Quasi-liquid Layer Research Articles

Investigation on the Adhesion Force between Tetrabutylammonium Bromide Hydrate Particles Using Atomic Force Microscopy.

This work investigates the adhesion force between tetrabutylammonium bromide (TBAB) hydrate particles dispersed in decane at different temperatures and TBAB concentrations using an atomic force microscopy. The thickness of the quasi-liquid layer (QLL) on the surface of the hydrate particles is calculated based on an adhesion force model. The results of force measurements indicate that the adhesion force between the hydrate particles increases with increasing temperature when TBAB concentration is 30 wt %. The increment of adhesion force between particles could be due to the increase in the QLL thickness on the particle surfaces. Furthermore, the force results also reveal that the adhesion force between hydrate particles(ice) at 253 K decreases when TBAB concentration increases from 0 to 30 wt %. The calculation indicates that QLL on the surface of formed hydrate particles becomes thinner at higher TBAB concentrations, which could be due to the conversion rate of water to hydrate within particles. The thickness of QLL is directly influenced by the temperature and TBAB concentration, which contributes to the adhesion force between hydrate particles.

Innovative ice mitigation: Exploring the potential of choline-based deep eutectic solvents and ionic liquids synergies

The development of anti-icing coatings for extremely low temperatures is still emerging. Deep eutectic solvents (DESs), as subset of ionic liquid (IL) analogues, have recently gained increasing attention for their unique and versatile applications. Given no investigation regarding anti-icing capabilities of DESs, our study focused on the exciting potential of choline-based DESs. The intriguing potential of hydrogen bonding through the synergistic combination of DESs and ILs offers significant promise for innovative solutions to ice-related challenges that remain largely unexplored. We conducted a comprehensive study on the anti-freezing properties of DESs by synthesizing choline-based ILs featuring both hydrophilic and hydrophobic anions. We aimed to explore how the diverse hydrogen-bond donors in DESs combined with the synthesized ILs to enhance the system’s ability to prevent ice formation. Substituting ethylene glycol (EG) with glycerol (GL) resulted in achieving an ice formation temperature of − 36 °C and an exceptionally low ice adhesion strength of 10 kPa, due to a thicker quasi-liquid layer on the coating surface, confirmed by solid-state NMR spectroscopy. The altered frost formation patterns of the DES-containing coatings demonstrated an enhance resistance against frost formation. This comprehensive study underscored the promising synergy between DESs and ILs for highly effective ice mitigation.

Is it possible to overheat ice? The activated melting of TIP4P/Ice at solid–vapour coexistence.

A widely accepted phenomenological rule states that solids with free surfaces cannot be overheated. In this work we discuss this statement critically under the light of the statistical thermodynamics of interfacial roughening transitions. Our results show that the basal face of ice as described by the TIP4P/Ice model can remain mechanically stable for more than one hundred nanoseconds when overheated by 1 K, and for several hundreds of nanoseconds at smaller overheating despite the presence of a significant quasi-liquid layer at the surface. Such time scales, which are often of little experimental significance, can become a concern for the determination of melting points by computer simulations using the direct coexistence method. In the light of this observation, we reinterpret computer simulations of ice premelting and show that current results for the TIP4P/Ice model all imply a scenario of incomplete surface melting. Using a thermodynamic integration path, we reassess our own estimates for the Laplace pressure difference between water and vapour. These calculations are used to measure the disjoining pressure of premelting liquid films and allow us to confirm a minimum of the interfacial free energy at finite premelting thickness of about one nanometer.

Enhancing Icephobic Coatings: Exploring the Potential of Dopamine-Modified Epoxy Resin Inspired by Mussel Catechol Groups.

A nature-inspired approach was employed through the development of dopamine-modified epoxy coating for anti-icing applications. The strong affinity of dopamine's catechol groups for hydrogen bonding with water molecules at the ice/coating interface was utilized to induce an aqueous quasi-liquid layer (QLL) on the surface of the icephobic coatings, thereby reducing their ice adhesion strength. Epoxy resin modification was studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR). The surface and mechanical properties of the prepared coatings were studied by different characterization techniques. Low-temperature ATR-FTIR was employed to study the presence of QLL on the coating's surface. Moreover, the freezing delay time and temperature of water droplets on the coatings were evaluated along with push-off and centrifuge ice adhesion strength to evaluate their icephobic properties. The surface of dopamine-modified epoxy coating presented enhanced hydrophilicity and QLL formation, addressed as the main reason for its remarkable icephobicity. The results demonstrated the potential of dopamine-modified epoxy resin as an effective binder for icephobic coatings, offering notable ice nucleation delay time (1316 s) and temperature (-19.7 °C), reduced ice adhesion strength (less than 40 kPa), and an ice adhesion reduction factor of 7.2 compared to the unmodified coating.

