High-gravity spreading of liquid coatings on wetting flexible substrates.

摘要

This work describes a mechanical approach with high gravity for manipulating the capillary length and spreading of liquid coatings on flexible substrates. Experimental verification in the literature has focused on cases under standard gravity on earth, and to the author's 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 increase the rate of spreading without producing wasted material inherent to conventional spin coating with acceleration tangent to a wetted substrate. 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. Then, the spreading shifts from a surface tension-driven regime or early transitional regime to a faster spreading regime, which is dominated by gravitational forces. 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-?l droplet to a film with thickness of 40 microns, 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 flexible substrates exposed to more than 100 g's of acceleration.