Unlocking Entropic Elasticity of Nematic Elastomers Through Light and Dynamic Adhesion
Unlocking Entropic Elasticity of Nematic Elastomers Through Light and Dynamic Adhesion
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DOI：
10.1002/admi.202100672
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发表时间：
2021-06
影响因子：
5.4
通讯作者：
T. Ohzono;H. Minamikawa;E. Koyama;Y. Norikane
中科院分区：
文献类型：
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作者：
T. Ohzono;H. Minamikawa;E. Koyama;Y. Norikane
向列相液晶弹性体（LCEs）通常表现出软弹性，掩盖了交联网络固有的熵弹性。由于向列相指向矢旋转所实现的软剪切模式，它们在应变下宏观变形时应力增加很小。此外，主链LCEs中的向列相互作用会抑制对循环应变的遍历响应。它表现出滞后、缓慢松弛和粘度增加，这对它们的机械应用（如驱动和粘附）产生重大影响。在此，我们表明，在向列相LCE中掺入的偶氮苯单元光异构化后，熵弹性完全恢复。在室温下，由于光诱导的弯曲顺式异构体，软弹性程度、粘度和粘附力都明显降低。力学响应表明，顺式异构体以与温度升高时相同的方式通过降低向列序来解锁冻结的构象自由度。目前的结果不仅揭示了向列相互作用如何抑制熵弹性从而导致软态，还为针对动态力学应用调节粘弹性提供了指导。
Nematic liquid crystal elastomers (LCEs) generally show soft elasticity, masking entropic elasticity inherent in crosslinked networks. They macroscopically deform with little stress increase under straining because of the soft shear mode attained by nematic director rotations. Moreover, the nematic interaction in main‐chain LCEs can arrest the ergodic response to cycling strain. It manifests hysteresis, slow relaxation, and increased viscosity, which critically affect their mechanical applications such as actuation and adhesion. Here, it is shown that entropic elasticity fully recovers after photo‐isomerization of azobenzene units incorporated in a nematic LCE. With the light‐induced bent cis‐isomers at room temperature, the degree of soft elasticity, viscosity, and adhesion are tangibly lowered. Mechanical responses rationalize that cis isomers unlock the frozen configurational degree of freedom by reducing nematic order in the same manner observed upon temperature increase. The present results not only unveil how the nematic interaction suppresses entropic elasticity leading to the soft state, but also offer a guide to tuning viscoelasticity toward dynamic mechanical applications.