Self-Aggregation of Sodium Dodecyl Sulfate within (Choline Chloride + Urea) Deep Eutectic Solvent

Abstract

Deep eutectic solvents (DESs) have shown tremendous promise as green solvents with low toxicity and cost. Understanding molecular aggregation processes within DESs will not only enhance the application potential of these solvents but also help alleviate some of the limitations associated with them. Among DESs, those comprising choline chloride and appropriate hydrogen-bond donors are inexpensive and easy to prepare. On the basis of fluorescence probe, electrical conductivity, and surface tension experiments, we present the first clear lines of evidence for self-aggregation of an anionic surfactant within a DES containing a small fraction of water. Namely, well-defined assemblies of sodium dodecyl sulfate (SDS) apparently form in the archetype DES Reline comprising a 1:2 molar mixture of choline chloride and urea. Significant enhancement in the solubility of organic solvents that are otherwise not miscible in choline chloride-based DESs is achieved within Reline in the presence of SDS. The remarkably improved solubility of cyclohexane within SDS-added Reline is attributed to the presence of spontaneously formed cyclohexane-in-Reline microemulsions by SDS under ambient conditions. Surface tension, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), density, and dynamic viscosity measurements along with responses from the fluorescence dipolarity and microfluidity probes of pyrene and 1,3-bis(1-pyrenyl)propane are employed to characterize these aggregates. Such water-free oil-in-DES microemulsions are appropriately sized to be considered as a new type of nanoreactor.

Deep Eutectic Solvents: The Organic Reaction Medium of the Century

“…[27] Moreover, the possibility of microemulsion formation, by typical tensioactive compounds [28] or directly, [29] ensures, at least, the partial solubility of less polar organic reagents, which highlights the enormous ability of these mixtures as a possible medium in Organic Synthesis.…”

Micellization of alkyltrimethylammonium bromide surfactants in choline chloride:glycerol deep eutectic solvent

“…24 In subsequent studies a mixture of choline chloride:urea with water was found to promote the selfassembly of sodium dodecyl sulfate (SDS). 25 Cationic surfactants were also found to be soluble and form aggregates in choline chloride:glycerol, although no structural detail on such aggregates has yet been reported. 26 Tan et al have shown the self-assembly of long chain ionic liquids in choline chloride:glycerol DES.…”

Pseudo ionic liquids and their applications

“…类离子液体 对于金属盐类、 有机化合物等均具有良好的溶解性能, 不但可起到溶剂的作用, 而且对于不同的反应还可 起到模板剂、表面剂、催化剂、氧化还原剂和金属/ 碳源的作用. Pal 等 [42] 发现十二烷基磺酸钠可增强环 己烷在尿素-氯化胆碱类离子液体中的溶解性, 并形 成环己烷-类离子液体微乳液, 该类无水型微乳液的 形成提供了一种新型纳米反应器. Abo-Hamad 等 [43] 指出类离子液体在纳米孔道或管体等限域条件下可 表现出不同于宏观尺度下的行为.…”