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 nm–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.

Materials undergoing pressure-driven solid–solid phase transformations can be a valuable alternative for eco-friendly refrigeration, heat pumping and waste heat recovery based on the barocaloric effect. Ferroelectric compounds and plastic crystals have shown their potential in these fields because they may undergo large changes in volume and entropy at the transition, which underpin a large pressure-induced caloric response. Recently, a new class of materials combining a high-temperature plastic phase with a low-temperature ferroelectric phase has been reported. Here we investigate the barocaloric properties of two such “ferroelectric plastic crystals”, namely quinuclidinium perrhenate (C₇H₁₄NReO₄) and tetramethylammonium tetrachloroferrate (N(CH₃)₄[FeCl₄]). The reversible adiabatic temperature changes under pressure of around 100 MPa (8 K for C₇H₁₄NReO₄ and 21 K for N(CH₃)₄[FeCl₄]) reach values comparable to other plastic crystals and other materials, which demonstrates a good prospect for this novel barocaloric materials family. The dynamics of the plastic phase for C₇H₁₄NReO₄ has been investigated by means of quasielastic neutron scattering.

We present the design and simulation of a high resolution inverted time-of-flight option for a neutron spectrometer with crystal analysers in backscattering, with specific reference to the IN16B spectrometer at the Institut Laue-Langevin, Grenoble. While the conventional configuration with Si 111 crystals provides sub-μeV resolution in an energy range limited to ±30 μeV, the novel BATS option (BATS: Backscattering and Time-of-flight Spectrometer) extends the energy window to 340 μeV with only a slightly increased resolution of 1.2 μeV. Moreover, the observation window can be shifted to inelastic energy transfers. To bring this about, a novel fast chopper system with disks of large diameter and complex slit pattern is used, offering high flexibility in resolution and repetition rate. The chopper system consists out of two counter rotating disk chopper pairs. It provides 7 different pulse lengths, three pulse repetition rates up to 237 Hz and can operate with Si 111 or Si 311 crystal analysers. The latter option is a unique feature which covers a Q-range up to 3.7 Å⁻¹ with a resolution of 6.8 μeV. Extensive ray-tracing simulations have been used to validate the design of the pulse chopper system, set limits on the sample size, and assess the achievable energy resolutions of the different chopper configurations.

Designing next-generation fuel cell and filtration devices requires the development of nanoporous materials that allow rapid and reversible uptake and directed transport of water molecules. Here, we combine neutron spectroscopy and first-principles calculations to demonstrate rapid transport of molecular H₂O through nanometer-sized voids ordered within the layers of crystalline carbon nitride with a polytriazine imide structure. The transport mechanism involves a sequence of molecular orientation reversals directed by hydrogen-bonding interactions as the neutral molecules traverse the interlayer gap and pass through the intralayer voids that show similarities with the transport of water through transmembrane aquaporin channels in biological systems. The results suggest that nanoporous layered carbon nitrides can be useful for developing high-performance membranes.