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    Item type:Publication, Access status: without files ,
    Colossal effect of nanopore surface ionic charge on the dynamics of confined water
    (American Chemical Society (ACS), 2025-09-29)
    Mozhdehei, Armin
    ;
    Lenz, Philip
    ;
    Gries, Stella Inge Martha
    ;
    Meinert, Sophia Marie
    ;
    Lefort, Ronan
    Interfacial interactions significantly alter the fundamental properties of water confined in mesoporous structures with crucial implications for geological, physicochemical, and biological processes. Herein, we focused on the effect of changing the surface ionic charge of nanopores with comparable pore sizes (3.5–3.8 nm) on the dynamics of confined liquid water. The control of the pore surface ionicity was achieved by using two periodic mesoporous organosilicas (PMOs) containing either neutral or charged forms of a chemically similar bridging unit. The effect on the dynamics of water at the nanoscale was investigated in the temperature range 245–300 K, encompassing the glass transition by incoherent quasi-elastic neutron scattering (QENS). For both types of PMOs, the water dynamics revealed two distinct types of molecular motions: rapid local movements and translational jump diffusion. While the neutral PMO induces a moderate confinement effect, we show that the charged PMO drastically slows down water dynamics, reducing translational diffusion by a factor of 4 and increasing the residence time by an order of magnitude. Notably, by changing the pore filling values, we demonstrate that for charged PMOs, this effect extends beyond the interfacial layer of surface-bound water molecules to encompass the entire pore volume. Thus, our observation indicates a dramatic change in the long-range character of the interaction of water confined in nanopores with surface ionic charge compared to a simple change in hydrophilicity. This is relevant for the understanding of a broad variety of applications in (nano)technological phenomena and processes such as nanofiltration and membrane design.
    Publicationtype: Journal Article
      31
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    Dynamics of Water Confined in Mesopores with Variable Surface Interaction
    (2021-03-07)
    Jani, Aicha
    ;
    Busch, Mark
    ;
    Mietner, J. Benedikt
    ;
    Ollivier, Jacques
    ;
    Appel, Markus
    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.
    Publicationtype: Journal Article
      70
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    Absolute determination of the orientational order quality in a columnar discotic liquid crystal
    (MRS, 2011-07-01)
    Ndao, Makha
    ;
    Lefort, Ronan
    ;
    Huber, Patrick
    ;
    Zanotti, Jean-Marc
    ;
    Frick, Bernhard
    Simple NMR techniques can provide an absolute quantification of the quality of the orientational order of discotic columnar phases, provided the anisotropic local magnetic interactions are thoroughly characterized. For the prototypical discotic liquid crystal hexapentoxy-triphenylene, we measure the 13C chemical shift anisotropy of the triphenylene carbons, and use this result to analyze the orientational order, that occurs through a first order phase transition from the high temperature liquid phase, and is almost saturated (order parameter close to 0.85).
    Publicationtype: Conference Paper
      23
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    Collective molecular reorientation of a calamitic liquid crystal (12CB) confined in alumina nanochannels
    (American Physical Society (APS), 2010-07-15)
    Chahine, Gilbert
    ;
    Kityk, Andriy V.
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    Démarest, Nathalie
    ;
    Jean, Fabien
    ;
    Knorr, Klaus
    We study the smectic director structure of the rodlike liquid crystal 4-n -dodecyl- 4′-cyanobiphenyl (12CB) confined in cylindrical cavities of 200 nm diameter in porous alumina templates by means of combined broadband dielectric spectroscopy, optical birefringence, and neutron scattering measurements. We show that the collective molecular orientation differs between entering the smectic A phase upon cooling from the isotropic state and entering the same phase upon heating while melting the confined crystal. We discuss this collective molecular realignment in terms of a competition between weak planar anchoring at the p -Al2 O3 /12CB interface and a preferred texture typical of the crystallization of rodlike molecules in nanochannels (Bridgman growth).
    Publicationtype: Journal Article
      32