Anisotropic particles are widely presented in nature, from colloidal to bacterial systems, and control over their interactions is of crucial importance for many applications, from self-assembly of novel materials to microfluidics. Placed in rapidly rotating external electric fields, colloidal particles attain a tunable long-range and many-body part in their interactions. For spherical colloids, this approach has been shown to offer rich capabilities to construct the tunable interactions via designing the internal structure of particles and spatial hodographs of external rotating fields, but in the case of anisotropic particles, the interactions remain poorly understood. Here, we show that tunable interactions between anisotropic rod-like and spheroidal colloidal particles in rotating electric or magnetic fields can be calculated and analyzed with the diagrammatic technique we developed in the present work. With this technique, we considered an in-plane rotating electric field, obtained the long-range asymptotics of the anisotropic interactions, calculated the tunable interactions between particles rotating synchronously, and found conditions for rotator repulsion. We compared the mechanisms providing tunable interactions to those for orientational (Keesom), induction (Debye), and dispersion (London) interactions in molecular systems and found that the tunable interactions between anisotropic particles represent a novel kind of dipole-like interaction. The method can be directly generalized for magnetically induced interactions, 3D systems, and fields with spatial hodographs. The results provide significant advance in theoretical methods for tunable interactions in colloids and, therefore, are of broad interest in condensed matter, chemical physics, physical chemistry, materials science, and soft matter.

中文翻译：

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旋转电场或磁场中各向异性胶体中可调相互作用的图解：新型偶极子相互作用

各向异性颗粒广泛存在于自然界中，从胶体系统到细菌系统，控制它们的相互作用对于许多应用至关重要，从新材料的自组装到微流体。置于快速旋转的外部电场中，胶体粒子在相互作用中获得了可调节的远程和多体部分。对于球形胶体，这种方法已被证明可以通过设计粒子的内部结构和外部旋转场的空间分布图来构建可调相互作用，但在各向异性粒子的情况下，相互作用仍然知之甚少。这里，我们表明，在旋转电场或磁场中各向异性棒状和球状胶体粒子之间的可调相互作用可以用我们在当前工作中开发的图解技术进行计算和分析。使用这种技术，我们考虑了面内旋转电场，获得了各向异性相互作用的长程渐近性，计算了同步旋转的粒子之间的可调相互作用，并找到了旋转体排斥的条件。我们将提供可调相互作用的机制与分子系统中的定向 (Keesom)、感应 (Debye) 和分散 (London) 相互作用进行了比较，发现各向异性粒子之间的可调相互作用代表了一种新型的偶极子相互作用。该方法可以直接推广到磁感应相互作用、3D 系统和具有空间全线图的场。该结果为胶体中可调相互作用的理论方法提供了重大进展，因此在凝聚态物质、化学物理、物理化学、材料科学和软物质方面具有广泛的兴趣。