Nanoscale Spatial Heterogeneity in Deep Eutectic Solvents

In this article, we report a molecular dynamics simulation study on the X-ray and neutron scattering structures of deep eutectic solvents (DESs) and show that the DESs studied possess unique spatial heterogeneity on molecular length scales. The simulated X-ray and neutron scattering structure functions (S(q)s) of the DESs made of alkylamide + Li(+)/ClO4(-) display two peaks in the intermolecular region of the S(q)s. As a signature of nanoscale structural organization/heterogeneity, a prepeak is observed at 0.1 < q/Å(-1) < 0.4. The principal peak observed at around 1.2 < q/Å(-1) < 2 is rendered by short-distance inter- and intraspecies correlations. For the DESs studied, we demonstrate that nanoscale spatial heterogeneity is exhibited profoundly by the segregated domains of the constituent electrolyte, and the principal peak in S(q) is because of all sorts of close-contact correlations. The extent of nanoscale morphology as well as the strength of ion pairing is enhanced for the longer-tail alkylamide DES.