Department of Physics and Materials Science, City University of Hong Kong , Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, China.
ACS Appl Mater Interfaces. 2017 Jan 18;9(2):1810-1819. doi: 10.1021/acsami.6b13129. Epub 2017 Jan 5.
Holographic photopolymer composites have garnered a great deal of interest in recent decades, not only because of their advantageous light sensitivity but also due to their attractive capabilities of realizing high capacity three-dimensional (3D) data storage that is long-term stable within two-dimensional (2D) thin films. For achieving high performance holographic photopolymer composites, it is of critical importance to implement precisely spatiotemporal control over the photopolymerization kinetics and gelation during holographic recording. Though a monochromatic blue light photoinitibitor has been demonstrated to be useful for improving the holographic performance, it is impractical to be employed for constructing holograms under green light due to the severe restriction of the First Law of Photochemistry, while holography under green light is highly desirable considering the relatively low cost of laser source and high tolerance to ambient vibration for image reconstruction. Herein, we disclose the concurrent photoinitiation and inhibition functions of the rose bengal (RB)/N-phenylglycine (NPG) system upon green light illumination, which result in significant enhancement of the diffraction efficiency of holographic polymer-dispersed liquid crystal (HPDLC) gratings from zero up to 87.6 ± 1.3%, with an augmentation of the RB concentration from 0.06 × 10 to 9.41 × 10 mol L. Interestingly, no detectable variation of the ϕk/k, which reflects the initiation efficiency and kinetic constants, is given when increasing the RB concentration. The radical inhibition by RBH is believed to account for the greatly improved phase separation and enhanced diffraction efficiency, through shortening the weight-average polymer chain length and subsequently delaying the photopolymerization gelation. The reconstructed colored 3D images that are easily identifiable to the naked eye under white light demonstrate great potential to be applied for advanced anticounterfeiting.
全息光聚合物复合材料在最近几十年引起了极大的关注，不仅因为它们具有有利的光敏性，还因为它们具有实现高容量三维（3D）数据存储的吸引力，这种存储在二维（2D）薄膜内长期稳定。为了实现高性能的全息光聚合物复合材料，精确控制光聚合动力学和全息记录过程中的凝胶化至关重要。虽然已经证明单色蓝光光引发剂对于提高全息性能很有用，但由于光化学第一定律的严格限制，它在绿光下构建全息图是不切实际的，而绿光下的全息术由于激光源成本相对较低和对环境振动的高容忍度，对于图像重建来说是非常理想的。在这里，我们揭示了玫瑰红（RB）/N-苯甘氨酸（NPG）体系在绿光照射下的并发光引发和抑制功能，这导致全息聚合物分散液晶（HPDLC）光栅的衍射效率从零显著提高到 87.6 ± 1.3%，随着 RB 浓度从 0.06×10增加到 9.41×10mol/L。有趣的是，当增加 RB 浓度时，没有检测到ϕk/k 的变化，ϕk/k 反映了引发效率和动力学常数。RBH 的自由基抑制作用被认为是通过缩短重均聚合物链长并随后延迟光聚合凝胶化，从而导致相分离和衍射效率的显著提高。在白光下肉眼可识别的重构彩色 3D 图像，具有应用于先进防伪的巨大潜力。
