Field-Driven Reversible Alignment and Gelation of Magneto-Responsive Soft Anisotropic Microbeads
Field-Driven Reversible Alignment and Gelation of Magneto-Responsive Soft Anisotropic Microbeads
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DOI：
10.1021/acs.jpcb.1c03158
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发表时间：
2021-07-13
影响因子：
3.3
通讯作者：
Velev, Orlin D.
中科院分区：
文献类型：
--
作者：
Castellanos, Natasha, I;Bharti, Bhuvnesh;Velev, Orlin D.
磁场可以不受限制地控制胶体颗粒的组装、动力学和重新配置。然而，合成具有可切换磁偶极矩的“软”胶体颗粒仍然是一个挑战，主要是由于相邻纳米颗粒的偶极子的强耦合。在这篇文章中，我们提出了一种方法来克服这一根本性的挑战的基础上的战略，合成软微珠与可调的剩余偶极矩。微珠由聚二甲基硅氧烷（PDMS）基质和内部嵌入的磁性纳米颗粒（MNP）组成。在合成过程中，MNP在PDMS珠基质内的分布和取向由外部磁场控制，从而允许制备具有内部磁性对齐的纳米颗粒链的各向异性PDMS微珠。我们研究并提出了磁排列的MNP微球和随机分布的MNP微球之间的磁相互作用的差异。微珠悬浮液中的颗粒间相互作用与嵌入对齐的MNP链的结果在自发形成的磁化网络，由于剩余磁化。我们证明了结构的可调谐性，通过施加磁化，退磁和再磁化周期，引起形成，分裂，和改造的二维离散网络。微珠悬浮液的机械响应通过振荡流变学进行量化，并与磁性微珠形成网络的倾向相关。我们还通过实验将微珠的二维排列与地球磁场的方向相关联。总的来说，结果证明，软磁微珠能够实现丰富的各种结构，并可以作为一个实验工具箱，用于模拟偶极系统中的相互作用，从而产生各种非线性网络，新型磁流变材料和智能凝胶。
Magnetic fields offer untethered control over the assembly, dynamics, and reconfiguration of colloidal particles. However, synthesizing "soft" colloidal particles with switchable magnetic dipole moment remains a challenge, primarily due to strong coupling of the dipoles of the adjacent nanoparticles. In this article, we present a way to overcome this fundamental challenge based on a strategy to synthesize soft microbeads with tunable residual dipole moment. The microbeads are composed of a polydimethylsiloxane (PDMS) matrix with internally embedded magnetic nanoparticles (MNPs). The distribution and orientation of the MNPs within the PDMS bead matrix is controlled by an external magnetic field during the synthesis process, thus allowing for the preparation of anisotropic PDMS microbeads with internal magnetically aligned nanoparticle chains. We study and present the differences in magnetic interactions between microbeads containing magnetically aligned MNPs and microbeads with randomly distributed MNPs. The interparticle interactions in a suspension of microbeads with embedded aligned MNP chains result in the spontaneous formation of percolated networks due to residual magnetization. We proved the tunability of the structure by applying magnetization, demagnetization, and remagnetization cycles that evoke formation, breakup, and reformation of 2D percolated networks. The mechanical response of the microbead suspension was quantified by oscillatory rheology and correlated to the propensity for network formation by the magnetic microbeads. We also experimentally correlated the 2D alignment of the microbeads to the direction of earth's magnetic field. Overall, the results prove that the soft magnetic microbeads enable a rich variety of structures and can serve as an experimental toolbox for modeling interactions in dipolar systems leading to various percolated networks, novel magneto-rheological materials, and smart gels.