Micelle Formation of Long-Chain Imidazolium Ionic Liquids in Aqueous Solution Measured by Isothermal Titration Microcalorimetry

Abstract

Self-association of three long-chain imidazolium ionic liquids (ILs), [C12mim]Br, [C14mim]Br, and [C16mim]Br, in aqueous solution was studied by surface tension measurements over a temperature range from (278.15 to 328.15) K. Effects of temperature and hydrocarbon chain length of the three long-chain ILs on the critical micelle concentration (CMC) were examined. Thermodynamic parameters, Δmic G, Δmic H, and Δmic S, of micellization were determined by applying a mass-action model equation. Isothermal titration microcalorimetry was used to obtain the enthalpy change upon micellization of the three long-chain ILs at 298.15 K. Moreover, the CMCs and the thermodynamic parameters (Δmic G, Δmic H, and Δmic S) were determined based on the isothermal titration microcalorimetry results. These CMC values are approximately equal to the CMCs obtained by surface tension measurement.

Apparent molar volume, conductivity, and fluorescence studies of ternary systems of dipeptides + ionic liquids ([Cnmim]Br, n = 10, 14) + water at different temperatures

“…These values of c cmc and α are given in Table S3 of the Supplementary Material. It can be seen from Table S3 that the c cmc of [C n mim]Br (n=10, 14) at different temperatures in aqueous solution is in good agreement with those previously reported [33][34][35]. Table S3 and Fig.…”

Enthalpy–entropy compensation of ionic liquid-type Gemini imidazolium surfactants in aqueous solutions: A free energy perturbation study

“…Therefore, according to the mass action model of micellization, the thermodynamic parameters can be predicted by making the solvation free energy changes substituted into the following equations [32]:…”

Effect of alkyl chain length and head group on surface active and aggregation behavior of ionic liquids in water

“…A proper and comprehensive understanding, especially of the adsorption behavior at air/water interface, and aggregation or association phenomenon in aqueous and non-aqueous solutions is a prerequisite before ILs are explored for surfactant based applications [9]. The surface, interfacial and aggregation characteristics of ILs based on 1-alkyl (butyl to hexadecyl)-3-methylimidazolium bromide, or chloride in water have been extensively studied by using various methods such as surface tension [12,13,16,[21][22][23][25][26][27], electrical conductivity [14][15][16][17][18][19][20][21][22][23][24][25]31,32], fluorescence [16,20,21,25,26], 1 H NMR [19,26,28], steady state fluorescence spectroscopy [25,29], isothermal titration calorimetry [30]. The main focus of these investigations were to determine the critical aggregation concentrations (CAC) mostly at 298.15 K. Some discrepancies between the CAC data as determined from different methods for the same IL were noted [31] and these discrepancies can be attributed to the presence of impurities of the sample as well as to the sensitivity of the method used.…”