Temperature-dependent solvation dynamics of water in sodium bis(2-ethylhexyl)sulfosuccinate/Isooctane reverse micelles

In this paper, for the first time, we report a detailed study of the temperature-dependent solvation dynamics of a probe fluorophore, coumarin-500, in AOT/isooctane reverse micelles (RMs) with varying degrees of hydration (w(0)) of 5, 10, and 20 at four different temperatures, 293, 313, 328, and 343 K. The average solvation time constant becomes faster with the increase in w(0) values at a particular temperature. The solvation dynamics of a RM with a fixed w(0) value also becomes faster with the increase in temperature. The observed temperature-induced faster solvation dynamics is associated with a transition of bound- to free-type water molecules, and the corresponding activation energy value for the w(0) = 5 system has been found to be 3.4 kcal mol(-1), whereas for the latter two systems, it is similar to 5 kcal mol-1. Dynamic light scattering measurements indicate an insignificant change in size with temperature for RMs with w(0) = 5 and 10, whereas for a w(0) = 20 system, the hydrodynamic diameter increases with temperature. Time-resolved fluorescence anisotropy studies reveal a decrease in the rotational restriction on the probe with increasing temperature for all systems. Wobbling-in-cone analysis of the anisotropy data also supports this finding.