Self-assembly of cationic gemini surfactants, alkanediyl-bis-(dimethyldodecyl-ammonium bromide), in cyclohexane: effects of spacer length on their association into reverse lyotropic liquid crystalline or reverse vesicles

Abstract

Herein, homogeneous solutions of cationic gemini surfactants, alkanediyl-α,ω-bis(dimethyldodecylammonium bromide), referred to as 12-s-12 where s = 2, 4, 6, 8, and 10, in cyclohexane have been prepared with the help of sodium hexanoate (SH) or sodium laurate (SL). These surfactants self-assembled in cyclohexane to form various aggregating structures, which were characterised by small-angle X-ray scattering (SAXS) together with polarised microscopy observations. The results showed that 12-2-12/SH, where the gemini had the shortest spacer among this series, formed an inverse micellar cubic liquid crystalline phase of the Fd3m structure. 12-s-12/SL, including s = 4, 6, and 8, which contained an adequate length spacer, formed an inverse hexagonal liquid crystalline phase packed by the cylindrical assemblies of surfactants. 12-10-12/SL, in which the gemini had a longer spacer, formed dispersed reverse vesicles (a lamellar structure). The rheological properties of liquid crystalline phases in a linear visco-elastic regime were studied. 12-2-12/SH formed a hard gel, whereas 12-s-12/SL formed soft gels. Dynamic light scattering and steady-state viscosity analyses were performed for the reverse vesicle solutions formed by 12-10-12/SL. In all these systems, the amount of added water W, denoting the mole ratio of water to the gemini surfactant, was demonstrated to influence the properties.

Self-assembly of quaternary ammonium gemini surfactants in cyclohexane upon reinforcement by simple counterions

“…For a gemini surfactant system without a salt, the length of the spacer chain dominates the size of the head, as found in our previous work. 16 The result of 12- s -12/SL(SH) association in cyclohexane is shown in the last row of Table 2 . A similar effect of the 12- s -12 spacer in the present salt-containing systems can also be found in Table 2 , where different structures corresponded to respective spacers at a fixed salt.…”

“…Generally, 12-s-12 is insoluble in cyclohexane, and we used a newly-developed method to prepare homogeneous solutions of 12-s-12, namely, we added another equi-charged anionic surfactant, sodium hexanoate (SH) or sodium laurate (SL), to neutralise the charge of 12-s-12. [16][17][18] Herein, these oppositely charged amphiphiles were guratively referred to as helping surfactants. By way of this method, we obtained homogeneous solutions of 12-2-12/SH and 12-s-12/SL (including s4, s6, s8, and s10).…”

“… 15 Very recently, we reported the self-assembly of a class of typical cationic gemini surfactants, alkanediyl-α,ω-bis(dimethyldodecylammonium bromide), in cyclohexane. 16 The chemical structure of their molecules is shown in Scheme 1 and this class of gemini surfactants is abbreviated to 12- s -12, where 12 and s represents the number of carbon atoms in each alkyl tail and in the spacer chain, respectively.…”

“…The study showed that the spacer length of 12- s -12 strongly influenced their self-assembly, resulting in the formation of various aggregates: 12-2-12/SH, where the gemini had the shortest spacer in this series, formed an inverse micellar cubic liquid crystalline phase of Fd 3 m structure; 12- s -12/SL, including s 4, s 6, and s 8, which contained an adequate length of spacer, formed an inverse hexagonal liquid crystalline phase packed by cylindrical assemblies of surfactants; 12-10-12/SL, in which the gemini had a longer spacer, formed dispersed reverse vesicles (in a lamellar structure). 16 Due to the difficulties associated with gemini surfactant dissolution in non-polar solvents, this was the first time that the effect of spacer length on complex aggregation in oil solution had been reported. Furthermore, we found that the addition of a helping surfactant can be replaced by the addition of a simple salt, by which a homogeneous solution was still obtained.…”

Flexible Semicrown Ether‐Linked Symmetric Cationic Gemini Surfactants: Synthesis and Evaluation as Catalysts for Acceleration of Diastereoselective [3 + 2] Cycloaddition Reaction in Reversed Phase Micellar Media

“…According to another possible alternative mechanism, the cycloaddition reaction may have occurred in the inverse vesicle (closed bilayer structure) as indicated in Fig. 1c (Deng and Zhao, 2018). The reagents are most likely interacting in the nonpolar interior of these vesicles to afford the desired cycloadduct.…”