Elastocapillary lifting and encapsulation of water by a triangular elastic film under gravity

Abstract

We investigate the encapsulation of water by a thin elastic film as a minimal model of elastocapillary self-folding with fluid transport. An equilateral triangular polydimethylsiloxane film is lifted quasi-statically from a water surface, while its side length and thickness are systematically varied. Depending on these parameters, the film exhibits three distinct morphologies: folding, recoiling, and liquid encapsulation. We show that the morphology is governed by the interplay of surface, gravitational, and bending energies, and that encapsulation occurs only within a narrow parameter region where the elastocapillary, elastogravity, and capillary length scales become comparable. This provides a simple physical criterion for liquid encapsulation by elastic films.