Director reorientation via stripe-domains in nematic elastomers: influence of cross-link density, anisotropy of the network and smectic clusters
Director reorientation via stripe-domains in nematic elastomers: influence of cross-link density, anisotropy of the network and smectic clusters
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DOI：
10.1002/macp.1998.021990423
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发表时间：
1998-04-01
影响因子：
2.5
通讯作者：
Finkelmann, H
中科院分区：
文献类型：
--
作者：
Kundler, I;Finkelmann, H
提出了一系列不同弹性体的新指向矢重取向实验。具有永久性单畴结构的弹性体垂直于其初始指向矢排列被拉伸。当应变超过阈值后，在各畴内形成平行于外应力方向的交替旋转的条带畴。随着网络密度的增加，条纹的平均间距减小。聚合物链的各向异性通过改变降低的温度和通过与形成近晶-A相的介晶元共聚引入近晶簇而变化。网络的各向异性是由平行于指向矢的样品的等压膨胀作为温度的函数来分析的。在不同的还原温度下的重取向实验表明，应变的间隔，其中指向矢旋转，取决于这种各向异性。对半共晶弹性体的实验表明，近晶涨落对阈值有显著的贡献。结果进行了比较，华纳和Terentjev的理论，产生一个很好的定性协议。
New director reorientation experiments with a series of different elastomers are presented. Elastomers with a permanent monodomain structure are stretched perpendicular to their initial director alignment. After a threshold strain is exceeded, stripe-domains are formed parallel to the external stress with alternating sense of rotation in each domain. With increasing network density the average spacing of the stripes decreases. The anisotropy of the polymer chains is varied both by changing the reduced temperature and by introducing smectic clusters via copolymerisation with a mesogen forming a smectic-A phase. The anisotropy of the network is analyzed by the isobaric expansion of the sample parallel to the director as a function of temperature. Reorientation experiments at different reduced temperatures show that the interval of strains, where the director rotates, depends on this anisotropy. The experiments on cybotactic-nematic elastomers reveal that smectic fluctuations give a significant contribution to the threshold. The results are compared to the theory of Warner and Terentjev, yielding a good qualitative agreement.