Interlayer Hydrogen Bonds Research Articles

Role of the structural order of the hydration layer in regulating the heterogeneous ice nucleation efficiency

Understanding the complex microscopic mechanisms of heterogeneous ice nucleation is crucial across diverse fields from cloud science to microbiology. In this work, we examined the ability of solid surfaces to promote ice nucleation as a function of the structural order of interfacial water, including the first and second hydration layers. Comprehensive all-atom molecular dynamics simulations using the TIP4P/ice water model were conducted on a water film atop a modeled surface inspired by the (0001) surface of AgI crystal, with varying surface charges. These simulations revealed non-monotonic nucleation rates. The first hydration layer formed a hexagonal hydrogen-bond network resembling ice structures, exhibiting low mobility essential for inducing ice nucleation. Notably, the second hydration layer, acting as a key-point bridge, displayed varying degrees of orientational preference facilitated by inter-layer hydrogen bonds. The calculation of fluctuation parameters indicated that the greater structural order of the second layer significantly enhances the surface’s ice-forming capabilities. Unlike previous studies that focused primarily on the role of the first layer of interfacial water, our findings demonstrate that the second layer provides a more accurate indicator of ice nucleation capabilities.

Utilizing supercritical fluid for efficient preparation of kaolinite nanosheets to enhance Ga(Ⅲ) adsorption

This study explores the efficient preparation of few-layered or monolayered kaolinite (K) nanosheets using supercritical gasification exfoliation technology, aiming to enhance their adsorption capacity for Ga(III). Crystal structure and morphology analysis indicated that the exfoliated K nanosheets maintained an excellent hexagonal lamellar crystal shape, with significantly reduced thickness (∼10 nm) while maintaining an unchanged lateral dimension (400 ∼ 600 nm). The exfoliation mechanism primarily relies on the considerable impact force generated by the rapid expansion of supercritical carbon dioxide (CO2) volume during fast pressure release, which facilitates exfoliation between K layers where the interlayer hydrogen bonds have been disrupted by potassium acetate. Batch adsorption experiments demonstrated a significant improvement in the removal rate of exfoliated K for Ga(III), increasing from 50.66 % to 80.47 % under the conditions of a Ga(III) concentration of 15 mg/L and an adsorbent dosage of 0.4 g/L, attributed to the exposure of numerous active sites. Kinetic and isotherm fitting results indicated a monomolecular adsorption process primarily controlled by chemical adsorption, with a maximum theoretical adsorption capacity of 32.90 mg/g for Ga(III). In multivariate mixed adsorption experiments, exfoliated K exhibited good adsorption selectivity for Ga(III), primarily through chemical adsorption of aluminum hydroxide (Al–OH) functional groups and electrostatic adsorption of silicon oxide (Si–O). Density functional theory (DFT) calculations further demonstrated that the bidentate adsorption coordination of K with Ga(III) exhibits higher stability compared to monodentate adsorption coordination, indicating that the adsorption process is mainly dominated by bidentate adsorption. Consequently, the supercritical gasification exfoliation technology, as a recyclable green process, offers efficient exfoliation of K, holding significance implications for the high-value and high-efficiency utilization of K resources, as well as for establishing a green, low-carbon, and recycling development economic system.

The oxidative thermal exfoliation-dependent microstructure and photocatalytic performance of g-C3N4 nanosheets

The preparation of ultrathin nanosheets is conducive to increasing the material's specific surface area and introducing suitable defect sites. This facilitates the enhancement of the separation efficiency of photogenerated charge carriers and improves the adsorption and degradation efficiency toward pollutants. Various nitrogen-rich precursors were employed for the synthesis of bulk g-C3N4 (BCN) and its ultrathin nanosheets, with a focus on investigating their photocatalytic performance. The degree of polymerization of g-C3N4 influenced its hydrogen bonding and C/N ratio, affecting the ultrathin nanosheet microstructure. Oxidation disrupted the tri-s-triazine rings in the ultrathin nanosheets of g-C3N4 prepared via dicyandiamide. However, g-C3N4 prepared from urea and melamine as precursors retained its primary characteristics after thermal oxidative exfoliation, attributed to interlayer hydrogen bonds, small lateral size at low polymerization degrees, and increased vacancy defects. In the photocatalytic degradation system, two-dimensional nanosheets of g-C3N4 synthesized from urea exhibited the highest catalytic efficiency.

