触发场中胶体悬浮液定向自组装的扩展状态图。,Langmuir

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触发场中胶体悬浮液定向自组装的扩展状态图。
Langmuir ( IF 3.7 ) Pub Date : 2020-07-22 , DOI: 10.1021/acs.langmuir.0c01616
Hojin Kim ₁ , Moujhuri Sau ₁ , Eric M Furst ₁

Affiliation

在恒定磁场强度H = 1750A·m ^{–1的情况}下，在0.3 < f的频率范围内切换磁场的开启和关闭时，研究了处于翻转磁场中的微米直径顺磁球的悬浮结构和组装动力学。<5 Hz和占空比值（在一个触发周期内磁场开启的时间分数）0.05≤ξ≤0.8。经过足够的时间后，在翻转场中形成了五个微结构，分别是流体，柱状，渗滤，椭圆形和垂直，并确定了它们的动力学路径。对于椭球形的微结构，在早期扩散驱动的颗粒聚集会被流体状破碎所取代。对于柱状和渗透结构，这种粗化在破裂之前就停止了。随着切换占空比的减小，每种结构的频率范围变窄，让位于非结构化流体。小于ξ<0.1，仅观察到流体状态。流体，柱状，渗滤和椭球形的微观结构的存在与Sherman等人的理论和计算工作所预言的一致。（谢尔曼（ZM）；罗森塔尔，H。天鹅，JW 朗缪尔 2018， 34，1029至41年）。垂直于磁场连接的微结构的识别值为0.1≤ξ≤0.3和1.6 < f <3.7 Hz。垂直微结构还显示出具有连续旋转，破裂和聚结事件的动力学。

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An Expanded State Diagram for the Directed Self-Assembly of Colloidal Suspensions in Toggled Fields.

The suspension structure and assembly kinetics of micrometer-diameter paramagnetic spheres in toggled magnetic fields are investigated at a constant field strength H = 1750A·m^–1 while toggling the field on and off over the frequency range 0.3<f<5 Hz and duty ratio values (the fraction of time the field is on over one toggle period) 0.05 ≤ ξ ≤ 0.8. Five microstructures form after sufficient time in the toggled field, fluid, columnar, percolated, ellipsoidal-shaped, and perpendicular, and their kinetic pathways are identified. For ellipsoidal-shaped microstructures, diffusion-driven particle aggregation at early times gives way to a fluid-like breakup. For columnar and percolated structures, this coarsening arrests before breakup. As the toggling duty cycle decreases, the range of frequencies for each structure narrows, giving way to an unstructured fluid; below ξ<0.1, only the fluid state is observed. The existence of fluid, columnar, percolated, and ellipsoidal-shaped microstructures agrees well with those predicted by the theoretical and computational work of Sherman et al. (Sherman, Z. M.; Rosenthal, H.; Swan, J. W. Langmuir 2018, 34, 1029−1041). Microstructures that connect perpendicularly to the magnetic field are identified for 0.1 ≤ ξ ≤ 0.3 and 1.6<f<3.7 Hz. Perpendicular microstructures also exhibit emergent dynamics with continuous rotation, breakup, and coalescence events.

更新日期：2020-08-25

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