The shear impedance, density and viscosity of the eutectic mixture NaCNS + CH3CONH2 have been measured in the temperature range 253-313 K and at the frequencies 31 and 87 MHz. The real parts of the complex impedance and of the rigidity modulus have been obtained. The relaxation region is shifted in comparison with that of the Maxwell model and is interpreted using the modified B.E.L. model. Irregularities in the real part of the mechanical impedance (around 283 K) and in the Arrhenius plot of the viscosity (around 293 K) may be attributed to changes in the liquid structure.

This paper presents a new method, using shear SH (shear horizontal) surface waves in solids, to determine the rheological parameters of viscoelastic liquids. Appropriate analytical formulas have been derived for Love and Bleustein–Gulyaev surface waves. The sensitivity of the proposed method is compared to that of the classical Mason method employing SH bulk waves. The measuring range of the proposed and classical methods is discussed in detail. Preliminary measurements are performed for typical mineral oil. The measured quantities agree very well with those obtained theoretically. The proposed method can be a few orders of magnitude more sensitive than the bulk wave method.

The attenuation of ultrasonic longitudinal waves in the eutectic mixture CH3CONH2 + NaCNS has been measured in the temperature range 255.2-303.2 K and frequency range 5-105 MHz, and the velocities of propagation at 298.4 K for 5 and 15 MHz have been obtained. A distinct structural relaxation process was found in the measured area. Comparing these results with previously reported shear results (G. Berchiesi, G. Vitali, P. Passamonti and R. Plowiec, J. Chern. Soc., Furuduy Trans. 2, 1983, 79, 1257), the variation of the loss modulus, M", as a function of frequency was determined. Agreement was found with theoretical expectations ; however, the influence of the eutectic relaxation process, which takes place in the same area, is evident. Additional shear measurements performed at 10 MHz showed this influence to be stronger than at the higher frequencies reported previously. ~ ~~~Electrolytic solutions in molten amides present some interesting features concerning liquid-solid behaviour, which has been discussed previously. 1-3 Remarkable supercooling phenomena are evident with alkali-metal salts coupled with anions of strong acids;2 in addition, sodium salts exhibit the formation of the incongruently melting compound NaX -2RCONH2.'93 Previously, the eutectic mixture NaCNS + CH3CONH2 was investigated by the technique of shear ultrasonic waves.4 These measurements allow one to determine the shear modulus, G,, and its variation as a function of temperature. The master curve was also plotted following the B.E.L. (Barlow, Erginsov, Lamb) model and the viscoelastic relaxation spectrum was determined. In this paper measurements of the attenuation of longitudinal waves are reported with the calculation of the longitudinal loss modulus, M", and the structural relaxation spectrum. However, additional shear measurements at 10 MHz had to be performed to explain the scattering of some results in the relaxation area. THEORY The longitudinal modulus of a liquid M * ( i w ) = M'(w)+iM"(u) consists of the bulk modulus where rv = vv/ K 2 and the shear modulus G*(iu) = G'(o)+iG"(o) = G,iw,/~l +iwT,,,)

Ultrasonic and viscoelastic relaxation spectra were determined for a mixture of acetamide and calcium nitrate [X (acetamide) = 0.76441. Retardation phenomena are present in the viscoelastic relaxation spectrum and they seem to be affected by the type of container used; the ultrasonic spectrum is due to a chemical equilibrium. There was no evident structural phenomenon.