Mitigating repulsions in close quarters: Copper tells us how!

Four copper(I) complexes of short bite ligands, bis(diphenylphosphino)amine (dppa) and bis(diphenylphosphino)isopropylamine (dppipa) were synthesized from appropriate precursors. All complexes were characterized by single crystal X-ray crystallography and spectroscopic techniques. In each of these complexes, two filled shell cations are forced into close proximity (≈2.7–2.8 Å). With no strong π acid ligands to siphon electron density from the filled d shell, the unavoidable repulsive d¹⁰–d¹⁰ interaction is mitigated when an unsymmetrical coordination environment around the copper atoms exists. The coordinatively saturated copper ion functions as a donor to the coordinatively unsaturated copper. A Cambridge Structural Database (CSD) search reveals the greater propensity of clusters with short contacts to adopt unsymmetrical coordination.     

Metal‐Functionalized Silicene for Efficient Hydrogen Storage

First‐principles calculations based on density functional theory are used to investigate the electronic structure along with the stability, bonding mechanism, band gap, and charge transfer of metal‐functionalized silicene to envisage its hydrogen‐storage capacity. Various metal atoms including Li, Na, K, Be, Mg, and Ca are doped into the most stable configuration of silicene. The corresponding binding energies and charge‐transfer mechanisms are discussed from the perspective of hydrogen‐storage compatibility. The Li and Na metal dopants are found to be ideally suitable, not only for strong metal‐to‐substrate binding and uniform distribution over the substrate, but also for the high‐capacity storage of hydrogen. The stabilities of both Li‐ and Na‐functionalized silicene are also confirmed through molecular dynamics simulations. It is found that both of the alkali metals, Li⁺ and Na⁺, can adsorb five hydrogen molecules, attaining reasonably high storage capacities of 7.75 and 6.9 wt %, respectively, with average adsorption energies within the range suitable for practical hydrogen‐storage applications.     

Rheological and sensory properties of toothpastes

Complex rheological trends of several commercially available and lab-made prototype toothpastes are reported. The flow curves are generated using the rotational rheometers with a series of rheological procedures, comprising of stress ramps, creep-recovery, stepped-shear rates, and dynamic oscillatory strain sweeps performed on toothpastes. Intricacies due to the history and the effects of pre-conditioning of the samples are discussed. However, the main goal of this work was to identify the correlations between the rheological measurements and the consumer-perceived properties of toothpastes. Shape retention and stringiness are the main sensory properties of interest that were identified and evaluated by the panelists. A custom-built experimental setup is used to quantify shape retention of a toothpaste ribbon on a brush and on a flat surface in a test which resonates with the popular slump test. It is demonstrated that the degree of shape retention correlates with the yield stress and the instantaneous viscosity. A comparison of yield stresses obtained using different methods in relation to degree of shape retention is presented. An experimental setup designed to measure stringiness of toothpastes is delineated. The stringiness measured with this device correlates well with human perception and also with the slope of the flow curve, i.e., the higher the degree of shear thinning, the less stringy the pastes tend to be. For lab-made prototype toothpastes, basic structure-property relations are established in terms of correlations between the three formulation variables: thickening silica, Xanthan gum, and carboxymethyl cellulose (CMC).

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Graphical abstract Two important consumer perceived properties of toothpastes: shape retention and stringiness

     

Rheology of cyclopentane hydrate slurry in a model oil-continuous emulsion

Liquid cyclopentane (CP)-based hydrate slurry is prepared at atmospheric pressure from a density-matched water-in-oil emulsion by quenching it to a lower temperature at a fixed shear rate. Viscosity increases by several orders of magnitude and is indicative of hydrate formation on the dispersed water droplets and subsequent agglomeration. A mechanism in which the hairy and porous hydrate growth combined with enhanced agglomeration due to liquid bridges formed by wetted water films leads to the development of a porosity, resulting in greater effective dispersed phase fraction, is proposed. This is supported by experiments performed for water volume fractions ranging from 10 to 45 % at variable shear rates, temperatures, and surfactant (Span 80) concentrations. The observed dependence on the degree of sub-cooling, with lower slurry viscosity obtained at higher sub-cooling, and the possible anti-agglomerant like effect of high Span 80 concentrations, support our proposed mechanism. The hydrate slurries are found to exhibit shear-thinning and a small degree of thixotropy.     

An NMR study of the electron beam-induced polymerization of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate

Electron beam-induced polymerization of trimethylolpropane triacrylate (TMPTA) and its methacrylate analog (TMPTMA) was studied using nuclear magnetic resonance (NMR) relaxation time measurements. Free induction decays (FID) of partially polymerized samples consist of a short Gaussian component and a longer component comprised of a distribution of simple exponentials. The relative intensity of the Gaussian component increases with radiation dose. T₁ and T_1ρ values were measured as a function of temperature and radiation dose. The relaxation is due primarily to methyl group reorientation at low temperatures, ethyl group reorientation at intermediate temperatures, and whole-molecule reorientation at high temperatures. In both compounds, the T₁ and T_1ρ values at the high temperature minima increase with increasing dose, and the minima values can be used to estimate the degree of polymerization. The temperature at which the T_1ρ minimum occurs increases with dose, suggesting an increase in the glass transition temperature, T_g, with polymerization. The polymerization appears to have very little effect on the low temperature CH₃ reorientation in TMPTA. In TMPTMA the polymerization appears to reduce the mobility of the methacrylate methyl groups.     

A magnetic Compton scattering study of Ga rich Co-Ni-Ga ferromagnetic shape memory alloys

The temperature dependent spin momentum densities of Co(1.8)NiGa(1.2) and Co(2)Ni(0.76)Ga(1.24) alloys have been measured using the magnetic Compton scattering technique. The individual contributions of constituents in the formation of the total spin moment are also calculated using Compton line shape analysis. The magnetic Compton data when compared with the magnetization data obtained using a vibrating sample magnetometer show a negligible orbital contribution. The spin moments deduced from the experimental Compton data are compared with the theoretical results obtained from the full potential linearized augmented plane wave method and are found to be in good agreement. The origin of the magnetism in both alloys is also described in terms of the e(g) and t(2g) contributions of Ni and Co.     

Hole mediated coupling in Sr2Nb2O7 for visible light photocatalysis

The band gap reduction and effective utilization of visible solar light are possible by introducing the anionic hole-hole mediated coupling in Sr(2)Nb(2)O(7). By using the first principles calculations, we have investigated the mono- and co-anionic doping (S, N and C) in layered perovskite Sr(2)Nb(2)O(7) for the visible-light photocatalysis. Our electronic structure and optical absorption study shows that the mono- (N and S) and co-anionic doped (N-N and C-S) Sr(2)Nb(2)O(7) systems are promising materials for the visible light photocatalysis. The calculated binding energies show that if the hole-hole mediated coupling could be introduced, the co-doped systems would be more stable than their respective mono-doped systems. Optical absorption curves indicate that doping S, (N-N) and (C-S) in Sr(2)Nb(2)O(7) can harvest a longer wavelength of the visible light spectrum as compared to the pure Sr(2)Nb(2)O(7) for efficient photocatalysis.