LAUSR

Abstract The solution properties of mixed amphiphiles system play a promising role in the surface chemical applications. Aggregation behavior of two cationic surfactants as tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB) has been taken into account in detail using conductivity measurements and theoretical calculations in water medium and urea (NH2-CO-NH2) solution over temperature range of 298.15 K to 318.15 K. The critical micelle concentration (cmc) for pure CTAB, TTAB and CTAB + TTAB mixtures as well as the ideal critical micelle concentration (cmcid) for CTAB + TTAB mixed system were evaluated in attendance/absence of urea (300 mmolkg−1 and 800 mmolkg−1). The cmc values of CTAB + TTAB mixtures are observed to be less than cmcid values imply that attractive interaction occurs between these two surfactants. The activity coefficients (f1 and f2) and the micellar mole fraction of CTAB (X1) were assessed by applying different models such as Rubingh, Motomura and Rodenas; the results suggest the existence of more contribution of CTAB in mixed micelles and their values increases by enhance of the mole fractions of CTAB. The β values were estimated to get insights of the interactions between the surfactants (TTAB & CTAB) by proposed Rubingh model. The ∆H0m and ∆S0m values reveal that the possible binding forces between TTAB and CTAB are hydrophobic as well as electrostatic interactions. The excess free energy (∆Gex), the compensation temperature (Tc) as well as the intrinsic enthalpy gain (∆H0,⁎m) were determined and discussed in detail.