Abstract
Ionic liquids (ILs) and deep eutectic solvents (DESs) are receiving increased attention from both academic and industrial research due to their immense application potential. These designer solvents are environmentally friendly in nature with tunable physicochemical properties. In the present investigation, we have studied the aggregation behavior of a short-chain IL 1-butyl-3-methylimidazolium octylsulphate [Bmim][OS] within aqueous DESs using fluorescence, UV-vis, dynamic light scattering (DLS) and FT-IR spectroscopic techniques. We have prepared two DESs, ChCl–urea and ChCl–Gly, which are obtained by heating a mixture of an ammonium salt choline chloride with hydrogen bond donor urea or glycerol, respectively, in 1 : 2 molar ratios. The local microenvironment and size of the aggregates are obtained from steady state fluorescence (using pyrene and pyrene-1-carboxaldehyde as polarity probes) and DLS measurements, respectively. DLS results shows that IL [Bmim][OS] forms relatively larger micelles within the aqueous solution of DES ChCl–urea (avg. hydrodynamic radii = 209 nm) than compared to ChCl–Gly (avg. hydrodynamic radii = 135 nm). A significant decrease in the critical micelle concentration and increase in the aggregation number (Nagg) are observed within DES solutions as compared to that in water, thus indicating that the micellization process of the IL [Bmim][OS] is much favored in the DES solutions. Molecular interactions of [Bmim][OS] in DESs are revealed from FT-IR spectroscopic investigation. Furthermore, these systems were applied to study the IL-drug binding of the antidepressant drug promazine hydrochloride (PH).
Highlights
Ionic liquids (ILs) possess unusual physicochemical properties and bright application potential in various elds.[1]
Arnold et al.[32] have investigated the self-assembly of anionic surfactant sodium dodecyl sulfate (SDS) within deep eutectic solvents (DESs), choline chloride/urea using X-ray re ectivity (XRR), small angle neutron scattering (SANS) and interestingly, the results propose that the micelle formation in DES solutions does not have the similar shape and size as those observed in water
The UV-vis absorption spectroscopy is a simple and accurate technique to determine the cmc of various amphiphilic molecules
Summary
Ionic liquids (ILs) possess unusual physicochemical properties and bright application potential in various elds.[1] Surface active ILs as a novel class of surfactants are of signi cant interest to researchers worldwide and have stimulated more signi cance due to their self-assembling behavior.[2,3,4,5] It has been reported that these ILs can display surface activity when dissolved in water, denoted by a decrease in the surface tension.[6,7,8,9,10] It is noteworthy that the ILs have analogous properties to surface active agents and are capable of forming micellar nano-aggregates in aqueous solution.[11,12] ILs show impressive physicochemical properties, The simple structure of short-chain IL based surfactants has produced a signi cant deviation in their micellar properties.[23] It is important to have a clear picture on the micellization and interfacial behaviour of short-chain IL based surfactants to concern them effectively in particular elds.[23,24,25] Several methods, such as, electrical conductivity, surface tension, dynamic light scattering (DLS), uorescence, UV-visible and NMR spectroscopic techniques has been successfully utilized to study their micellization and interfacial behavior.[24,25,26,27] Due to their structural exibility and outstanding properties, shortchain IL based surfactant systems have generated immense signi cance, which is revealed in the increasing number of applications that have been reported in recent years.[25,26,27]
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