Spontaneous localized fluid release on swelling fibres

When immersed into a favourable solvent, many fibres, in particular vegetable, wood or animal fibres, will absorb liquid and swell. When a single drop of solvent is deposited, the fibre first locally swells at the drop position, then the liquid slowly diffuses within the fibre. We study the absorption dynamics of several drops placed on a fibre of fixed length. We show that during absorption, there is a swelling-induced global change in the tension of the fibre. If the drops are close enough to one another, this change induces the release of fluid out of the fibre (i.e. deswelling) in previously fluid-saturated regions. We identify the mechanisms underlying this transient localized fluid release, and identify the conditions for which it occurs in order to build a phase diagram as a function of the drops volume and distance, both experimentally and numerically using a linear poroelastic model.