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arXiv 0911.3513cond-mat.soft
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多畴液晶弹性体的弹性

Elasticity of Polydomain Liquid Crystal Elastomers

J. S. Biggins, M. Warner, K. Bhattacharya

摘要:

我们通过扩展新古典软和半软自由能成功地描述单畴样品的多畴液晶弹性体模型。我们发现,有一个显着的差异之间的多畴交联均匀的高对称性状态,然后冷却到低对称性的多畴状态和那些直接交联的低对称性的多畴状态。例如,在各向同性状态下交联然后冷却到多畴的弹性体在理想极限下将是完全柔软的,并且随着非理想性的引入,将在非常低的应力下变形,直到它们宏观上对齐。在它们中观察到的指向矢图案将是无序的,是随机变形组合的特征,而不是向错图案。我们期望这些样品表现出比单畴样品明显更软的弹性。在双多畴状态下交联的多畴将在机械上更硬,并且包含特征性纹影指向矢图案。我们用于多域弹性体的模型在空间上是不均匀的,所以我们不是精确地解决它们,而是通过使用泰勒(兼容的测试应变场)和萨克斯(恒定应力)限制扩展到非线性弹性来限制能量来阐明这种行为。发现良好的协议与实验,揭示了超软响应的一些polydomains。我们还分析了近晶多畴弹性体,并提出多畴SmC* 弹性体交联的SmA单畴状态是有前途的候选人低场电致动。

英文摘要:

We model polydomain liquid-crystal elastomers by extending the neo-classical soft and semi-soft free energies used successfully to describe monodomain samples. We show that there is a significant difference between polydomains cross-linked in homogeneous high symmetry states then cooled to low symmetry polydomain states and those cross-linked directly in the low symmetry polydomain state. For example, elastomers cross-linked in the isotropic state then cooled to a nematic polydomain will, in the ideal limit, be perfectly soft, and with the introduction of non-ideality, will deform at very low stress until they are macroscopically aligned. The director patterns observed in them will be disordered, characteristic of combinations of random deformations, and not disclination patterns. We expect these samples to exhibit elasticity significantly softer than monodomain samples. Polydomains cross-linked in the nematic polydomain state will be mechanically harder and contain characteristic schlieren director patterns. The models we use for polydomain elastomers are spatially heterogeneous, so rather than solving them exactly we elucidate this behavior by bounding the energies using Taylor-like (compatible test strain fields) and Sachs (constant stress) limits extended to non-linear elasticity. Good agreement is found with experiments that reveal the supersoft response of some polydomains. We also analyze smectic polydomain elastomers and propose that polydomain SmC* elastomers cross-linked in the SmA monodomain state are promising candidates for low field electrical actuation.

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