Synthesis and physicochemical properties of ester-bonded gemini pyrrolidinium surfactants and a comparison with single-tailed amphiphiles

A series of ester-bonded gemini pyrrolidinium surfactants 2,2'-((adipoylbis(oxy)) bis(methylene))bis(1-alkyl-1-methylpyrrolidin-1-ium) bromide (abbreviated C-n-6-C-n, where n = 12, 14, and 16) were synthesized and characterized using H-1 NMR, ESI-MS, and IR spectra. Self-aggregation and physicochemical properties between C-n-6-C-n-and their corresponding monomers 2-(hydroxymethyl)-1-methyl-1-alkyl pyrrolidinium bromide (abbreviated C-m PB, where m = 12, 14, and 16) were compared using surface tension, electrical conductivity, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The results show that the critical micellar concentration (CMC) values and surface tension at the CMC of the gemini surfactants C-n-6-C-n are lower than those of the monomeric surfactants CmPB. The conductivity measurement revealed the formation of premicellar aggregates in the C-14-6-C-14 and C-16-6-C-16 solution at sufficiently low concentration below their CMC values. DLS and TEM showed that C-m PB and C-n-6-C-n can spontaneously self-assemble into spherical or ellipsoid aggregates, whereas C-n-6-C-n can form larger aggregates with an increased degree of oligomerization and with longer alkyl chain because of greater hydrophobic interactions. (C) 2019 Elsevier B.V. All rights reserved.