Surface force apparatus concentration dependence

Experimentally, electrostatic double-layer forces versus distance were first quantitatively measured in foam films [444—446]. Aqueous foam films with adsorbed charged surfactant at air-liquid interfaces are stabilized by double-layer forces, at least for some time. Voropaeva ef al. measured the height of the repulsive barrier between two platinum wires at different applied potentials and in different electrolyte solutions [447]. U sui et al. [448] observed that the coalescence of two mercury drops in aqueous electrolyte depends on the applied potential and the salt concentration. Accurate measurements between solid-liquid interfaces were first carried out between rubber and glass with a special setup [449]. In the late 1970s, DLVO force could be studied systematically with the surface forces apparatus [424,450,451]. With the introduction of the atomic force microscope, DLVO forces between dissimilar surfaces could be measured [198, 199, 452, 453]. 

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