Pressure-induced luminescence evolution of 3,3′-diamino-4,4′-azofurazan: Role of restricting chemical bond vibration and conformational modification

The luminescence and electronic structure of 3,3′-Diamino-4,4′-azofurazan (DAAzF) were studied under high pressure conditions through experimental and calculation approaches. The transition of π* → π was primarily responsible for DAAzF's broad light emission. Upon applying pressure to DAAzF, high-pressure-stiffened hydrogen-bond interactions enable the restriction of the stretching vibration of NH2 group. The reduced energy loss through nonradiative rotational relaxation and molecular motions lead to a ∼20 times luminescent enhancement of DAAzF from 1 atm to 8.9 GPa. With the further strengthening of interlayer hydrogen bond interactions at higher pressure, the deviation of hydrogen atoms in amino groups from the molecular plane lessens the radiation transition efficiency. In addition, the bending of the C–C–N=N bond further leads to molecular conformation changes at approximately 20.7 GPa, which induces an abrupt redshift and moderate quenching of the luminescence. Furthermore, the band gap of DAAzF is significantly influenced by pressure. As the color undergoes a transition from yellow to red, and becomes darker as the pressure increases, the absorption edge shifted towards red. At 3.4, 9, and 21 GPa, three conformational variations were identified in conjunction with electronic structural alterations.

Mechanical properties of defective kaolinite in tension and compression: A molecular dynamics study

Influenced by the external environment, clays often contain a large number of lattice defects inside, and the defects have an essential influence on the physical and mechanical properties of clays. In order to reveal the mechanical properties and deformation failure mechanism of defective kaolinite, kaolinite containing Si vacancy defects was constructed, and the mechanical properties of two types of perfect/defective kaolinite were investigated under uniaxial tensile and compressive conditions, respectively, by using molecular dynamics methods. The anisotropy of the micromechanical behavior of kaolinite and the formation mechanism was revealed. Based on the radial distribution function between atoms, the cutoff distance of individual bonds inside the crystal was determined, and the evolution rules of individual bonds inside the crystal during the deformation and destruction were elucidated. Results showed that the introduction of point defects caused different degrees of reduction in the peak strength and elastic modulus of kaolinite, and the decrease was related to the loading direction, and the decline was more significant for parallel clay layers (x- and y-) than for perpendicular clay layers (z-), with pronounced anisotropy. When the defected kaolinite was extended along the x- and y-directions, the silicon‑oxygen tetrahedral and aluminum‑oxygen octahedral sheets were fractured, and the broken sites were concentrated at the defected locations; when extended along the z-direction, the failure was dominated by the fracture of interlayer hydrogen bonds. When the defective kaolinite was compressed along the x- and y-directions, the failure was mainly caused by the gradual accumulation of the bending of the clay layer, which was distinctly different from the direct fracture under the tensile condition, and when compressed along the z-direction, the clay layer collapsed until it was failure. The tendency of the broken bonds within kaolinite corresponded well with the stress-strain curve, the number of broken bonds increased with the increase of strain, and the number of broken bonds of various bonds stabilized when the crystal structure was destroyed. The bond-break types and the number of bonds broken under different simulation conditions were somewhat different, affected by the layered structure of kaolinite and the loading patterns.

