Vol. 7, Issue 4 (2019)
Effect of some potassium salts on the Krafft temperature and related thermodynamic behavior of Cetylpyridinium Bromide (CPB) in aqueous solution
Author(s): Khokan Chandra Sarker and Dr. Md. Rafique Ullah
Abstract: The Krafft temperature (Tk) and Critical micelle concentration (CMC) of Cetylpyridinium bromide (CPB) have been determined in the presence of some potassium salts. Kosmotropic F−, Cl−, NO3−, CO32−, SO42− and HPO42− decrease while chaotropic Br−, I− and SCN− were found to increase the TK of CPB compared to that of CPB in pure water. More chaotropic anions such as SCN− and I− form contact ion pairs with the cetylpyridinium ion and thus reduce the electrostatic repulsion between the surfactant molecules and show salting out behavior with a consequent increase in the Tk of the surfactant solution. On the other hand, less chaotropic NO3−, Cl− increase the activity of free water molecules and thus enhance the hydration of CPB molecules showing a decrease in the Tk. In spite of being strong kosmotropes SO42−, CO32−, HPO42− and F− behave like moderate chaotropes and lower the Tk. In terms of deceasing the TK the ions follows the trend: NO3− >Cl− >SO42− >CO32− >HPO42- >F− >Br− >SCN− >I−. Added salt screen the charge of the micelle head group and facilitate closer packing of the surfactant. Thus added salt always decrease the CMC of the surfactant. Different salts interact differently with surfactant and thus decrease the CMC differently. In case of decreasing the CMC ions follow the order: SCN−> I−> SO42−> NO3− > HPO42-> CO32- > Br−> Cl−> F−. Added salt also affects the surface adsorption and bulk micelization of CPB in aqueous solution. Thermodynamic parameters such as free energy change (ΔGmic, ΔGad), enthalpy change (ΔHmic, ΔHad), entropy change (ΔSmic, ΔSad) were calculated from the specific conductance and tensiometric data. The negative value of free energy change indicates the process to be spontaneous. The enthalpy and entropy terms are found to compensate each other for both micellization and adsorption. The solubilization behavior of a water insoluble dye, 1-(2-pyridylazo)-2-naphthal (PAN), in the micellar system was studied by the UV–visible spectrophotometric technique. The molar solubilization ratio in the presence of KNO3 was found to be about 15.5 times higher than surfactant in pure water, indicating that the solubilization of PAN in the CPB micelles significantly increases in the presence of KNO3.
Pages: 97-107 | 433 Views 57 Downloads
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How to cite this article:
Khokan Chandra Sarker, Dr. Md. Rafique Ullah. Effect of some potassium salts on the Krafft temperature and related thermodynamic behavior of Cetylpyridinium Bromide (CPB) in aqueous solution. Int J Chem Stud 2019;7(4):97-107.
