Yongli Huang

Density, Elasticity, and Stability Anomalies of Water Molecules with Fewer than Four Neighbors

Goldschmidt-Pauling contraction of the H-O polar-covalent bond elongates and polarizes the other noncovalent part of the hydrogen bond (O:H-O), that is, the O:H van der Waals bond, significantly, through the Coulomb repulsion between the electron pairs of adjacent oxygen (O-O). This process enlarges and stiffens those H2O molecules having fewer than four neighbors such as molecular clusters, hydration shells, and the surface skins of water and ice. The shortening of the H-O bond raises the local density of bonding electrons, which in turn polarizes the lone pairs of electrons on oxygen. The stiffening of the shortened H-O bond increases the magnitude of the O1s binding energy shift, causes the blue shift of the H-O phonon frequencies, and elevates the melting point of molecular clusters and ultrathin films of water, which gives rise to their elastic, hydrophobic, highly-polarized, ice-like, and low-density behavior at room temperature.Chang Q Sun, 2, ∗ Xi Zhang, 3 Ji Zhou, Yongli Huang, Yichun Zhou, and Weitao Zheng † Key Laboratory of Low-dimensional Materials and Application Technologies, and Faculty of Materials and Optoelectronics and Physics, Xiangtan University, Hunan 411105, China School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 3 College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China Key Laboratory of Low-Dimensional Materials and Application Technologies, and Faculty of Materials and Optoelectronics and Physics, Xiangtan University, Hunan 411105, China School of Materials Science, Jilin University, Changchun 130012, China (Dated: May 3, 2014)

Hydrogen-bond relaxation dynamics: Resolving mysteries of water ice

Abstract We present recent progress in understanding the anomalous behavior of water ice under mechanical compression, thermal excitation, and molecular undercoordination (with fewer than four nearest neighbors in the bulk) from the perspective of hydrogen (O:H O) bond cooperative relaxation. We modestly claim the resolution of upwards of ten best known puzzles. Extending the Ice Rule suggests a tetrahedral block that contains two H2O molecules and four O:H O bonds. This block unifies the density-geometry-size-separation of molecules packing in water ice. This extension also clarifies the flexible and polarizable O:H O bond that performs like a pair of asymmetric, coupled, H-bridged oscillators with short-range interactions and memory as well as extreme recoverability. Coulomb repulsion between electron pairs on adjacent oxygen atoms and the disparity between the O:H and the H O segmental interactions relax the O:H O bond length and energy cooperatively under stimulation. A Lagrangian solution has enabled mapping of the potential paths for the O:H O bond at relaxation. The H O bond relaxation shifts the melting point, O 1s binding energy, and high-frequency phonon frequency whereas the O:H relaxation dominates polarization, viscoelasticity, and the O:H dissociation energy. The developed strategies have enabled clarification of origins of the following observations: (i) pressure-induced proton centralization, phase transition-temperature depression and ice regelation; (ii) thermally induced four-region oscillation of the mass density and the phonon frequency over the full temperature range; and (iii) molecular-undercoordination-induced supersolidity that is elastic, hydrophobic, thermally stable, with ultra-low density. The supersolid skin is responsible for the slipperiness of ice, the hydrophobicity and toughness of water skin, and the bi-phase structure of nanodroplets and nanobubbles. Molecular undercoordination mediates the O:H and H O bond Debye temperatures and disperses the quasi-solid phase boundary, resulting in freezing point depression and melting point elevation. O:H O bond memory and water-skin supersolidity ensures a solution to the Mpemba paradox — hot water freezes faster than its cold. These understandings will pave the way toward unveiling anomalous behavior of H2O interacting with other species such as salts, acids and proteins, and excitation of H2O by other stimuli such as electrical and magnetic fields.

Hydrogen Bond Asymmetric Local Potentials in Compressed Ice

A combination of the Lagrangian mechanics of oscillators vibration, molecular dynamics decomposition of volume evolution, and Raman spectroscopy of phonon relaxation has enabled us to resolve the asymmetric, local, and short-range potentials pertaining to the hydrogen bond (O:H-O) in compressed ice. Results show that both oxygen atoms in the O:H-O bond shift initially outwardly with respect to the coordination origin (H), lengthening the O-O distance by 0.0136 nm from 0.2597 to 0.2733 nm by Coulomb repulsion between electron pairs on adjacent oxygen atoms. Both oxygen atoms then move toward right along the O:H-O bond by different amounts upon being compressed, approaching identical length of 0.11 nm. The van der Waals potential VL(r) for the O:H noncovalent bond reaches a valley at -0.25 eV, and the lowest exchange VH(r) for the H-O polar-covalent bond is valued at -3.97 eV.Combining the Lagrangian-Laplace mechanics and the known pressure dependence of the length-stiffness relaxation dynamics, we have determined the critical, yet often-overlooked, short-range interactions in the hydrogen bond of compressed ice. This approach has enabled determination of the force constant, cohesive energy, potential energy of the vdW and the covalent segment at each quasi-equilibrium state as well as their pressure dependence. Evidencing the essentiality of the inter-electron-pair Coulomb repulsion and the segmental strength disparity in determining the asymmetric H-bond relaxation dynamics and the anomalous properties of ice, results confirmed that compression shortens and stiffens the OH bond and meanwhile lengthens and softens the covalent bond.

