Published online by Cambridge University Press: 20 January 2020
We present the results of a combined experimental and theoretical study of the spin coating of the inner surface of capillary tubes with viscous liquids, and the modified Rayleigh–Plateau instability that arises when the spinning stops. We show that during the spin coating, the thinning of the film is governed by the balance of viscous and centrifugal forces, resulting in the film thickness scaling as $h\sim t^{-1/2}$. We demonstrate that the method enables us to reach uniform micrometre-scale films on the tube walls. Finally, we discuss potential applications with curable polymers that enable precise control of film geometry and wettability.
Video shows the viscous slug motion inside spinning capillary tubes. The capillary tubes are placed into slots 2, 4, 7, and 12. Orange liquid slugs are placed near the inner end of the tubes. As the system is spun, the slugs move outwards, depositing a film on the inner walls. Therefore, the length of the slugs diminishes as they move outwards.
Video shows the modified Rayleigh-Plateau instability of the micron-scale films that are generated with the spin-coating method. The timescale of the instability is uniform throughout the tube, which points at the uniform thickness of the film considering FIG.4(d).