ELECTROCAPILLARITY AND WETTING OF INSULAT OR FILMS BY WATER

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