Non-classical scaling for forced wetting of a nematic fluid on a polymeric fiber

Abstract

We report on the forced wetting of a liquid crystal on a polymer fiber in the nematic and isotropic phase under partial wetting conditions. As the cylindrical fiber exits from the fluid reservoir, the fluid forced-coated on the fiber is immediately broken into droplets due to capillary-driven instability, even in the wetting conditions. For the nematic fluid, the initial film thickness, h, before breakup, scales almost linearly with the capillary number, Ca, as h ∼ Ca^0.94, while h ∼ Ca^2/3 for the isotropic fluid, as predicted for a Newtonian fluid. The amount of the fluid coated on a fiber is larger in the nematic phase than in the isotropic phase at a given velocity within the velocity range studied. Analysis using Ericksen-Leslie equations shows that Frank elasticity plays no role in increasing the coating thickness for the nematic fluid, while viscous anisotropy is the source of observed rescaling, h ∼ Ca. This non-classical scaling is attributed to the deformation-stress cross-coupling and the existence of extensional kinematics in the meniscus formation region.