Force measurements at liquid interfaces

Other Force Measurement Techniques at Liquid/Liquid Interfaces 

A more recently developed force measurement technique, coined the liquid siu-face force apparatus (LSFA), brings a drop made from a micropipette close to a flat liquid/liquid interface [29-32]. A piezo electric drive is used to change the position of the micropipette while the deflection of the pipette and the radius of the drop are recorded with piezo motion. The drop radius and thus the film thickness between the two liquid/liquid interfaces are recorded using interferometry. The method requires a calibration of the interferometer, where the drop must come into contact with the other liquid interface. The distance resolution of the film is about 1 nm at a 50-nm separation and 5 nm at a separation of 10 nm. This is a very robust technique where the authors have proposed attaching a particle to the end of the pipette instead of a drop [29]. In comparing this method to AFM, the only drawback of the LSFA is the weaker distance resolution. It is important point out that both methods required a contact point for distance calibration. 

Two similar techniques to probe hydrodynamic behaviour have been recently developed by Horn et al. [33] and Gee and co-workers [34-37]. The measurements by Horn et al. employ interferometry to measure the shape of a mercury drop at the end of a microcapillary as it approaches a flat interface. The capillaries are much larger than those used in an LSFA, where the drop profile is recorded under hydrodynamic forces. The work by Gee [34-37] is similar but uses hydrocarbon drops and determines the separation using imaging ellipsometry/reflectometry. This method is useful for systems 

Two Liquid/Liquid interfaces. Measuring the interactions between two liquid droplets with AFM is a natural extension of the one droplet problem and more relevant to emulsion stability. The first and only such measurement is between alkane droplets in 

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