Aggregation, Counter Ion Binding and Adsorption Behaviors of Cetylpyridinium Chloride in Water/Glycerol Media at 25 °C

Abstract

The critical micelle concentrations (CMC) of cetylpyridinium chloride (CPC) in water/glycerol media and in the presence of sodium chloride were determined at 25 °C by surface tension and conductance methods. Variation in CMC follows the normal trend, i.e., it increases with increases in glycerol content and decreases on adding NaCl. Empirical analysis of the exponential increase in CMC of CPC with weight per cent of glycerol is indicative of CMC having two components; one component being dependent while the other independent of the glycerol amount. The counter ion binding constant was determined from both slope–ratio and Corrin-Harkins methods and showed no dependence on glycerol amount, thus confirming the unusual trend in the behavior of β in water/glycerol media. In a water/glycerol medium, the ratio of solvent surface tension to limiting surface tension at CMC is also independent of the glycerol amount, whereas the Gordon Parameter decreases with increasing glycerol content as in other aqueous organic solvents. The air–solution interface becomes saturated by the adsorption of CPC when the concentration of added NaCl is about 0.02 mol kg⁻¹ irrespective of the glycerol amount.