Determination of thermodynamic parameters for the cloud point extraction of different dyes using TX-100 and TX-114 Original Research Article

The thermodynamics of cloud point extraction (CPE) of three different dyes are investigated. Dyes used are congo red, eosin and chrysoidine. Iso-octyl phenoxy polyethoxy ethanol (TX-100) and octyl phenol poly ethylene glycol ether (TX-114) are used as non-ionic surfactant. The effects of different operating conditions (e.g., temperature and concentrations of surfactants and dyes) on various thermodynamic parameters such as change in Gibbs free energy (ΔG0), change in enthalpy (ΔH0) and change in entropy (ΔS0) are observed and presented in detail. It is found that the values of ΔG0 increase with temperature but decreases with the concentrations of surfactant and dye. The values of ΔH0 and ΔS0 increase with surfactant concentration but decrease with dye concentration. Comparisons of all the thermodynamic parameters are made for chrysoidine–TX-100 and chrysoidine–TX-114 systems. Negative values of ΔG0 of all three dyes dictate that the solubilizations are spontaneous phenomena. Endothermic nature of the solubilization process of all dye is governed by the positive value of ΔH0. On the other hand, positive values of ΔS0 prove that dye molecules are organized on the mantle of aqueous hydrophilic chains in a more random fashion.