Ionic Liquid-Induced Unprecedented Size Enhancement of Aggregates within Aqueous Sodium Dodecylbenzene Sulfonate

Abstract

Physicochemical properties of aqueous micellar solutions may change in the presence of ionic liquids (ILs). Micelles help to increase the aqueous solubility of ILs. The average size of the micellar aggregates within aqueous sodium dodecylbenzene sulfonate (SDBS) is observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) to increase in a sudden and drastic fashion as the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) is added. Similar addition of [bmim][PF(6)] to aqueous sodium dodecyl sulfate (SDS) results in only a slow gradual increase in average aggregate size. While addition of the IL [bmim][BF(4)] also gives rise to sudden aggregate size enhancement within aqueous SDBS, the IL 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF(4)]), and inorganic salts NaPF(6) and NaBF(4), only gradually increase the assembly size upon their addition. Bulk dynamic viscosity, microviscosity, dipolarity (indicated by the fluorescent reporter pyrene), zeta potential, and electrical conductance measurements were taken to gain insight into this unusual size enhancement. It is proposed that bmim(+) cations of the IL undergo Coulombic attractive interactions with anionic headgroups at the micellar surface at all [bmim][PF(6)] concentrations in aqueous SDS; in aqueous SDBS, beyond a critical IL concentration, bmim(+) becomes involved in cation-π interaction with the phenyl moiety of SDBS within micellar aggregates with the butyl group aligned along the alkyl chain of the surfactant. This relocation of bmim(+) results in an unprecedented size increase in micellar aggregates. Aromaticity of the IL cation alongside the presence of sufficiently aliphatic (butyl or longer) alkyl chains on the IL appear to be essential for this dramatic critical expansion in self-assembly dimensions within aqueous SDBS.

Monomerization of crown-containing phthalocyanines in microheterogeneous organized systems

“…The obtained value of the hydrody namic diameter of SDBS micelles is 4.2 nm. This agrees rather well with the results from [15,20,21] and is in the range of values characteristic for spherical micelles [8].…”

Formation of Novel Aqueous Two-Phase Systems with Piperazinium-Based Ionic Liquids and Anionic Surfactants: Phase Behavior and Microstructure

“…32 They may be size-enhanced micelles which are similar to those reported in literature. 20,33,34 Additional DLS analyses have been carried out at a fixed mass ratio of [C 2 pi][BF 4 ]/SDS of 7:5, and the results are presented in Figure 7. The samples were measured at the same time as soon as prepared.…”

“…20,33,34 In the latter situation, one example is the work reported by Rai et al, who discussed the size enhancement of aggregates in the aqueous solution mixed with imidazolium-based IL and SDS or SDBS. 33 They observed that the size of aggregates increased much more in the IL + SDBS + water system than that in the IL + SDS + water system, which was mainly attributed to the benzene ring in SDBS and the generated cation−π interaction. To get a more comprehensive understanding of the microstructures of the ATPS in this work, different structural models are proposed for the ATPS under study.…”

The effect of hydrophilic ionic liquid 1-butyl-2,3-dimethylimidazolium bromide on the aggregation behavior of tetradecyltrimethylammonium bromide in aqueous media

“…Pandey et al have shown the effect of ILs on the aggregation behavior of different types of surfactants [23][24][25]. Inoue's group has highly explored the effect of ILs on aggregation of polyoxyethylene (POE)-type non-ionic surfactants [26,27].…”