Experimental and DFT studies on foam performances of lauryl ether sulfate-based anionic surface active ionic liquids

Abstract

Three lauryl ether sulfate-based anionic surface active ionic liquids (SAILs), 1-butyl-3-methylimidazolium lauryl ether sulfate ([Bmim][C12H25O(C2H4O)2SO3]), 1-hexyl-3-methylimidazolium lauryl ether sulfate ([Hmim][C12H25O(C2H4O)2SO3]), and 1-octyl-3-methylimidazolium lauryl ether sulfate ([Omim][C12H25O(C2H4O)2SO3]) were synthesized. Physicochemical properties (surface properties, micellization, adsorption, and aggregation parameters) of three anionic SAILs and sodium lauryl ether sulfate (SLES) were determined. The critical micelle concentration (CMC) values of [Bmim][C12H25O(C2H4O)2SO3], [Hmim][C12H25O(C2H4O)2SO3], and [Hmim][C12H25O(C2H4O)2SO3] (from surface tension) were 0.569 mmol/L, 0.361 mmol/L, and 0.190 mmol/L, respectively. Micellization of three SAILs were spontaneous, endothermic, and entropy-driven. Foaming performances (foaming ability, foam stability, and foam composite index) of three anionic SAILs and SLES were determined using Ross-Miles methods. The foaming abilities of three SAILs followed: [Hmim][C12H25O(C2H4O)2SO3] > [Bmim][C12H25O(C2H4O)2SO3] > [Omim][C12H25O(C2H4O)2SO3]. While the foam stabilities and foam composite index (FCI) of three SAILs followed: [Omim][C12H25O(C2H4O)2SO3] > [Hmim][C12H25O(C2H4O)2SO3] > [Bmim][C12H25O(C2H4O)2SO3]. The structure effect of SAILs on foam performances were analyzed using density functional theory (DFT) calculations. Binding energy values of three SAIL hydrates followed the trend: [Omim][C12H25O(C2H4O)2SO3](H2O)n > [Hmim][C12H25O(C2H4O)2SO3](H2O)n > [Bmim][C12H25O(C2H4O)2SO3](H2O)n. DFT results showed the increase of alkyl chain length of imidazolium cation was beneficial for the stability of SAIL hydrates, which resulted in higher foam performances. The information will shed light on screening of novel SAILs for surfactant foam enhanced oil recovery (EOR).