An FFT approach to the analysis of dynamic properties of gas/liquid interfaces

TL;DR

This paper introduces an FFT-based method to analyze the dynamic properties of gas/liquid interfaces using pulse propagation, enabling faster and more volume-efficient measurements with some trade-offs in precision.

Contribution

It presents a novel FFT approach for analyzing electrocapillary wave propagation in a pulsed mode, reducing measurement time and sample volume compared to traditional continuous methods.

Findings

Pulse analysis provides rapid interfacial property assessment.

The method reduces measurement time and liquid volume requirements.

Resonance effects influence measurement precision.

Abstract

The characterisation of the dynamic properties of viscoelastic monolayers of surfactants at the gasliquid interface is very important in the analysis and prediction of foam stability. With most of the relevant dynamic processes being rapid (thermal fluctuation, film coalescence etc.) it is important to probe interfacial dynamics at high deformation rates. Today, only few techniques allow this, one of them being the characterisation of the propagation of electrocapillary waves on the liquid surface. Traditionally, this technique has been applied in a continuous mode (i.e. at constant frequency) in order to ensure reliable accuracy. Here we explore the possibility to analyse the propagation of an excited pulse in order to access the interfacial properties in one single Fourier treatment over a wide range of frequencies. The main advantage of this approach is that the measurement times and the required liquid volumes can be reduced significantly. This occurs at the cost of precision in the measurement, due partly to the presence of a pronounced resonance of the liquid surface. The pulsed approach may therefore be used to prescan the surface response before a more in-depth scan at constant frequency; or to follow the changes of the interfacial properties during surfactant adsorption.