A common supersolid skin covering both water and ice

Skins of water and ice share the same attribute of supersolidity characterized by the identical H-O vibration frequency of 3450 cm-1. Molecular undercoordination and inter-electron-pair repulsion shortens the H-O bond and lengthen the O:H nonbond, leading to a dual process of nonbonding electron polarization. This relaxation-polarization process enhances the dipole moment, elasticity,viscosity, thermal stability of these skins with 25% density loss, which is responsible for the hydrophobicity and toughness of water skin and for the slippery of ice.

Size, separation, structural order, and mass density of molecules packing in water and ice

The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (dOO = dL + dH or the O:H length dL) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the dL and the dH symmetrization of the O:H-O bond in compressed ice, ii) the dOO relaxation of cooling water and ice and, iii) the dOO expansion of a dimer and between molecules at water surface. With any one of the dOO, the density ρ(g·cm−3), the dL, and the dH, as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice.

Hydrogen-bond memory and water-skin supersolidity resolving the Mpemba paradox

We demonstrate that the Mpemba paradox arises intrinsically from the release rate of energy initially stored in the covalent H-O part of the O:H-O bond in water albeit experimental conditions. Generally, heating raises the energy of a substance by lengthening and softening all bonds involved. However, the O:H nonbond in water follows actively the general rule of thermal expansion and drives the H-O covalent bond to relax oppositely in length and energy because of the inter-electron-electron pair coupling [J Phys Chem Lett 4, 2565 (2013); ibid 4, 3238 (2013)]. Heating stores energy into the H-O bond by shortening and stiffening it. Cooling the water as the source in a refrigerator as a drain, the H-O bond releases its energy at a rate that depends exponentially on the initially storage of energy, and therefore, Mpemba effect happens. This effect is formulated in terms of the relaxation time τ to represent all possible processes of energy loss. Consistency between predictions and measurements revealed that the τ drops exponentially intrinsically with the initial temperature of the water being cooled.

Elastic-plastic properties of thin film on elastic-plastic substrates characterized by nanoindentation test

To characterize the elastic-plastic properties of thin film materials on elastic-plastic substrates, a simple theory model was proposed, which included three steps: dimensionless analysis, finite element modeling and data fitting. The dimensionless analysis was applied to deriving two preliminary nondimensional relationships of the material properties, and finite element modeling and data fitting were carried out to establish their explicit forms. Numerical indentation tests were carried out to examine the effectiveness of the proposed model and the good agreement shows that the proposed theory model can be applied in practice.

Coordination-resolved local bond relaxation and electron binding-energy shift of Pb solid skins and atomic clusters

Lead (Pb) demonstrates pronounced energy states pertaining to undercoordinated skin and edge atoms. The physical origin of these excessive states still remains unclear. Here, we show that the consistency between the density functional theory calculations and photoelectron spectroscopy measurements confirmed our theoretical predictions on the 5d core-level shift of Pb skins and clusters. It is clarified that shorter and stronger bonds between the undercoordinated atoms cause the local densification and entrapment of core electrons, which, in turn, polarize the otherwise conducting electrons in the skins and edges, resulting in the respective electron binding-energy shift. Numerical analysis has revealed that 5d5/2 level shifts from 18.283 eV for an isolated Pb atom to 3.478 eV upon bulk formation. Meanwhile, this strategy has enabled the determination of local bond length, bond energy, binding energy density, and atomic cohesive energy at the undercoordinated atomic sites.

Fabrication, lattice strain, corrosion resistance and mechanical strength of nanocrystalline nickel films

Abstract Nanocrystalline nickel films of 17–40 nm grain sizes were prepared using pulsejet electrodeposition. Structure, corrosion and lattice strain were analysed by transmission electron microscope, electrochemical workstation and X-ray diffraction, revealing that with decreasing of grain size, the lattice strain, corrosion rate of the films are enhanced. The observations can be consistently understood in terms of the bond-order-length-strength correlation mechanism indicating that the shortened and strengthened bonds between the under-coordinated atoms modify the energy density and the atomic cohesive energy in the surface skins of the grains. The surface energy density gain is responsible for the residual atomic cohesive energy for the activation energy of corrosion. Additionally, a novel algorithm was proposed to extract the elastic-plastic properties of nickel films and results that the nickel film has much higher yield strength than bulk nickel.

Ice Regelation: Hydrogen-bond extraordinary recoverability and water quasisolid-phase-boundary dispersivity

Regelation, i.e., ice melts under compression and freezes again when the pressure is relieved, remains puzzling since its discovery in 1850’s by Faraday. Here we show that hydrogen bond (O:H-O) cooperativity and its extraordinary recoverability resolve this anomaly. The H-O bond and the O:H nonbond possesses each a specific heat ηx(T/ΘDx) whose Debye temperature ΘDx is proportional to its characteristic phonon frequency ωx according to Einstein’s relationship. A superposition of the ηx(T/ΘDx) curves for the H-O bond (x = H, ωH ~ 3200 cm−1) and the O:H nonbond (x = L, ωL ~ 200 cm−1, ΘDL = 198 K) yields two intersecting temperatures that define the liquid/quasisolid/solid phase boundaries. Compression shortens the O:H nonbond and stiffens its phonon but does the opposite to the H-O bond through O-O Coulomb repulsion, which closes up the intersection temperatures and hence depress the melting temperature of quasisolid ice. Reproduction of the Tm(P) profile clarifies that the H-O bond energy EH determines the Tm with derivative of EH = 3.97 eV for bulk water and ice. Oxygen atom always finds bonding partners to retain its sp3-orbital hybridization once the O:H breaks, which ensures O:H-O bond recoverability to its original state once the pressure is relieved.