Microstructure of Deep Eutectic Solvents: Current Understanding and Challenges

In the past decade, researchers have put forth a lot of efforts to conceive a precise structural arrangement and properties of deep eutectic solvents (DESs) that provide designer pathways in order to broaden the application domain of these solvents. However, these contributions are limited to a few experimental and computational techniques. In this review, we have encompassed experimental techniques employed to establish the structure-property relationship of bulk DESs along with recent growth witnessed in this domain from a computational perspective. The nanostructuring plays an important role in various task specific applications of DESs. These solvents are found to exhibit unique heterogeneity at nanolength scales, the origin of which is unique and primarily depends on the constituent species involved. The hygroscopic nature of some DESs makes it crucial to explore the structural anatomy of hydrated DESs. Hence, this opens another subdomain to explore the impact of hydration on the bulk microscopic structure of DES and to know whether the nature is destructuring or structuring with respect to the neat solvents. This review highlights the recent successes attained in developing a thorough bulk microstructural understanding of neat and hydrated DESs.