Murugadoss Karthik, Dhar Purbarun, Das Sarit K
Department of Mechanical Engineering, Indian Institute of Technology Madras, 600036, Chennai, India.
Department of Mechanical Engineering, Indian Institute of Technology Ropar, 140001, Rupnagar, India.
Eur Phys J E Soft Matter. 2017 Jan;40(1):1. doi: 10.1140/epje/i2017-11491-x. Epub 2017 Jan 16.
The impact dynamics and spreading behavior of droplets impinging on structured superhydrophobic surfaces are dependent on both the droplet initial conditions and the surface texture. The equivalence of wetting and dewetting pressures is classically known to be a critical factor in determining the state of a droplet during the contact and spreading phases. The present study extensively examines the underlying physics behind this pressure balance during the impact process and its direct role in determining the wetting process. Extensive three-dimensional simulations employing droplet impact on a structured superhydrophobic surface has been performed to reveal the intricacies of the interactivities of the fluid with the microstructure. Insight onto the acute role of wetting pressures and the implications of the same on determining the wetting dynamics, with internal fluidics of the droplet during the impact process, has been discussed. The phenomenon of state transition from the Cassie-Baxter to the Wenzel up on impact is also investigated and the intricate flow mechanics at play within the posts has been presented. Knowledge of pressure distribution and internal flow structures within the droplet during its interaction with the surface at different instances of time reveals the root mechanism behind the impalement of the droplet to a fully wetting state. Analysis of the internal pressure and flow distribution also presents necessary justification for the existence of a partially impaled state. The time evolution of spread for different scenarios is in agreement with experimental results and the article provides insight onto the role of wetting pressure in determining fluidic interactions on such surfaces.
液滴撞击结构化超疏水表面的冲击动力学和扩散行为取决于液滴的初始条件和表面纹理。经典地，润湿压力和去湿压力的等效性是决定液滴在接触和扩散阶段状态的关键因素。本研究广泛考察了冲击过程中这种压力平衡背后的潜在物理原理及其在确定润湿过程中的直接作用。通过对结构化超疏水表面上的液滴撞击进行广泛的三维模拟，揭示了流体与微观结构相互作用的复杂性。讨论了润湿压力的关键作用及其对确定润湿动力学的影响，以及液滴在冲击过程中的内部流体情况。还研究了冲击时从卡西 - 巴克斯特状态到文策尔状态的转变现象，并展示了柱体内部复杂的流动力学。了解液滴在不同时刻与表面相互作用时内部的压力分布和流动结构，揭示了液滴完全润湿状态下刺入背后的根本机制。对内部压力和流动分布的分析也为部分刺入状态的存在提供了必要的依据。不同情况下扩散的时间演变与实验结果一致，本文还深入探讨了润湿压力在确定此类表面上流体相互作用中的作用。
