  赖彬  王会杰  朱明刚  李卫 《中国物理 B》2011,20(10):107503-107503
Radially oriented Nd-Fe-B rings are prepared by backward extrusion of fine grained melt-spun powder. Melt-spun powder with the nominal composition of Nd30.5Febal.Co6.0Ga0.6Al0.2B0.9 (wt%) is used as starting material. The effects of process variables, such as deformation temperature (Td), strain rate (ε) and height reduction (Δh%), on the magnetic properties of the rings are investigated. A scanning electron microscope (SEM) equipped with an energy spectrum device is used to study the metallograph and microfracture of the extruded rings. The Br and (BH)max reach the optimum values at Td=800℃, ε =0.01 mm/s, and Δh% =70%. It is found by SEM observations that the particle boundaries, which seemingly correspond to the interfaces of the starting melt-spun powders, emerge after the corrosion of metallography specimens. This is helpful for studying the effects of powder-powder interface on the local deformation and deformation homogeneity in the rings. For different spatial positions of the extruded rings, there are characteristic metallographies and microfractures. The upper end of the rings has the least deformation and worst texture, and therefore the worst magnetic properties. The magnetic properties in the radial direction increase slightly along the axis from the bottom to the middle, then steeply decrease at the upper end of the ring. The deformation and the formation-of-texturing processes are discussed. The deformation and the texturing formation of melt-spun Nd-Fe-B alloys probably involve grain boundary sliding and grain rotation, the solution-precipitation process and preferential growth of Nd2Fe14B nanograins along the easy growth a-axis.  相似文献   
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