Hydrogen-Bond Configurations of Hydration Water around Glycerol Investigated by HOH Bending and OH Stretching Analysis

Lightweight Calcium-Silicate-Hydrate Nacre with High Strength and High Toughness

Low flexural strength and toughness have posed enduring challenges to cementitious materials. As the main hydration product of cement, calcium silicate hydrate (C-S-H) plays important roles in the mechanical performance of cementitious materials while exhibiting random microstructures with pores and defects, which hinder mechanical enhancement. Inspired by the "brick-and-mortar" microstructure of natural nacre, this paper presents a method combining freeze casting, freeze-drying, in situ polymerization, and hot pressing to fabricate C-S-H nacre with high flexural strength, high toughness, and lightweight. Poly(acrylamide-co-acrylic acid) was used to disperse C-S-H and toughen C-S-H building blocks, which function as "bricks", while poly(methyl methacrylate) was impregnated as "mortar". The flexural strength, toughness, and density of C-S-H nacre reached 124 MPa, 5173 kJ/m3, and 0.98 g/cm3, respectively. The flexural strength and toughness of the C-S-H nacre are 18 and 1230 times higher than those of cement paste, respectively, with a 60% reduction in density, outperforming existing cementitious materials and natural nacre. This research establishes the relationship between material composition, fabrication process, microstructure, and mechanical performance, facilitating the design of high-performance C-S-H-based and cement-based composites for scalable engineering applications.

Modeling of the Hydrogen Bond-Induced Frequency Shifts of the HOH and HOD Bending Modes of Water

The intramolecular bending mode of water is a possible useful probe of the hydrogen-bond situations in aqueous systems, but the behavior of its frequency and intensity should be further elucidated for better understanding on its nature and, hence, for its better utilization as a probe. Here, an analysis toward this goal is conducted by doing theoretical calculations on molecular clusters of normal isotopic and deuterated species of water and examining the correlations among the vibrational, structural, and electrostatic properties. It is shown that electrostatic interactions, particularly both of the in-plane components of the electric field along the OH bond and perpendicular to it, play a major role in controlling the hydrogen bond-induced shifts of the force constant, but additional factors, including the intermolecular structural and/or charge-transfer properties, are also important. Models of the hydrogen bond-induced shifts of the force constant are presented in a form that may be combined with classical molecular dynamics. With regard to the infrared intensity changes, it is shown on the basis of the electron density analysis that the intermolecular charge flux and polarization effect play an important role, depending on the angular characteristics of the hydrogen bond.

Water Structure in the First Layers on TiO2: A Key Factor for Boosting Solar-Driven Water-Splitting Performances

The water hydrogen-bonded network is strongly perturbed in the first layers in contact with the semiconductor surface. Even though this aspect influences the outer-sphere electron transfer, it was not recognized that it is a crucial factor impacting the solar-driven water-splitting performances. To fill this gap, we have selected two TiO2 anatase samples (with and without B-doping), and by extensive experimental and computational investigations, we have demonstrated that the remarkable 5-fold increase in water-splitting photoactivity of the B-doped sample cannot be ascribed to effects typically associated to enhanced photocatalytic properties, such as band gap, heterojunctions, crystal facets, and other aspects. Studying these samples by combining FTIR measurements under controlled humidity with first-principles simulations sheds light on the role and nature of the first-layer water structure in contact with the photocatalyst surfaces. It turns out that the doping hampers the percolation of tetrahedrally coordinated water molecules while enhancing the population of topological H-bond defects forming approximately linear H-bonded chains. This work unveils how doping the semiconductor surface affects the local electric field, determining the water splitting rate by influencing the H-bond topologies in the first water layers. This evidence opens new prospects for designing efficient photocatalysts for water splitting.

Charge Transfer Quenching and Maximum of a Liquid-Air Contact Line Moving over a Hydrophobic Surface

Charge transfer when a hydrophobic fluoropolymer surface comes in contact with salt solutions of water, methanol, and glycerol is investigated. It is found that the charge transfer decreases faster with an increasing fraction of glycerol in water than it does with methanol in water. It is also demonstrated that for both mixtures, the charge transfer increases with the amount of added sodium chloride for small concentrations but then reaches a maximum and subsequently decreases. Surprisingly, this maximum charge transfer shifts toward higher salt concentrations with increasing amount of glycerol in water. However, in water-methanol mixtures, one does not observe a similar shift in charge transfer maximum toward higher salt concentrations. These observations are explained using a model, taking into account the decreased shear distance from the hydrophobic surface for which ions are removed from the electrical double layer due to an interplay of forces acting on the ions.

Sensing Liquid- and Gas-Phase Hydrocarbons via Mid-Infrared Broadband Femtosecond Laser Source Spectroscopy

In this study, we demonstrate the combination of a tunable broadband mid-infrared (MIR) femtosecond laser source separately coupled to a ZnSe crystal horizontal attenuated total reflection (ATR) sensor cell for liquid phase samples and to a substrate-integrated hollow waveguide (iHWG) for gas phase samples. Utilizing this emerging light source technology as an alternative MIR radiation source for Fourier transform infrared (FTIR) spectroscopy opens interesting opportunities for analytical applications. In a first approach, we demonstrate the quantitative analysis of three individual samples, ethanol (liquid), methane (gas), and 2-methyl-1-propene (gas), with limits of detection of 0.3% (ethanol) and 22 ppmv and 74 ppmv (methane and isobutylene), respectively, determined at selected emission wavelengths of the MIR laser source (i.e., 890 cm-1, 1046 and 1305 cm-1). Hence, the applicability of a broadband MIR femtosecond laser source as a bright alternative light source for quantitative analysis via FTIR spectroscopy in various sensing configurations has been demonstrated.

1H-NMR Karplus Analysis of Molecular Conformations of Glycerol under Different Solvent Conditions: A Consistent Rotational Isomerism in the Backbone Governed by Glycerol/Water Interactions

Glycerol is a symmetrical, small biomolecule with high flexibility in molecular conformations. Using a 1H-NMR spectroscopic Karplus analysis in our way, we analyzed a rotational isomerism in the glycero backbone which generates three kinds of staggered conformers, namely gt (gauche-trans), gg (gauche-gauche), and tg (trans-gauche), at each of sn-1,2 and sn-2,3 positions. The Karplus analysis has disclosed that the three rotamers are consistently equilibrated in water keeping the relation of 'gt:gg:tg = 50:30:20 (%)' at a wide range of concentrations (5 mM~540 mM). The observed relation means that glycerol in water favors those symmetric conformers placing 1,2,3-triol groups in a gauche/gauche geometry. We have found also that the rotational isomerism is remarkably changed when the solvent is replaced with DMSO-d6 or dimethylformamide (DMF-d7). In these solvents, glycerol gives a relation of 'gt:gg:tg = 40:30:30 (%)', which means that a remarkable shift occurs in the equilibrium between gt and tg conformers. By this shift, glycerol turns to also take non-symmetric conformers orienting one of the two vicinal diols in an antiperiplanar geometry.