The onset of rigidity in Se& Ge glasses is probed by room-temperature longitudinal and transverse elastic moduli determined by ultrasonic measurements.The longitudinal modulus displays linear behavior with increasing x up to x=0. 3, corresponding to an average coordination number (r ) =2.6. The transverse modulus displays linear behavior with a slight upturn at (r ) =2. 4, saturating beyond 2.5. The onset of rigidity percolation at (r)=2.4, predicted on the basis of random-network models, is not seen. Other experiments indicate a rigidity threshold near 2.7. The present results are consistent with a departure from random-network models in the form of medium-range structural order.
The experimental value of the slope of α/f 2 vs f −1.06 of the ultrasonic attenuation for the critical mixture is compared to the calculated value based on the dynamic scaling theory at the critical temperature. The values of α/f 2 vs f −1.06 yield a straight line as predicted by theory. The adiabatic coupling constant g is calculated and compared to the experimental value. The experimental values of α/αc for methanol and cyclohexane are compared to the scaling function F(ω*) and to the values of α/αc for 3He and Xe.
The absorption and velocity of ultrasound were studied for solutions of 10 000 molecular-weight poly (ethylene glycol) and distilled water. The frequency used was 21 MHz and the concentration (by weight) ranged from 1% to 9% of poly (ethylene glycol) in water. The shear viscosity was also measured. Temperatures of 25, 30, 35, 40, 45 °C were used for the measurements. Observations showed that the ultrasonic absorption decreases with increasing temperature at a given concentration and also increases with concentration at a given temperature. The velocity increases with increasing temperature and concentration. Finally, the shear viscosity measurements show it decreasing with temperature but also increasing with concentration.
Velocity and attenuation measurements of compressional waves at 3 and 5 MHz, as a function of solid volume concentration, are reported for different suspensions. The suspensions were made of 1 μm size particles of kaolinite or glass beads in water or light oil. At a volume concentration of 40%, a sharp peak in attenuation accompanied by a change in velocity is observed. The volume concentration at which this peak occurs is independent of frequency and particle geometry. The observed critical change in attenuation around 40% is consistent with an excess attenuation induced by the fluid-shearing processes between neighboring particles, and corresponds to the jamming point concentration predicted by particle packing simulations.
The ultrasonic-absorption coefficient has been measured by pulse techniques in solutions of 0.05 and 0.02 molal MgSO. for pure-water solvent and for various mixtures of methanol and water, up to 70% methanol by weight. The high-frequency relaxation peak decreases steadily in frequency with increase in methanol while the height of the peak rises to a maximum and then decreases. An attempt is made to interpret thes~ findings in terms of the dissociation model. Inadequacies in available chemical data prevent a satisfactory detailed comparison with theory.
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