Oscillation Dynamics of Drops on Immiscible Thin Liquid Films

Abstract

While drop oscillation dynamics has been widely studied for many decades, the influence of a moving contact line on the oscillation modes of drops remains underexplored. Herein, we report the oscillation dynamics of drops on thin liquid films with different viscosities where lower viscosities provide a slipping surface and higher viscosities immobilize the contact line. A gently deposited drop onto an oil film undergoes shape oscillations due to capillarity, where the frequency, amplitude, and apparent contact angle are tracked via a high-speed camera. This study demonstrates that restraining the mobility of the drop contact line by increasing the viscosity of a thin oil film underneath the drop increases the extent of the drop oscillation time as well as affecting the natural frequency of the drop oscillation. The drop oscillation time was defined by the time at which the changes in the drop height dropped to values less than 1% of the equilibrium height. The experimental results for the first longitudinal mode oscillation frequencies as a function of the equilibrium contact angles for the pinning and slipping contact lines were in good agreement with previously reported numerical simulations and model predictions.

Numerical Analysis of Droplet Impact on the Convex Surface with Liquid Film

“…Many researchers use the CLSVOF method to simulate the process of droplet impact on the liquid film, and the numerical simulation results are consistent with the experimental results, thereby proving that the CLSVOF method is effective in analyzing a droplet impact. 24−26 Although a substantial number of studies have been carried out on the dynamic behavior of droplets impinging on the liquid film, most of them focus on the effects of the physical properties, 27,28 thickness, 29 and impact velocity. However, a few studies have been conducted on the surface shape.…”

“…Although a substantial number of studies have been carried out on the dynamic behavior of droplets impinging on the liquid film, most of them focus on the effects of the physical properties, , thickness, and impact velocity. However, a few studies have been conducted on the surface shape.…”