Unexpected molecular dynamics of ethanol in hydrogen-bonded binary mixtures, ethanol-octanol and ethanol-water

Ingo Hoffmann (1) , Firoz Malayil Kalathil (1, 2) , Tobias Lopian (1) , Didier Touraud (3) , Orsolya Czakkel (1) , Marie Plazanet (2) , Christiane Alba-Simionesco (4, 5)

1 ILL - Institut Laue-Langevin
2 LIPhy - Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]
3 UR - Universität Regensburg
4 LLB - UMR 12 - Laboratoire Léon Brillouin
5 MMB - LLB - Matière molle et biophysique

In view of getting a quantitative picture of the dynamics in mixtures of hydrogen-bonded liquids, in particular the ternary water-ethanol-octanol, we examine in this paper the dynamics of two binary systems: ethanol-water and ethanol-octanol. Our multiscale investigation includes quasi-elastic neutron scattering for the characterization of the dynamics at the molecular scale, completed by NMR at the mesoscopic scale and eventually compared with macroscopic viscosity properties. We highlight the decrease of diffusivity in pure alcohols when increasing the lengthscale and conjecture its relation with the two processes measured in dielectric spectroscopy. While the behaviour of ethanol-water is well understood, unexpected inversion of the slowest component between the micro and the mesoscale are evidenced in the ethanol-octanol mixture. This effect could be at the origin of the negative viscosity excess in the mixture of alcohols.

Domaines: Chimie théorique et/ou physique

Ingo Hoffmann, Firoz Malayil Kalathil, Tobias Lopian, Didier Touraud, Orsolya Czakkel, et al.. Unexpected molecular dynamics of ethanol in hydrogen-bonded binary mixtures, ethanol-octanol and ethanol-water. EPJ Web of Conferences, 2022, QENS/WINS 2022 – 15th Edition of the QENS Series and 10th of the WINS Workshops San Sebastian (Online), Spain, May 23-27, 2022, 272, pp.01003. ⟨10.1051/epjconf/202227201003⟩. ⟨hal-03876668⟩