Conductometric and molecular dynamics studies of the aggregation behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) in aqueous and electrolytes solution

• Published in: Journal of molecular liquids 2019-06, Vol.283, p.263-275
• Main Authors: Mahbub, Shamim, Molla, Mohammad Robel, Saha, Mousumi, Shahriar, Imrul, Hoque, Md. Anamul, Halim, Mohammad A., Rub, Malik Abdul, Khan, Mohammed Abdullah, Azum, Naved
• Format: Article
• Language: English
• Subjects: Cetyltrimethylammonium bromide (CTAB); Hydrophobic interaction; Interaction parameter; Mixed micelle; Sodium dodecyl sulfate (SDS); Thermodynamic parameter
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2019.03.045

Herein, we have studied the mixed micellization of Cetyltrimethylammonium bromide (CTAB) and Sodium dodecyl sulfate (SDS), in aqueous/various salts medium at several temperatures (298.15–318.15 K) by conductivity measurement method. The extent of interaction between CTAB and SDS was assessed from the values of ideal critical micelle concentration (cmcid) as well as experimental cmc. In attendance of salts, cmc values are obviously decreased from the corresponding values in aqueous medium. The magnitudes of micellar mole fraction of CTAB (X1) and activity coefficients of CTAB & SDS (f1 &f2) were estimated based on different theoretical model and outcome disclose the effective involvement of CTAB in the mixed micellization. The executed values of both interaction parameters (β) and excess free energy of micellization were negative signifying the attractive interaction and stability of mixed micelles respectively. The executed negative values of Gibbs free energy change of micellization, ∆Gom illustrate the spontaneous micellization of individual/mixed surfactant system. The other thermodynamic parameters ΔHom (enthalpy change), and ∆Som (entropy change) were also calculated from the conventional standard equations. Molecular level interactions are disclosed by molecular dynamics (MD) simulation which showed that salts promote more interactions between the surfactants. Simulation snapshot of SDS-CTAB complex in H2O + KCl after 20 ns simulation (CTAB in blue-carbon, K in Magenta, Cl in green). [Display omitted] •Aggregation of TTAB and CTAB is studied in the absence/presence of electrolytes.•Electrolytes reduce cmc of both pure and mixed surfactant systems.•Both the X1 > X1id and negative values of β reveal the synergism between SDS and CTAB.•The ΔGex values show the stability of mixed micelles.•MD simulation shows that salts promote more interactions between SDS and CTAB.