Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
J Chem Phys. 2014 Mar 28;140(12):124505. doi: 10.1063/1.4869113.
Spatially non-uniform electric fields can phase separate initially homogeneous mixtures of liquids. Here, we investigate the dynamics of phase separation using a modified Cahn-Hilliard equation and find three kinetically distinct regimes in the phase diagram: (1) discontinuous and (2) continuous interface formation kinetics and (3) a metastable state. By considering all possible solutions of the free energy density, we are able to map the time behavior in the vicinity of the interface as a series of equilibrium interfaces "moving" in the parameter space of the equilibrium phase diagram. The kinetic phase diagram, consequently, contains an "emergence line" that delineates the experimental conditions where a non-equilibrium interface can be forbidden from forming close to a charged surface. When the interface can form on the charged surface, an abrupt transition occurs that produces electrical signatures which distinguish the discontinuous from the continuous transition region. The third kinetic regime describes non-spontaneous phase separation and potential metastable states, and is bounded by the "electrostatic spinodal" line. The equivalent kinetic regimes exist in closed systems and can be found by considering an effective concentration in an open system.
非均匀电场会使最初均匀的液体混合物发生相分离。在这里，我们使用改进的 Cahn-Hilliard 方程研究了相分离动力学，在相图中发现了三个动力学上不同的区域：（1）不连续和（2）连续界面形成动力学和（3）亚稳状态。通过考虑自由能密度的所有可能解，我们能够将界面附近的时间行为映射为一系列在平衡相图的参数空间中“移动”的平衡界面。因此，动力学相图包含一条“出现线”，它划定了实验条件，在这些条件下，非平衡界面可以被禁止在带电表面附近形成。当界面可以在带电表面上形成时，会发生突然的转变，产生可以区分不连续和连续转变区域的电信号。第三个动力学区域描述了非自发的相分离和潜在的亚稳状态，由“静电旋节线”限定。在封闭系统中存在等效的动力学区域，可以通过在开放系统中考虑有效浓度来找到。
