Making waves in a photoactive polymer film.
Making waves in a photoactive polymer film.
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DOI：
10.1038/nature22987
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发表时间：
2017-06-28
期刊：
影响因子：
64.8
通讯作者：
Broer DJ
中科院分区：
文献类型：
--
作者：
Gelebart AH;Jan Mulder D;Varga M;Konya A;Vantomme G;Meijer EW;Selinger RLB;Broer DJ
随着外界刺激而改变形状的振荡材料在医学和机器人领域具有广阔的应用前景。液晶网络在这一领域具有突出的作用，因为它们可以被编程为经历刺激诱导的各种几何形状的变形，包括对光的反应。为了使这些聚合物网络具有光响应性，通常会加入偶氮苯分子。文献中的大多数例子都报道了这些偶氮苯改性薄膜的弯曲响应，其中光异构化后的松弛相当缓慢。对偶氮苯部分进行核心修饰或添加取代基可导致光物理和光化学性质的剧烈变化，从而有机会避开复杂结构的使用。本文报道了在液晶网络薄膜(LCN)中掺入具有快速热弛豫的偶氮衍生物，以产生在恒定光照下呈现连续的、定向的宏观机械波的薄膜，其反馈回路由自阴影驱动。理论模型和数值模拟验证了这一机理，并与实验进行了定性的比较。我们探索了在光驱动移动和自清洁表面方面的潜在应用。
Oscillating materials that adapt their shape in response to an external stimulus are of interest for emerging applications in medicine and robotics. Liquid crystal networks have a prominent role in this area because they can be programmed to undergo stimulus-induced deformations in a variety of geometries, including in response to light. In order to make these polymer networks photoresponsive, azobenzene molecules are often incorporated. Most examples in the literature report on bending responses of these azobenzene modified films, where relaxation after photo-isomerization is rather slow. Modification of the core or addition of substituents to the azobenzene moiety can lead to drastic changes in photophysical and photochemical properties giving opportunity to circumvent the use of a complex set-up. Here we report on the incorporation of azo-derivatives with fast thermal relaxation into liquid crystal network films (LCN), to generate films that can exhibit continuous, directional macroscopic mechanical waves under constant light illumination, with a feedback loop driven by self-shadowing. A theoretical model and numerical simulation demonstrate this mechanism and show good qualitative agreement with experiments. We explore potential applications in light-driven locomotion and self-cleaning surfaces.