Onset of thin film meniscus along a fibre

The dynamics of spreading of a macroscopic liquid droplet over a wetting surface is often described by a power-law relaxation, namely, the droplet radius increases as for time , which is known as Tanner's law. Here we show, by both experiments and theory, that when the liquid spreading takes place between a thin soap film and a glass fibre penetrating the film, the spreading is significantly slowed down. When the film thickness becomes smaller than the fibre diameter , the strong hydrodynamic confinement effect of the soap film gives rise to a logarithmic relaxation with fibre creeping time . Such a slow dynamics of spreading is observed for hours both in the measured time-dependent height of capillary rise on the fibre surface and viscous friction coefficient felt by the glass fibre in contact with the soap film. A new theoretical approach based on the Onsager variational principle is developed to describe the dynamics of thin film spreading along a fibre. The newly derived equations of motion provide the analytical solutions of and contact angle , which are found to be in good agreement with the experimental results. Our work thus provides a common framework for understanding the confinement effect of thin soap films on the dynamics of spreading along a fibre.