Premelting Layer Research Articles

Molecular dynamics characterization of the interfacial structure and forces of the methane-ethane sII gas hydrate interface

The nucleation of gas hydrates is of great interest in flow assurance, global energy demand, and carbon capture and storage. A complex molecular understanding is critical to control hydrate nucleation and growth in potential applications. Molecular dynamics is employed combined with the mechanical definition of surface tension to assess the surface stresses controlling interfacial behavior. We characterize the interfacial tension for sII methane/ethane hydrate and gas mixtures for different temperatures and pressures. We find that the surface tension trends positively with temperature in a balance of water-solid and water-gas interactions. The molecular dipole shows the complexities of water molecule behavior in small, compressed pre-melting layer that emerges as a quasi-liquid. These behaviors contribute to the developing knowledge base surrounding practical applications of this interface.

Exploring the Premelting Transition through Molecular Simulations Powered by Neural Network Potentials

The premelting layer on crystal surfaces significantly affects the stability, surface reactivity, and phase transition behaviors of crystals. Traditional methods for studying this layer—experimental techniques, classical simulations, and even first-principle simulations—have significant limitations in accuracy and scalability. To overcome these challenges, we employ molecular dynamic simulations based on neural network potentials to investigate the structural and dynamic behavior of the premelting layer on ice. This approach matches the accuracy of first-principle calculations while greatly improving computational efficiency, allowing us to simulate the ice–vapor interface on a much larger scale. In this study, we conducted a one-nanosecond simulation of the ice–vapor interface involving 1024 water molecules. This significantly exceeds the time and size scales of previous first-principle studies. Our simulation results indicate complete surface melting. Furthermore, our simulation results reveal dynamic heterogeneity within the premelting layer, with molecules segregated into clusters of low and high mobility.

The improvement of hydrogen storage capacity via bubbles nucleated in ice-like nanotubes

The existing methods of hydrogen storage bottlenecked advancements in its commercialization on an industrial scale. Here, the hydrogen storage capacity via the hydrogen clathrate hydrate in ice Ih (HCHinIh) with the aid of nanobubbles is further improved to 3.442–3.494 wt% from the previous 3.441 wt%. These nanobubbles are designedly arranged within 0.5 mm diameter individual ice spheres which initially pack in simple cubic form, and then used to synthesize the hydrogen clathrate hydrate as does HCHinIh. The total volume of nanobubbles is adjustable by deploying their different space layouts. In addition, we propose that the bubble formation is driven by transforming the pre-melted quasi-liquid layer (PMQLL) to solid ice-like in an ice-like nanotube, which is a structure comprised of PMQLL and ice surrounding PMQLL (PMQLL-ice) analogous to a carbon nanotube-graphene sheet (CNT-GS) structure, where the interaction energy related to O–O and O–H in PMQLL-ice is 0.08–6.17 times that of C–O and C–H in the CNT-GS structure.

Enhancing the strength of the PCBN/M42 joint via a solid solution brazed seam design involving a pre-melted CuNi layer and a Ti interlayer

We present a two-step method to achieve high-strength PCBN-M42 joints by employing a pre-melted CuNi layer combined with a Ti interlayer. Reliable interface bonding with PCBN is established through the Cu-Ni-Ti eutectic reaction while effectively retaining a considerable solid solution content within the joint, thus significantly enhancing the joint strength.

A close look at the hydration layer and at the premelting layer of K-feldspar

In this work, we perform molecular dynamics simulations to investigate the structural properties of water at the interface with K-feldspar. We aim at understanding the modifications induced on water structure by the presence of this mineral. We analysed both the hydration layer of K-feldspar in supercooled water and the premelting layer at the interface between K-feldspar and hexagonal ice. We studied the density profile, the orientational tetrahedral order parameter, the distribution of the cos ⁡ ( γ ) function, the hydrogen bond distribution, the number of water molecules belonging to different phases close to the surface of the feldspar. We focused on the interplay between high-density water and low-density water to inquire on local modifications of water structure with respect to the bulk phase. We investigated four different pressures where the structure of bulk water spans from high-density liquid (locally more disordered) to low-density liquid (locally more ordered). The investigation showed that both the hydration and the premelting layers present a low-density liquid water component and similarities as a function of pressure with the corresponding bulk. We also find that the premelting layer shows structural features intermediate between the liquid and the crystalline state acting as a matching layer.

