Pronounced effects of cross-linker geometries on the orientation coupling between dangling mesogens and network backbones in side-chain type liquid crystal elastomers
Pronounced effects of cross-linker geometries on the orientation coupling between dangling mesogens and network backbones in side-chain type liquid crystal elastomers
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DOI：
10.1016/j.polymer.2015.01.069
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发表时间：
2015-03
期刊：
影响因子：
4.6
通讯作者：
Akane Tsuchitani;Haruhisa Ashida;K. Urayama
中科院分区：
文献类型：
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作者：
Akane Tsuchitani;Haruhisa Ashida;K. Urayama
我们证明，交联剂的几何形状，如分子长度和官能度有一个显着的影响，在侧链型液晶弹性体，这是由单官能的介晶和多官能的非介晶交联剂共聚的悬挂的介晶和网络骨架之间的取向耦合。对于具有平面排列的弹性体（内斯），冷却导致悬挂的介晶的有序性增加，而与交联剂的几何形状无关。相应地，对于具有双官能度（F= 2）和足够长的交联剂（N ≥ 6（N;官能团之间的亚甲基单元的数目））的内斯，诱导了沿着指向矢的有限宏观伸长沿着，而对于具有短交联剂（N ≤ 4）的内斯，不依赖于F而驱动宏观变形。当相应的内斯与多畴排列由外部施加的应变拉伸，悬挂的介晶的重新取向沿着的拉伸方向独立于N的情况下ofF= 2，而没有重新取向的介晶的情况下驱动的短的三和四官能交联剂（N= 3和F = 3，4）。这种惊人的和复杂的影响的交联剂的几何形状的悬挂的介晶和网络骨架之间的取向耦合的预期从非均相网络结构组成的密集和稀疏的区域的交联，这是由单官能和多官能单体的共聚形成的聚合物网络的特征。
We demonstrate that the cross-linker geometries such as molecular length and functionality have a pronounced effect on the orientation coupling between the dangling mesogens and network backbones in the side-chain type liquid crystal elastomers which are made by the copolymerization of mono-functional mesogens and multi-functional non-mesogenic cross-linkers. For the nematic elastomers (NEs) with planar alignment, the cooling causes an increase in nematic order of the dangling mesogens independently of the cross-linker geometries. Correspondingly, a finite macroscopic elongation along the director is induced for the NEs with the bi-functional (F= 2) and sufficiently long cross-linkers withN≥ 6 (N; the number of methylene units between the functional groups), but no macroscopic deformation is driven for the NEs with the short cross-linkers withN≤ 4 independently ofF. When the corresponding NEs with polydomain alignment are stretched by externally imposed strain, the dangling mesogens are reoriented along the stretching direction independently ofNin the case ofF= 2 whereas no reorientation of the mesogens is driven in the cases of the short tri- and tetra-functional cross-linkers (N= 3 andF= 3, 4). Such striking and complicated effects of the cross-linker geometries on the orientation-coupling between the dangling mesogens and network backbones is expected from the heterogeneous network structure composed of the dense and sparse regions of cross-links which are characteristic of the polymer networks formed by the copolymerization of mono- and multi-functional monomers.