Capillary Rise between Elastic Fibers and the Dynamics of the Transition to a Coalesced Equilibrium

When slender elastic fibers separated by a small gap are partially submerged in a reservoir of wetting liquid, attractive capillary forces may cause them to draw nearer to each other and snap into contact. After the fibers make contact, the system transitions via capillary rise towards a stable coalesced equilibrium state in which the two fibers are joined by a capillary bridge whose equilibrium height is determined by a balance between elasticity and capillarity. The dynamics of this transition to a coalesced equilibrium state were investigated experimentally. Data were acquired for different fiber diameters, lengths, and elastic moduli. We report measurements of the rates of capillary rise of liquid into the narrow gap between the fibers and their simultaneous self-assembly into a corner-like configuration. In all cases, we observe an intermediate regime in which capillary rise is characterized by power-law growth. Although the exponent appears to be constant, the prefactor depends on both the radius and elastic modulus of the fibers. We will rationalize these findings as well as other results regarding the late stages of rise and the final approach of the capillary bridge to its equilibrium height.