Are bubbles in ice the potential space for hydrogen storage?

A major challenge in hydrogen storage is to achieve higher storage capacity, simpler storage technology, less capital cost, lower storage risk, and near zero-carbon emissions. Here, we suggested that bubbles formed in the ice provide the potential space for hydrogen storage as needs. Further, we proposed a coupled mechanism of the supercooled pre-melted quasi-liquid layer to thermoelectric force under a temperature gradient for explaining the bubble formation in ice, based on both diverse laboratory experiments from the firn specimens at different stresses and temperatures and related assumption of thermoelectric effect. As a result, the size of the bubble nucleated was estimated to be 5.8–7 nm. Nanobubbles strengthen the role of the pressure booster of bubbles for improving the hydrogen storage capacity via the hydrogen clathrate hydrate (HCH). Additionally, the post-nucleation growth of nanobubbles in ice from 5.8 to 7 nm to ∼13.8 ± 3.3 μm likely connects the molecular to geological hydrogen storages. Lastly, this work is helpful to design and develop 3-D printed programmable bubble-born cryo-materials coupled to other hydrogen storage systems, e.g. the HCH.

Distinguishing the glass, crystal, and quasi-liquid layer in 1-methylnaphthalene by using fluorescence signatures

The fluorescence of crystalline 1-methylnaphthalene is monomer-like, while liquid and glass exhibit excimeric emissions. We detail the temperature dependence of the fluorescence emission and excitation spectra in the range of between 77 K and 295 K. These spectra provide exhaustive information about the state and temperature of 1-methylnaphthalene. The glass, formed by abrupt quenching in liquid nitrogen or methane, devitrifies at (155 ± 5) K, and the liquid then undergoes cold crystallization at around 170 K. In 1-methylnaphthalene crystals, an excimeric emission appears at approximately 40 K below the melting point, a process we ascribe to the formation of dimers due to surface premelting; such a quasi-liquid layer exists at the surface well below the freezing point, remaining uncrystallized. The premelted layer is clearly distinguishable from the bulk glass via fluorescence spectroscopy, which facilitates state identification.

Ice friction at the nanoscale

The origin of ice slipperiness has been a matter of great controversy for more than a century, but an atomistic understanding of ice friction is still lacking. Here, we perform computer simulations of an atomically smooth substrate sliding on ice. In a large temperature range between 230 and 266 K, hydrophobic sliders exhibit a premelting layer similar to that found at the ice/air interface. On the contrary, hydrophilic sliders show larger premelting and a strong increase of the first adsorption layer. The nonequilibrium simulations show that premelting films of barely one-nanometer thickness are sufficient to provide a lubricating quasi-liquid layer with rheological properties similar to bulk undercooled water. Upon shearing, the films display a pattern consistent with lubricating Couette flow, but the boundary conditions at the wall vary strongly with the substrate's interactions. Hydrophobic walls exhibit large slip, while hydrophilic walls obey stick boundary conditions with small negative slip. By compressing ice above atmospheric pressure, the lubricating layer grows continuously, and the rheological properties approach bulk-like behavior. Below 260 K, the equilibrium premelting films decrease significantly. However, a very large slip persists on the hydrophobic walls, while the increased friction on hydrophilic walls is sufficient to melt ice and create a lubrication layer in a few nanoseconds. Our results show that the atomic-scale frictional behavior of ice is a combination of spontaneous premelting, pressure melting, and frictional heating.

