title: 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.
authors.affiliation: Department of Chemistry, and ‡Department of Chemical Engineering, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
authors.forename: Mahi
authors.initials: M
authors.lastname: Pal
authors.forename: Rewa
authors.initials: R
authors.lastname: Rai
authors.forename: Anita
authors.initials: A
authors.lastname: Yadav
authors.forename: Rajesh
authors.initials: R
authors.lastname: Khanna
authors.forename: Gary A
authors.initials: GA
authors.lastname: Baker
authors.forename: Siddharth
authors.initials: S
authors.lastname: Pandey