Comparison of dynamic and static interfacial tension at aqueous/perfluorocarbon interfaces

Abstract

The dynamic and static interfacial tension of four different perfluorocarbons at aqueous interfaces were compared using a PTFE Wilhelmy plate method and a platinum du Nouy ring method, respectively. The dynamic values were measured continuously for at least 6 h without disturbing the interfaces, and the static values were measured after 20 min of aging. The perfluorocarbons investigated were 1,2- trans-(bisperfluorobutyl) ethylene (F44E), perfluorodecalin, perfluoroheptane, and I- H-perfluoroheptane. “Surface slip” due to the high affinity of platinum for the aqueous phase caused premature breakage of the interface during the du Nouy ring measurements, and consequently the static values were lower than the dynamic values. The PTFE Wilhelmy plate method proved an excellent technique for studying systems in which the interfacial tension changed as a function of the age of the interface, such as the perfluorocarbon/PTFE/double-distilled and deionized water interface. The dynamic interfacial tension of perfluoroheptane and 1- H-perfluoroheptane increased slightly with time, whereas that of F44E and perfluorodecalin decreased with time. The dynamic interfacial tension profiles appeared to be a function of both the molecular weights and structures of the perfluorocarbons.