Wetting and Wicking

The fundamentals of wetting and wicking are reviewed. Wetting is the displacement of a fiber-air interface with a fiber-liquid interface. Wicking is the spontaneous flow of a liquid in a porous substrate, driven by capillary forces. Because capillary forces are caused by wetting, wicking is a result of spontaneous wetting in a capillary system. Fiber wettability is therefore a prerequisite for the occurrence of wicking. The inter action of liquids with textile fabrics may involve one or several physical phenomena. On basis of the relative amount of liquid involved and the mode of the liquid-fabric contact, the wicking processes can be divided into two groups: wicking from an infinite liquid reservoir (immersion, transplanar wicking, and longitudinal wicking), and wicking from a finite (limited) liquid reservoir (a single drop wicking into a fabric). According to fiber-liquid interactions, each of the four wicking processes can be divided into four categories: capillary penetration only, simultaneous capillary penetration and imbibition by the fibers (diffusion of the liquid into the interior of the fibers), capillary penetration and adsorption of a surfactant on fibers, and simultaneous cap illary penetration, imbibition by the fibers, and adsorption of a surfactant on fibers. When designing tests to simulate liquid-textile interactions of a practical process, it is essential to understand the primary processes involved and their kinetics.