Photoreversible Order–Disorder Transitions in Block Copolymer/Ionic Liquid Solutions
Photoreversible Order–Disorder Transitions in Block Copolymer/Ionic Liquid Solutions
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DOI：
10.1021/acs.macromol.2c00397
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发表时间：
2022-05
期刊：
影响因子：
5.5
通讯作者：
Claire L. Seitzinger;Cecilia C. Hall;T. Lodge
中科院分区：
文献类型：
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作者：
Claire L. Seitzinger;Cecilia C. Hall;T. Lodge
外界刺激对控制自组装聚合物材料的纳米级形态很有兴趣。虽然温度通常用于控制嵌段聚合物溶液中的微相分离状态，但光是一种高度可调的非接触式方法，可以在空间上进行选择。在这里，我们利用紫外光照射在三种咪唑基离子液体中诱导了四种聚甲基丙烯酸甲酯-b-聚(甲基丙烯酸苄酯-S-4-苯基偶氮苯基甲基丙烯酸酯)嵌段共聚物在浓溶液中的有序-无序转变。由于苯基偶氮苯基甲基丙烯酸酯单体在紫外光照射下发生了显著的极性变化，在黑暗和紫外光照射下的ODT之间存在一个双稳态温度窗口，从而允许光触发ODT。利用紫外光照射的小幅度振荡剪切流变学来定位双稳窗口，然后用光可逆地触发ODT。在黑暗中形成的有序态是由小角X射线散射确定的。在该体系中考察了三个可调因素：共聚链段的相对长度、溶剂的选择性和光活性单体的含量。研究发现，嵌段组成主要影响微相分离后体系形成的有序态。溶剂的选择性是调节ODT温度的最有前景的方法，而光活性单体的量控制着双稳窗口的宽度。
External stimuli are of interest in controlling the nanoscale morphology in self-assembling polymer materials. While temperature is commonly used to control the state of microphase separation in block polymer solutions, light is a highly tunable, contactless method that can be spatially selective. Here, we use UV irradiation to induce order–disorder transitions (ODTs) in concentrated solutions of four poly(methyl methacrylate)-b-poly(benzyl methacrylate-s-4-phenylazophenyl methacrylate) block copolymers in three imidazolium-based ionic liquids. Due to a significant change in polarity in the phenylazophenyl methacrylate monomer upon UV irradiation, a bistable temperature window exists between the ODT in the dark and under UV irradiation, allowing for light-triggered ODTs. UV-irradiated small-amplitude oscillatory shear rheology is used to locate the bistable window and then to trigger ODTs reversibly with light. The ordered states formed in the dark are determined by small-angle X-ray scattering. Three tunable factors are explored within the system: the relative lengths of the copolymer blocks, the selectivity of the solvent, and the content of the photoactive monomer. The block composition was found to mainly influence the ordered state formed by the system after microphase separation. The selectivity of the solvent is the most promising method for tuning the ODT temperature, and the amount of photoactive monomer controls the width of the bistable window.