Size-controlled synthesis of unusual hydrogen-bonded imine-linked covalent organic framework for trypsin immobilization and drug delivery

The interlayer hydrogen-bonded, uniform, and spherical covalent organic frameworks (USCOFs) and non-hydrogen bonded, and spherical covalent organic polymers (USCOPs) were synthesized in a series of aromatic and nonaromatic solvents at room temperature. The presence of interlayer hydrogen bonds between USCOFs were investigated via electron density difference (EDD) and stacking energy calculation in various solvents by DFT methods. The in-situ mid-angle X-ray scattering measurements indicate that the (100)-plane at 0.33 Å continuously grows in USCOFs, which was absent in USCOPs. The crystalline USCOFs exhibit a high surface area of 658 m2g−1, with a pore size of 3 nm, whereas USCOPs exhibit a surface area of 16 m2 g−1 with a pore size of 19 nm. Therefore, USCOFs formation in aromatic solvents, involving solvation and reduced π–π stacking, which allow the defective intermediates to dissociate and react reversibly, leading to well-ordered molecular arrangements. These solvent characteristics are absent in nonaromatic solvents; therefore, they fail to produce well-ordered molecular arrangement, forming amorphous USCOPs. Finally, the as-synthesized USCOFs were used for a protein(trypsin)-loading and drug delivery application. In addition, the loaded protein retains its original activity. Notably, the conducted MTT assay and cellular uptake proved COF-DOX selectively killed the cancer cells rather than normal cells.

Temperature-pressure phase diagram of confined monolayer water/ice at first-principles accuracy with a machine-learning force field

Understanding the phase behaviour of nanoconfined water films is of fundamental importance in broad fields of science and engineering. However, the phase behaviour of the thinnest water film – monolayer water – is still incompletely known. Here, we developed a machine-learning force field (MLFF) at first-principles accuracy to determine the phase diagram of monolayer water/ice in nanoconfinement with hydrophobic walls. We observed the spontaneous formation of two previously unreported high-density ices, namely, zigzag quasi-bilayer ice (ZZ-qBI) and branched-zigzag quasi-bilayer ice (bZZ-qBI). Unlike conventional bilayer ices, few inter-layer hydrogen bonds were observed in both quasi-bilayer ices. Notably, the bZZ-qBI entails a unique hydrogen-bonding network that consists of two distinctive types of hydrogen bonds. Moreover, we identified, for the first time, the stable region for the lowest-density 4cdot {8}^{2} monolayer ice (LD-48MI) at negative pressures (<−0.3 GPa). Overall, the MLFF enables large-scale first-principle-level molecular dynamics (MD) simulations of the spontaneous transition from the liquid water to a plethora of monolayer ices, including hexagonal, pentagonal, square, zigzag (ZZMI), and hexatic monolayer ices. These findings will enrich our understanding of the phase behaviour of the nanoconfined water/ices and provide a guide for future experimental realization of the 2D ices.

Elucidating the structure-nonlinear optical property relationship of Te2O4(OH)2

A mixed-valent tellurium oxide hydroxide, Te2O4(OH)2, containing both tetravalent (IV) and hexavalent (VI) tellurium cations has been synthesized using a hydrothermal reaction method. Single crystal X-ray diffraction reveals that the compound crystallizes in the polar noncentrosymmetric space group, Pna21 (no. 33). The reported compound has a layered structure consisting of Te(VI)O4(OH)2 octahedra and Te(IV)O4 seesaw, in which each layer is aligned through interlayer hydrogen bonds. In addition to the structural refinements, the structure and optical properties of the material have been studied and compared with Te2O5, which is dehydrated residue of the title compound. Second harmonic generation (SHG) measurements indicate that the Te2O4(OH)2 exhibits a large SHG efficiency of ca. 4.7 times that of KH2PO4. The ultraviolet–visible diffuse reflectance spectrum shows that the material has a band gap of ca. 3.5 eV, corresponding to a UV cutoff edge of 354 nm. These values suggest that the compound has expanded its band gap while maintaining its SHG response, compared to Te2O5. Theoretical calculations using the density functional theory have been also performed to clarify the structure-property relationship of the reported material more effectively.

