Transition from molecular- to nano-scale segregation in a deep eutectic solvent - water mixture

Fate of a Deep Eutectic Solvent upon Cosolvent Addition: Choline Chloride–Sesamol 1:3 Mixtures with Methanol

“…This behavior is different from what was previously observed for water/ChCl/sesamol W :1:3 mixtures, where the segregation between sesamol- and water-rich regions was promoted by the saturation of the sesamol–water HBs after the W = 6–8 threshold. 15 Differently, the ability of MeOH to interplay with all of the DES components through all of the explored molar ratios is at the basis of the observation of no segregation effects in the studied MeOH/ChCl/sesamol mixtures. Such results can also be observed at a more qualitative level from the snapshots of the simulated MD systems in Figure S9 .…”

“…It should be mentioned that the highest SAXS intensity detected for the MeOH/ChCl/sesamol mixtures ( M = 24) was less than half of that measured for a water/ChCl/sesamol mixture with 16:1:3 molar ratios, which has been found to be the macroscopically homogeneous water/DES mixture with the highest water content that can be prepared before phase separation. 15 Considering also that for the water/ChCl/sesamol 16:1:3 mixture the corresponding estimate for √3ξ from the SAXS data was 29 Å, it is understandable by comparison that in the MeOH/ChCl/sesamol system a phenomenon of segregation at the nanoscale level does not occur at any composition. Indeed, as previously mentioned, R g can be considered as a rough approximation of the biggest aggregate dimensions, and the values obtained for the present mixtures are not compatible with nanoscale aggregations, but rather with small clusters governed by short-range order interactions.…”

“…This result differs from that obtained for mixtures of the ChCl/sesamol 1:3 DES with water, where segregation between sesamol- and water-rich regions was observed, up to the formation of aqueous pools of ∼70 Å diameter for high water molar fractions. 15 In the framework of the FTIR analysis, the formation of such heterogeneities was detected from the split of the spectral bands connected with distinct water populations: weakly H-bonded water interacting with the DES components absorbing at higher wavenumbers, and a second ensemble of water aggregates showing a network of HBs similar to bulk water. Note that IR studies of nonideal mixtures have been reported also for other DESs 26 , 64 and hydrophobic ILs 65 − 67 using MeOH as the cosolvent and, in those cases, the formation of imbalanced intermolecular interactions led to the splitting and/or blue shifting of the stretching bands connected to MeOH.…”

“…The g ( r )’s have been multiplied by the numerical density of the observed atoms (ρ) to properly compare systems with different compositions. 15 , 54 − 57 The coordination numbers N have been computed integrating each curve up to a cutoff distance chosen at the position of the first minimum and the obtained values have been reported as a function of M .…”

“…Here, we present a study on the structural modifications of a DES formed by ChCl and sesamol ( Figure 1 ) in the 1:3 molar ratio upon methanol (MeOH) addition. The quasihydrophobic ChCl/sesamol 1:3 DES has been only recently developed and showed outstanding results for what concerns liquid–liquid microextraction applications in food and biological samples, 15 , 32 , 33 , 35 − 37 besides an intrinsically eco-friendly nature provided by the peculiarities of its components. 32 , 33 , 35 In fact, ChCl is known to be a low-price nontoxic compound, while sesamol is a powerful antioxidant able to prevent the spoilage of oils and presents chemoprotective, antimutagenic, and antihepatotoxic properties.…”