Influence of surface rheology on dynamic wetting of droplets coated with insoluble surfactants

Wetting phenomena are crucial to many problems, including wetting and dewetting in the tear film in the eye. Here we introduce insoluble surfactants to the surface of advancing droplets of pure water. Three pure surfactants were chosen with similar Gibbs elasticity but distinct interfacial shear properties. The effects of arachidyl alcohol, a Newtonian monolayer, on dynamic wetting are compared to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesteryl myristate, which both form monolayers with shear elasticity. In addition, meibomian lipids, a natural mixture of lipids found in the tear film, were also studied. We show that while droplets covered with arachidyl alcohol follow classical hydrodynamics, surface shear elasticity introduces unique behavior including stick–release phenomena at low velocities and non-ideal behavior at higher velocities.