Microheterogeneity structure of water-dimethylformamide (DMF) mixtures

Some binary liquid mixtures display “microheterogeneity” (MH), where molecular clustering of each component is observed on the microscale, but on the macroscale the components are fully miscible. This is suggested to be the reason behind certain mixture characteristics, such as non-ideal thermodynamic quantities and water activity.
Our overarching project aims to investigate how the structure of binary solvent mixtures influences the outcome of solute recrystallisation. The groups prior work using MH water-acetonitrile mixtures has shown that solute-solute and solute-solvent interactions change with the occurrence of solvent clustering. Water-DMF mixtures have been chosen for this experiment, as MD simulations suggest these mixtures show MH. Water, DMF and mixtures are valuable solvents in industrial synthesis and recrystallisation, hence it is important to know how these solvents are structured so we can link structure to experimental outcomes.
We propose to investigate mixtures at 15, 35 & 50 mole% DMF as this will provide a wide compositional range to gauge clear differences in the solution structure. 7 isotopic substitutions will be used to differentiate between DMF and water hydrogen atoms, totalling to 21 samples. Assuming 4 hours per sample and 2 hours per standard, we request 5 days of beamtime on NIMROD. This will (dis-)prove the existence of molecular clustering and provide a baseline for future experiments investigating these mixtures with solute.