Interplay between complexation and dynamical heterogeneity in alkylamide deep eutectic solvents

Abstract

Deep eutectic solvents (DESs) offer a sustainable alternative to conventional ionic liquids through their cost-effective synthesis and benign constituents. In this study, we employed all-atom molecular dynamics simulations to investigate how the alkyl chain length of DES constituents influences microscopic diffusion and complexation dynamics in systems composed of lithium perchlorate with acetamide and propanamide. Our analysis identifies distinct diffusion regimes – ranging from ballistic to sub-diffusive and Fickian behaviour – with dynamic heterogeneity becoming more pronounced as the alkyl chain length increases. Importantly, the study reveals that this enhanced dynamical heterogeneity is strongly linked to the stability and extended lifetimes of Li⁺-alkylamide complexes, as evidenced by elevated non-Gaussian parameters, delayed transition to Gaussian dynamics, and reinforced radial distribution peaks. These insights highlight the critical interplay between molecular architecture and complexation dynamics, paving the way for the rational design of DESs for advanced electrochemical and catalytic applications.

Graphical Abstract

This study reveals that increasing the alkyl chain length in DESs strengthens Li⁺-amide complexation, leading to longer lifetimes. This enhanced complex stability directly induces pronounced dynamical heterogeneity, as evidenced by delayed Fickian diffusion and elevated non-Gaussian behaviour, highlighting the intricate link between complex stability and microscopic transport properties.