Interfacial and volumetric melting regimes of Sn nanoparticles

A thermodynamically consistent phase field formulation was developed to describe what has been historically known as the premelted surface layer in Sn nanoparticles. Two interfacial phases were identified: 1) a disordered interfacial phase, i.e., the experimentally observed premelted surface layer; and 2) an ordered surficial phase displaying a remnant degree of order in fully melted particles. A volumetric partially disordered particle core is predicted to exist for small particle sizes, r<7 nm. Four regimes of behavior are discussed: a) the classic premelting regime, for r≳20 nm, in which the surface of the particle forms a liquid shell at temperatures below melting with clear delineation between the solid core and the premelted surficial liquid shell, as traditionally expected; b) the transition regime, for 5<r<20 nm, in which the volumetric chemical potential and interfacial forces balance each other out; c) the disordered volume phase regime, for r≤5 nm, in which a disordered interphase dominates the thermodynamic equilibrium of the system resulting in a partially crystalline core, and d) the mesoscale regime, in which the nanoparticles are no longer considered crystalline and experience an associated decrease in latent heat.

Interior Melting of Rapidly Heated Gold Nanoparticles.

Normal melting invariably starts from surfaces or interfaces due to the weaker bonding constraints in these regions. However, we show that melting can be initiated from the interior of gold nanoparticles with high heating rates. We find that melting starts from the surface with the formation of a premelting layer, as usual, but that the premelting layer does not extend to the interior under certain conditions. Instead, liquid nucleation occurs in the core of the nanoparticle. This unexpected interior melting is connected to the slower melting kinetics, which is related to heat transfer near the premelted surface. The required conditions for interior melting are a suitable size of the nanoparticle and a sufficiently fast heating rate. The present results point to a novel melting regime in nanoparticles. We note that the time scales are now accessible using ultrafast tools such as X-ray lasers that can probe dynamical structure changes, suggesting opportunities for experiments.

Interface migration in aluminum bicrystals via premelting

We investigate solid-solid phase transformation and migration of interface between ambient and strained crystal of Al using molecular dynamics simulation by means of premelting. In agreement with previous observations both Al(100) and Al(110) exhibit premelting near melting temperature and strain enhance the thickness of melt irrespective to sign. In bicrystal of Al, if one of crystal is subjected to strain then internal stresses completely relax during premelting and additionally provides thermodynamic driving force. This melt recrystallise into ambient crystal in pico seconds. The propagating interface velocity as function of temperature and strain both are quantitatively measured. Two types of interface propagation is observed, for thin interfacial melt (two times of lattice constant or less) interface migration is not continuous it is stickslip and stochastic, and for thick premelted layer interface migration is barrier less. The results obtained are applicable to many structural changes like grain evolution, twinning, fracture and dislocations, phase transformation such as melting-solidification and solid-solid.

Water Mobility in the Interfacial Liquid Layer of Ice/Clay Nanocomposites.

At solid/ice interfaces, a premelting layer is formed at temperatures below the melting point of bulk water. However, the structural and dynamic properties within the premelting layer have been a topic of intense debate. Herein, we determined the translational diffusion coefficient Dt of water in ice/clay nanocomposites serving as model systems for permafrost by quasi‐elastic neutron scattering. Below the bulk melting point, a rapid decrease of Dt is found for charged hydrophilic vermiculite, uncharged hydrophilic kaolin, and more hydrophobic talc, reaching plateau values below −4 °C. At this temperature, Dt in the premelting layer is reduced up to a factor of two compared to supercooled bulk water. Adjacent to charged vermiculite the lowest water mobility was observed, followed by kaolin and the more hydrophobic talc. Results are explained by the intermolecular water interactions with different clay surfaces and interfacial segregation of the low‐density liquid water (LDL) component.

Ion Dissociation Dynamics in an Aqueous Premelting Layer.

