Chen Kejun, Watanabe Mayuko, Takeda Yoshihiro, Maruyama Takayuki, Uesugi Masayuki, Takeuchi Akihisa, Suzuki Motohiro, Uesugi Kentaro, Yasutake Masahiro, Kawai Mika, Mitsumata Tetsu
Graduate School of Science and Technology, Niigata University, Niigata950-2181, Japan.
Rigaku Corporation, Tokyo196-8666, Japan.
Langmuir. 2022 Nov 8;38(44):13497-13505. doi: 10.1021/acs.langmuir.2c02004. Epub 2022 Oct 26.
In situ observation of the migration and structure formation of magnetic particles in polyurethane elastomers was carried out by X-ray computed tomography using synchrotron radiation. The mean diameter of the magnetic particles was 7.0 μm, and the volume fraction was = 0.24 at its maximum. The exposure time was 100 ms/frame, and the pixel size was 0.458 μm/pixel. The orientation angle and the volume fraction of the maximum aggregate were analyzed using commercial software for image analysis. The orientation angle for magnetic elastomers with = 0.24 was approximately 55° at 0 mT and decreased remarkably with the magnetic field. At magnetic fields above 150 mT, the orientation angle gradually decreased with the field and showed a constant value of 38° at 300 mT, suggesting that magnetic particles move and form a chain-like structure although the chains do not align perfectly in the direction of the magnetic field. On the other hand, the volume fraction of the maximum aggregate was constant at magnetic fields below 100 mT, and it significantly increased with the field, indicating that magnetic particles were connected to each other and developed into a macroscopic structure with anisotropy. Dynamic viscoelastic measurements revealed that the storage modulus of the magnetic elastomers cannot be simply scaled by the orientation angle. It was also found that the volume fraction of the maximum aggregate is a good parameter for explaining the huge increase in the storage modulus. The dynamic movement of magnetic particles when a magnetic field of 300 mT was switched on and off was also successfully observed. When the field was switched on, magnetic particles connected instantly and their aggregates were rapidly elongated in the direction of the magnetic field. When the field was switched off, some of the connections between aggregates were broken; however, most of the aggregates did not return to the original position even 5 min after being switched off.
利用同步辐射X射线计算机断层扫描技术对聚氨酯弹性体中磁性颗粒的迁移和结构形成进行了原位观察。磁性颗粒的平均直径为7.0μm，其最大体积分数为0.24。曝光时间为100ms/帧，像素尺寸为0.458μm/像素。使用商业图像分析软件分析了最大聚集体的取向角和体积分数。体积分数为0.24的磁性弹性体在0mT时的取向角约为55°，并随磁场显著减小。在高于150mT的磁场下，取向角随磁场逐渐减小，在300mT时呈现38°的恒定值，这表明磁性颗粒移动并形成链状结构，尽管链并未完全沿磁场方向排列。另一方面，在低于100mT的磁场下，最大聚集体的体积分数保持恒定，并且随磁场显著增加，这表明磁性颗粒相互连接并发展成具有各向异性的宏观结构。动态粘弹性测量表明，磁性弹性体的储能模量不能简单地通过取向角来缩放。还发现最大聚集体的体积分数是解释储能模量大幅增加的一个良好参数。还成功观察到了300mT磁场开启和关闭时磁性颗粒的动态运动。当磁场开启时，磁性颗粒立即连接，其聚集体在磁场方向迅速伸长。当磁场关闭时，聚集体之间的一些连接被破坏；然而，即使在关闭5分钟后，大多数聚集体也没有回到原始位置。
