Investigation of surface adsorption and thermodynamic properties of 1-tetradecyl-3-methylimidazolium bromide in the absence and presence of tetrabutylammonium bromide in aqueous medium

Abstract

The aggregation behavior of imidazolium-based long-chain ionic liquid 1-tetradecyl-3-methylimidazolium bromide [C₁₄mim][Br] has been investigated in the absence and presence of (1, 2, and 5) mM tetrabutylammonium bromide (C₄H₉)₄NBr at three temperatures (298.15, 308.15, and 318.15) K. The critical micelle concentration (CMC), surface parameters such as maximum surface excess concentration (${\Gamma }_{\mathit{max}}$), the minimum area surfactant monomer at the air/water interface ($A_{\mathit{min}}$), surface tension at CMC (${\gamma }_{\mathit{cmc}}$) and surface pressure (${ᴨ}_{\mathit{cmc}}$) are determined by employing conductivity and surface tension measurements. Various thermodynamic parameters of micellization such as standard free energy of micellization ($\mathrm{\Delta }{G}_m^0$), standard enthalpy of micellization (${\mathrm{\Delta }H}_m^0$), and standard entropy of micellization ($\mathrm{\Delta }{S}_m^0$) are calculated by utilizing the temperature dependence of CMC observed using conductivity study. Other thermodynamic parameters such as free energy of adsorption (Δ$G_{ad}^0$) and surface free energy ($G_{\mathit{min}}^s$) are also evaluated. Refractive index measurements and UV–vis spectroscopic studies have been utilized to confirm the values of CMC obtained via conductivity and surface tension measurements. FTIR spectroscopic studies signify the various interactions prevailing in the system constituting long-chain ionic liquid and electrolyte.

Graphical Abstract

Keywords:

• [C₁₄mim][Br]
• (C₄H₉)₄NBr
• micellization
• self-assembly
• thermodynamic parameters

Acknowledgements

The authors are also thankful to DST, New Delhi for DST-FIST [CSI-228/2011] Program and The Director and Head, Department of Chemistry for providing necessary facilities.

Additional information

Funding

Authors (H.K) are thankful to Science and Engineering Research Board (SERB), New Delhi for providing financial assistance to carry out research work vide sanction order number EMR/2015/002059.