Nematic Elastomers: The Dependence of Phase Transformation and Orientation Processes on Crosslinking Topology
Nematic Elastomers: The Dependence of Phase Transformation and Orientation Processes on Crosslinking Topology
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向列弹性体：相变和取向过程对交联拓扑的依赖性
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
H. Finkelmann
中科院分区：
文献类型：
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作者：
A. Greve;H. Finkelmann
研究了不同类型交联剂及其浓度下，弹性体在机械力作用下的取向过程和相转变。对于相应的线性聚合物熔体的机械场导致的指向矢取向垂直于外场轴。然而，对于具有棒状交联剂的网络，观察到与外部场平行的方向。只有低浓度的三官能的盘状交联剂才能引起如线性聚合物所获得的垂直取向。在更高的浓度下，指向矢再次变得平行于场有序。的取向行为进行了分析，通过应力-光学测量和网络的热膨胀行为，其中的热膨胀直接反映了在各向同性的网络构象的变化，以ε相变。网络的不同取向行为可以简单地解释。由于交联分子的轮廓长度，交联剂不能再被认为是“点状”交联，而是作为网络链的一部分。由于与中间相的相互作用，与纯聚合物熔体的取向相比，它以拮抗的方式定向介晶基团。
The orientation process in response to a mechanical field and the phase transformation of nematic elastomers are investigated for different types of crosslinkers and their concentration. For the corresponding linear polymer melt a mechanical field causes a director orientation perpendicular to the external field axis. For networks with rod-like crosslinkers, however, an orientation with the director parallel to the external field is observed. Only a trifunctional, disk-like crosslinker at low concentrations causes the perpendicular orientation as obtained for the linear polymer. At higher concentrations the director again becomes ordered parallel to the field. The orientation behaviour is analysed by stress-optical measurements and the thermal expansion behaviour of the network, where the thermal expansion directly reflects the change of the network conformation at the isotropic to nematic phase transformation. The different orientation behaviour of the networks can be simply explained. Because of the contour length of the crosslinking molecules the crosslinker can no longer be considered as “point-like” crosslink, but rather as a part of the network chains. Due to interactions with the mesophase it orients the mesogenic groups in an antagonistic manner compared to the orientation of the pure polymer melt.