Ultrasonic relaxation study in gelatin sols and gels

Ultrasonic absorption was measured in gelatin sols and gels in the frequency range of 0.2-35 MHz. Two techniques, a plano-concave resonator method and optical beam deflection by ultrasonic waves, were used to cover the wide frequency range. The absorption spectra observed both in the sets and gels were well fitted to the relaxation curves, assuming the Cole-Cole-type distribution of relaxation times. A change in relaxation parameters upon gelation was obtained: the relaxation frequency decreased, the relaxation strength increased and the distribution became wider The relaxation mechanism is discussed in the light of the hydration equilibrium ui gelatin polymers.