Abstract
Young and Petrauskas [Bull Am. Phys. Soc. Ser. II, 1, 122(A) (March, 1956), paper H8] have found relaxational sound absorption in certain liquids having rotational isomerism. We consider this phenomenon as a case of structural relaxation. The absorption parameter α/ρcν2 should be approximately proportional to (ρ/T2) exp [(F-PV)/RT], where F is a free energy difference and V has the dimensions of volume, and also to the square of ΔV, a volume difference between equilibrium states. Some new measurements are reported, in which the effects of pressure up to 1500 kg/cm2 on the velocity and absorption of ultrasonic waves in 2-methyl-butane are examined in the range −25 to +25°C. The theory gives a self-consistent, quantitative explanation of the experimental results if the quantity V is given a positive temperature coefficient. Approximately, V is 0.2 times the molar volume, and F is one kcal/mole. ΔV is several tenths of the molar volume. Static PVT measurements are also reported. The isothermal compressibility is much greater than the relaxational part of the ultrasonic adiabatic compressibility. (Supported by the Office of Naval Research.)
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