Thermodynamic Investigation of the Interaction between Mono-s-chloroTriazinyl (MCT) Reactive Dyes and Cetylpyridinium chloride in Aqueous Solution

The interactions of two synthetic triazinyl reactive dyes (Mono-s-chloroTriazinyl reactive dyes with the cationic surfactant N-hexadecylpyridinium chloride were studied using a conductometric method at 25, 30, 35, 40 and 45 ?C. The equilibrium constants 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 results showed that the equilibrium constants and the negative standard free energy difference values for all systems decreased by increasing the temperature. According to the thermodynamics data, the formation of ion pair between the dye and the surfactant were revealed to be an enthalpy-driven process which is highly dependent on the temperature and the structures of dyes for both investigated systems. Therefore, both long range and short range interactions are responsible for the formation of the ion pair. The importance of long range electrostatic forces is basically to bring the dye anion and the surfactant cation close enough to drive short range interactions whose contribution represents the major part of the standard free enthalpy difference for the formation of anionic dye- cationic surfactant ion pair.