Synthesis And Properties Of Ionic Liquid Surfactants

Ionic liquids (ILs) surfactants possess many characteristics of both surfactants and ionic liquids. Recently, the synthesis and the surface activities of these novel surfactants have been one of the attractive topics in the fields of ILs and surfactants. Here, two novel ILs surfactants, a hydroxy-functional ILs cationic surfactant and a zwitterionic ILs surfactant, have been designed and synthesized using imidazole as the starting material.(1) A hydroxy-functionalized ILs cationic surfactant, namely 1-hydroxyethyl-3-dodecyl imidazolium chloride ([C₂OHC₁₂im]Cl). [C₂OHC₁₂im]Cl was synthesized using imidazole, 1-bromododecane and 2-chloroethanol via alkylation and quarter amination. The molecular structure was confirmed by means of fourier transform infrared spectroscopy, electrospray mass spectrometry, elemental analysis and nuclear magnetic resonance. The first critical micelle concentration (CMC₁) was determinated by surface tension method, conductive method and steady-state fluorescence probe method. The experimental results show that [C₂OHC₁₂im]Cl had the second critical micelle concentration (CMC₂). The sodium halides (NaX, X=Cl, Br, I) cause a decrease of CMC values. The smaller the hydration of the anion was, the smaller the CMC was. In the presence of NaX, the adsorption efficiency (pC20), the surface pressure at the CMC (ΠCMC) and the maximum surface excess (Γ_m) values increase, and the minimum molecular cross-sectional area (Amin) values decreases. For NaBr-[C₂OHC₁₂im]Cl systems, the relationship between CMC and the concentration of NaBr (CNaBr) is logarimic. Under the conditions of with or without NaX, the micelle aggregation number (Nm) increase with the concentration of [C₂OHC₁₂im]Cl (C) increasing. The relationship between Nm and C was fitted by power law and linear equation, respectively. Consequently, the critical micelle aggregation number (Nm,c) was deduced by the equations. In NaBr-[C₂OHC₁₂im]Cl system, the Nm exponentially grows with CNaBr increasing.(2) A zwitterionic ionic liquid surfactant, namely 1-carboxylmethyl-3-dodecyl imidazolium inner salt (CMDim). CMDim was prepared using imidazole, 1-bromododecane and sodium chloroacetate via alkylation and quarter amination. The molecular structure was confirmed by means of fourier transform infrared spectroscopy, electrospray mass spectrometry, elemental analysis and nuclear magnetic resonance. The Krafft point is 18±0.2 oC, and isoelectric point is 3.8±0.2. The critical micelle concentration (CMC) and the micelle aggregation number (Nm) were determinated by surface tension method and steady-state fluorescence probe method, respectively. The experimental results show that CMC andΓm values decrease, pC20 and Amin values increase,ΠCMC values unchanges with the pH values increasing. In pH=7 aqueous solution, the Nm increase with the concentration of CMDim (C) increasing. The relationship between Nm and C was fitted by power law and linear equation, respectively. Consequently, the critical micelle aggregation number (Nm,c) was deduced by the equations.