Abstract
In this work, azobenzene-containing polyurethane liquid crystal networks (PULCN(AZO)s) were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effects. Based on the step-growth nature of hydroxyls and isocyanates, the architectures of the networks were adjusted by controlling the stoichiometries of chemical materials. A uniform monodomain sample was prepared by external stress relaxation via a reversible addition reaction of a dynamic carbamate bond. Two independent transition temperatures assigned to glass transition temperature/melting temperature and liquid crystal phase transition temperature were employed to thermally trigger triple shape memory effects and two-way autonomous actuation. In addition, taking advantage of the trans-cis photoisomerization of azobenzene, the programmed network showed a reversible bending and unbending shape change upon irradiation by visible light at 450 and 550 nm, respectively. Coupling the autonomously thermo-induced contraction/extension actuation and reversible photo-induced bending/unbending behaviors of PULCN(AZO)s in one system will expand their potential applications in emerging multifunctional devices.
摘要
本文以羟基修饰偶氮液晶小分子为单体、异氰酸酯为扩链 剂、四臂聚乙二醇为交联剂一锅法合成了一系列液晶聚氨酯网络 (PULCN(AZO)s), 并通过调节反应原料的投料比精确控制网络结 构. 该交联网络呈现两个独立的热转变温度 (Ttrans), 以此为驱动温 度可实现热致三重形状记忆效应. 进一步利用氨酯键在高温下的 动态热交换获得单畴化液晶交联网络, 该交联网络不仅可呈现热 致无应力双向形状记忆效应, 同时利用偶氮苯光致异构转变特性, 还可以在450和550 nm 可见光的照射下分别展示出弯曲与回复的 光致形变能力. 将光、热响应的无应力可逆形变结合在单一循环 中, 可实现材料在多个形状之间的可逆变化. 该材料有望应用于多功能设备中
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Acknowledgements
Wen ZB gratefully acknowledges the use of facilities and instrumentation supported by the National Science Foundation of Materials Research Science and Engineering Centers Grant (DMR-1420736, University of Colorado, Boulder). This work was supported financially by the National Natural Science Foundation of China (51773131 and 51721091) and the Fundamental Research Funds for the Central Universities.
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Wen ZB designed the structure, performed the experiments, analyzed the data and wrote the draft of manuscript with support from Yang KK; Yang KK and Wang YZ proposed the project and gave critical comments of the manuscript; Snap RF and Clark NA analyzed the experimental results of POM and WAXD; Raquez JM checked and approved the manuscript. All authors contributed to the general discussion.
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Experimental details and supporting data are available in the online version of the paper.
Zhi-Bin Wen received his PhD degree in polymer chemistry and physics from Sichuan University in 2018. He currently does his post-doctoral research at the University of Mons. His research focuses on shape-memory polymers, liquid crystal materials and covalent adaptable networks.
Ke-Ke Yang received her BSc degree in polymer materials (1994), MSc degree in chemical fiber (1997), and PhD degree in material science from Sichuan University in China. She joined Sichuan University in 1997, and now is a full professor in polymer chemistry and physics. Her research focuses on biodegradable polymers, polymer composites, shape-memory polymers and self-healing materials.
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Wen, ZB., Snap, RF., Raquez, JM. et al. Unique two-way free-standing thermo- and photo-responsive shape memory azobenzene-containing polyurethane liquid crystal network. Sci. China Mater. 63, 2590–2598 (2020). https://doi.org/10.1007/s40843-020-1406-1
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DOI: https://doi.org/10.1007/s40843-020-1406-1