Effects of polymer concentration and type on the interactions between 1-methyl-3-tetradecylimidazolium bromide and polymers in aqueous solution

Abstract

The interactions between the long-chain ionic liquid of 1-methyl-3-tetradecylimidazolium bromide (C14mimBr) and five polymers have been studied in detail using surface tension, electric conductivity, isothermal titration microcalorimetry (ITC), and steady-state fluorescence methods. The polymers used include neutral polymers of polyethylene glycol (PEG) and polyvinyl alcohol (PVA), triblock copolymers of PEO13PPO30PEO13 (L64) and PEO79PPO30PEO79 (F68), and polyelectrolyte of sodium carboxymethylcellulose (NaCMC). This paper focuses on the effects of polymer concentration and type on the surfactant-polymer interactions. The curves in the absence and in the presence of the polymer have more or less differences, exhibiting the cooperative interaction of the surfactant and five polymers. Although the effects of each polymer addition on the surfactant aggregates can be proved by various techniques, for one system, the inflection points on the curves from different method are difficult to unify and an attempt to show the concurrence of the data is only diluting the essence of this area. It is concluded that the interacting intensity between C14mimBr and the polymer has the order of NaCMC > L64 >F68 >PVA > PEG, which is determined by the strong electrostatic attraction, relatively strong hydrophobic interaction, and/or weak ion-dipole interaction relating to the polymer structure. Due to the precipitation formation of NaCMC and cationic surfactant aqueous solution, copolymers especially the existence of PPO chain not only has a good synergistic effect with surfactant, but also can adjust the viscosity of the system.