ULTRASONIC-ABSORPTION OF NITROBENZENE ISOOCTANE MIXTURES OF NONCRITICAL COMPOSITION

The dynamic scaling theory of Ferrell and Bhattacharjee (Phys. Rev. A, 1985, 31, 1788) has been used to analyse ultrasonic absorption data o f two nitrobenzene-isooctane mixtures of non-critical composition. The measurements were carried out as a function of temperature [1 less th an or equal to (T - T-p)/K less than or equal to 20; T-p, temperature of phase separation] and frequency (3 less than or equal to f/MHz less than or equal to 57). The data describing the temperature- and freque ncy-dependent contributions of composition fluctuations to the ultraso nic absorption follow a single curve. The data can be represented by a modified dynamic scaling function similar to that proposed by Ferrell and Bhattacharjee to describe the ultrasonic absorption of a mixture of critical composition. The temperature dependence of the scaling var iable Omega(nc) for the mixtures of non-critical composition is calcul ated by replacing the critical temperature T-c by an empirical pseudos pinodal temperature T-ps or the temperature of phase separation T-p of the mixture of non-critical composition. The frequency- and temperatu re-independent parameter omega(o,nc) of the scaling variable Omega(nc) , is used as the only free parameter of the fit of the scaling functio n F(Omega(nc)) to the experimental data. The value of omega(o) is foun d to be composition dependent.