ELECTROCAPILLARITY AND WETTING OF INSULATOR FILMS BY WATER

Wetting of a solid insulator film (dielectric constant epsilon, thickness epsilon) by a water drop is favoured if a voltage V is applied between the drop and an electrode placed on the rear side of the film. The correction to the effective solid-liquid interfacial energy is - (1/2) (epsilonepsilon0/e)V2, and hydrophobic insulator surfaces become reversibly hydrophilic. The measured water contact angle on polymer films under a.c. voltages are in agreement with the theoretical predictions up to some field where the contact angle saturates. At highfield the surface becomes irreversibly hydrophilic near the wetting line.