Part I
A quasi-elastic light scattering spectrometer has been constructed and used to measure the binary mutual diffusion coefficient DAB as a function of concentration in eight binary mixtures and the thermal diffusivity x in nine pure liquids and two binary mixtures. The resulting values are in close agreement with the available bulkvalues and are accurate to within 3% for mass diffusivities and 5% for thermal diffusivities. Because neither type of measurement is dependent on the imposition of a macroscopic gradient, many of theproblems associated with conventional bulk measurements are eliminated.
Determinations require less than 2 hours for thermal diffusivities and 30 minutes for mass diffusivities, in contrast to the more time consuming classical approaches.
On the basis of these experimental results, light scattering spectroscopy is established as an effective tool in the determination of liquid mass and thermal diffusivities. The technique should have wide industrial application.
Part II
Quasi-elastic light scattering experiments on solutions ofɸX174 RF DNA and PM2 I DNA reveal spectral contributions from translational and intramolecular motion. A tentative interpretation of the data in terms of Rouse-Zimm theory indicates lowest order relaxationtimes qualitatively consistent with theoretical predictions. Further experiments on linear and form II DNA should provide information about the changes in molecular flexibility and translational diffusivity associated with an alteration in conformation.
