The mixing behavior of n-alkylpyridinium bromide–NP-9 mixed surfactant systems

The interaction between n-alkylpyridinium bromide (CmPB, m = 16, 14, 12, and 10) cationic surfactants and nonylphenyl ethoxylates (4-C9H19C6H4(OCH2CH2)9OH, NP-9) nonionic surfactant are investigated using surface tension method. The mixed critical micellar concentration (CMC) values determined from the experimental data are used to calculate the interaction parameter (β12) using regular solution theory (RST) of the mixed surfactant systems. Four different alkylpyridinium bromide surfactants show almost ideal behavior when mixed with NP-9, the interaction parameter values calculated using RST is close to zero. The micellar mole fraction of the cationic surfactant decreases in the mixed micelle with decreasing the alkyl chain length of the cationic surfactant.