Urano Rio, Kawai Mika, Mitsumata Tetsu
Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan.
Soft Matter. 2023 Nov 1;19(42):8091-8100. doi: 10.1039/d3sm01061a.
The magnetic response of dynamic modulus was investigated for polyurethane-based magnetic elastomers densely packed with magnetic particles with different diameters (7 μm and 235 μm). The density indicated that voids were created at volume fractions of magnetic particles above 0.47 (87 wt%) for 7 μm and 0.44 (85 wt%) for 235 μm. At volume fractions below these critical volume fractions, no apparent increase in the storage modulus was observed for the magnetic elastomers by applying a magnetic field of 500 mT. At above the critical volume fractions, dramatic increase in the storage modulus was observed; the maximum changes in the storage modulus were 8.0 MPa and 6.0 MPa, which corresponds to the relative changes in the modulus (Δ/) of 74% and 11%, for magnetic elastomers of 7 μm and 235 μm, respectively. These results strongly indicate that the creation of a space enables the movement of magnetic particles in the elastomer resulting in the formation of chain structure. It was also found that the creation of a space in the matrix of elastomers can be detected by the critical strain, the amplitude of Payne effect, or the critical magnetic field since significant changes in these parameters were found at the critical volume fraction for both magnetic elastomers. SEM images displayed a clear difference in the creation process of voids that magnetic particles of 7 μm suddenly formed many macroscopic voids at the critical volume fraction, meanwhile, magnetic particles of 235 μm formed gaps around magnetic particles. The storage modulus for both magnetic elastomers changed perfectly in response to the magnetic field even after the on-off switching of the magnetic field with 20 cycles.
研究了填充不同直径（7μm和235μm）磁性颗粒的聚氨酯基磁性弹性体动态模量的磁响应。密度表明，对于7μm的磁性颗粒，当体积分数高于0.47（87 wt%）时会产生空隙；对于235μm的磁性颗粒，当体积分数高于0.44（85 wt%）时会产生空隙。在低于这些临界体积分数时，对磁性弹性体施加500 mT的磁场，未观察到储能模量有明显增加。在高于临界体积分数时，观察到储能模量急剧增加；对于7μm和235μm的磁性弹性体，储能模量的最大变化分别为8.0 MPa和6.0 MPa，分别对应模量相对变化（Δ/）为74%和11%。这些结果有力地表明，空隙的产生使磁性颗粒能够在弹性体中移动，从而形成链状结构。还发现，由于在两种磁性弹性体的临界体积分数处这些参数都有显著变化，因此可以通过临界应变、佩恩效应振幅或临界磁场来检测弹性体基质中空隙的产生。扫描电子显微镜图像显示了空隙产生过程中的明显差异，7μm的磁性颗粒在临界体积分数时突然形成许多宏观空隙，而235μm的磁性颗粒在磁性颗粒周围形成间隙。即使在磁场进行20次开-关切换后，两种磁性弹性体的储能模量仍能完美地响应磁场变化。
