Dynamics of water absorbed in polyamides

We investigate the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copolymers. 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 American Chemical Society.We thank support by the DIPC, Rhodia, the European Commission NoE SoftComp, Contract NMP3- CT-2004-502235, the projects MAT2007-63681 (Spanish Ministerio de Educacion y Ciencia) and IT-436-07 (GV) (Basque Government). M.L. acknowledges support from CNRS.Peer Reviewe

Dynamics of Water Absorbed in Polyamides

We investigate the dynamics of water absorbed in amorphous and semicrystalline aromatic polyamide copolymers. 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 American Chemical Society