Influence of some added electrolytes on the surface and thermodynamic properties of cetylpyridinium chloride in aqueous medium

Abstract

The effect of some added electrolytes, viz. NaCl, CaCl₂ and AlCl₃, on the critical micelle concentration (CMC), maximum surface excess concentration (G_max) and minimum area per molecule (A_min) at air-liquid interface of a cationic surfactant cetylpyridinium chloride (CPC) in aqueous solutions have been studied at 288.15, 293.15 and 298.15 K using tensiometric method. The effect of an added electrolyte on decreasing CMC of CPC is found to be in the order (AlCl₃) > (CaCl₂) > (NaCl), which falls in the same order as of the moles chloride ions furnished by each mole of the added electrolyte. The G_max decreases with increasing temperature and electrolyte concentration leading to an enhanced available area per molecule at the air-liquid interface. The process of micellization and adsorption of CPC at air-liquid interface are both favoured by exothermic enthalpy change as well as entropy gain. The observed features such as lowering of CMC, higher thermodynamic micellar stability, more relaxed surfactant molecules at the interface, due to an added electrolyte, may be exploited for improving the efficiency of the surfactant as a detergent, solubilizing agent, froth floatation process for concentrating ores, petroleum oil recovery and oil spill management.