Structure, Organization and Heterogeneity of Water-Containing Deep Eutectic Solvents

TL;DR

This study combines spectroscopy and molecular dynamics to explore how water content influences the structure and heterogeneity of deep eutectic solvents, revealing molecular-level insights into their organization.

Contribution

It introduces a combined spectroscopic and simulation approach to understand the heterogeneity and structural dynamics of water-containing deep eutectic solvents.

Findings

Spectroscopy and MD simulations reveal water-induced structural changes.

High water content leads to parallel alignment of SCN$^-$ anions.

Water clustering significantly affects THz absorption.

Abstract

The spectroscopy and structural dynamics of a deep eutectic mixture (KSCN/acetamide) with varying water content is investigated from 2D IR (with the C-N stretch vibration of the SCN$^-$ anions as the reporter) and THz spectroscopy. Molecular dynamics simulations correctly describe the non-trivial dependence of both spectroscopic signatures depending on water content. For the 2D IR spectra, the MD simulations relate the steep increase in the cross relaxation rate at high water content to parallel alignment of packed SCN$^-$ anions. Conversely, the non-linear increase of the THz absorption with increasing water content is mainly attributed to the formation of larger water clusters. The results demonstrate that a combination of structure sensitive spectroscopies and molecular dynamics simulations provides molecular-level insights into emergence of heterogeneity of such mixtures by modulating their composition.