The solvent relaxation of pure water molecules is very fast. It takes place within 200 femtoseconds. The solvent relaxation dynamics of water molecules are retarded dramatically when it is confined within a reverse micelle or micelles. In recent years we have investigated the solvation dynamics of polar liquids other than water, e.g. methanol, acetonitrile, formamide within a confined cavity of non-aqueous micelles using various 7-amino coumarins. The most interesting observation of our investigation is that the solvent relaxation of methanol and acetonitrile are retarded to several nanoseconds in non-aqueous reverse micelles compared to a few picoseconds for pure methanol and acetonitrile. We have investigated the water dynamics in mixed micellar systems e.g. bile salt – Tx100, bile salt – CTAB, bile salt – lecithin. The mixed micelles are important model systems for Cholesterol solubility in the human body. The dynamics of water molecules in various mixed micelles are also retarded several thousand times compared to pure water. We have also investigated the solvation dynamics of environmental-friendly pure ionic liquids (IL’s) and IL’s confined in micelles and reverse micelles or microemulsions. The solvation dynamics of IL’s in confined cavities like micelles or reverse micelles are retarded only 2-3 times compared to pure IL’s, contrary to several thousand times for aqueous micelles.
Depeartment of Chemistry, Indian Institute of Technology, Kharagpur, India