Michael Fröba, Jacques Ollivier, Denis Morineau, J. Benedikt Mietner, Patrick Huber, Aziz Ghoufi, Mark Busch, Aicha Jani, Markus Appel, Bernhard Frick, Jean-Marc Zanotti, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Hamburg University of Technology (TUHH), University of Hamburg, Institut Laue-Langevin (ILL), ILL, Laboratoire Léon Brillouin (LLB - UMR 12), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay, LLB - Matière molle et biophysique (MMB), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay, Universität Hamburg (UHH), ANR-18-CE92-0011-01, DFG: FR 1372/25-1, DFG Hu850/111 - Projektnummer 407319385, ANR-18-CE92-0011,NanoLiquids,Modifications des Propriétés de Fluides Multiphasiques par Confinement Géométrique dans des Matériaux Mésoporeux Avancés(2018), Morineau, Denis, APPEL À PROJETS GÉNÉRIQUE 2018 - Modifications des Propriétés de Fluides Multiphasiques par Confinement Géométrique dans des Matériaux Mésoporeux Avancés - - NanoLiquids2018 - ANR-18-CE92-0011 - AAPG2018 - VALID, Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Technische Universität Hamburg-Harburg (TUHH), Numerische Strukturanalyse mit Anwendungen in der Schiffstechnik (M-10), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Faculty of Physics and Mechatronics Engineering, Saarland University [Saarbrücken], and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
International audience; We have investigated the dynamics of liquid water confined in mesostructured porous silica (MCM-41) and periodic mesoporous organosilicas (PMOs) by incoherent quasielastic neutron scattering experiments. The effect of tuning the water/surface interaction from hydrophilic to more hydrophobic on the water mobility, while keeping the pore size in the range 3.5-4.1 nm, was assessed from the comparative study of three PMOs comprising different organic bridging units and the purely siliceous MCM-41 case. An extended dynamical range was achieved by combining time-of-flight (IN5B) and backscattering (IN16B) quasielastic neutron spectrometers providing complementary energy resolutions. Liquid water was studied at regularly spaced temperatures ranging from 300 K to 243 K. In all systems, the molecular dynamics could be described consistently by the combination of two independent motions resulting from fast local motion around the average molecule position and the confined translational jump diffusion of its center of mass. All the molecules performed local relaxations, whereas the translational motion of a fraction of molecules was frozen on the experimental timescale. This study provides a comprehensive microscopic view on the dynamics of liquid water confined in mesopores, with distinct surface chemistries, in terms of non-mobile/mobile fraction, self-diffusion coefficient, residence time, confining radius, local relaxation time, and their temperature dependence. Importantly, it demonstrates that the strength of the water/surface interaction determines the long-time tail of the dynamics, which we attributed to the translational diffusion of interfacial molecules, while the water dynamics in the pore center is barely affected by the interface hydrophilicity.