High-gravity spreading of liquid puddles on wetting flexible substrates

Abstract

This work describes a mechanical approach for manipulating the capillary length and spreading of liquid coatings on flexible substrates with high gravity. Experimental verification in the literature has focused on cases under standard gravity on earth, and to the authors' knowledge, this work is the first to explore its relevance to spreading puddles under high gravity. By using centrifugation with a high-density liquid base underneath a coated substrate, it is possible to apply acceleration normal to a substrate to decrease the capillary length and increase the rate of spreading. Due to the nature of centrifugation, this method works primarily on flexible substrates, which bend with a curvature that conforms to a contour of uniformly distributed centrifugal acceleration. With high gravity of 600 g applied, the capillary length reduces by a factor of 24.5, and the spreading shifts from "transient spreading" between the surface tensiondriven and gravity-driven regimes to the gravity-driven regime. Experimental results show that high gravitational acceleration will enhance the rate of spreading such that a puddle, which would require 12 hours under standard gravity on earth to go from an 8-µl droplet to a 40-µm thick puddle, would require less than 1 minute under 600 g. Overall, this work suggests that previously derived expressions for gravity-driven spreading of puddles under earth's standard gravity extend to predicting the behavior of puddles spreading on smooth, wetting substrates exposed to more than 100 g's of acceleration.

Viscous Force Retards Initial Droplet Spreading

“…The inertial force and the viscous force act as resistance forces during spreading. Plenty studies have been carried out on the spreading dynamics of liquid due to its importance in science and engineering applications [7][8][9][10][11][12][13][14][15][16][17][18][19][20] .…”

“…In previous studies on the spreading dynamics, the geometrical evolution of liquid droplet was usually captured by a high-speed camera. − However, it is very expensive to achieve a time resolution of 1 μs. Recently, an electrical method with a high temporal and spatial resolution has been proposed to characterize the spreading process of conductive droplets.…”