Using molecular dynamics simulations and methods of importance sampling, we study the thermodynamics and dynamics of sodium chloride in the aqueous premelting layer formed spontaneously at the interface between ice and its vapor. We uncover a hierarchy of time scales that characterize the relaxation dynamics of this system, spanning the picoseconds of ionic motion to the tens or hundreds of nanoseconds associated with fluctuations of the liquid-crystal interface in their presence. We find that ions distort both local interfaces, incurring restoring forces that result in the ions preferentially residing in the middle of the layer. While ion pair dissociation is thermodynamically favorable, these structural and dynamic effects cause its rate to vary by over an order of magnitude through the layer, with a maximum rate significantly depressed from the corresponding bulk value. The solvation environment of ions in the premelting layer is distinct from that in a bulk liquid, being dominated by slow reorganization of water molecules and a water structure intermediate between ice and its melt.

Alloy amorphization through nanoscale shear localization at Al-Fe interface

Achieving reliable metallic bonding directly between steel and aluminum alloys has a broad societal impact on sustainability from transportation systems to space exploration and biomedical devices. This is because steel and aluminum alloys are the top two most available and widely used metals. However, the development of detrimental intermetallic compounds (IMCs) at the Al-Fe interface has frustrated researchers and engineers for decades. Here, we present a new mechanism on how a nanoscale amorphous layer can be introduced at the Al-Fe interface without undesirable IMC: (i) a rapid sliding at the Al-Fe interface can generate a nanoscale premelting layer, leading to nanoscale shear localization; (ii) the resulting high shear strain rate within the premelting layer is high enough to suppress crystallization; (iii) as long as sufficiently high shear strain rate can be sustained within the premelting layer until the interfacial temperature is low enough, a stable amorphous can be retained without relying on rapid solidification. The findings provide a mechanistic basis for devising novel alloy amorphization and dissimilar metal joining techniques.

Premelting-Induced Agglomeration of Hydrates: Theoretical Analysis and Modeling.

Resolving the long-standing problem of hydrate plugging in oil and gas pipelines has driven an intense quest for mechanisms behind the plug formation. However, existing theories of hydrate agglomeration have critical shortcomings, for example, they cannot describe nanometer-range capillary forces at hydrate surfaces that were recently observed by experiments. Here, we present a new model for hydrate agglomeration which includes premelting of hydrate surfaces. We treat the premelting layer on hydrate surfaces such as a thin liquid film on a substrate and propose a soft-sphere model of hydrate interactions. The new model describes the premelting-induced capillary force between a hydrate surface and a pipe wall or another hydrate. The calculated adhesive force between a hydrate sphere (R = 300 μm) and a solid surface varies from 0.3 mN on a hydrophilic surface (contact angle, θ = 0°) to 0.008 mN on a superhydrophobic surface (θ = 160°). The initial contact area is 4 orders of magnitude smaller than the cross-sectional area of the hydrate sphere and can expand with increasing contact time because of the consolidation of hydrate particles on the solid surface. Our model agrees with the available experimental results and can serve as a conceptual guidance for developing a chemical-free environmentally friendly method for prevention of hydrate plugs via surface coating of pipe surfaces.

Ice premelting layer of ice-rubber friction studied using resonance shear measurement.

We performed a resonance shear measurement (RSM) based on a low-temperature surface force apparatus to evaluate the frictional properties of the interface between butadiene rubber and ice at various temperatures below 0 °C. Friction between the rubber and ice was high and constant at temperatures below -5 °C, but sharply decreased when the temperature rose above -5 °C. We performed the same measurement by replacing the rubber with polystyrene and silica films which were rigid and exhibited practically minimal elastic deformation in comparison to the rubber. The friction decreased gradually with the increase in temperature from -20 °C to 0 °C at both the polystyrene-ice and the silica-ice interfaces. These results indicated that the elasticity of rubber was responsible for the differences in the rubber-ice interface and the other two samples. To understand the detailed mechanism of friction between the rubber and the ice, we analyzed the obtained RSM data using a physical model. The result indicated that the friction between ice and rubber was determined by the elastic deformation of the rubber film at temperatures below -5 °C, and by the viscosity of the ice premelting layer above -5 °C.

