Oscillating bubble technique
The oscillating bubble technique allows the determination of the surface dilational viscoelastic properties of an adsorption layer at the liquid-air and liquid-liquid interfaces. The technique has been developed at the Max-Planck Institute of Colloid and Interfaces. The principle of the oscillating bubble technique is sketched in the following Figure showing a cross sectional view of the chamber.
A small hemispherical bubble is formed at the tip of a capillary with a radius of about 0.2 mm. The bubble is forced in a sinusoidal oscillation by a piezoelectric translator which is directly immersed in the liquid. As a result, a harmonic modulation of the pressure in the chamber is observed and recorded by a sensitive pressure transducer located at the bottom of the chamber. The amplitude of the pressure response and the phase-shift between piezo oscillation and pressure signal are evaluated via a phase sensitive lock-in detection scheme. The amplitude of the pressure response is proportional to the magnitude of the complex surface dilational module E, while the phase-shift yields the imaginary part of the modulus, in other words the surface dilational viscosity.
The implemented design give access to the frequency range of 1-500 Hz and allows the determination the real- and imaginary part of the complex surface dilatational elasticity module