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We report picosecond absorption-recovery laser spectroscopic studies of the orientational relaxation times ( T~J of the structurally similar probe molecules resorufin (anion) and cresyl violet (cation) in a series of binary systems comprising MezSO and water. While these probe molecules exhibit a hydrodynamic-like response in pure H-bonded solvents, a qualitatively different behavior is recorded in these binary systems. A distinctive curvilinear dependence of T~~~ on viscosity is observed. The introduction of dielectric friction to the theoreticaIly calculated response of the host molecular fluid is investigated, but in contrast to results for 7r0t in H-bonded systems, this does not appear to predict the observed behavior. Attention is focused on investigating the microscopic dynamics in electrolyte solutions as an alternative approach.

done with the system 0.03 m CTAB + 0.04 and 0.08 m K(Br:Cl). The results for R(90) and Z)app are plotted against the bromide molar fraction XBr in Figure 10, a and b. At 0.04 m both systems have small aggregates and the difference in all properties is small and monotonic from = 0 to 1. At 0.08 m K(Br:Cl), J?(90) and Z>app are almost constant up to XBr = 0.6. At higher bromide content the growth is reflected in both properties. The parameter µ2/ 21 2 is related to the polydispersity of the system.17 It has been mentioned that the polydispersity of spherical aggregates is smaller than for large cylin order to investigate the correlations between orientational relaxation times (rrot) and properties of the single-solvent or binary systems. A sequence of normal and substituted alcohols, dimethyl sulfoxide, formamide, TV-methylformamide, and dimethylformamide has been investigated. While good agreement with hydrodynamic-based theories is seen for the pure alcohol systems, the binary propanol-H20 systems show a surprising curvilinear dependence of rrot vs. beyond the realms of any expectations in simple hydrodynamic responses, as has been shown previously. If a dielectric friction model is applied, then these curvilinear profiles are predicted at least qualitatively. The successful ingredients of such a model are discussed and its limitations assessed for its application to polar fluids, given the poor agreement with the relaxation times or trends in the dimethyl sulfoxide and amide solvents.

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