Synthesis and vesicle formation of cationic surfactants based on trisubstituted perfluoroalkylated thiourea

Abstract

New perfluoroalkyl double-chain surfactants were synthesized based on trisubstituted perfluoroalkylated thiourea. These amphiphiles have a modular structure consisting of hydrophobic tails, thiourea as connector, alkyl spacer, and ammonium head group. The modular organization allows an independent variation of the key features in the amphiphilic structure. The synthesis strategy was based on the condensation reaction of 2-(F-alkyl)ethyl isothiocyanates with 3-(dimethylamino)-N-(2-hydroxy-2-F-alkyl)ethyl)alkylamines and subsequent quatemization by methyl iodide to produce the trisubstituted perfluoroalkylated thiourea. The two reaction steps proceed with high yields. The surface activity properties of the new amphiphiles were studied and the ability to self-assemble into bilayer vesicles was determined by freeze fracture electron microscopy and quasi-elastic light scattering.

Cationic–anionic vesicle templating from fluorocarbon/fluorocarbon and hydrocarbon/fluorocarbon surfactants

“…3a). The aggregate diameters, 20-100 nm, are comparable to those reported for vesicles with fully fluorinated bilayers (50-180 nm) [30,32]. Larger vesicles (%100 nm) are interspersed with smaller, uniform vesicles (%20 nm).…”

“…However, geometric factors, such as stiffness of the fluorinated chains and asymmetry of HFDPC (10 Â (CF 2 ) in the surfactant tail) and SPFO (7 Â (CF 2 ) in the surfactant tail) may contribute to the same phenomenon in the HFDPC/SPFO systems. Polydisperse vesicles have been reported for other fully fluorinated surfactant bilayer systems [30]. Structural changes in the HFDPC/SPFO system at higher concentration (2% wt/wt, c = 0.8) are revealed as multi-lamellar polygonal vesicles (%500 nm) (Fig.…”

“…These mixed surfactant aggregates have been characterized by a variety of techniques, including freeze-fracture electron microscopy [30,45], SANS [6], cryo-TEM [1,11] and DLS [6,45]. Utilizing negatively stained TEM imaging, NMR and DLS characterization techniques, Szonyi et al [32] investigated the formation of vesicles with fully fluorinated bilayers comprising mixtures of short chain fluorinated cationic surfactants with trimethyl headgroups and fluorinated anionic surfactants with carboxylic headgroups (i.e., ammonium perfluorooctanoate).…”

“…The properties of surfactants with a fluorinated carbon chain which distinguish them from traditional hydrocarbon surfactants include a greater driving force to self-aggregate [29][30][31][32][33][34][35][36]. Fluorinated surfactants have lower critical micelle concentrations and are both hydrophobic and lipophobic in nature, with a tendency to form structures with lower curvature (i.e., rod-like micelles, vesicles and lamellar phases) than analogous hydrocarbon surfactants [29,35,37,38].…”

“…The properties of fluorinated surfactants are ascribed to the weaker intermolecular interactions versus intramolecular forces in fluorinated molecules, resulting in thermal and chemical stability [36]. In addition, the bulkiness and stiffness of the fluorinated carbon chains restricts random motion of the chains resulting in trans-conformation as opposed to gauche chain type packing in the bilayer [29,30]. The tightly packed chains of fluorinated bilayers reduce permeability and provide greater membrane rigidity [39], factors that may impact their performance in potential storage, transport and material synthesis applications.…”