条带织构装饰技术观察含T─型液晶基元的热致性聚芳酯液晶态的向错

采用条带织构装饰新技术研究了含Ｔ─型液晶基元的热致性聚芳酯液晶态的向错形态．经过培养的液晶样品无需剪切，淬火后便可呈现出围绕向错点取向排列的条带织构，而条带织构长轴的垂直方向正代表了液晶基元的指向矢方向，这样，在普通偏光显微镜下就能直接观察到这些条带织构装饰的强度Ｓ＝±１／２和Ｓ＝±１的向错，并观察到Ｓ＝－３／２的高强度向错和闭环状的反转壁．     

氰乙基纤维素溶致性液晶的研究

氰乙基纤维素在二甲基甲酰胺、二甲基乙酰胺、二甲基亚砜、乙腈以及丙酮等溶剂中可以形成溶致性液晶。随浓度增加,溶液从各向同性状态经两相共存态转变成为完全的液晶态。升高温度到T_c,液晶相消失;降低温度到T′_c,液晶相再生成。T_c总大于T′_c。而且,浓度越高,过冷温度△T=T_c—T′_c越小。在各向同性,两相共存或完全的液晶状态,溶液平均折射率和消光度均与浓度呈线性关系。但在两相间相互转变时,即在C_1~*和C_2~*处,n-C和 A-C 曲线上出现转折点。高聚物与溶剂的相互作用参数X_(12)愈小,临界浓度C_1~*愈小。把描述大分子链柔顺性的参数f与X_(12)联系起来,可用 1956年 Flory的理论定性地解释溶剂对高聚物溶致性液晶形成的影响。     

Heterogeneities of grain boundary arrangement in polycrystals

Data on mutual arrangements of different types of grain boundaries in polycrystals are presented. The heterogeneity in grain boundary distribution, namely, the effect of gathering low-angle or special tilt grain boundaries is found in pure aluminum thin films, in sheets of Fe-3% Si alloy and in Al₂O₃ doped with MgO or MgO and Y ₂O₃. The local texture, i.e., formation of colonies or clusters of close-oriented grains is considered as a reason of this heterogeneity. The influences of grain boundary gathering on the transport properties of polycrystals and on the crack propagation are discussed. A new concept of effective grain size is suggested to analyze the relationship between material microstructures and material properties.     

MORPHOLOGY OF A THERMOTROPIC AROMATIC POLYESTER

The crystalline morphology of a thermotropic aromatic polyester has been studied by microscopy techniques. Spherulites with ringed structure under polarizing micioscope were observed for solution cast specimens, They were composed of radially growing crystalline lamellae of thickness around 100. It was found that the molecules were packed in the thickness direction. Banded texture was observed in randomly packed domains for melt cast specimens. The bands have the same width and internal structure as those usually observed in oriented specimens of these polymers obtained by shearing their mesomorphic melt.     

BANDED TEXTURE FORMATION IN NEMATIC SOLUTION OF POLY (1,4-BENZAMIDE) IN SULFURIC ACID

The banded texture in films prepared from nematic poly (1,4-benzamide) (PBA)/H_2SO_4 solution by shearing and without shearing has been studied by using microscopy techniques. The kinetic parameters of banded texture formation γ_c and τ_b were measured for nematic solution of PBA by using parallel-plate shearing apparatus. The banded texture was also observed in randomly packed domains for nematic solution of PBA on standing without shearing. The properties of banded texture show no difference between the two samples with or without shearing.     

