Investigations of interactions between surface active ionic liquid 1-butyl-3-methyl imidazolium dodecylbenzenesulfonate and cationic polyelectrolyte poly(diallyldimethylammonium chloride) in aqueous solution

In the present study, we have reported a comprehensive assessment of interactional behavior between the surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium dodecylbenzene sulfonate [C4mim][DBS] and cationic polyelectrolyte poly(diallyldimethylammonium chloride) [PDADMAC] solution in aqueous solution. Various techniques such as surface tension, isothermal titration calorimetry (ITC), conductivity, dynamic light scattering (DLS) and turbidity have been employed to get insight into interactions among [C4mim][DBS] and polyelectrolyte in the interfacial region. Then surface parameters such as surface excess concentration (Γcmc), 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) have been calculated from tensiometric measurements. The values of cmc decrease with increase in concentration of polyelectrolyte indicating towards the predominance of electrostatic interactions except at intermediate concentration (0.01 g/L PDADMAC) for which hydrophobic interactions can be held responsible. The standard enthalpy of micellization (∆Hm°) has been obtained from ITC measurements. Further, thermodynamic parameters i.e. standard free energy of micellization (∆Gm°) and standard entropy of micellization (∆Sm°) have been evaluated from conductivity measurements. The size of complexes formed among [C4mim][DBS] and polyelectrolyte have been characterized using DLS and turbidity measurements. Overall, the electrostatic interactions play a major role among SAIL and polyelectrolyte which is generally expected from oppositely charged systems. The process of micellization has been found to be exothermic and spontaneous thermodynamically in presence of PDADMAC supported by gain in entropy.