Aggregation Behavior of Sodium Dodecyl Sulfate and Cetyltrimethylammonium Bromide Mixtures in Aqueous/Chitosan Solution at Various Temperatures: An Experimental and Theoretical Approach

A conductometric study of the mixed micellization behavior between cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic surfactant) was carried out in the absence/presence of various percentages of chitosan in the temperature range of 298.15-318.15K. The deviations of critical micelle concentration (cmc) from the ideal values indicate the interaction between CTAB and SDS. The micellar mole fraction values according to different proposed models X-1(Rub) (Rubingh), X-1(M) (Motomura), X-1(Rod) (Rodenas), and X-1(id) (ideal mole fraction) were estimated and the results obtained reveal the high contribution of CTAB in the mixed micellization, which enhances with the increase of the mole fraction of CTAB. The negative magnitudes of Gm0 indicate the spontaneous formation of mixed micelles between CTAB and SDS. The values of activity coefficients (f(1) and f(2)) were less than unity and the values of the interaction parameter () are negative in all cases, which indicate the attractive interaction between CTAB and SDS. The negative values of excess free energy of micellization (G(ex)) signify the stability of the mixed micelles. The negative values of Hm0 in the chitosan systems indicate that micellization is exothermic. The values of Sm0 were found to be positive in all cases.