Thermodynamic investigation of the interaction between Mono-s-chloroTriazinyl MCT Reactive Dyes and cetylpyridinium chloride inaqueous solution

The interactions two synthetic triazinyl reactive dyes Mono-s-chloro Triazinyl reactive dyes DI and DII with the cationic surfactant N-hexadecyl pyridinium chloride CPC were studied using a conductometric method in 25, 30, 35, 40 and 45ºC. 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 change values for all systems decreased as temperature increased. According to thermodynamics data, formation ion pair between the dye and the surfactant was revealed to be an enthalpy-driven process which is highly dependent on the temperature and the structures of dye for both systems. These results indicate DI dye molecular structure has hydrophobic centers that make it suitable for both electrostatic and hydrophobic interactions with CPC cationic surfactant when this interaction for the DII dye with CPC can be explained only the long range electrostatic forces and short-range hydrophobic forces do not cause the formation of dye-surfactant complex.