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Decoding disorder: unravelling entropy effects in deep eutectic systems with neutron spectroscopy.

Rafael A F Serrano1, Catarina F Araújo1, Paulo Ribeiro-Claro1

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This study reveals how cation asymmetry influences deep eutectic systems (DES) with ammonium salts and urea. It shows asymmetry impacts urea organization, affecting the system's phase behavior and deviation from ideal mixing.

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Area of Science:

  • Physical Chemistry
  • Materials Science
  • Chemical Physics

Background:

  • Deep eutectic systems (DES) are tunable solvents with unique properties.
  • Understanding their phase behavior is crucial for applications.
  • The role of cation structure in DES is not fully elucidated.

Purpose of the Study:

  • To investigate the vibrational dynamics and phase behavior of ammonium salt-urea DES.
  • To determine the impact of cation asymmetry on molecular interactions within these systems.
  • To elucidate the origins of non-ideal behavior in DES.

Main Methods:

  • Computational chemistry simulations.
  • Inelastic neutron scattering (INS) spectroscopy.
  • Isotopic substitution (deuterated urea) for selective component analysis.

Main Results:

  • Cation asymmetry significantly affects the vibrational modes of urea.
  • Two distinct urea molecular organizations were identified based on cation symmetry.
  • INS spectral analysis revealed changes in intermolecular interactions due to cation structure.
  • The findings support that cation asymmetry influences urea's solid-liquid equilibrium.

Conclusions:

  • Cation asymmetry is a key factor governing urea organization and interactions in DES.
  • The non-ideal phase behavior of these DES arises from deviations in urea's equilibrium.
  • This work provides molecular-level insights into DES structure-property relationships.