Solvation dynamics in the water pool of aerosol sodium dioctylsulfosuccinate microemulsion: effect of polymer

Abstract

Solvation dynamics of 2,6-p-toluidinonaphthalene sulfonate (TNS) is studied in a large water pool (w₀ = 56) of aerosol sodium dioctylsulfosuccinate (AOT) microemulsion in n-heptane in the absence and the presence of a hydrophilic polymer, poly(vinylpyrrolidone) (PVP). The solvation dynamics of TNS in AOT microemulsions without polymer is found to be biexponential with a major component of 300 ± 30 ps (75%) and a slow component of 500 ± 50 ps (25%) with an average solvation time of 350 ps. In the presence of a polymer (0.75 wt % PVP) in the water pool, the solvation dynamics of TNS is found to be faster with components 70 ± 10 ps (75%) and 250 ± 25 ps (25%) and having an average solvation time of 115 ps. The very fast solvation dynamics in the presence of 0.75 wt % PVP in the water pool is similar to that in bulk water and is ascribed to strong binding of TNS to PVP. When the concentration of the polymer is increased to 2.5 wt % PVP, the solvation dynamics of TNS in polymer encapsulated microemulsions is found to be markedly slower. In the presence of 2.5 wt % PVP, the solvation dynamics in the water pool exhibits components of 100 ± 10 ps (33%), 600 ± 50 ps (47%) and 11 ± 1 ns (20%), with an average solvation time 2500 ps. This clearly indicates that, at high concentration of the polymer, dynamics of the water molecules inside the water pool of microemulsion is severely constrained.