Departamento de Ingeniería Aeroespacial y Mecánica de Fluidos, Universidad de Sevilla , Camino de los Descubrimientos S/N, 41092 Sevilla, Spain.
Langmuir. 2016 Jul 12;32(27):6815-24. doi: 10.1021/acs.langmuir.6b01241. Epub 2016 Jun 29.
The effect of a surrounding, dielectric, liquid environment on the dynamics of a suddenly electrified liquid drop is investigated both numerically and experimentally. The onset of stability of the droplet is naturally dictated by a threshold value of the applied electric field. While below that threshold the droplet retains its integrity, reaching to a new equilibrium state through damped oscillations (subcritical regime), above it electrical disruption takes place (supercritical regime). In contrast to the oscillation regime, the dynamics of the electric droplet disruption in the supercritical regime reveals a variety of modes. Depending on the operating parameters and fluid properties, a drop in the supercritical regime may result in the well-known tip streaming mode (with and without whipping instability), in droplet splitting (splitting mode), or in the development of a steep shoulder at the elongating front of the droplet that expands radially in a sort of "splashing" (splashing mode). In both splitting and splashing modes, the sizes of the progeny droplets, generated after the breakup of the mother droplet, are comparable to that of the mother droplet. Furthermore, the development in the emission process of the shoulder leading to the splashing mode is described as a parametrical bifurcation, and the parameter governing that bifurcation has been identified. Physical analysis confirms the unexpected experimental finding that the viscosity of the dynamically active environment is absent in the governing parameter. However, the appearance of the splitting mode is determined by the viscosity of the outer environment, when that viscosity overcomes a certain large value. These facts point to the highly nonlinear character of the drop fission process as a function of the droplet volume, inner and outer liquid viscosities, and applied electric field. These observations may have direct implications in systems where precise control of the droplet size is critical, such as in analytical chemistry and "drop-on-demand" processes driven by electric fields.
周围介电液体环境对突然带电液滴动力学的影响进行了数值和实验研究。液滴的稳定性起始于施加电场的阈值。低于该阈值时，液滴保持完整，通过阻尼振荡达到新的平衡状态（亚临界状态），高于该阈值则发生电击穿（超临界状态）。与振荡状态相比，超临界状态下的电液滴破坏动力学呈现出多种模式。根据操作参数和流体特性，超临界状态下的液滴可能会导致众所周知的尖端流动模式（有和没有鞭打不稳定性）、液滴分裂（分裂模式），或在伸长的液滴前端形成陡峭的肩部，以某种“飞溅”（飞溅模式）径向扩展。在分裂和飞溅模式中，母液滴破裂后产生的子液滴的尺寸与母液滴相当。此外，肩部引发飞溅模式的发射过程的发展被描述为参数分岔，并且已经确定了控制该分岔的参数。物理分析证实了一个意外的实验发现，即动态活跃环境的粘度在控制参数中不存在。然而，当外部环境的粘度超过一定大的值时，分裂模式的出现取决于外部环境的粘度。这些事实表明，液滴裂变过程作为液滴体积、内部和外部液体粘度以及施加电场的函数，具有高度的非线性特征。这些观察结果可能对需要精确控制液滴尺寸的系统有直接影响，例如在分析化学和电场驱动的“按需滴液”过程中。
