Quasi-Elastic Laser Scattering Method for Monitoring Capillary Wave Frequency at a Water/Nitrobenzene Interface

Abstract

A quasi-elastic laser scattering (QELS) method was applied to monitoring the capillary wave frequencies at a water/ nitrobenzene interface. A digital spectrum analyzer was adopted to improve the time resolution of the QELS method. As a result, each power spectrum could be obtained in 1 s and saved in an additional 1 s. The equipment was checked by monitoring capillary wave frequencies at a water/ nitrobenzene interface covered with a monolayer of dipalmitoylphosphatidylcholine (DPPC), i.e. changes of interfacial tension caused by the formation of the monolayer at the interface were detected. The equipment was then applied to a chemical oscillation system. It was found that the interface of the chemical oscillation system was covered with a high density membrane during the chemical oscillation.

Effect of Organic Phase on Dynamic and Collective Behavior of Surfactants at Liquid/Liquid Interfaces by a Time-Resolved Quasi-Elastic Laser-Scattering Method

“…In the present case, only the peak frequency is used for the analysis. Since the square of the capillary wave frequency is proportional to the interfacial tension, which is approximately inversely proportional to the number density of surfactant molecules at the interface, 13,21 details can be added to the above outline by estimating the molecular number density of surfactants at the interface.…”

“…So it has been assumed that these chemical processes can be monitored by observing changes of interfacial tension. As we described previously, 13,21 the capillary wave frequency is a function of interfacial tension and the change in the interfacial tension depends on the change in the number density of surfactant molecules at the interface; then the QELS method allows observation of the dynamic change of L/L interfaces such as the formation of a lipid monolayer, 13 or the adsorption of surfactant molecules. 21,22 Compared with conventional interfacial tension measurements, the QELS method has the obvious advantage of being able to probe interfaces between two bulk phases without any mechanical perturbation.…”

“…[23][24][25][26][27][28][29][30][31] Since capillary waves reflect the fundamental properties of the surface or interfacial region, much effort has been made to observe them and to analyze their spectra. The theoretical understanding of these waves is well estimated in hydrodynamics, and light scattering from the waves is also widely used to monitor the L/L interfaces.2 In our previous papers, 13,21,22 we reported that a developed timeresolved quasi-elastic laser-scattering (QELS) method was a powerful tool for studying molecular dynamics at L/L interfaces. The QELS method monitors the change of the frequencies of the capillary waves, which are spontaneously generated by thermal fluctuation at L/L interfaces.…”

“…2 In our previous papers, 13,21,22 we reported that a developed timeresolved quasi-elastic laser-scattering (QELS) method was a powerful tool for studying molecular dynamics at L/L interfaces. The QELS method monitors the change of the frequencies of the capillary waves, which are spontaneously generated by thermal fluctuation at L/L interfaces.…”

Dynamic Behaviors of Molecular Assemblies at Liquid/Liquid Interfaces Studied by Time-Resolved Quasi-Elastic Laser Scattering Spectroscopy

“…[6][7][8][9] The improvement in time resolution allows us to monitor the time course of the interfacial tension through the change in frequency of the Ripplon with millisecond time resolution. [10][11][12][13] The changes in interfacial tension provide us useful information on various kinds of dynamic behaviors of molecules at liquid/liquid interfaces. We named this surface-selective, dynamic light scattering method: "Time-Resolved Quasi-Elastic Light Scattering (TR-QELS)".…”