Front dynamics and fingering of a driven contact line
Front dynamics and fingering of a driven contact line
复制标题
DOI：
10.1017/s0022112098002390
复制
发表时间：
1998-10
影响因子：
3.7
通讯作者：
Igor Veretennikov;A. Indeikina;Hsueh-Chia Chang
中科院分区：
文献类型：
--
作者：
Igor Veretennikov;A. Indeikina;Hsueh-Chia Chang
使用摄影成像和染料追踪实验，我们仔细研究了当有限体积的部分润湿流体在重力驱动下在稍微倾斜的干燥平面上扩散时接触线的动力学。与分子力驱动的铺展机制不同，在干燥平面上的重力驱动铺展被证明具有特征界面“鼻子”，当膜厚度超过毛细管长度时，该界面“鼻子”悬于接触线之上。鼻子前部内存在一个独特的循环涡流，其传播速度与超过 10−2 的毛细管数量相对应。我们的实验表明，当薄膜变薄且表观接触角 θ 达到 π/2 且上述鼻部配置无法在整个前端持续时，就会发生重力驱动的直前端的指法。指状件保持鼻子结构，而前部的其余部分演变成楔形结构，并由于对流体流动的巨大阻力而突然停止。这种指法机制对流体润湿性、噪音或表面异质性不敏感。通过匹配渐近，我们在 θ=π/2 处获得了指法位置和速度的准确估计，与测量值非常一致。这种新机制与其他不稳定和敏感的指法机制不同，并且当薄膜变薄时，只要直前端的 θ 从上方接近 π/2 即可发挥作用。
Using photographic imaging and dye tracking experiments, we scrutinize the dynamics of a contact line when a finite volume of partially wetting fluid is driven by gravity to spread over a slightly inclined dry plane. Unlike spreading mechanisms driven by molecular forces, gravity-driven spreading over a dry plane is shown to possess a characteristic interfacial ‘nose’ that overhangs the contact line when the film thickness is in excess of the capillary length. A unique recirculating vortex exists within the nose front which spreads at speeds corresponding to capillary numbers in excess of 10−2. Our experiments show that fingering from a gravity-driven straight front occurs when the above nose configuration cannot be sustained across the entire front as the film thins and the apparent contact angle θ reaches π/2. The fingers retain the nose configuration while the remaining segments of the front evolve into a wedge configuration and stop abruptly due to their large resistance to fluid flow. This fingering mechanism is insensitive to fluid wettability, noise or surface heterogeneity. Via matched asymptotics, we obtain accurate estimates of fingering position and speed at θ=π/2 that are in good agreement with measured values. This new mechanism is distinct from other instability and sensitivity fingering mechanisms and can be in play whenever θ of the straight front approaches π/2 from above as the film thins.