Ghorbanishiadeh Zoya, Bhuyan Ankita, Zhou Bojun, Sheibani Karkhaneh Morteza, Kuzyk Mark G
Department of Physics, Washington State University, Pullman, WA 99163, USA.
Polymers (Basel). 2025 Jan 20;17(2):254. doi: 10.3390/polym17020254.
This work aims to determine the mechanism of the photomechanical response of poly(Methyl methacrylate) polymer doped with the photo-isomerizable dye Disperse Red 1 using the non-isomerizable dye Disperse Orange 11 as a control to isolate photoisomerization. Samples are free-standing thin films with thickness that is small compared with the optical skin depth to assure uniform illumination and photomechanical response throughout their volume, which differentiates these studies from most others. Polarization-dependent measurements of the photomechanical stress response are used to deconvolute the contributions of angular hole burning, molecular reorientation and photothermal heating. While photo-isomerization of dopant molecules is commonly observed in dye-doped polymers, the shape changes of a molecule might not couple strongly to the host polymer through steric mechanical interactions, thus not contributing substantially to a macroscopic shape change. To gain insights into the effectiveness of such mechanical coupling, we directly probe the dopant molecules using dichroism measurements simultaneously while measuring the photomechanical response and find mechanical coupling to be small enough to make photothermal heating-mediated by the transfer of optical energy as heat to the polymer-the dominant mechanism. We also predict the fraction of light energy converted to mechanical energy using a model whose parameters are thermodynamic material properties that are measured with independent experiments. We find that in the thin-film geometry, these dye-doped glassy polymers are as efficient as any other material but their large Young's modulus relative to other organic materials, such as liquid crystal elastomers, makes them suitable in applications that require mechanically strong materials. The mechanical properties and the photomechanical response of thin films are observed to be significantly different than in fibers, suggesting that the geometry of the material and surface effects might play an important role.
这项工作旨在确定掺杂有光致异构染料分散红1的聚甲基丙烯酸甲酯聚合物的光机械响应机制，使用非异构染料分散橙11作为对照以分离光异构化。样品为独立的薄膜，其厚度与光学趋肤深度相比很小，以确保在其整个体积内有均匀的光照和光机械响应，这使这些研究有别于大多数其他研究。利用光机械应力响应的偏振相关测量来解卷积角孔烧蚀、分子重排和光热加热的贡献。虽然在染料掺杂聚合物中通常会观察到掺杂剂分子的光异构化，但分子的形状变化可能不会通过空间机械相互作用与主体聚合物强烈耦合，因此对宏观形状变化的贡献不大。为了深入了解这种机械耦合的有效性，我们在测量光机械响应的同时，使用二向色性测量直接探测掺杂剂分子，发现机械耦合小到足以使通过将光能作为热量传递给聚合物介导的光热加热成为主导机制。我们还使用一个模型预测转换为机械能的光能分数，该模型的参数是通过独立实验测量的热力学材料特性。我们发现，在薄膜几何结构中，这些染料掺杂的玻璃态聚合物与任何其他材料一样高效，但相对于其他有机材料（如液晶弹性体），它们的杨氏模量较大，这使其适用于需要机械强度高的材料的应用。观察到薄膜的机械性能和光机械响应与纤维中的显著不同，这表明材料的几何形状和表面效应可能起重要作用。
