An investigation of the microscopic structure and dynamics of binary liquid mixtures.

摘要

We have used dynamic light scattering to study the dynamics of binary liquid mixtures. Through the use of photon correlation and Brillouin spectroscopy we have measured mutual diffusion coefficients and hypersonic speeds of sound as a function of concentration in several systems. The experimental systems were chosen because they possessed seemingly anomalous maxima and minima in both their thermodynamic properties and diffusion coefficients as a function of concentration.; By using our hypersonic speed of sound data we determined the value for a high frequency relaxation process in the water-rich region of the t-butyl alcohol/water system. The agreement of these acoustic relaxation times and activated state parameters as compared to literature values from high frequency dielectric relaxation measurements was interpreted as showing that the relaxation time might be associated with a structural relaxation in the solution.; We also studied two aggregating binary liquid mixtures by photon correlation spectroscopy. In the case of 2-butoxyethanol (BE)/water there existed an apparent microphase transition in the water-rich region. The absence or existence of this transition was, however, found to depend on the source from which the BE was obtained. The time dependent aggregation observed in the aqueous {dollar}alpha{dollar}-hydro {dollar}omega{dollar}-methoxy poly(1,2-oxyethanediyl) was analyzed using an assumed particle geometry to obtain weight cumulant curves for the particles in the system. Aggregation was shown to be strongly dependent on the end group which terminates these poly(ethylene glycol) analogs.; Models for predicting diffusion in these nonideal mixtures were studied. Kirkwood-Buff (KB) parameters were calculated for eight test systems as a means of determining the local solution static structure. For these same systems we calculated the experimental velocity cross correlation coefficients (VCC's). With an approximation for the solution radial distribution functions and the experimental KB parameters we then predicted the VCC's of the experimental test systems. Finally, by using an ideal liquid KB parameter model in our VCC predictive equation we obtained a VCC reference system against which the VCC's of experimental systems can be compared.