Superior mechanical properties of multilayer covalent-organic frameworks enabled by rationally tuning molecular interlayer interactions

Two-dimensional (2D) covalent-organic frameworks (COFs) with a well-defined and tunable periodic porous skeleton are emerging candidates for lightweight and strong 2D polymeric materials. It remains challenging, however, to retain the superior mechanical properties of monolayer COFs in a multilayer stack. Here, we successfully demonstrated a precise layer control in synthesizing atomically thin COFs, enabling a systematic study of layer-dependent mechanical properties of 2D COFs with two different interlayer interactions. It was shown that the methoxy groups in COFTAPB-DMTP provided enhanced interlayer interactions, leading to layer-independent mechanical properties. In sharp contrast, mechanical properties of COFTAPB-PDA decreased significantly as the layer number increased. We attributed these results to higher energy barriers against interlayer sliding due to the presence of interlayer hydrogen bonds and possible mechanical interlocking in COFTAPB-DMTP, as revealed by density functional theory calculations.

Single-Layer 2D Ni-BDC MOF Obtained in Supercritical CO2 -Assisted Aqueous Solution.

The development of an efficient strategy for fabricating two-dimensional metal-organic framework (MOF) nanosheets with high yield and high stability is desirable. Herein, we demonstrate for the first time that large, single-layer 2D nickel-benzene dicarboxylate (Ni-BDC) MOF nanosheets can be fabricated with the assistance of supercritical (SC) CO2 in a pure aqueous system. Detailed experimental evidence reveals that the SC CO2 molecule can exchange with the lattice-coordinated H2 O molecules, side-on coordinate with the metal Ni1 sites on the Ni-BDC surface, and finally break the interlayer hydrogen bond to exfoliate the bulk Ni-BDC into a 2D MOF. More importantly, a thin SC CO2 layer building up at the water-Ni-BDC interfaces can transform the pristine hydrophilic interface into a super-hydrophobic one. This super-hydrophobic layer at the water-MOF interface can effectively prevent dissociation, thus promoting the stability of Ni-BDC in aqueous system.

Realizing Two-Electron Transfer in Ni(OH)2 Nanosheets for Energy Storage.

The theoretical capacity of a given electrode material is ultimately determined by the number of electrons transferred in each redox center. The design of multi-electron transfer processes could break through the limitation of one-electron transfer and multiply the total capacity but is difficult to achieve because multiple electron transfer processes are generally thermodynamically and kinetically more complex. Here, we report the discovery of two-electron transfer in monolayer Ni(OH)2 nanosheets, which contrasts with the traditional one-electron transfer found in multilayer materials. First-principles calculations predict that the first oxidation process Ni2+ → Ni3+ occurs easily, whereas the second electron transfer in Ni3+ → Ni4+ is strongly hindered in multilayer materials by both the interlayer hydrogen bonds and the domain H structure induced by the Jahn-Teller distortion of the Ni3+ (t2g6eg1)-centered octahedra. In contrast, the second electron transfer can easily occur in monolayers because all H atoms are fully exposed. Experimentally, the as-prepared monolayer is found to deliver an exceptional redox capacity of ∼576 mA h/g, nearly 2 times the theoretical capacity of one-electron processes. In situ experiments demonstrate that monolayer Ni(OH)2 can transfer two electrons and most Ni ions transform into Ni4+ during the charging process, whereas bulk Ni(OH)2 can only be transformed partially. Our work reveals a new redox reaction mechanism in atomically thin Ni(OH)2 nanosheets and suggests a promising path toward tuning the electron transfer numbers to multiply the capacity of the relevant energy storage materials.

