Molecularly Heterogeneous Structure of a Nonionic Deep Eutectic Solvent Composed of N-Methylacetamide and Lauric Acid.

Deep eutectic solvents (DES) are a new class of designer solvents with a wide range of possible applications. DESs are typically made from an ionic compound and a hydrogen bond donor, but lately DESs made of nonionic compounds with interesting properties have started to appear. This study focuses on describing the structure, dynamics, and interactions of a nonionic DES composed of  N-methylacetamide (NMA) and lauric acid (LA). Linear IR and time-resolved IR experiments show that LA-NMA DES is the result of hydrogen bond interaction between the two molecular components, though the interaction energy is only favored by ∼1 kJ/mol with respect to the pure components. The IR experiments also reveal the presence of molecular heterogeneities produced by the nanosegregation of polar and nonpolar domains formed by N-methylacetamide and lauric acid, respectively. In addition, it is observed that the hydrogen bond interaction between components occurs at the interface of the two distinct polarity domains. The proposed molecular picture is also supported by the observation of nanodomains with the approximate size of two lauric acids via small-angle X-ray scattering.