Department of Materials Science and Engineering, Northwestern University, Evanston, IL, 60208, USA.
Department of Chemistry, Northwestern University, Evanston, IL, 60208, USA.
Soft Matter. 2023 Feb 1;19(5):851-857. doi: 10.1039/d2sm01519f.
The dynamic motion produced by precessing magnetic fields can drive matter into far-from-equilibrium states. We predict 1D periodic ordering in systems of precessing rods when magnetic interactions between rods remain insignificant. The precession angle of the rods is completely determined by the field's precession angle and the ratio of the field's precession frequency and the characteristic response frequency of the rods. We develop a molecular dynamics model that explicitly calculates magnetic interactions between particles, and we also simulate rods in the limit of a strong and fast precessing magnetic field where inter-rod magnetic interactions are negligible, using a purely steric model. Our simulations show how steric interactions drive the rods from a positionally disordered phase (nematic) to a layered (smectic) phase. As the rod precession angle increases, the nematic-smectic transition density significantly decreases. The minimization of unfavorable steric interactions also induces phase separation in binary mixtures of rods of different lengths. This effect is general to any force that produces precession in elongated particles. This work will advance the understanding and control of out-of-equilibrium soft matter systems.
进动磁场产生的动态运动可以将物质驱动到远离平衡的状态。当棒之间的磁相互作用可以忽略不计时，我们预测进动棒系统中会出现一维周期性有序。棒的进动角完全由磁场的进动角和磁场进动频率与棒的特征响应频率的比值决定。我们开发了一个分子动力学模型，该模型可以明确计算粒子之间的磁相互作用，并且我们还使用纯位模型模拟了强且快速进动磁场中的棒，其中棒之间的磁相互作用可以忽略不计。我们的模拟显示了位错相互作用如何将棒从无序位置（向列相）驱动到分层（近晶相）相。随着棒进动角的增加，向列-近晶相转变密度显著降低。不利的位错相互作用的最小化也会在不同长度棒的二元混合物中诱导相分离。这种效应对于任何产生细长粒子进动的力都是普遍存在的。这项工作将推动对非平衡软物质系统的理解和控制。
