Measurements of the surface elasticity in medium frequency range using theoscillating bubble method

Various experimental techniques are available for the investigation of dyna mic surface tension, and a generally accepted theoretical model of these dy namics has been established. However, reliable rheological parameters of a fluid surface are very scarce. Therefore, comparisons of rheological parame ters resulting from slow and faster processes or from theoretical calculati ons are required. In particular, a comprehensive experimental verification of the complex surface elasticity modulus which characterizes the dynamic b ehavior of a fluid surface in an appropriate manner is desirable. For this reason a new version of oscillating bubble method was developed wh ich allows exact measurements of the complex elasticity modulus in the freq uency range 3-500 Hz,With this method the assumptions of the theory of dyna mic surface tension can be verified for medium frequencies. The new experim ental results, in particular the experimental determination of the Gibbs el asticity, reveal that these assumptions are only approximately valid for fa ster processes. However, with a slight modification of the established mode l the experimental results can be explained. These experiments were carried out with solutions of tridecyl dimethyl phos phine oxide, fatty acids, n-alkanols, and triton X-100 at different surfact ant concentrations. (C) 1998 Academic Press.