CO2‐Induced 2D Ni‐BDC Metal–Organic Frameworks with Enhanced Photocatalytic CO2 Reduction Activity

AbstractThe rational design of 2D metal–organic framework (MOF) nanosheets with high active exposed surfaces and ultrathin thickness is a critical issue for CO2 reduction. How to fabricate 2D MOFs and simultaneously fulfill the strong adsorption and activation of CO2 molecules is a great challenge. Here, it is reported that CO2 molecules can help to fabricate single‐layer [Ni3(OH)2(1,4‐BDC)2‐(H2O)4]·2H2O, BDC = 1,4‐benzenedicarboxylate, (Ni‐BDC) MOF nanosheets with large sizes and uniform thickness by exchanging with the coordinated H2O molecules at Ni sites and further orientated chemically adsorption on it. CO2 molecules can not only help break the interlayer hydrogen bond of bulk materials realizing the successful transformation from 3D to 2D, but also contribute to expose the (200) planes with highly active in photocatalytic CO2‐to‐CO conversion, and a high production rate of 104 mmol g−1 h−1 and a high Faraday efficiency of 96.8% can be obtained. This strategy provides a novel prototypical model based on the strong interaction between metal active centers and reactive molecules to obtain 2D MOFs with high quality and activity.

Hydrothermal synthesis of hierarchical boehmite (γ-AlOOH) hollow microspheres with highly active surface

In this study, hierarchical boehmite (γ-AlOOH) hollow microspheres with highly active surface were prepared by hydrothermal synthesis. Scanning electron microscopy images showed that the hierarchical structure of the product was composed of hexagonal nanoflake units. Transmission electron microscopy images confirmed that the (010) plane was the main exposed surface of the crystal, and the ratio of the (010) plane to the total surface area of the crystal units was about 91.5%. The (010) plane of γ-AlOOH is occupied by hydroxyl groups with adsorption activity, which has a great influence on the adsorption performance of the materials. The possible mechanism of the product was proposed. Cetyltrimethylammonium bromide, which was used as the structure inducer, broke the interlayer hydrogen bonds of γ-AlOOH. As a result, the separated layers of the crystal formed thin flake-like structure units. The (010) crystal surface, which was usually caught between the lattice layers, could be exposed on the surface with this unique morphology. The N2 adsorption–desorption experiment showed that the specific surface area of the as-synthesized product was 43.5 m2 g−1. The adsorption capacity test revealed that γ-AlOOH hollow microspheres had an excellent adsorption performance, namely, the maximum adsorption capacity of the product for Congo red is 110 mg g−1.

Three-Dimensional MOFs@MXene Aerogel Composite Derived MXene Threaded Hollow Carbon Confined CoS Nanoparticles toward Advanced Alkali-Ion Batteries.

MXene combining high metal-like conductivity, high hydrophilicity, and abundant surface functional groups has been recognized as a class of versatile two-dimensional materials for many applications. However, the aggregation of MXene nanosheets from interlayer van der Waals force and hydrogen bonds represents a major problem that severely limits their practical use. Here, we report an aerogel structure of MOFs@MXene, in which the in situ formed MOF particles can effectively prevent the accumulation of MXene, enabling a three-dimensional (3D) hierarchical porous conductive network to be composed with an ultralight feature. Subsequently, a 3D porous MXene aerogel threaded hollow CoS nanobox composite ((CoS NP@NHC)@MXene) derived from the MOFs@MXene aerogel precursor was synthesized, and the highly interconnected MXene network and hierarchical porous structure coupled with the ultrafine nanocrystallization of the electrochemically active phase of CoS yield the hybrid system with excellent electron and ion transport properties. Benefiting from the synergistic effect of the components, the (CoS NP@NHC)@MXene composite manifests outstanding electrochemistry properties as electrode materials for all of the lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs). It demonstrated the excellent cycle stability and high capacities of 1145.9 mAh g-1 at 1 A g-1 after 800 cycles and 574.1 mAh g-1 at 5 A g-1 after 1000 cycles for LIBs, 420 mAh g-1 at 2 A g-1 after 650 cycles for SIBs, and 210 mAh g-1 at 2 A g-1 after 500 cycles for PIBs. First-principle calculations confirmed that the (CoS NP@NHC)@MXene hybrid could enhance the charge transfer reaction kinetics, particularly at the interface. More importantly, the excellent rate performance under high mass loading and the high volumetric energy and power density of the entire electrode represent the potential of (CoS NP@NHC)@MXene composites for applications to practical electrochemical energy storage devices. The synthesis method reported in this Article is versatile and can be easily extended to produce other porous MXene-aerogel-based materials for various applications.

