NONLINEAR ULTRASONICS TO DETERMINE MOLECULAR-PROPERTIES OF PURE LIQUIDS

Wave propagation of ultrasound through condensed media is fundamentall y non-linear in nature. The extent of non - linearity is related to th e ratio of the third to second virial coefficients (B/A) of the equati on of state of the medium. This ratio can be directly measured by dete rmining the rate of change in sound speed with pressure. Several simpl e relations are developed that relate acoustic non-linearity to the mo lecular properties, namely internal pressure, free energy of binding, the effective van der Waals' constants, the translational diffusion co efficient, and the rotational correlation time. Using these relationsh ips and the measured the acoustic non-linearity parameter and the soun d speed, the molecular properties are determined for the liquids: wate r, alcohols and fluorocarbons. In all cases the values obtained from u ltrasonic measurements compare closely with the values reported in the literature based on alternative measurements. In conclusion, the non- linear propagation of ultrasound offers an independent means of determ ining the molecular properties of condensed media.