Two Routes to Vesicle Formation:  Metal−Ligand Complexation and Ionic Interactions

Abstract

Two routes to vesicle formation were designed to prepare uni- and multilamellar vesicles in salt-free aqueous solutions of surfactants. The formation of a surfactant complex between a double-chain anionic surfactant with a divalent-metal ion as the counterion and a single-chain zwitterionic surfactant with the polar group of amine-oxide group is described for the first time as a powerful driving force for vesicle-phases constructed from salt-free mixtures of aqueous surfactant solutions. As a typical example, a Zn(2+)-induced charged complex fluid, vesicle-phase has been studied in aqueous mixtures of tetradecyldimethylamine oxide (C(14)DMAO) and zinc 2,2-dihydroperfluorooctanoate [Zn(OOCCH(2)C(6)F(13))(2)]. This ionically charged vesicle-phase formed due to surfactant complexation has interesting rheological properties and is not shielded by excess salts because there are no counterions in the solution. Such a vesicle-phase of surfactant complex is important for many applications; for example, the vesicle-phase was further used to produce in situ the vesicle-phase of the salt-free cationic/anionic (catanionic) surfactants, C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13). The salt-free catanionic vesicle-phase could be produced through injecting H(2)S gas into the C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) vesicle-phase, because the zwitterionic surfactant C(14)DMAO can be charged by the H(+) released from H(2)S to become a cationic surfactant and Zn(2+) was precipitated as ZnS. After the ZnS precipitates were removed from C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) solutions, the final mixed solution does not contain excess salts as do other cationic/anionic surfactant systems. Both the C(14)DMAO-Zn(OOCCH(2)C(6)F(13))(2) complex and the resulting catanionic C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13) solution are birefringent Lalpha-phase solutions that consist of uni- and multilamellar vesicles. Ring-shaped semiconductor ZnS materials with encapsulated ZnS precipitates and regular spherical ZnS particles were prepared, which resulted in a transition from vesicles composed of metal-ligand complexes to vesicles held together by ionic interactions in the salt-free aqueous systems. This strategy should provide a new method to prepare inorganic materials. The present routes to form vesicles solve a problem: how to prepare nanomaterials using surfactant self-assembly, with structure controlled not by the growing material, but by the phase behavior of the surfactants.

Self‐Assembled Structure in Room‐Temperature Ionic Liquids

“…By simply mixing C 14 DMAO and Zn(OOCCH 2 C 6 F 13 ) 2 , we prepared a La-phase with unilamellar and multilamellar vesicles in aqueous solutions and attempted to provide a new method for preparing nanoscale semiconductor ZnS particles by means of a vesicle template. [17,18] We have placed self-assembling systems in ionic liquids, and we report herein on the first self-assembled surfactant vesicles formed by Zn(OOCCH 2 C 6 F 13 ) 2 alone or by mixtures of C 14 DMAO and Zn(OOCCH 2 C 6 F 13 ) 2 . The two common RTILs I and II were used and these RTILs are slightly Keywords: ionic liquids · self-assembly · surfactants · vesicles Abstract: Self-assembled vesicles, structurally equivalent to some hydrotropes, have been obtained from a Zn 2 + -fluorous surfactant or in the mixture of Zn 2 + -fluorous surfactant/zwitterionic surfactant in room-temperature ionic liquids (RTILs).…”

Vesicles of a New Salt‐Free Cat‐anionic Fluoro/Hydrocarbon Surfactant System

“…The vesicle phase was induced by M 2 + -ligand coordination, in which M 2 + is the central ion and forms charged bilayers without counterions in the mixtures. [12][13][14] Herein we report the construction of a new salt-free catanionic vesicle phase in aqueous solution from an unsaturated fluorocarbon carboxylic surfactant, C 7 F 15 CF=CHCOOH, mixed with a weakly basic surfactant, C 14 DMAO. C 14 DMAO molecules were protonated to form the cationic surfactant C 14 DMAOH + by the unsaturated fluorocarbon carboxylic surfactant C 7 F 15 CF=CHCOOH.…”

Metal-ligand coordinated Ca(DS)2/C14DMAO/H2O system: Phase behavior and rheological property

“…However, precipitates usually form near equimolar mixed ratios of cationic and anionic surfactants because of the screening of salts on the charged aggregates. In recent years, salt-free surfactant systems have come to the front because electrostatic interactions between the aggregates are not screened and very rich phase behaviors can be observed [4][5][6][7][8][9][10][11][12][13][14][15][16]. To obtain salt-free systems, two routes are often employed.…”

“…One is to mix alkyltrimethylammonium hydroxide (C n TAOH) or alkyldimethylamine oxide (C n DMAO) with acids having long hydrophobic tails [4][5][6][7][8][9][10][11][12]. The other is to construct metalligand coordinated systems by mixing multivalent metal surfactants with C n DMAO [13][14][15][16]. Different aggregates, especially vesicles, can be obtained through this way.…”