Spatafora-Salazar Aldo, Lobmeyer Dana M, Cunha Lucas H P, Joshi Kedar, Biswal Sibani Lisa
Department of Chemical and Biomolecular Engineering, Rice University, Houston, TX 77005.
Department of Physics, Institute for Soft Matter Synthesis and Metrology, Georgetown University, Washington, DC 20057.
Proc Natl Acad Sci U S A. 2024 Oct 8;121(41):e2404145121. doi: 10.1073/pnas.2404145121. Epub 2024 Sep 30.
Precise control at the colloidal scale is one of the most promising bottom-up approaches to fabricating new materials and devices with tunable and precisely engineered properties. Magnetically driven colloidal assembly offers great versatility because of the ability to externally tune particle-particle interactions and to construct a host of particle arrangements. However, despite previous efforts to probe the parameter space, global orientational control in conjunction with two-dimensional microstructural control has remained out of reach. Furthermore, the magnetic relaxation time of superparamagnetic beads has been largely overlooked despite being a key feature of the magnetic response. Here, we take advantage of the magnetic relaxation time of superparamagnetic beads in an alternating rotating magnetic field and show how harnessing this feature facilitates the formation of oriented clusters. The orientation of these clusters can be controlled by field parameters. Using experiments, simulations, and theory, we probe a two-particle system (dimer) under this alternating rotating magnetic field and use its dynamics to provide insights into the collective response that forms clusters. We find that the type of field has significant implications for the dipolar interactions between the colloids because of the nonnegligible magnetic relaxation. Moreover, we find that the competing time scales of the magnetic relaxation and the alternating field generate an anisotropic interaction potential that drives cluster alignment. By exploiting the magnetic relaxation time of magnetic systems, we can tailor new types of interparticle interactions, thereby expanding the capabilities of colloidal assembly in engineering unique materials and devices.
在胶体尺度上进行精确控制是制造具有可调谐和精确工程特性的新材料和器件最有前景的自下而上方法之一。磁驱动胶体组装具有很大的通用性，因为它能够从外部调节粒子间相互作用并构建多种粒子排列。然而，尽管此前人们努力探索参数空间，但实现二维微观结构控制下的全局取向控制仍然难以企及。此外，超顺磁珠的磁弛豫时间尽管是磁响应的一个关键特征，但在很大程度上被忽视了。在此，我们利用超顺磁珠在交变旋转磁场中的磁弛豫时间，并展示了如何利用这一特性促进取向团簇的形成。这些团簇的取向可以通过场参数来控制。我们通过实验、模拟和理论研究了在这种交变旋转磁场下的双粒子系统（二聚体），并利用其动力学来深入了解形成团簇的集体响应。我们发现，由于不可忽略的磁弛豫，场的类型对胶体间的偶极相互作用有重大影响。此外，我们发现磁弛豫和交变场相互竞争的时间尺度产生了一种驱动团簇排列的各向异性相互作用势。通过利用磁系统的磁弛豫时间，我们可以定制新型的粒子间相互作用，从而扩展胶体组装在制造独特材料和器件方面的能力。
