INFLUENCE OF COUNTERION IDENTITY ON THE PROPERTIES OF DODECYL-SULFATE MICELLES - A STUDY BY IR AND FLUORESCENCE METHODS

The effect of the identity of the counter-ion on the structural characteristics of dodecylsulphate micelles was investigated using techniques based on the interpretation of the IR and fluorescence spectroscopic behavior of guest molecules. 6-Undecanone and pyrene were used as guests in the IR and fluorescence studies respectively. The counter-ions considered were lithium, sodium, tetramethylammonium and tetraethylammonium ions. The structural features of the micelles were revealed by monitoring parameters which allow for a qualitative analysis of the extent of exposure of the guest molecules to water. The spectroscopic behaviour of the probes was also examined in the micellar solutions in the presence of additives (n-hexanol and salts). The results obtained indicate that, of the counter-ions investigated, lithium promotes the formation of micelles with the roughest surfaces, followed in decreasing order by sodium, tetramethylammonium and tetraethylammonium ions. The micelles modified by incorporation of n-hexanol or addition of salt induce the displacement of the probes from the surface; the effect is greatest in lithium dodecylsulphate micelles.