Wetting of fibers

The capillary length is defined as the length for which surface tension and gravity balance each other. It is typically of the order of one millimeter for a liquid/air system. For interfaces with dimensions larger than the capillary length, gravity dominates the shape the interface takes. Conversely, for small interfaces, capillary forces dictate the shape. Flow in a confined geometry such as a capillary tube, fiber or fiber networks will therefore be driven by capillary morphology and surface effects. In this chapter, we focus on the behavior of liquids on single fibers and move onto fibrous networks. First, the formation of drops on a fiber is considered, analyzing their shapes, with emphasis on the existence of axisymmetric and asymmetric drops. Next, wetting along conical fibers, and finally within a network of fibers is treated. In both of these systems, the substrate curvature is not homogeneous, and leads to displacement of liquid in order to decrease surface energy.