磁响应固体光子晶体制备与防伪等应用研究

Based on theoretical and experimental study on magnetic-field-induced assembly of magnetic nanoparticles in a solution, we intend to develop a novel photonic printing that allows for patterns with brilliant colours to be hidden in a photonic-printing-paper （PDMS matrix）by creating a contrast of degree of magnetic-responsive photonic activity with UV-irradiation. A 0.5 ml glycol (EG) solution (10 mg/ml) containing the carbon-capped superparamagnetic colloidal nanoparticles was mixed with 2.0 g Sylgard 184 and 0.4 g curing agent respectively. After intense mechanical agitation for 5 min, the viscous mixture (take 1ml) was transferred to a cubic container (2.0 cm ×2.0 cm×1 cm), crosslinked 2 hours at 60 C. A two-step process was used to prepare the invisible photonic prints. First, graphics designed on a PC were printed on a transparent slide with common office laser printer. Then, as a mask, the printed slides were sealed to the surface of the prepared P-printing-paper under the UV-irradiation for 30 minutes and peeled off after the irradiation.The showing and hiding of the latent photonic prints is instantaneous, and the only required instrument is a magnet （NdFeB，0.05 T）, which is easy to obtain and harmless to human body. The colour of the visualized prints could be controlled only by adjusting the average particle size of the superparamagnetic colloidal nanocrystal clusters included in EG droplets. In addition, the novel invisible printing strategy allows end-user control of structural design of patterns utilizing software on a PC and is also applicable to a handwritten-pattern printing method, which reveals the excellent flexibility of the novel invisible printing. Therefore, it is believe that with these superior features, this invisible photonic printing may attract more research interest across the science and engineering disciplines in academia and industry because of its potential applications in security printing and information storage. Herein, based on the spatial mixing mechanism taken from the nature, the purpose of modulation of the structural color as creatures do by space evenly mixing periodically arranged primary microstructures with single photonic band-gap will also be explored.

磁响应性光子晶体在湿度、生化试剂检测、指纹识别、军事伪装等方面有广泛的应用前景。本课题将开展磁场诱导碳包覆磁性胶体粒子组装的理论和实验研究。制备碳包覆四氧化三铁胶体粒子并进行表面羧基化修饰，通过将上述胶体粒子均匀分散在乙二醇溶液中，然后与PDMS（硅橡胶）前躯体和固化剂混合，引发聚合，在PDMS固体内形成大量微米级的乙二醇液滴，液滴内装载有大量磁性胶体粒子，这样固体PDMS里就有了液态环境，液滴内胶体粒子就能够对外界磁场的诱导有响应，制备出磁响应的固体光子晶体。研究利用紫外光照射掩膜（有商标或文字的胶片），将文字和图案"书写"或"印制"在固体光子晶体表面的技术，紫外光通过掩膜后，透过的光照射在材料表面，破坏了PDMS和液滴结构，内部的磁性粒子不再对外磁场的诱导产生响应，而未照射的部分（文字或图案遮挡）其液滴内磁性粒子仍然有响应，外加磁场后能彩色显示文字和图案，据此开发磁防伪商标制作等应用。

液态悬浮体系中，磁性胶体粒子对磁场有相应，藉此可以制备磁响液态光子晶体，但制备磁响应固态光子晶体几乎不可能，因为胶体粒子固定在固体中后就难以移动。本课题通过把含有超顺磁性胶态纳米粒子的乙二醇溶液以微米液滴的形式包封在聚二甲基硅氧烷聚合物中，制备了一种具有磁响应光子晶体活性的固态聚合物薄膜。通过紫外光在光掩模的作用下局部照射引起聚二甲基硅氧烷照射区域网络状结构的断裂，进而导致在此区域内的乙二醇微液滴的毁坏。使得超顺磁性胶态纳米粒子自组装所需的液态环境的丧失，最终导致照射区域光子晶体纸的磁响应光子晶体活性的丧失。当把局部丧失磁响应光子晶体活性的固态聚合物薄膜放入在垂直磁场中时，只有具有磁响应光子晶体活性的部分才会发生改变。由于改变后的区域和背景之间巨大的衍射光波长差异，从而实现了隐形光子晶体印迹的制备与显现，在本课题的支持下我们探索了它在防伪等领域的应用。