Effect of surface elasticity on the motion of a droplet in a viscous fluid.

The motion of a droplet with adsorption layer in a viscous incompressible fluid is studied on the basis of the linearized Navier-Stokes equations. It is shown that dilatational elasticity of the layer has a strong effect on the decay of velocity after a sudden impulse. If the elasticity is sufficiently strong the droplet shows backtracking, i.e., during part of the time the velocity relaxation function becomes negative. The motion is independent of the surface shear modulus or surface shear viscosity. The friction coefficient of the droplet at zero frequency is the same as for a rigid sphere with stick boundary conditions, independent of the elasticity modulus.