Li Xu, Huang Hao, Wu Bing, Liao Chuyi, Wang Xiaogong
Department of Chemical Engineering, Laboratory of Advanced Materials (MOE), Tsinghua University Beijing 100084 P. R. China
RSC Adv. 2021 Oct 28;11(55):34766-34778. doi: 10.1039/d1ra06111a. eCollection 2021 Oct 25.
Photoinduced surface-relief-gratings (SRGs) on azo polymer and azo molecular glass films, caused by - isomerization of azo chromophores, have attracted wide interest for their intriguing nature and many possible applications in recent years. Understanding the mechanical properties of SRGs at the nanoscale is critically important for elucidating their formation mechanism and exploring their applications. In this work, a representative azo polymer (BP-AZ-CA) and a typical azo molecular glass (IAC-4) were comparatively studied for the first time concerning their properties related to SRG formation through a variety of methods. The results indicate that when inscribing SRGs on the films, IAC-4 shows a much higher efficiency for forming SRGs relative to that of BP-AZ-CA. The overall average moduli of SRGs measured by nanomechanical mapping techniques are obviously smaller compared with the moduli of the corresponding films of both materials. The moduli at different regions of SRGs are periodically varied along the grating vector direction for both BP-AZ-CA and IAC-4 gratings. The moduli at the trough regions of SRGs are always larger than those of the crests, while the moduli at the hillsides are the smallest. Distinct from BP-AZ-CA, even the moduli at the trough regions of IAC-4 SRG are smaller compared with that of the original film, and the ratio between the trough and crest moduli is significantly larger for IAC-4. These results provide deep understanding of the SRG formation mechanism and reveal the clear distinction between these two types of glassy materials for their SRG-forming behavior, which are important for future applications.
近年来，由偶氮发色团的 - 异构化引起的偶氮聚合物和偶氮分子玻璃薄膜上的光致表面起伏光栅（SRG），因其引人入胜的性质和许多可能的应用而备受关注。了解纳米尺度下SRG的力学性能对于阐明其形成机制和探索其应用至关重要。在这项工作中，首次通过多种方法对一种代表性的偶氮聚合物（BP - AZ - CA）和一种典型的偶氮分子玻璃（IAC - 4）与SRG形成相关的性质进行了比较研究。结果表明，在薄膜上写入SRG时，IAC - 4相对于BP - AZ - CA表现出更高的SRG形成效率。通过纳米力学映射技术测量的SRG的整体平均模量明显小于两种材料相应薄膜的模量。对于BP - AZ - CA和IAC - 4光栅，SRG不同区域的模量沿光栅矢量方向呈周期性变化。SRG谷底区域的模量总是大于波峰区域的模量，而山坡区域的模量最小。与BP - AZ - CA不同，即使IAC - 4 SRG谷底区域的模量也比原始薄膜的模量小，并且IAC - 4的谷底和波峰模量之比明显更大。这些结果为SRG形成机制提供了深入理解，并揭示了这两种玻璃态材料在SRG形成行为上的明显区别，这对未来的应用很重要。
