Effect of Counterions and Temperature on the Association and Partition Balances of Hexadecylpyridinium Halides in Aqueous Solutions

Abstract

Abstract The effect of counterions and temperature on the association (critical micelle concentration, thermodynamics of micellization) and partition balances (experimental partition coefficient) of three quarternary ammonium surfactants (CPX) having a common hexadecylpyridinium cation and different anions (chloride, bromide, iodide) were studied in aqueous solutions at the temperature range 20–50°C, using conductometry, potentiometry, UV spectroscopy and measurement of surface tension. All methods used gave closely similar values for critical micelle concentration. From calculated thermodynamics parameters the process of micellization was found to be spontaneous and exothermic. Experimental partition coefficient of hexadecylpyridinium halides increased from chloride to iodide. The objective of this work was to check whether surfactant counterions can affect the micellization and partition processes. From the results obtained it seems that the differences found in micellization and partitioning of all compounds studied, may be attributed to the different physicochemical properties of chloride, bromide and iodide anions as their differences in mobility etc.