Capillary flows in flexible structures

Abstract

Interactions between capillary and elastic effects are relevant to a variety of applications, from micro- and nano-scale manufacturing to biological systems. In this thesis, we investigate capillary flows in extremely flexible, millimeter-scale cylindrical elastic tubes. We demonstrate that surface tension can cause sufficiently flexible tubes to collapse and coalesce spontaneously through non-axisymmetric buckling, and develop criteria for the initial deformation and complete collapse of a circular tube under capillary pressure. Experimental results are presented for capillary rise and evaporation of a liquid in a flexible tube. Several regimes are seen for the equilibrium state of a flexible tube under capillary pressure, and deformations of the tube walls are measured in different regimes and compared with a shell theory model. Good agreement is found between experiments and theory overall. Analysis and experimental results show that despite the complex and non-axisymmetric deformed shapes of cylindrical structures, the elastocapillary length used in previous literature for flat plates and sheets can also apply for flexible tubes, if the tube radius is used as the characteristic length scale.