Critical Divergence of Ultrasonic Absorption in Critical Binary Mixtures of Triethylamine-Water

Abstract

Ultrasonic attenuation of critical binary mixtures triethylamine-water has been measured over the frequencies 15–95 MHz and at temperatures 12.5–18.0°C. The total sound absorption Ψ(ε, ω) can be well expressed by three terms,
Ψ(ε, ω)=Ψ_crit.(ε, ω)+Ψ_bg(ε, ω)+σ(T),
where ε=(T_c−T)⁄T_c is the reduced temperature, ω is the angular frequency of the sound. The first term is the critical relaxation, the second the background relaxation, and the last the classical contribution. The reduced absorption per wavelength (αλ)^* vs the reduced frequency ω^* follows the theoretical universal function over a wide range of ω^*(=1×10⁰∼3×10³). From numerical analysis of Ψ_crit.(ε, ω) based on the Kawasaki mode-mode coupling theory, the characteristic frequency of order-parameter fluctuations is expressed by f_D(ε)=f₀ε^3ν with ν=0.65 and a relaxation parameter is written by Q(ε)=Q₀ε^−α with α=0.084 for ε>6×10⁻³ and α=0.49 for ε<6×10⁻³. Discussions are given on the validity of hyper scaling relation and of correlation functions in the binary system studied.