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Abstract
In this paper, spectrophotometric and conductometric methods were used to study the interaction phenomenon between oppositely charged anionic Eosin-Y and cationic surfactants; dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, cetyltrimethylammonium bromide, cetylpyridinium bromide and cetylpyridinium chloride. Conductivity measurements of surfactants were performed and the degree of micellar ionization was determined in the absence and presence of Eosin-Y. The ionization degree and counterion binding parameter obtained from conductivity data are used to evaluate the interaction mechanism of Eosin-Y in wide range of different hydrophobic cationic microenvironments as well. The absorption spectra were used to quantify the binding constants by means of Benesi-Hildebrand equation. Comparison of the binding degree of Eosin-Y to micelles indicates a direct correlation between binding constant and hydrophobicity. The micellar properties of cationic surfactants at levels below and above their CMCs in aqueous and in the presence of Eosin-Y were also studied using conductivity and spectrophotometry. It was observed that the CMC values of cationic surfactants decreased in the presence of Eosin-Y. The spectrophotometric behavior of Eosin-Y in water-EOH mixture of varying composition was also monitored in order to gain more information about the localization of Eosin-Y in cationic micelles.