Touch Down of a Sphere in Viscoelastic Media

Many fluids of practical interest contain polymers and show non-Newtonian behavior such as shear-thinning viscosity and elasticity. Lubrication forces in such fluids depend on conformation changes of polymer molecules and at sufficiently high strain-rates can become nonlinear. Here, we experimentally investigate the (lubrication) forces that arise as a sphere approaches the solid surface as a function of fluid elasticity. We use an Instron with a sphere-and-rod attachment to directly measure the forces experienced by a sphere that approaches a smooth surface in fluids with different levels of elasticity.