Relaxation rate in the critical dynamics of the micellar isobutoxyethanol-water system with lower consolute point

For the isobutoxyethanol-water mixture of critical composition acoustical scaling function measurements have been performed at frequencies between 200 kHz and 3 MHz. Using the relaxation rates of concentration fluctuations as resulting from dynamic light scattering and shear viscosity measurements, the acoustical data can be well represented by the Bhattacharjee-Ferrell empirical scaling function. The theoretically predicted scaled half attenuation frequency Omega(BF)(1/2)=2.1 follows from the experiments. However, the adiabatic coupling constant, derived from the amplitude of the Bhattacharjee-Ferrell critical term, displays an unreliably strong temperature dependence. It is shown that this dependence upon temperature likely reflects a hidden low-frequency and low amplitude relaxation term in the acoustical spectra of the mixture of critical composition.