Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers
Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers
复制标题
DOI：
10.1007/s00396-004-1128-x
复制
发表时间：
2004-06-01
影响因子：
2.4
通讯作者：
Stühn, B
中科院分区：
文献类型：
--
作者：
Ivanova, R;Staneva, R;Stühn, B
采用DSC、偏光显微镜、宽角和小角X射线散射等方法，在较宽的温度范围（25-170 ℃）内研究了一系列嵌段体积分数不同的侧链液晶/各向同性（LC/I）二嵌段共聚物的微区结构和液晶相.在所有温度下，嵌段共聚物都是微相分离的。PSLC嵌段共聚物在两个长度尺度上表现出有序性：一方面，具有特征长度尺度为0.43 nm（介晶间距）的PSLC介晶相;另一方面，具有特征长度尺度为27-44 nm（晶格参数）的层状、六方或立方结构微结构。LC块位于基质中或被限制在微区内。热致行为的特征在于序列g/类似于35 ℃/n/类似于115 ℃/i，并且不受域微观结构和/或尺寸的影响。层状尺寸的分析表明，LC链被拉伸。随着温度的升高，两个嵌段的热膨胀发生，随后LC链在T-NI以上缩回。相图是不对称的，并且在T-NI以上不改变。没有观察到由向列相-各向同性转变触发的有序到有序的转变。结果表明，域微结构的低界面曲率（层状和六边形）是积极的青睐几何预期的高界面曲率（胶束立方），由于在基体中或在微域中的CNOLC中间相的存在。通过与理论的比较，从层状/六方相边界的位置推导出LC嵌段的Kuhn段长度B（LC）=0.86 nm。
The domain microstructure and the nematic LC mesophase in a series of side-chain liquid crystalline/isotropic (LC/I) diblock copolymers with systematically varied block volume fractions were studied in a broad temperature range (25-170 degreesC) by DSC, polarized microscopy, and wide and small angle X-ray scattering. At all temperatures the block copolymers are microphase separated. The PSLC block copolymers exhibit order at two length-scales: on one hand, a nematic LC mesophase with characteristic length-scale of 0.43 nm (intermesogen distance); on the other hand, lamellar, hexagonal or cubic domain microstructures with characteristic length-scales of 27-44 nm (lattice parameter). The LC block was either located in the matrix or confined inside the microdomains. The thermotropic behavior is characterized by the sequence g/similar to35 degreesC/n/similar to115 degreesC/i and is not affected by the domain microstructure and/or dimensions. Analysis of the lamellar dimensions showed that the LC chain is stretched. With increasing temperature, a thermal expansion of both blocks takes place followed by a retraction of the LC chain above T-NI. The phase diagram is asymmetric and does not alter above T-NI. No order-to-order transitions triggered by the nematic-isotropic transition are observed. It was shown that domain microstructures of low interfacial curvature (lamellar and hexagonal) are energetically favored over the geometrically expected ones of high interfacial curvature (micellar cubic) due to the presence of nematic LC mesophase in the matrix or in the microdomains. By comparison to theory a Kuhn segment length of the LC block b(LC)=0.86 nm was derived from the location of the lamellar/hexagonal phase boundaries.