Ice Premelting Layer Studied by Resonance Shear Measurement (RSM).

The viscosity of the ice premelting layer in contact with silica in the temperature range of -18 to -1 °C was studied by resonance shear measurement (RSM). The viscosity of the ice premelting layer was determined to be ∼5 orders of magnitude greater than that of the bulk liquid water and continuously decreased with the increasing sliding speed between the two surfaces over the temperature range employed in this study, which was the same behavior as for the typical confined liquids including water. On the other hand, the normal load and the contact pressure did not influence the viscosity, indicating that the premelting layer behaved differently from the typical confined liquids.

Surface premelting of water ice

Frozen water has a quasi-liquid layer at its surface that exists even well below the bulk melting temperature; the formation of this layer is termed premelting. The nature of the premelted surface layer, its structure, thickness and how the layer changes with temperature have been debated for over 160 years, since Faraday first postulated the idea of a quasi-liquid layer on ice. Here, we briefly review current opinions and evidence on premelting at ice surfaces, gathering data from experiments and computer simulations. In particular, spectroscopy, microscopy and simulation have recently made important contributions to our understanding of this field. The identification of premelting inhomogeneities, in which portions of the surface are quasi-liquid-like and other parts of the surface are decorated with liquid droplets, is an intriguing recent development. Untangling the interplay of surface structure, supersaturation and surface defects is currently a major challenge. Similarly, understanding the coupling of surface structure with reactivity at the surface and crystal growth is a pressing problem in understanding the behaviour and formation of ice on Earth. A quasi-liquid layer on the surface of ice makes it slippery even below the bulk melting temperature. The nature of this premelted layer has long been debated, and this Review gathers experimental and theoretical data and discusses opinions and evidence on premelting at ice surfaces.

Interfacial premelting of ice in nano composite materials.

The interfacial premelting in ice/clay nano composites was studied by high energy X-ray diffraction. Below the melting point of bulk water, the formation of liquid water was observed for the ice/vermiculite and ice/kaolin systems. The liquid fraction is gradually increasing with temperature. For both minerals, similar effective premelting layer thicknesses of 2-3 nm are reached 3 K below the bulk melting point. For the quantitative description of the molten water fraction in wet clay minerals we developed a continuum model for short range interactions and arbitrary pore size distributions. This model quantitatively describes the experimental data over the entire temperature range. Model parameters were obtained by fitting using a maximum entropy (MaxEnt) approach. Pronounced differences in the deviation from Antonow's rule relating interfacial free energy between ice, water, and clay are observed for the charged vermiculite and uncharged kaolin minerals. The resultant parameters are discussed in terms of their ice nucleation efficiency. Using well defined and characterized ice/clay nano composite samples, this work bridges the gap between studies on single crystalline ice/solid model interfaces and naturally occurring soils and permafrost.

Why Is It So Difficult to Identify the Onset of Ice Premelting?

Premelting of ice at temperatures below 0 °C is of fundamental importance for environmental processes. Various experimental techniques have been used to investigate the temperature at which liquid-likewaterfirst appears at the ice-vapor interface, reporting onset temperatures from -160 to -2 °C. The signals that identify liquid-likeorderat the ice-vapor interface in these studies, however, do not show a sharp initiation with temperature. That is at odds with the expected first-order nature of surface phase transitions, and consistent with recent large-scale molecular simulations that show the first premelted layer to be sparse and to develop continuously over a wide range of temperatures. Here we perform a thermodynamic analysis to elucidate the origin of the continuous formation of the first layer of liquid at the ice-vapor interface. We conclude that a negative value of the line tension of the ice-liquid-vapor three-phase contact line is responsible for the continuous character of the transition and the sparse nature of the liquid-like domains in the incomplete first layer.