No abstract

The velocity of sound in seven vegetable oils has been measured to an accuracy o f f 0.3 ms-'. The different values of the velocities are correlated on the basis of composition. Average values for the temperature coefficient of velocity, at room temperature, and for the dispersion between 2 and 10 MHz are also given. Fat Sci. Technol. 90.Jahrgang Nr.2 I988

Ultrasonic attenuation and velocity are studied for edible oils over the frequency range 2-95 MHz at 19.4 C. Shear and compressional (volume) relaxation spectra are evaluated and compared. Viscoelastic (shear) contribution to attenuation is estimated by Rouse theory. The ratio of volume to shear viscosities decreases with frequency (except for castor oil), indicating that the shear and compressional relaxations are separated on the frequency scale. The results indicate that the molecular rearrangements in the compressional relaxation are long range and require a greater degree of co-operation compared with the shear relaxation. Possible mechanisms for the shear and compressional relaxations are discussed.

The implications of a fractal model of medium structure for the angular dependence of the ultrasonic differential scattering cross section and for the frequency dependence of the total ultrasonic scattering cross section are explored. The results for the differential scattering cross section agree well with published experimental values for liver and those for the total scattering cross section are not inconsistent with the literature data.