A Comparison of Energy Flow in Micelle and Vesicle Structures

Abstract

We have investigated the vibrational population relaxation dynamics and state-dependent orientational relaxation behavior of perylene in micelles and vesicles formed using the same amphiphile(s). Decanoic acid and its conjugate base sodium decanoate can form either micelle or vesicle structures in aqueous solution depending on amphiphile concentration and solution pH. The issue of interest in this work is whether or not different assemblies of a given amphiphile manifest different efficiencies with the dissipation of energy. Vibrational population relaxation data show that initial energy flow from the chromophore to the amphiphile aliphatic chains is more efficient in micelles than in vesicles. Longer time scale relaxation, gauged by transient local heating induced by the dissipation of excess energy from perylene shows that the local environment formed by micelles experiences greater temperature change than the local environment formed by vesicles. This finding suggests that the strength of coupling between the bath and the amphiphiles differs for the two structural motifs.