Aggregation of an anionic azo dye with conventional cationic surfactants in premicellar region: A conductometric study


1 Department of Physical Chemistry, Tarbiat Modares University

2 Department of Physical Chemistry, Payame Noor University, Urmiah Branch


The interaction of Congo Red CR with a series of Alkyltrimethylamoniumbromide CnTAB, N-hexadecylpyridinium bromide CPB and N-hexadecylpyridinium CPC were investigated using conductometry technique. It was observed that the formation of dye-surfactant ion pairs takes place at surfactant concentration far below the critical micelle concentration of the individual surfactants. Aggregation was reflected by the appearance of a break point at conductometry plots. The equilibrium constant and other thermodynamic parameters for the ion pair formation were calculated on the basis of a theoretical model using the data obtained by conductometry. The reaction between dye and surfactants was revealed to be an enthalpy-driven reaction which is highly dependent on temperature and the structures of both dye and surfactant.