Interaction between two homologues of cationic surface active ionic liquids and the PEO-PPO-PEO triblock copolymers in aqueous solutions

The interaction of nonionic triblock copolymers of poly(ethyleneoxide) (PEO) and poly(propyleneoxide) (PPO) (PEO_nPPO_mPEO_n) with a series of cationic surface-active ionic liquids in aqueous solutions have been investigated. The cationic surface-active ionic liquids include 1-alkyl-3-methylimidazolium bromide (C_nmimBr, n?=?8, 10, 12, 14, 16) and N-alkyl-N-methylpyrrolidinium bromide (C_nMPB, n?=?12, 14, 16). For different polymer-surfactant systems, the critical aggregation surfactant concentration (cac), the surfactant concentration to form free micelles (C _m), and the saturation concentration of surfactant on the polymer chains (C ₂) were determined using isothermal titration microcalorimetry (ITC) and conductivity measurements. The structure of the formed aggregates depended strongly on the hydrophobicity of the surfactant and the ratio of polymer/surfactant concentration. For C₈mimBr, there were not any micelle-like surfactant?Cpolymer clusters detected in the solution, and only micelles appeared. For other surfactants, the polymer?Csurfactant aggregates were formed in the solution, which was verified by the appearance of a broad endothermic peak in the ITC thermograms. The intensity of polymer?Csurfactant interaction increased with the hydrophobicity of the surfactants and the polymers but was not affected by the surfactant headgroups.