We report a direct measurement of the friction coefficient ${\xi }_c$ of two fluctuating contact lines formed on a fiber surface when a long glass fiber intersects the two water-air interfaces of a thin soap film. The glass fiber of diameter $d$ in the range of 0.4–4 $\mu \text{m}$ and length 100–300 $\mu \text{m}$ is glued onto the front end of a rectangular cantilever used for atomic force microscopy. As a sensitive mechanical resonator, the hanging fiber probe can accurately measure a minute change of its viscous damping caused by the soap film. By measuring the broadening of the resonant peak of the hanging fiber probe with varying viscosity $\eta$ of the soap film and different surface treatments of the glass fiber, we confirm that the contact line dissipation obeys a universal scaling law, ${\xi }_c=\alpha \pi d\eta$, where the coefficient $\alpha =1.1\pm 0.3$ is insensitive to the change of liquid-solid contact angle. The experimental result is in good agreement with the numerical result based on the phase field model under the generalized Navier boundary conditions.

• Received 17 September 2014

DOI:https://doi.org/10.1103/PhysRevE.91.012404