Effect of high-frequency in-plane substrate vibration on a three-phase contact angle

Abstract

We investigate analytically the contribution of high-frequency horizontal (in-plane) vibration of a solid substrate to the apparent contact angle of a liquid meniscus in the framework of the lubrication approximation. We show that oscillatory excitation invokes a drift of liquid within the meniscus resulting from nonlinear contributions from both the motion of the solid surface and acoustically induced capillary waves at the free surface of the liquid. Our analysis reveals that under this type of excitation, the relative increase of the steady apparent contact angle is proportional to the product of the capillary and Reynolds numbers.

Volume and Frequency-Independent Spreading of Droplets Driven by Ultrasonic Surface Vibration

“…This threshold was relatively similar for all combinations of fluids, droplet sizes, and vibration frequencies. This is a significant departure from droplet spreading at low frequencies where spreading is very sensitive to droplet volume, liquid type, and vibration frequency [8,10,[12][13][14][15]. The initiation of droplet spreading is calculated using a post-processing algorithm and is noted as a black 'x' in each example.…”

“…Vibration has been shown to affect the wetting state of liquids [8][9][10][11][12][13][14][15][16][17], but the effects are highly coupled to droplet volume, surface structure, and fluid properties. Even contact angle changes the natural frequencies of the droplet oscillation [18].…”

“…Prior research examining the wetting effects of low-frequency vibration has focused on high amplitude vibrations that are tuned to droplet volume vibration modes. The studies can be generally split into two categories: vertical [8][9][10] and horizontal surface excitation [11][12][13][14][15]19]. Low-frequency excitations have been shown to excite droplet vibrations at the excitation frequency and multiples of transitions) on textured surfaces [11,20].…”