Synthesis of layered double hydroxide nanosheets in an aqueous solvent and their Ni2+ uptake characteristics

Two-dimensional (2D) nanomaterials have drawn widespread attention because of their unique physical characteristics compared to three-dimensional materials. Delamination and nanosheet formation of layered composites are necessary for 2D nanomaterials. Layered double hydroxides (LDH) exhibit anion exchange properties that can be maximized using different methods such as organic modifications and crystal growth control; delamination is one such method. Delamination of LDH render them in the form of nanosheets, which could not be expressed as interlayers, allowing them to exhibit physical properties completely different from those of bulk LDH. Herein, we propose a novel synthesis method to delaminate LDH in an aqueous solvent. In this method, heat reflux is used to break interlayer hydrogen bonds in the LDH, and the remaining hydrogen bonds are broken using ultrasonic treatment. Finally, we dispersed the material in the solvent to obtain LDH nanosheets. We compared the delamination of MgAl LDH intercalated with lactate (lactate•Mg–Al LDH) and MgAl LDH intercalated with NO3− (NO3·Mg–Al LDH) in an aqueous solvent. Furthermore, we used the nanosheets obtained from NO3·Mg–Al LDH and described their Ni2+ uptake characteristics. Our results show that without using organic solvents, we could delaminate lactate•Mg–Al LDH and NO3·Mg–Al LDH by applying the proposed method. The lactate•Mg–Al LDH had approximately ten MgAl LDH host layers, whereas the corresponding nanosheets had three MgAl LDH host layers. NO3·Mg–Al LDH had 14–15 Mg–Al LDH host layers, whereas the corresponding nanosheets had 2–3 Mg–Al LDH host layers. Furthermore, NO3·Mg–Al LDH and its nanosheets could adsorb Ni2+ in an aqueous solvent. Thus, Ni2+ uptake capabilities were enhanced by delaminating NO3·Mg–Al LDH to fabricate nanosheets.

Quantum paraelectricity in the Kitaev quantum spin liquid candidates H3LiIr2O6 and D3LiIr2O6

H3LiIr2O6 is the first honeycomb-lattice system without any signs of long-range magnetic order down to the lowest temperatures, raising the hope for the realization of an ideal Kitaev quantum spin liquid. Its honeycomb layers are coupled by interlayer hydrogen bonds. Static or dynamic disorder of these hydrogen bonds was proposed to strongly affect the magnetic exchange and to make Kitaev-type interactions dominant. Using dielectric spectroscopy, here we provide experimental evidence for dipolar relaxations in H3LiIr2O6 and deuterated D3LiIr2O6, which mirror the dynamics of protons and deuterons within the double-well potentials of the hydrogen bonds. The detected hydrogen dynamics reveals glassy freezing, characterized by a strong slowing down under cooling, with a crossover from thermally-activated hopping to quantum-mechanical tunneling towards low temperatures. Thus, besides being Kitaev quantum-spin-liquid candidates, these materials also are quantum paraelectrics. However, the small relaxation rates in the mHz range, found at low temperatures, practically realize quasi-static hydrogen disorder, as assumed in recent theoretical works to explain the quantum-spin-liquid ground state of both compounds.

