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We illustrate functionality and performances of the oscillating bubble tensiometer, used for studying the influence of atmospheric organic carbon on the interfacial properties of clouds and aerosols. We report experimental observations of the responses of dynamic surface tension consequent to harmonic disturbances of surface area, for samples of cloud-water and of aerosol dissolved in water. The oscillating-air-bubble tensiometer appears a suitable instrument for the assessment of the ‘availability to the air–water interface’ of natural and man-made adsorption-film-forming organic materials, present in the atmosphere.

The characteristics of transverse and longitudinal surface waves on solutions of polyethylene glycols (PEG) and polyethylene oxides (PEO) have been measured as a function of time. These data allow to determine the kinetic dependence of the dynamic surface elasticity. It is shown that conformational transitions in the surface layer of polymer solutions can take place when the surface tension is almost constant. Therefore one has to be especially careful while trying to use experimental surface tension data in order to characterise the structure of polymer adsorption films.

A survey of the earlier results of analytical investigation of the dilational surface viscoelasticity of surfactant solutions by means of methods of non-equilibrium thermodynamics is presented. The case of an arbitrary number of surfactants and mixed adsorption kinetics is considered for liquid–gas and liquid–liquid interfaces only at low surface coverages. Analytical study of the surface viscoelasticity at arbitrary surface coverages is possible when additional restrictions are made. Special attention is paid to the surface viscoelasticity of a system with a non-equilibrium non-perturbed state. The results for the latter system allow us to study the linear stability of longitudinal surface waves.

We studied the effects of perturbation by vibration on the surface tension and surface area data obtained with the bubble-profile fitting method, using a typical laboratory apparatus. Examining an air bubble issuing downwards from a capillary tip, inside a vessel containing water, we report experimental observations about the effect of multifrequency vibrations on the bubble profile, either in the non-resonance or in the resonance condition, for some normal oscillation modes of the bubble and of the liquid body. Experimental results are given with regard to multifrequency-vibration disturbances on determination of the static surface tension of the liquid and the geometrical properties of the bubble, as a function of acceleration amplitude of vibration. Also, illustrative experimental observations are presented of the dynamic surface tension response to a surface area change, for a surfactant solution, under the action of vibration motion. In the frequency–acceleration plane, we show negligible effects on surface data in the 0–100 Hz and 0–5mg domain, for the geometrical configuration examined and the overall experimental system. The tolerability limit appears at 10mg acceleration, where excitation of the bubble resonance oscillation may occur with significant amplitude. The conclusions are also useful for estimation of the vibration effects in different configurations.

We describe the construction of a software-driven instrument for the measurement of the properties of gas-liquid interfaces under not-far-from-equilibrium conditions. Instrumental design and operation are based on the formalism of systems' theory applied to surface processes (network surface thermodynamics). The apparatus forms a large bubble at a (circular) capillary tip immersed in a liquid solution. The bubble image, observed by a videocamera-microscope system, is acquired by a personal computer through a digitizing board. The computer controls the bubble size as a function of time by a feedback loop. In practice, the bubble volume is changed, according to a given functional form, by changing the wall curvature (and hence the volume) of an air chamber (made with piezoelectric discs) in pneumatic connection with the bubble (no mechanical part is in motion). Adopting a similar procedure to that already developed by Neumann et al. [14] for axisymmetric drop shape analysis, the observed geometrical profile (derived from the bubble image) is compared with the calculated profile from the Gauss-Laplace equation. The static and dynamic interfacial properties are determined from the fit parameters and from the bubble pressure. The experimental results, obtained by the instrument, appear to be useful for the physical characterization of marine waters.