Electrostatic Suppression of the “Coffee-stain Effect”

The dynamics of a slender, nano-particle laden droplet are examined when it is subjected to an electric field. Under a long-wave assumption, the governing equations are reduced to a coupled pair of nonlinear evolution equations prescribing the dynamics of the interface and the depth-averaged particle concentration. This incorporates the effects of viscous stress, capillarity, electrostatically- induced Maxwell stress, van der Waals forces, evaporation and concentration-dependent rheology. It has previously been shown27 that electric fields can be used to suppress the ring effect typically exhibited when such a droplet undergoes evaporation. We demonstrate here that the use of electric fields affords many diverse ways of controlling the droplets.