Spontaneous drop interactions on swellable fibres

Swelling of individual fibers when exposed to a favourable solvent is very common for most natural fibrous materials. In this study, we analyze experimentally the absorption dynamics of two drops placed on a swellable fiber. We observe that for some configurations, a local oversaturation of the polymer may occur between the two drops, causing some solvent to escape the elastomeric network leading to the creation of a new drop at the fiber surface that may coalesce with the two initial drops. We rationalize these observations using a linear poroelastic model that can quantitatively predict the absorption dynamics of the drops and the configurations for which fluid escaping the fibre (deswelling) may be observed.