Ultrasonic relaxation studies of alkylammonium salt solutions and methyl cyanide-water mixtures.

This thesis reports the results of a detailed investigation into the ultrasonic absorption properties of two liquid systems; solutions of alkylammonium salts and methyl cyanide - water mixtures. The background theory of sound absorption in liquids is briefly reviewed, followed by a description of the apparatus and experimental procedure employed. Two techniques were used to measure the absorption of liquids. Over the frequency range, 200 to 1500 kHZ. a reverberation technique was employed and over the range 1.5 to 230 MHz., a pulse technique. The ultrasonic absorption properties of methyl cyanide - water mixtures have been measured as a function of frequency, temperature and mixture composition. The ultrasonic absorption properties are compared with the thermodynamic and spectroscopic properties of these same mixtures. The trends observed are compared with those of the corresponding alcohol - water mixtures, particularly t. butyl alcohol - water mixtures. Various methods of analyising the ultrasonic absorption properties of binary mixtures are examined, including those treatments which link the excess absorption with a tendency towards phase separation and critical solution behaviour. The ultrasonic absorption properties of solutions containing tetra-n-alkylammonium salts are reported as a function of frequency, temperature and salt concentration. In most solvents the absorption is characterised by two relaxation processes. In aqueous solution, the absorption properties are discussed in terms of a clathrate hydrate model. Comparison of the absorption properties of these salts in aqueous and non-aqueous solvents and of the hydrocarbon, 3, 3-diethylpentane, shows that an important contribution to the excess absorption is due to the presence of the different conformational isomers of the alkylammonium ion.