title: Component dynamics in polyvinylpyrrolidone concentrated aqueous solutions.
abstract: (2)H-nuclear magnetic resonance (NMR) and neutron scattering (NS) on isotopically labelled samples have been combined to investigate the structure and dynamics of polyvinylpyrrolidone (PVP) aqueous solutions (4 water molecules/monomeric unit). Neutron diffraction evidences the nanosegregation of polymer main-chains and water molecules leading to the presence of water clusters. NMR reveals the same characteristic times and spectral shape as those of the slower process observed by broadband dielectric spectroscopy in this system [S. Cerveny et al., J. Chem. Phys. 128, 044901 (2008)]. The temperature dependence of such relaxation time crosses over from a cooperative-like behavior at high temperatures to an Arrhenius behavior at lower temperatures. Below the crossover, NMR features the spectral shape as due to a symmetric distribution of relaxation times and the underlying motions as isotropic. NS results on the structural relaxation of both components-isolated via H/D labeling-show (i) anomalously stretched and non-Gaussian functional forms of the intermediate scattering functions and (ii) a strong dynamic asymmetry between the components that increases with decreasing temperature. Strong heterogeneities associated to the nanosegregated structure and the dynamic asymmetry are invoked to explain the observed anomalies. On the other hand, at short times the atomic displacements are strongly coupled for PVP and water, presumably due to H-bond formation and densification of the sample upon hydration.
authors.affiliation: Donostia International Physics Center, Paseo Manuel de Lardizabal 4, E-20018 San Sebastián, Spain.
authors.forename: Rémi
authors.initials: R
authors.lastname: Busselez
authors.forename: Arantxa
authors.initials: A
authors.lastname: Arbe
authors.forename: Silvina
authors.initials: S
authors.lastname: Cerveny
authors.forename: Sara
authors.initials: S
authors.lastname: Capponi
authors.forename: Juan
authors.initials: J
authors.lastname: Colmenero
authors.forename: Bernhard
authors.initials: B
authors.lastname: Frick
mesh_terms: D009682:Magnetic Resonance Spectroscopy; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D033363:Neutron Diffraction; D011205:Povidone / Q000737:chemistry*; D053838:Scattering, Small Angle; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: D012996:Solutions; D014867:Water; D011205:Povidone