芳香共聚酯B-N多种向列织构的形态研究

从一种聚芳酯B-N得到了丝状(包括细丝和粗丝)、纹影状和大理石纹状等与小分子向列液晶相似的多种织构。由于样品淬火后晶片装饰在织构上而不影响分子取向矢的分布,因而可以用化学刻蚀和电镜技术揭示其向错和取向矢图。电镜和光学显微镜的结果相互补充,表明了细丝和粗丝状织构的分子取向矢分布很不相同,是两种不同的织构,而粗化始于第二熔融降温。在这些向列织构中分别发现了S=±(1/2)和s=+1的向错的例子和平面内微区转向壁的证据。     

FRS-XRSA表征双轴取向聚对苯二甲酸乙二酯薄膜的取向分布

Ｘ－射线散射理论分析（ＦＲＳ－ＸＲＳＡ）是作者为了研究和表征取向高聚物结晶度与晶粒取向分布（ＯＤＣ）的一种新方案．在表征ＯＤＣ方面应用分峰法（ＣＰＲ）消除了传统极图法（ＰＦＭ）中高重叠峰相互干扰的困难，克服了取向分布函数分析（ＯＤＦＡ）中出现虚织构的困难，并且经一次系统的ＦＲＳ－ＸＲＳ测定，可以得到几乎所有主要（ｈｋｌ）晶面法向的ＯＤＣ．作者应用ＦＲＳ－ＸＲＳＡ对二类双轴取向ＰＥＴ磁带薄膜进行了ＯＤＣ的研究。基于结晶几何学原理（ＣＧＰ），建立了三斜晶系晶粒坐标系与试样坐标系的关系，并用于推演未测定方位角（αｉ，βｉ）（ｈｋｌ）的晶面散射以及未测（ｈ′ｋ′ｌ′）晶面的ＯＤＣ．作者关系建立了双轴取向函数〈ｃｏｓ２φｈｋｌ，ｉ〉，ｉ＝Ｎ、Ｍ、Ｔ的计算公式．按照ＦＲＳ－ＸＲＳＡ获得了反映取向分布的１０个晶面的双轴极图、三个主晶面（１００）、（０１０）、（１０５）的总极图，以及反映平均取向的各种取向函数，如〈ｃｏｓ２φｈｋｌ，ｉ〉、ｆｃｈｋｌ，ｉ等，结果十分令人满意．     

True spin and pseudo spin entanglement around Dirac Points in graphene with Rashba spin–orbit interaction

We analytically obtained the Schmidt decomposition of the entangled state between the pseudo spin and the true spin in graphene with Rashba spin–orbit coupling. The entangled state has the standard form of the Bell state, where the SU(2) spin symmetry is broken. These states can be explicitly expressed as the superposition of two nonorthogonal, but mirror symmetrical spin states entangled with the pseudo spin states. Because of the closely locking between the pseudo spin and the true spin, it is found that the orbit curve in the spin-polarization parameter space for the fixed equi-energy contour around Dirac points has the same shape as the $\delta \overrightarrow{k}$-contour. Due to the spin–orbit coupling that cause the topological transition in the local geometry of the dispersion relation, the new equi-energy contours around the new emergent Dirac Points can be obtained by squeezing the one around the original Dirac point. The spin texture in the momentum space around the Dirac points is analyzed under the Rashba spin–orbit interaction and it is found that the orientation of the spin polarization at each crystal momentum $\overrightarrow{k}$ is independent of the Rashba coupling strength.     

A field-reversal method for measuring the parameters of a ferroelectric liquid crystal

A method for measuring the spontaneous polarization P _s, the switching time, the rotational viscosity γ_φ, and the d.c. conductivity σ is presented. The possibilities of estimating the azimuthal angle φ₀, the dielectric anisotropy δε and the dielectric permittivity ε_⊥ in the same experiment are also discussed. It is explicitly shown that the switching delay, though primarily dependent on the material and the applied field, is also dependent on the geometry of the cell.     

Effect of cooling rate on microstructure of friction-stir welded AA1100 aluminum alloy

In this work, the microstructural changes occurring during cooling of friction-stir welded aluminum alloy AA1100 were evaluated. To this end, friction-stir welding (FSW) was performed in a wide range of cooling rates of 20–62 K/s and the evolved microstructures were studied by using electron backscatter diffraction. Below 0.6 T_m (T_m being the melting point), the stir zone material was found to experience no significant changes during cooling. At higher FSW temperatures, however, notable changes occurred in the welded material, including grain growth, sharpening of texture, reduction of the fraction of high-angle boundaries and material softening.