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.

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