Molecular order and dynamics of water in hybrid cellulose acetate–silica asymmetric membranes

M. Jardim Beira, M. P. Silva, M. Condesso, P. Cosme, P. L. Almeida, M. C. Corvo, P. J. Sebastião, J. L. Figueirinhas, M. N. de Pinho

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Abstract

In this work 2 H NMR spectroscopy and 1 H NMR relaxometry and diffusometry were used to characterise water order and dynamics in cellulose acetate/silica asymmetric membranes. Two hydrated membranes were characterised allowing the identification of extra ordering of the water molecules and the presence in each membrane of up to two spectral components with different degrees of order and different T 1 values. The mechanism behind this order increase was ascribed to the rapid exchange of the water molecules between the pore walls and its interior. T 1 relaxometry dispersions allowed for the identification of the relevant mechanisms of pore-confined water motion, with rotations mediated by translational displacements (RMTD) as the dominant mechanism in the low frequency region. Using the RMTD low cut off frequency along with the in situ directly measured diffusion constant it was possible do determine characteristic lengths of correlated water motion in both membranes studied, which fall in ranges compatible with typical pore dimensions in similar membranes.

Original languageEnglish
JournalMolecular Physics
DOIs
Publication statusAccepted/In press - 1 Jan 2018

Keywords

  • asymmetric membranes
  • Cellulose acetate
  • dynamic processes
  • molecular dynamics
  • proton relaxometry

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    Beira, M. J., Silva, M. P., Condesso, M., Cosme, P., Almeida, P. L., Corvo, M. C., ... Pinho, M. N. D. (Accepted/In press). Molecular order and dynamics of water in hybrid cellulose acetate–silica asymmetric membranes. Molecular Physics. https://doi.org/10.1080/00268976.2018.1537526