Features of the Structural Organization and Sorption Properties of Cellulose

An improved model of the layered structure of cellulose microfibrils is proposed, taking into account the presence of slit-like pores between its structural elements. The scheme of the formation of donoracceptor intramolecular, intermolecular and interlayer hydrogen bonds of one glucopyranose unit in the cellulose crystallite is presented. The mechanism of specific adsorption interactions of water molecules in a monolayer with active centers located on the hydrophilic surfaces of elementary fibrils is described. The energy of dipole-dipole interactions was calculated depending on the distance between the active center and the adsorbate water molecule. The thermodynamic parameters characterizing the state of the adsorbate in the adsorption layers are determined by the proton magnetic relaxation method and sorption measurements. The possibility of determining the net heat of adsorption in a bilayer taking into account the Arrhenius nature of the correlation times of the thermal molecular motions of the adsorbate was established. An increase in the entropy of adsorbed water during the adsorption process was revealed. It was found that during adsorption, a part of the inner regions of crystallites transitions to their surface with the participation of cellulose hydroxyl groups, and during desorption, the reverse process is observed.

Strong hydrogen bonding in a dense hydrous magnesium silicate discovered by neutron Laue diffraction.

A large amount of hydrogen circulates inside the Earth, which affects the long-term evolution of the planet. The majority of this hydrogen is stored in deep Earth within the crystal structures of dense minerals that are thermodynamically stable at high pressures and temperatures. To understand the reason for their stability under such extreme conditions, the chemical bonding geometry and cation exchange mechanism for including hydrogen were analyzed in a representative structure of such minerals (i.e. phase E of dense hydrous magnesium silicate) by using time-of-flight single-crystal neutron Laue diffraction. Phase E has a layered structure belonging to the space group R 3 m and a very large hydrogen capacity (up to 18% H2O weight fraction). It is stable at pressures of 13-18 GPa and temperatures of up to at least 1573 K. Deuterated high-quality crystals with the chemical formula Mg2.28Si1.32D2.15O6 were synthesized under the relevant high-pressure and high-temperature conditions. The nuclear density distribution obtained by neutron diffraction indicated that the O-D dipoles were directed towards neighboring O2- ions to form strong interlayer hydrogen bonds. This bonding plays a crucial role in stabilizing hydrogen within the mineral structure under such high-pressure and high-temperature conditions. It is considered that cation exchange occurs among Mg2+, D+ and Si4+ within this structure, making the hydrogen capacity flexible.

Atomic-level insights into nano-salt droplets wetting on the MgO surface using molecular dynamics simulations

The effects of NaCl solution concentrations on the water wettability of the MgO surface have been studied using molecular dynamics simulations. We find that ion hydration has a strong ability to dominate the structure of water network in the hydration layer. It can transform the orientation of water OH bonds, and reconstruct an ordered water network in the first layer, which in turn reduces the density of inter-layer hydrogen bonds. This further results in weak interactions between the first hydration layer and the actual droplet above the hydration layer, eventually increasing the hydrophobicity of the MgO(001) surface and corrosion resistance.

Exploring the Anomalous Phase Behavior of High-Pressure Ices in Diamond Confinement

Inspired by the discovery of high-pressure ice inclusions in diamond, we investigate the rich structural diversity of high-pressure phases of quasi-two-dimensional water constrained by diamond matrices, using molecular dynamics simulations. Monolayer ices formed are structurally similar to monolayer ices constrained by graphene. We report new bilayer and trilayer ice phases, specifically, the AB II, ABC I, ABC II, and AAB/ABB ordered phases. The relative stability of the interlayer hydrogen bonds between adjacent layers reveals differences in structural properties. We observe grain-boundary migration between pockets of AAB and ABB ices, during the pressurization process. The compression-limit phase diagram in the slit width–lateral pressure plane has been constructed and analyzed. Our results indicate that the phase behavior of confined ice is qualitatively independent of the diamond–water force-field parameters and is significantly influenced by the lattice structure and geometry of the confining surfaces.