Role of molecular structure in defining the dynamical landscape of deep eutectic solvents

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Deep eutectic solvents (DESs) possess complex molecular dynamics with significant spatial and temporal heterogeneity.
• Understanding DES dynamics is key for optimizing transport properties like diffusion, viscosity, and ionic conductivity.
• Molecular diffusion in DESs involves transient caging and jump mechanisms, influenced by molecular structure.

Purpose of the Study:

• To investigate the effect of alkyl chain length on the dynamical behavior of alkylamide-lithium perchlorate based DESs.
• To elucidate the relationship between molecular structure and the transport properties of DESs.
• To analyze both long-range and localized diffusion mechanisms in relation to alkyl chain variations.

Main Methods:

• Quasielastic Neutron Scattering (QENS) was employed to study molecular dynamics.
• Molecular Dynamics (MD) simulations were utilized to complement experimental findings.
• Analysis focused on distinct degrees of freedom, including center-of-mass diffusion and localized motion.

Main Results:

• Acetamide, despite its shorter chain, showed lower mobility than propanamide (PRM) and butyramide (BUT).
• Long-range jump diffusion generally slowed with increasing alkyl chain length due to size, mass, and complexation effects.
• Localized dynamics displayed an unusual trend, with PRM being fastest due to a balance of flexibility and reduced caging.

Conclusions:

• Alkyl chain length has a complex, non-linear influence on DES dynamics.
• Localized dynamics are governed by a delicate interplay between molecular flexibility and caging effects.
• Molecular structure is a critical determinant of dynamical behavior and transport properties in DESs.