Maestas Joseph R, Ma Fuduo, Wu Ning, Wu David T
Department of Chemistry, Colorado School of Mines, Golden, Colorado 80401, United States.
Department of Chemical and Biological Engineering, Colorado School of Mines, Golden, Colorado 80401, United States.
ACS Nano. 2021 Feb 23;15(2):2399-2412. doi: 10.1021/acsnano.0c04939. Epub 2021 Feb 11.
Externally applied electric fields have previously been utilized to direct the assembly of colloidal particles confined at a surface into a large variety of colloidal oligomers and nonclose-packed honeycomb lattices ( , , 7839-7842). The colloids under such confinement and fields are observed to spontaneously organize into bilayers near the electrode. To extend and better understand how particles can come together to form quasi-two-dimensional materials, we have performed Monte Carlo simulations and complementary experiments of colloids that are strongly confined between two electrodes under an applied alternating current electric field, controlling field strength and particle area fraction. Of particular importance, we control the fraction of particles in the upper lower plane, which we describe as asymmetric confinement, and which effectively modulates the coordination number of particles in each plane. We model the particle-particle interactions using a Stockmayer potential to capture the dipolar interactions induced by the electric field. Phase diagrams are then delineated as a function of the control parameters, and a theoretical model is developed in which the energies of several idealized lattices are calculated and compared. We find that the resulting theoretical phase diagrams agree well with simulation. We have not only reproduced the structures observed in experiments using parameters that are close to experimental conditions but also found several previously unobserved phases in the simulations, including a network of rectangular bands, zig zags, and a sigma lattice, which we were then able to confirm in experiment. We further propose a simple way to precisely control the number ratio of particles between different planes, that is, superimposing a direct current electric field with the alternating current electric field, which can be implemented conveniently in experiments. Our work demonstrates that a diverse collection of materials can be assembled from relatively simple ingredients, which can be analyzed effectively through comparison of simulation, theory, and experiment. Our model further explains possible pathways between different phases and provides a platform for examining phases that have yet to be observed in experiments.
外部施加的电场此前已被用于引导限制在表面的胶体颗粒组装成各种各样的胶体低聚物和非密堆积蜂窝晶格（，，7839 - 7842）。在这种限制和电场条件下，观察到胶体在电极附近自发组织成双层结构。为了扩展并更好地理解颗粒如何聚集形成准二维材料，我们进行了蒙特卡罗模拟以及补充实验，研究在施加的交流电场下被强烈限制在两个电极之间的胶体，控制场强和颗粒面积分数。特别重要的是，我们控制上下平面中颗粒的比例，我们将其描述为非对称限制，这有效地调节了每个平面中颗粒的配位数。我们使用斯托克迈耶势来模拟颗粒间相互作用，以捕捉电场诱导的偶极相互作用。然后根据控制参数描绘相图，并建立一个理论模型，计算并比较几种理想化晶格的能量。我们发现所得的理论相图与模拟结果吻合良好。我们不仅使用接近实验条件的参数重现了实验中观察到的结构，还在模拟中发现了几个先前未观察到的相，包括矩形带网络、之字形和西格玛晶格，然后我们能够在实验中证实这些相。我们进一步提出了一种精确控制不同平面间颗粒数量比的简单方法，即叠加直流电场和交流电场，这在实验中可以方便地实现。我们的工作表明，可以从相对简单的成分组装出各种不同的材料，通过模拟、理论和实验的比较可以有效地对其进行分析。我们的模型进一步解释了不同相之间可能的转变途径，并为研究实验中尚未观察到的相提供了一个平台。
