Neutron Scattering Analysis of Water’s Glass Transition and Micropore Collapse in Amorphous Solid Water

The question of the nature of water’s glass transition has continued to be disputed over many years. Here we use slow heating scans (0.4 K min−1) of compact amorphous solid water deposited at 77 K and an analysis of the accompanying changes in the small-angle neutron scattering signal, to study mesoscale changes in the ice network topology. From the data we infer the onset of rotational diffusion at 115 K, a sudden switchover from nondiffusive motion and enthalpy relaxation of the network at 121 K, in excellent agreement with the glass transition onset deduced from heat capacity and dielectric measurements. This indicates that water’s glass transition is linked with long-range transport of water molecules on the time scale of minutes and, thus, clarifies its nature. Furthermore, the slow heating rates combined with the high crystallization resistance of the amorphous sample allow us to identify the glass transition end point at 136 K, which is well separated from the crystallization onset at 144 K—in contrast to all earlier experiments in the field

Atomic and vibrational origins of mechanical toughness in bioactive cement during setting

Bioactive glass ionomer cements (GICs) have been in widespread use for ~40 years in dentistry and medicine. However, these composites fall short of the toughness needed for permanent implants. Significant impediment to improvement has been the requisite use of conventional destructive mechanical testing, which is necessarily retrospective. Here we show quantitatively, through the novel use of calorimetry, terahertz (THz) spectroscopy and neutron scattering, how GIC’s developing fracture toughness during setting is related to interfacial THz dynamics, changing atomic cohesion and fluctuating interfacial configurations. Contrary to convention, we find setting is non-monotonic, characterized by abrupt features not previously detected, including a glass–polymer coupling point, an early setting point, where decreasing toughness unexpectedly recovers, followed by stress-induced weakening of interfaces. Subsequently, toughness declines asymptotically to long-term fracture test values. We expect the insight afforded by these in situ non-destructive techniques will assist in raising understanding of the setting mechanisms and associated dynamics of cementitious materials

Bulk and Confined Benzene-Cyclohexane Mixtures Studied by an Integrated Total Neutron Scattering and NMR Method

From Springer Nature via Jisc Publications RouterHistory: accepted 2021-04-10, registration 2021-04-10, pub-electronic 2021-04-23, online 2021-04-23, pub-print 2021-08Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000266; Grant(s): N008995, N009304Abstract: Herein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement

Structure and interactions in simple solutions

Neutron scattering with hydrogen/deuterium isotopic substitution techniques has been used to investigate the full range of structural interactions in a dilute 0.02 mol fraction solution of tertiary butanol in water, both in the absence and in the presence of a small amount of sodium chloride. Emphasis is given to the detailed pictures of the intermolecular interactions that have been derived using the empirical potential structure refinement technique. Analysis has been performed to the level of the spatial density distribution functions that illustrate the orientational dependence of the intermolecular interactions between all combinations of molecular and ionic components. The results show the key structural motifs involved in the interactions between the various components in a complex aqueous system. They underline the structural versatility of the water molecule in accommodating a range of different kinds of interactions while retaining its characteristic first-neighbour interaction geometry. Within this framework, the results highlight the complex interplay between the polar, non-polar and charged molecular interactions that exist in the system

The hydration structure of Cu2+: more tetrahedral than octahedral?

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.A comprehensive multi-technique approach has been used to address the controversial question of the preferred geometric form of the Cu2+ aqua-ion hydration shell. A combination of H/D isotopic substitution neutron scattering and X-ray scattering has been used to refine atomistic models of 0.5 m and 2.0 m solutions of Cu(ClO4)2, that have also been constrained to simultaneously reproduce detailed local structure information about the cation environment obtained by X-ray Absorption spectroscopy. The adoption of the Empirical Potential Structure Refinement (EPSR) technique as a single unified analytical framework minimises the chances for biasing the result in favour of a specific pre-conceived outcome. The results are consistent with an average coordination for each Cu2+ ion of 4.5 ± 0.6 water molecules that matches the more recent picture of five-fold coordination in a 2.0 m solution, but interestingly this combined study highlights that the preferred local geometry of the ion sites is found to have a mixed character of tetrahedral, trigonal bipyramidal and octahedral components. A further point to note is that this new model adds support to a largely ignored result in the literature relating to the linear electric field effect induced g-shifts observed in the electron paramagnetic resonance spectra of glassy Cu 2+ complexes (Peisach and Mims, Chem. Phys. Lett., 1976, 37, 307-310) that first highlighted the importance of tetrahedral distortions in the cation's hydration shell structure. This journal is © The Royal Society of Chemistry.RB acknowledges support from the Ministerio de Economía y Competitividad of Spain.We would like to thank Red de Bibliotecas del CSIC for their support to publish this work in open format.Peer Reviewe

Dataset supporting "Neutron diffraction study of indole solvation in deep eutectic systems of choline chloride, malic acid, and water"

This dataset includes neutron diffraction data from samples of indole in choline chloride:malic acid deep eutectic solvent in the presence and absence of water. The data has been processed using the program Gudrun to remove background scattering and instrumental effects, (creating .mint01 files) so it is ready for use in data fitting. The text files contain a header describing the name of the sample, the experimenters, and then three columns: Q (x-axis), differential scattering cross section (y-axis), error in intensity.Solutions of indole in choline chloride:malic acid deep eutectic solvent were prepared using h- or d-choline chloride, and h- or d-malic acid. The solutions were loaded into TiZr cuvettes, sealed and attached to the sample changer at 25C. Neutron scattering data was collected using the NIMROD instrument at the ISIS Neutron and Muon Source, UK. The raw neutron diffraction data files are available from the ISIS Neutron and Muon Source Data Journal under the title "Denitrogenation of fuel oils using hydrated choline chloride:malic acid DES".Raw data was processed to remove backgrounds and instrumental factors, to create the .mint01 files containing differential scattering cross-section against Q.The Gudrun software (https://www.isis.stfc.ac.uk/Pages/Gudrun.aspx) was used to process the data.The data are in three-column text files (x, y, error in y), with a 14 line header including sample and experimenter names