How the formation of ultra-soft microemulsions affects dynamical properties at different lengthscales

The nanoscopic organization of liquid molecular mixtures has a major impact on their macroscopic properties, including solubilization, viscosity, and transport. Despite its importance in transport and reactivity modeling, the role of molecular dynamics in shaping these properties is still not well understood. This study focuses into the molecular dynamics of the ternary ethanol-octanol-water mixture, selected for its well-defined structure across critical point fluctuations, pre-Ouzo, and Ouzo phases, with organization occurring on a mesoscopic scale of a few nanometers. Using a combination of Neutron Scattering, NMR, rheology, and classical molecular simulations, we present a detailed description of molecular dynamics across diverse composition lines and structural domains. A subtle shift in individual dynamics marks the boundary of the monophasic meso-structured region, helping to identify the dynamic signature of the so-called Lifshitz line. Neutron Spin-Echo experiments reveal the collective nature of molecular dynamics, with a de Gennes narrowing effect slowing diffusion in the nano-structured octanol-rich region and a dramatic slowdown in droplet diffusion in the pre-Ouzo zone. The measurements eventually provide a characterization of the droplets lifetime, estimated here close to 20 nanoseconds.