Noncanonical Relationship between Heterogeneity and the Stokes-Einstein Breakdown in Deep Eutectic Solvents

Area of Science:

• Physical Chemistry
• Complex Fluids
• Materials Science

Background:

• The Stokes-Einstein breakdown (SEB) and dynamical heterogeneity (DH) are key concepts in understanding complex fluid behavior.
• Investigating the interplay between SEB and DH is crucial for advancing the physical chemistry of these systems.

Purpose of the Study:

• To probe the relationship between SEB and DH in deep eutectic solvents (DESs) using acetamide and lithium salts.
• To elucidate the contrasting behaviors of SEB and DH under different conditions.

Main Methods:

• Utilized neutron scattering techniques, specifically quasielastic neutron scattering (QENS) and elastic incoherent neutron scans (EINS).
• Examined a series of DESs comprising acetamide and various lithium salts (lithium perchlorate, lithium bromide).

Main Results:

• Observed SEB in the jump diffusion of acetamide, characterized by a fractional Stokes-Einstein relationship.
• Found that lithium perchlorate DES exhibited the most pronounced SEB, while lithium bromide showed the weakest.
• Identified that the bromide DES was the most dynamically heterogeneous, and the perchlorate DES was the least.

Conclusions:

• Unveiled a novel and counterintuitive incommensurate relationship between DH and SEB in DESs.
• Demonstrated that the SEB-DH relationship exhibits contrasting characteristics when studied near versus far from the glass-transition temperature.