Synthesis and Evaluation of Surface Active Properties of Ester-Based Cationic Imidazolium Monomeric Surfactants

Abstract

New imidazolium cationic surfactants have been synthesized by esterification of halogenated carboxylic acids with long-chain fatty alcohols furnishing respective esters (dodecyl-2-chloroacetate, tetradecyl-2-chloroacetate, hexadecyl-2-chloroacetate, dodecyl-2-bromoacetate, tetradecyl-2-bromoacetate, and hexadecyl-2-bromoacetate) followed by their subsequent treatment with 1-trifluoro acetyl imidazole resulting into the formation of title monomeric surfactants: 3-(2-(hexadecyloxy)-2-oxoethyl)-1-(2,2,2-trifluoroacetyl)-1H-imidazol-3-ium chloride (7); 3-(2-(tetradecyloxy)-2-oxoethyl)-1-(2,2,2-trifluoroacetyl)-1H-imidazol-3-ium chloride (8); 3-(2-(dodecyloxy)-2-oxoethyl)-1-(2,2,2-trifluoroacetyl)-1H-imidazol-3-ium chloride (9); 3-(2-(hexadecyloxy)-2-oxoethyl)-1-(2,2,2-trifluoroacetyl)-1H-imidazol-3-ium bromide (10); 3-(2-(tetradecyloxy)-2-oxoethyl)-1-(2,2,2-trifluoroacetyl)-1H-imidazol-3-ium bromide (11) and 3-(2-(dodecyloxy)-2-oxoethyl)-1-(2,2,2-trifluoroacetyl)-1H-imidazol-3-ium bromide (12). Their identifications are based on IR, 1H, 13C NMR, DEPT, and mass spectral studies. The dynamics of surface activity of these surfactants have also been investigated in the presence of sodium halides (NaCl and NaBr) by surface tension measurement. A series of useful parameters like critical micelle concentration (cmc), surface tension at the cmc (γcmc), adsorption efficiency (pC20), effectiveness of surface tension reduction (Πcmc), Gibbs free energy of the micellization (ΔG0mic), and Gibbs free energy of adsorption (ΔG0ads) have been determined from the measurements obtained by surface tension and conductivity method. Further with the application of the Gibbs adsorption isotherm, maximum surface excess concentration (Γmax), and minimum surface area/molecule (Amin) at the air-water interface were also estimated. Thermal stability of these long-chain cationics have been measured by thermal gravimetric analysis under nitrogen atmosphere. Analysis of thermal stability measurement indicated that the thermal stability of these long-chain imidazoliums increase with an increase in chain length.