Effect of cationic head group on micellization behavior of new amide-functionalized surface active ionic liquids

Abstract

Amide-functionalized surface active ionic liquids (SAILs), 1-methyl-1-dodecyl piperidinium chloride, [C₁₂APip][Cl]; 1-methyl-1-dodecyl pyrrolidinium chloride, [C₁₂APyrr][Cl]; 1-methyl-3-dodecyl imidazolium chloride, [C₁₂Amim][Cl], and 1-methyl-1-dodecyl morpholinium chloride, [C₁₂AMorph][Cl], have been synthesized, characterized and investigated for thermal stability, and micellization behavior in aqueous medium. The introduction of an amide moiety in the alkyl chain decreased the thermal stability of the functionalized SAILs compared to non-functionalized SAILs bearing a simple alkyl chain. A variety of state of the art techniques, viz. tensiometry, conductometry, steady-state fluorescence, isothermal titration calorimetry (ITC), dynamic light scattering (DLS) and atomic force microscopy (AFM), have been employed to investigate the micellization behavior. Amide-functionalized SAILs have shown much lower critical micelle concentration, cmc, and better surface active properties as compared to homologous non-functionalized SAILs. Steady-state fluorescence has provided information about cmc, aggregation number (N_agg) and polarity of the cybotactic region of the micelles, whereas ITC has provided insights into the thermodynamics of micellization. Furthermore, the size and shape of the micelles have been investigated using DLS and AFM techniques.