Modulating the Aggregation Behavior of 1-Methyl-3-Octylimidazolium Chloride by Alcohols in Aqueous Media

摘要

The self-organization and aggregation behavior of a surface active ionic liquid (SAIL) 1-methyl-3-octylimidazolium chloride [C(8)mim]Cl, was investigated in aqueous solutions of alcohols 1,2-propanediol and 1-propanol in different compositions using conductivity, surface tension and fluorescence measurements at room temperature. This surface active ionic liquid was synthesized by the reaction of 1-methylimidazole with 1-chlorooctane. Fluorescence spectroscopy was employed to get detailed insight into the local microenvironment of the aggregates, critical aggregation concentrations (CAC) and aggregation number (N (agg.)). Degree of ionization (alpha), CAC and various thermodynamic parameters like the standard Gibbs free energy of aggregation (Delta G (agg.) (0) ), standard enthalpy of aggregation (Delta H (agg.) (0) ) and standard entropy of aggregation (Delta S (agg.) (0) ) were calculated using conductivity measurements at different temperatures (288.15, 298.15 and 308.15 K). The surface activity of the IL in various mixed solvents was evaluated from surface tension measurements by calculating various surface parameters like the minimum surface area occupied by a single ionic liquid molecule (A (min)), adsorption efficiency (pC (20)), maximum excess concentration at the surface (I" (max)), effectiveness of surface tension reduction(I (CAC)), surface tension at CAC (gamma (CAC)), p (packing parameter) and CAC at different compositions. Increases in the CAC values were observed with the increase in the amount of alcohols which is attributed to the balancing between electrostatic and hydrophobic interactions. The results from different techniques show that the CAC increases with increase in the amount of the alcohol which is due to the solubilization of the IL molecules which delays the aggregation process. This shows that the spontaneity of the aggregation process of IL decreases with the increase in the concentration of alcohols in water.