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arXiv · 2310.04320

Molecular Structural Dynamics in Water-Ethanol Mixtures: Spectroscopy with Polarized Neutrons Simultaneously Accessing Collective and Self-Diffusion

Riccardo Morbidini·Robert M. Edkins·Mark Devonport·Gøran Nilsen·Tilo Seydel·Katharina Edkins
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Abstract

Binary mixtures of water with lower alcohols display non-linear phase behaviour upon mixing which are attributed to potential cluster formation at molecular level. Unravelling such elusive structures requires the investigation of hydrogen-bonding sub-nanosecond dynamics. We employ high-resolution neutron time-of-flight spectroscopy with polarization analysis in combination with selective deuteration to study the concentration-dependent structural dynamics, in the water rich part of the phase diagram of water-ethanol mixtures. This method enables the simultaneous access to atomic correlations in space and time, and allows us to separate spatially incoherent scattering probing self-diffusion of the ethanol fraction from the coherent scattering probing collective diffusion of the water network as a whole. Our observations indicate an enhanced rigidity of the hydrogen bond network at mesoscopic lengthscale compared to the intra-molecular scale as the ethanol fraction increases, which is consistent with the hypothesis of clusters.

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Riccardo Morbidini, Robert M. Edkins, Mark Devonport, Gøran Nilsen, Tilo Seydel, Katharina Edkins. 2023-10-06. Molecular Structural Dynamics in Water-Ethanol Mixtures: Spectroscopy with Polarized Neutrons Simultaneously Accessing Collective and Self-Diffusion. https://arxiv.org/abs/2310.04320

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