Microfabricated deflection tensiometers for insoluble surfactants

Abstract

We describe a technique that enables sensitive surface pressure measurements of insoluble surfactants with small quantities in enclosed systems. We microfabricate free-floating microtensiometers that rest at liquid interfaces. Our devices isolate clean interfaces from surfactant-laden ones and deform in response to the surface pressure difference. Elastic beam theory enables straightforward interpretation of the measurements and the deliberate engineering of the sensitivity and dynamic range of the device. Surface pressure isotherms for model surfactant monolayers measured using our microtensiometer show excellent agreement with a conventional Wilhelmy plate. (C) 2010 American Institute of Physics. [doi:10.1063/1.3491549]