Wetting Kinetics of Polymer Solutions and Force-Based Contact Angles

The effect of the shear thinning behavior and elasticity of polymer solutions on the dynamic contact angles are investigated. Under dynamic conditions, the contact angle of a liquid on a solid surface changes significantly with the substrate velocity from its equilibrium value. The dynamic contact angles for polyethylene oxide (PEO) solutions of two molecular weights 3 x 105 and 4 x 106 have been measured using a polyethylene terephthalate (PET) plate. The three-parameter Ellis model to fit the rheological data to obtain shear thinning power n, characteristic shear stress, and the zero-shear viscosity is used. The theory indicates that dynamic contact angles follow power law in this instance instead of showing Newtonian behavior with zero-shear viscosity when the shear thinning effects are considered. The elastic effect becomes important at larger polymer concentrations that reduces the dependence on capillary number, that is, reduces n keeping with the experiments