| Abstract
| - A new micropipet technique has been developed to measure the equilibrium and dynamic interfacialtensions of microscopic liquid−gas and liquid−liquid interfaces. In this technique, a liquid−gas or liquid−liquid interface with a radius of curvature ranging from 1 to 100 μm can be created inside a taperedmicropipet. On the basis of the Laplace equation (a work balance between tension and applied pressurefor the curved interface), the equilibrium interfacial tension between the two phases (clean or surfactantadsorbed) can be determined by measuring the radius of curvature of the interface for a series of pressurechanges. With an additional surfactant-delivering micropipet, we show how this technique also offers aneffective way to study adsorption/desorption dynamics upon exposure and washout for various surfactantsand provides the whole history of surfactant exchange for microscopic interfaces. Here, we verify that theresults of this technique are consistent with the interfacial tension values previously obtained by othermethods typically conducted on macroscopic interfaces. The technique has been used to study the adsorptionof PEG-40-Stearate as a monolayer at the liquid−gas interface. From a plot of the measured surfacetension as a function of PEG-40-Stearate concentration, the critical micelle concentration and area permolecule have been determined to be 40 ± 2 μM and 1.19 nm2, respectively. In a companion paper, wereport additional new data on a series of phospholipid monolayers.
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