Curvature-driven propulsion of floating films: Part 1

Water striders can propel themselves up a curved liquid meniscus by repositioning their feet to match the curvature of their destination, providing one example of propulsion along an interface due to a mismatch in geometry [1]. How does a highly-flexible elastic solid respond when it is placed on a liquid surface with a curvature different than its own? We find that flat films spontaneously flee highly-curved menisci towards flatter regions, whereas curved shells are attracted to regions with finite curvature. These findings are borne out of experiments where polymer films are released from different initial positions in overfilled petri dishes. Focusing on flat films that are ~1 cm wide and ~100 nm thick, we examine the effects of film thickness, liquid viscosity, and meniscus curvature on the velocity of this motion. Our data across a wide range of parameters are in agreement with a theoretical picture in which the sheet is propelled by its ability to cover progressively more liquid surface area in the regions where it is attracted [2]. We develop this model and its consequences in the next talk. (This is part 1 of a 2-talk series.)

[1] Huet al. Nature (2005)
[2] Paulsen et al., Nat. Mater. 14 (2015).