Behaviour of a surface active cyanine dye in water and surfactant solutions

Abstract

N-Cetyl-4-(<i>p</i>-N,N-dimethylamino)styrylpyridinium bromide (<b>I</b>) has been used as a probe to study the effect of hydrophonic chain in organising the dye molecule in water medium. (<b>I</b>) forms a condensed monolayer on water surface covering 65 Ų<i> /</i>molecule. An L- L type of aggregation has been proposed on the basis of the calculated area of the molecule. A hypsochromic shift in the absorption of (<b>I</b>) in aqueous medium in the presence of CTAB (below CMC) suggests formation of a dimer. But above the CMC of CTAB, (<b>I</b>) forms aggregates with CTAB Ieading to a mixed micelle formation. However, in revers d micelle, a bathochromic shift is observed with increasing water concentration. This shift reveals a J-type aggregation of the dye at the interface.