Effects of soluble surfactants on the dip coating of fibers. Numerical simulations at different regimes

DIEGO M. CAMPANA; SEBASTIÁN UBAL; MARÍA D. GIAVEDONI; FERNANDO A. SAITA

Tandil

Congreso; XIII Reunión sobre Recientes Avances en Física de Fluidos y sus Aplicaciones (FLUIDOS 2014); 2014

Instituto de Física "Arroyo Seco", Universidad Nacional del Centro de la Provincia de Buenos Aires

The withdrawal of a fiber or cylindrical wire from a fluid bath is a common industrial process used to produce a continuous coating on the solid surface. This operation is known as dip coating and has been extensively studied both analytically and experimentally. The thickness of the coated film depends on the withdrawal velocity, fluid properties and the fiber radius. It is well known that surface active agents (surfactants) adsorbed at the interface produce a thickening of the coated film due to Marangoni tractions. Simplified hydrodynamic models have been developed to capture the main aspects of the problem, but because they are based on lubrication and thin film theory, its results are valid only at low extraction velocities. We present here a full 2D model based on the axisymmetric Navier-Stokes equations, surfactant mass balance at the interface and considering a constant surfactant concentration in the bulk phase. The model is solved with the finite element method and an Arbitrary Eulerian-Lagrangian technique to calculate, simultaneously, the unknown domain, fluid velocity, pressure and interfacial surfactant concentration. The results agree well with experimental measurements of the film thickness for a wide range of problem parameters.