We investigate the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copoly- mers. The combination of dielectric spectroscopy and quasi- elastic neutron scattering experiments allows us to characterize the water dynamics over a wide range of temperatures (dielectric spectroscopy) and at microscopic length scales (neutron scattering). The dielectric investigation evidences two relaxations associated with water motions: a fast process corresponding to motions of loosely bonded water molecules and a slower process corresponding to motions of amide−water complexes. While the slower process presents the characteristic Arrhenius temperature dependence of a secondary local relaxation over the whole temperature range, the fast process shows a crossover from Arrhenius to Vogel−Fulcher−Tamman (VFT) behavior at T ≈ 225 K, characteristic of confined water dynamics. The microscopic investigation by neutron scattering shows than in the VFT regime of the fast process the dynamics present a diffusive nature similar to bulk water. A large distribution of diffusion coefficients indicates possible differences in the connectivity of the hydrogen bond network. Diffusive heterogeneous dynamics can arise from a nonuniform distribution of water. The confinement effect of the polymer matrix is detected as a considerable reduction of the diffusion coefficient of water with respect to bulk. The presence of a crystalline phase results in a slowing down of both the fast and slow processes involving water motions. This could give a hint to the presence of a rigid amorphous phase in the semicrystalline material.

Dynamics of water absorbed in polyamides / Laurati M.; Sotta P.; Long D.R.; Fillot L.-A.; Arbe A.; Alegria A.; Embs J.P.; Unruh T.; Schneider G.J.; Colmenero J.. - In: MACROMOLECULES. - ISSN 0024-9297. - ELETTRONICO. - 45:(2012), pp. 1676-1687. [10.1021/ma202368x]

Dynamics of water absorbed in polyamides

Laurati M.
;
2012

Abstract

We investigate the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copoly- mers. The combination of dielectric spectroscopy and quasi- elastic neutron scattering experiments allows us to characterize the water dynamics over a wide range of temperatures (dielectric spectroscopy) and at microscopic length scales (neutron scattering). The dielectric investigation evidences two relaxations associated with water motions: a fast process corresponding to motions of loosely bonded water molecules and a slower process corresponding to motions of amide−water complexes. While the slower process presents the characteristic Arrhenius temperature dependence of a secondary local relaxation over the whole temperature range, the fast process shows a crossover from Arrhenius to Vogel−Fulcher−Tamman (VFT) behavior at T ≈ 225 K, characteristic of confined water dynamics. The microscopic investigation by neutron scattering shows than in the VFT regime of the fast process the dynamics present a diffusive nature similar to bulk water. A large distribution of diffusion coefficients indicates possible differences in the connectivity of the hydrogen bond network. Diffusive heterogeneous dynamics can arise from a nonuniform distribution of water. The confinement effect of the polymer matrix is detected as a considerable reduction of the diffusion coefficient of water with respect to bulk. The presence of a crystalline phase results in a slowing down of both the fast and slow processes involving water motions. This could give a hint to the presence of a rigid amorphous phase in the semicrystalline material.
2012
45
1676
1687
Laurati M.; Sotta P.; Long D.R.; Fillot L.-A.; Arbe A.; Alegria A.; Embs J.P.; Unruh T.; Schneider G.J.; Colmenero J.
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1175739
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