Excess Ultrasonic Absorption in Diethylamine-Water Mixtures

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Abstract
The ultrasonic absorption and velocity as well as the density and shear viscosity of mixtures of diethylamine and water have been measured as a function of composition and temperature. The absorption, which is strongly temperature dependent, reaches a large peak value at a composition of approximately 10 mole percent diethylamine. Less pronounced maxima are observed in the sound velocity and shear viscosity. The system exhibits a pronounced volume contraction on mixing with evolution of heat. The origin of the large ``excess'' sound absorption can be accounted for in terms of a compressional relaxation and a simple molecular model based on the properties of the hydrogen bonds between like and unlike molecules in the binary solution. During compression an excess number of AB bonds are formed at the expense of AA and BB bonds leading to a relaxation process. The calculated absorption curves satisfactorily reproduce the main features of the experimental curves and yield approximate values of the mean relaxation frequency.

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