Synthesis and Characterization of Liquid-Crystalline Networks: Toward Autonomous Shape-Memory Actuation
Synthesis and Characterization of Liquid-Crystalline Networks: Toward Autonomous Shape-Memory Actuation
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DOI：
10.1021/acs.jpcc.7b04610
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发表时间：
2017-10-12
影响因子：
3.7
通讯作者：
Ambrogi, Veronica
中科院分区：
文献类型：
--
作者：
Belmonte, Alberto;Lama, Giuseppe Cesare;Ambrogi, Veronica
本文合成了基于环氧树脂的形状记忆液晶轻交联网络（LCN），并对其进行了表征，通过将LCN与外部环氧树脂矩阵耦合，展望了双向自主形状记忆致动器的未来发展。不同脂肪链长度的羧酸作为固化剂用于刚性棒环氧基中间体。通过对未拉伸和拉伸样品的量热分析和x射线衍射分析，研究了LCN的热性能和液晶性能。通过拉伸和动态力学分析研究了结构和热机械性能，并根据部分约束和完全约束热机械程序下的驱动应变和应力分析了形状记忆能力。结果表明，通过改变固化剂的脂肪链长度，可以获得各向同性温度在100℃以上、液体结晶度可控、高驱动应力和应变的LCN。此外，通过适当调整编程条件（应力水平），可以优化和稳定作动性能。此外，还讨论了在不同应力水平下，液晶畴对编程后网络弛豫及其取向程度的影响。总体而言，适当的链长和应力水平设计允许应变驱动从低（类似于60%）到高（类似于160%）进行调制。结果表明，通过平衡脂肪链长度和编程条件，可以通过可控和稳定的驱动协议微调LCN。
In this paper, epoxy-based shape-memory liquid crystalline lightly cross-linked networks (LCN) are synthesized and characterized with a view to the future development of two-way autonomous shape-memory actuators by coupling the LCN with an external epoxy-matrix. Carboxylic acids of different aliphatic chain lengths are used as curing agents for a rigid-rod epoxy-based mesogen. Thermal and liquid-crystalline (LC) properties of the LCN are investigated, through calorimetric and X-ray diffraction analysis on unstretched and stretched samples. Structural and thermomechanical properties are studied by means of tensile and dynamic-mechanical analyses and the shape-memory capabilities are analyzed in terms of actuation strain and stress under partially- and fully constrained thermomechanical procedures. The results possibility to obtain LCN with isotropization temperatures above 100 degrees C, controlled degree of liquid crystallinity, and high actuation stress and strain by simply varying the aliphatic chain length of the curing agent. Moreover, by properly adjusting the programming conditions (stress level), it is possible to optimize and stabilize the actuation performance. In addition, the effects of the liquid-crystalline domains on the network relaxation and their degree of orientation after programming at the different stress levels have been discussed. Overall, proper design of chain length and stress level allows strain actuation to be modulated from low, similar to 60%, to high, similar to 160% strain levels. The results evidence the possibility of finely tuning LCN with controlled and stable actuation protocols by balancing the aliphatic chain length and programming conditions.