反相气相色谱法表征1-烯丙基-3-甲基氯代咪唑离子液体的表面性质

采用反相气相色谱(IGC)技术研究了不同温度下1-烯丙基-3-甲基氯代咪唑(［AMIM］Cl)的表面性质。以正己烷、正庚烷、正辛烷和正壬烷作为非极性探针分子测定［AMIM］Cl在343.15、353.15、363.15和373.15 K温度下的表面色散自由能;以二氯甲烷、三氯甲烷、丙酮、乙酸乙酯、四氢呋喃作为极性探针分子测定离子液体Lewis酸碱性质,并测定了吸附自由能和吸附自由焓变等热动力学参数。实验结果表明,［AMIM］Cl的酸解离平衡常数Ka为0.34,碱解离平衡常数Kb为1.68,其表面呈Lewis两性偏碱性特点。在343.15、353.15、363.15和373.15 K温度下,［AMIM］Cl的表面色散自由能分别为52.26、50.82、46.08和42.05 mJ/m2。这一结果对研究离子液体的表面性质及应用有指导作用。

Characterization of surface properties of 1-allyl-3-methylimidazolium chloride ionic liquid by inverse gas chromatography

The determination of the dispersive component of surface free energies (γds) at different temperatures and Lewis acid-base parameters of 1-allyl-3-methylimidazolium chloride ionic liquid (［AMIM］Cl) were investigated by means of inverse gas chromatography (IGC). Four n-alkanes, including n-hexane (C6), n-heptane (C7), n-octane (C8) and n-nonane (C9), were chosen as the apolar probes to characterize the dispersive component of the surface free energies at 343.15, 353.15, 363.15 and 373.15 K, respectively; and dichloromethane (DCM), trichloromethane (TCM), tetrahydrofuran (THF), ethyl acetate (EtAc), acetone (Acet) as the polar probes to estimate the Lewis acid-base parameters to judge the interactions between ［AMIM］Cl and the solvents. The IGC characterizations encompassed the adsorption thermodynamic parameters to acid-base surface interactions, including the standard enthalpy (ΔHsa) and the free energy change of adsorption (ΔGsa) at different temperatures. The results showed that the Lewis acid parameter Ka of ［AMIM］Cl was 0.34, and the base parameter Kb was 1.68, which indicated it was Lewis amphoteric with predominantly basic character. Furthermore, the free energy of adsorption ΔGsa was also figured out. It was found that the γds of the ［AMIM］Cl were 52.26, 50.82, 46.08 and 42.05 mJ/m2 at 343.15, 353.15, 363.15 and 373.15 K, respectively. The results are of great importance to the study of the surface properties and the application of ionic liquid.