Document Type

Article

Date of Original Version

1993

DOI

10.1557/JMR.1993.0573

Abstract

Sessile drops of aqueous electrolyte as well as cationic and anionic surfactant solutions are placed on the lower plate of a stainless steel parallel plate capacitor and the variation of static advanced contact angles with the field strength between the plates is monitored. Even at field strengths where changes in electrical body forces are negligible, these drops spreads outward, irreversibly, in response to variations in the externally applied potential gradient. Contact angles always decrease, regardless of the polarity of the applied electric field. However, the magnitude of the change is sensitive to both the polarity and strength of the field. These angles relax over time scales that are an order of magnitude higher than that predicted by diffusional resistance alone. The variation in solution surface tension in response to the externally applied electric field has been obtained experimentally from the drop shapes. For both ionic surfactant and simple electrolyte solutions, the surface tension always decreases as the electric field is increased, regardless of its polarity. For sessile drops placed on a stainless steel plate having a passivating oxide layer, reductions in both the liquid-vapour and solidliquid interfacial energy must occur to account for the observed changes in contact angle (provided Young's equation is assumed to be valid). However, for drops place on platinum coated stainless steel plates, the changes in contact angles are entirely accounted for by changes in surface tension only, implying that the solid-liquid interfacial energy does not vary with the external field.

Publisher Statement

Copyright 1993 Materials Research Society.