Micellization behavior of anionic surface active ionic liquid 1-butyl-3-methylimidazolium dodecylbenzenesulfonate in aqueous solutions of nonionic polymer polyethylene glycol: Insights into competing mechanisms

Abstract

In this study, an understanding of interactions among the anionic surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium dodecylbenzenesulfonate [C4mim][DBS] and non-ionic low molecular weight polymer polyethylene glycol 400 (PEG 400) in aqueous solution has been developed systematically. Various techniques such as tensiometry, conductivity, dynamic light scattering (DLS), nephelometric turbidity and rheology have been employed to understand the exquisite interplay of different competing mechanisms prevailing between these unlike molecules in bulk as well as in the interfacial region. Surface activity of the current systems at air-aqueous interface have been evaluated using by deriving various important surface parameters, such as surface excess concentration (Гmax), surface pressure at interface (Πcmc), minimum area occupied by one molecule of SAIL at air-solvent interface (Αmin), adsorption efficiency (pC20) and surface tension at critical micelle concentration (cmc) (γcmc). Also, the thermodynamic parameters such as standard free energy of micellization (ΔGm°), standard enthalpy of micellization (ΔHm°) and standard entropy of micellization (ΔSm°) have been evaluated from conductivity measurements. The process of micellization has been found to be exothermic and spontaneous thermodynamically in presence of PEG supported by gain in entropy. The values of critical micelle concentration (cmc) decrease with increase in concentration of PEG which signals towards the predominance of ion-dipole interactions as well as hydrophobic interactions. However, at the higher concentration (0.045 g/L PEG), the cmc has been found to increase due to modification in surface and bulk structure of system. These results have been confirmed by the electrical conductivity measurements. The aggregate formation has also been tracked with the help of dynamic light scattering and nephelometric turbidimetry which provides useful information regarding the complexation dynamics. The rheological measurements have been carried out with the intent of understanding the complex behavior of these SAIL-polymer systems.