The characterisation of the dynamic properties of viscoelastic monolayers ofsurfactants at the gasliquid interface is very important in the analysis andprediction of foam stability. With most of the relevant dynamic processes beingrapid (thermal fluctuation, film coalescence etc.) it is important to probeinterfacial dynamics at high deformation rates. Today, only few techniquesallow this, one of them being the characterisation of the propagation ofelectrocapillary waves on the liquid surface. Traditionally, this technique hasbeen applied in a continuous mode (i.e. at constant frequency) in order toensure reliable accuracy. Here we explore the possibility to analyse thepropagation of an excited pulse in order to access the interfacial propertiesin one single Fourier treatment over a wide range of frequencies. The mainadvantage of this approach is that the measurement times and the requiredliquid volumes can be reduced significantly. This occurs at the cost ofprecision in the measurement, due partly to the presence of a pronouncedresonance of the liquid surface. The pulsed approach may therefore be used toprescan the surface response before a more in-depth scan at constant frequency;or to follow the changes of the interfacial properties during surfactantadsorption.
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