Investigating the Impact of Water on a Menthol-Based Deep Eutectic Solvent: A Combined Experimental and Molecular Dynamics Study

High Resolution Image Download MS PowerPoint Slide Deep eutectic solvents (DESs) have emerged as potential alternatives to traditional solvents, offering unique properties and potential applications. However, the excessively viscous nature of DESs limits their applications in extraction, separation, electrodeposition, battery and energy storage, and drug delivery. The presence of water as a cosolvent can substantially reduce the viscosity and density of DESs and open widespread applications. The aim of this research is to elucidate the nanostructures of DESs in the presence of water, which is key to understanding and tuning their properties for various applications. Multitechnique approaches such as Raman spectroscopy, differential scanning calorimetry (DSC), 1 H nuclear magnetic resonance, and an all-atom molecular dynamics (MD) simulation were employed to determine how water affects the molecular-level arrangement, dynamics, and interactions of a L-menthol/acetic acid (AA)-based hydrophobic DES at various hydration levels. A pure DES exhibits significant H-bonding interactions with menthol and AA. As water is added, these interactions weaken, new H-bonding interactions between the DES system and water emerge, and the DES turns into a binary mixture as evident from visual inspection and DSC and Raman experiments. As the contacts between menthol and AA weaken and the number of contacts between water molecules increases, about 50%–60% of water leads to a different system. Additionally, principal component analysis assists us in identifying the sequences in which the characteristics of the DES change with the gradual addition of water. The changes detected in the nanostructural characteristics of the L-menthol/AA DES can aid to develop a less viscous and dense DES suited for special applications. The combined Raman spectroscopic and MD simulation analysis provided deep molecular-level insights into the structural and dynamic changes occurring in the Men–AA system with varying water content. The findings obtained from this research not only enhance our comprehension of the influence of water on altering the characteristics of DES but also facilitate the development of DES systems specifically designed for industrial operations that need reduced viscosity and density.