Coating a fiber with an elastomeric shell

Coating cylindrical fibers with a geometrically uniform shell is of great importance in many different industrial and biological applications. As a viscous liquid coats the outer surface of a fiber, capillary effects lead to the Rayleigh-Plateau instability and the growth of initial perturbations in the coating profile. This leads to undesirable beads that form periodically along the fiber and consequently a non-uniform final coating. It is known that bead formation can be avoided, for vertically-held fibers, through a gravity-driven primary flow in the annular film. We investigate this free-surface flow phenomenon and study its applications under different flow conditions. We coat cylindrical fibers with viscous polymer solutions that gradually go through a sol-gel transition and transform into permanent elastic shells around the fiber. The kinetics of the gelation process is coupled with the spatiotemporal evolution of the interfacial disturbances in the coating layer and, together, set the final profile of these elastomeric cylindrical shells. We analyze the final profile of these elastic shells and discuss our results in view of a simple analysis based on the nonlinear saturation of the Rayleigh-Plateau instability.