基于长程空间位阻效应的磁响应性光子晶体的构筑与光学性能

The so far developed magnetically tunable photonic crystals (MTPCs) are generally based on eletrostatic repulsion forces, which are susceptible to ionic strength and polarity of the solvents. As a consequence, the optical properties have a poor stability and the MTPCs in organic solvents only show a limited tunability in photonic bandgap. On the other hand, we have just synthesized superparamagnetic monodisperse Fe3O4@polyvinylpyrrolidone (PVP) core-shell submicrosphere colloidal particles by reducing FeCl3o6H2O with ethylene glycol (EG) in a one-pot solvothermal autoclave containing glucose and PVP. The Fe3O4@PVP core-shell particles could be steadily dispersed in various organic solvents including alkanol, dichloromethane due to the presence of long-range steric repulsions, and exhibit the tunabilities of photonic bandgap as wide as almost the entire visible light range by adjusting external magnetic field. On a basis of our previous results, this project proposes a novel kind of MTPCs with a wide tunability in photonic bandgap, which is constructed by dispersing superparamagnetic monodisperse Fe3O4 nanocrystal clusters coated with a steric layer of polymer brushes in organic solvents with different polarities. The controlled fabrication methods and formation mechanisms of the superparamagnetic monodisperse colloidal particles will be investigated in terms of the chemical compositions and microstructures. The magnitude and length scale of the long-range steric repulsions of the superparamagnetic monodiseperse colloidal particles as well as their dependence on the composition and structure, polarity of the media, ionic strength, pH values and viscosity will be elucidated. Furthermore, the magnetic properties, Zeta potential, colloidal stability of the building blocks, especially the periodical array structures and optical properties of the MTPCs under different external magnetic fields will be studied in detail. The results of this project are expected to provide new physical mechnism and fabrication meothds to construct MTPCs, promoting the integration of MTPCs into existing optical devices and expanding their application field.

现有的磁响应性光子晶体大多以胶体粒子的静电斥力为长程排斥力，它们对离子强度和溶剂极性敏感，从而导致其光学性能稳定性差和在非水体系中的带隙调控范围窄。为此，本项目结合我们前期研究制备的超顺磁Fe3O4@聚乙烯基吡咯烷酮亚微球粒子在烷醇、二氯甲烷等多种有机溶剂中表现出长程空间排斥力，在外磁场下有宽的光子带隙调控范围的发现，提出用表面包覆聚合物空间位阻层的超顺磁胶体粒子构建带隙调控范围宽的磁响应性光子晶体。研究其组装基元单分散的超顺磁胶体粒子的化学组成和结构的控制方法与原理；阐明它们在分散介质中的空间排斥力的作用距离和大小，及其对胶体粒子的组成和结构、分散体系的极性、离子强度、pH值和粘度等的依赖规律，和对组装基元的静磁性能、Zeta电位、分散稳定性，特别是在外磁场作用下形成有序结构的演变行为和光学性能等的影响规律。预期成果能为发展磁响应性光子晶体集成技术和扩大应用范围提供理论基础和技术途径。

单分散超顺磁胶体亚微米球是磁响应性光子晶体的重要组装基元，依靠相邻粒子间的长程排斥力和磁相互吸引力间的平衡，能够在外加磁场作用下迅速组装成一维链状光子晶体结构。在外加磁场作用下，粒子间距的连续可调赋予其光学性能在可见光谱范围内的连续、可逆调控，因而在彩色显示、传感、防伪和光学伪装领域拥有着重要的应用前景。. 本项目针对基于静电斥力组装的磁响应性光子晶体存在的在非水体系中带隙调控范围窄、光学性能易遭离子强度和溶剂极性破坏、以及与聚合物基体集成性差等问题，从组装基元单分散超顺磁纳米晶簇粒子的组成与结构设计出发，开展了基于空间位阻长程排斥力的磁响应性光子晶体的构建及其光学性能研究。我们以葡萄糖和聚乙烯基吡咯烷酮(PVP)分别作为磁性Fe3O4纳米晶粒的尺寸控制剂和纳米晶聚集体的表面改性剂，用一步溶剂热法成功地制备了单分散的超顺磁Fe3O4@PVP亚微米球并阐明了它的结构与尺寸控制原理。以Fe3O4@PVP亚微米球为组装基元，成功地在多种不同极性的溶剂中构筑了光子带隙调控范围宽的磁响应性光子晶体，详细探讨了溶剂性质对其光子带隙调控范围的影响，发现PVP 壳层提供的空间位阻排斥力是Fe3O4@PVP亚微米球在溶剂中得以稳定分散的关键，且排斥力的作用距离和大小决定于壳层PVP与溶剂的相容性、PVP链段的构象而对溶剂的极性、离子强度、pH等不敏感。同时借助磁响应性光子晶体光学性能和粒子间距间的相互依赖性，本项目也提供了一种简单监测粒子表面聚合物在溶剂中的溶剂化层厚度、空间位阻排斥力的方法。此外，本项目基于所研制的磁响应性光子晶体所表现出来的光学稳定性，结合磁控组装技术和快速聚合反应，发展了聚合物基响应性光子晶体材料包括温敏响应性光子晶体薄膜和兼具温敏、溶剂响应和磁控开关效应的光子晶体球，带隙可调的磁性光子纳米链和纳米棒。. 综上，本项目的研究成果不仅对构建带隙调控范围宽、光学性能稳定性好的磁响应性光子晶体材料有重要意义，而且为磁响应性光子晶体与聚合物基体的复合及其在多领域的实际应用奠定基础。