The photoinduced crawling motion of crystals is a continuous motion that azobenzene molecular crystals exhibit under light irradiation. Such motion enables object manipulation at the microscale with a simple setup of fixed LED light sources. Transportation of nano-/micromaterials using photoinduced crawling motion has recently been reported. However, the details of the motion mechanism have not been revealed so far. Herein, we report visualization of the dynamics of fine particles in 4-(methylamino)azobenzene (4-MAAB) crystals under light irradiation via diffracted X-ray tracking (DXT). Continuously repeated melting and recrystallization of 4-MAAB crystals under light irradiation results in the flow of liquid 4-MAAB. Zinc oxide (ZnO) particles were introduced inside the 4-MAAB crystals to detect diffracted X-rays. The ZnO particles rotate with the flow of liquid 4-MAAB. By using white X-rays with a wide energy width, the rotation of each zinc oxide nanoparticle was detected as the movement of a bright spot in the X-ray diffraction pattern. It was clearly shown that the ZnO particles rotated increasingly as the irradiation light intensity increased. Furthermore, we also found anisotropy in the rotational direction of ZnO particles that occurred during the crawling motion of 4-MAAB crystals. It has become clear that the flow perpendicular to the supporting film of 4-MAAB crystals is enhanced inside the crystal during the crawling motion. DXT provides a unique means to elucidate the mechanism of photoinduced crawling motion of crystals.

中文翻译：

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通过衍射 X 射线跟踪可视化 4-(甲基氨基)偶氮苯晶体光致爬行运动的动力学


晶体的光致爬行运动是偶氮苯分子晶体在光照射下表现出的连续运动。这种运动可以通过固定 LED 光源的简单设置实现微尺度的物体操纵。最近报道了利用光诱导爬行运动运输纳米/微米材料。不过，目前尚未透露运动机制的细节。在此，我们通过衍射 X 射线跟踪 (DXT) 报告了光照射下 4-(甲基氨基)偶氮苯 (4-MAAB) 晶体中细颗粒动力学的可视化。 4-MAAB晶体在光照射下不断重复熔化和重结晶，导致液体4-MAAB的流动。将氧化锌 (ZnO) 颗粒引入 4-MAAB 晶体内部以检测衍射 X 射线。 ZnO 颗粒随着液体 4-MAAB 的流动而旋转。通过使用具有宽能量宽度的白色X射线，每个氧化锌纳米粒子的旋转被检测为X射线衍射图案中亮点的移动。清楚地表明，随着照射光强度的增加，ZnO 颗粒的旋转逐渐增加。此外，我们还发现了 4-MAAB 晶体爬行运动过程中 ZnO 颗粒旋转方向的各向异性。很明显，在爬行运动期间，晶体内部垂直于 4-MAAB 晶体支撑膜的流动得到增强。 DXT 提供了一种独特的方法来阐明晶体光致爬行运动的机制。