Effect of Shear Loading Conditions on the Measured Strength of Ice Adhesion to Superhydrophobic Surfaces

Despite the significant interest of researchers, icing of aircraft, vehicles, ships, and equipment of offshore oil structures remains to be an urgent problem. This paper considers the factors that promote a decrease in the strength of the contact between ice and surfaces under an applied shear load. The main attention is focused on studying the influence of the rate of shear loading on the fracture of the interfacial contact between ice and superhydrophobic coatings. The strength of the adhesive contact under the conditions of controlled variations in the applied load is measured using a technique based on the detachment of ice from a surface under the influence of centrifugal force. The study is carried out for large ensembles of samples in the temperature range from −5 to −20°C, thereby making it possible to evaluate the influence of the quasi-liquid layer and the Rehbinder effect on a decrease in the shear adhesive strength. The results obtained indicate that the contact between ice and a superhydrophobic coating is fractured through a mixed viscous–brittle mechanism. In this case, a decrease in temperature or an increase in the loading rate causes a transition from the viscous to the brittle fracture. These results indicate a potential acceleration of ice shedding with an increase in the growth rate of the shear stress.

In-layer inhomogeneity of molecular dynamics in quasi-liquid layers of ice

Quasi-liquid layers (QLLs) are present on the surface of ice and play a significant role in its distinctive chemical and physical properties. These layers exhibit considerable heterogeneity across different scales ranging from nanometers to millimeters. Although the formation of partially ice-like structures has been proposed, the molecular-level understanding of this heterogeneity remains unclear. Here, we examined the heterogeneity of molecular dynamics on QLLs based on molecular dynamics simulations and machine learning analysis of the simulation data. We demonstrated that the molecular dynamics of QLLs do not comprise a mixture of solid- and liquid water molecules. Rather, molecules having similar behaviors form dynamical domains that are associated with the dynamical heterogeneity of supercooled water. Nonetheless, molecules in the domains frequently switch their dynamical state. Furthermore, while there is no observable characteristic domain size, the long-range ordering strongly depends on the temperature and crystal face. Instead of a mixture of static solid- and liquid-like regions, our results indicate the presence of heterogeneous molecular dynamics in QLLs, which offers molecular-level insights into the surface properties of ice.

From theory to application: Innovative ice-phobic polyurethane coatings by studying material parameters, mechanical insights, and additives

This investigation introduces new insights into the influence of material parameters on the anti-icing properties of polyurethane (PU) coatings, encompassing chemical characteristics, cross-link densities, mechanical analysis, and additive diversity. To comprehensively address these aspects, a meticulous exploration was conducted to delve into the effects of these parameters on wettability and icephobicity. To fabricate the PU coatings, three distinct acrylic polyols with various hydroxyl content along with two widely employed aliphatic isocyanates boasting diverse %NCO values were utilized. By employing stoichiometric and non-stoichiometric ratios, an array of coatings with different crosslink densities and mechanical properties was fabricated. The principal influence of crosslink density alterations in PU coatings on ice nucleation temperature and ice adhesion strength emerged distinctly, underpinned by the establishment of hydrogen bonds between water molecules and polar functional groups within the coating, coupled with the appearance of a quasi-liquid layer (QLL). The mechanical properties, wettability characteristics, and surface roughness of the coatings were examined and it was clearly demonstrated that Young's modulus and physicochemical properties play significant roles in the characteristics of ice adhesion strength. In particular, lower Young's modulus in the samples was associated with reduced ice adhesion, albeit with compromised durability. In the next step of this investigation, the matrix demonstrating optimal mechanical properties and icephobicity was subjected to surface energy adjustment. This was accomplished by introducing various concentrations of both fluorinated and non-fluorinated additives. This adjustment led to a significant reduction of ice adhesion strength, measuring less than 100 Kpa as an icephobic PU coating. Nevertheless, it was observed that the effectiveness of the fluorinated additives diminished after repetitive icing-deicing cycles, while the non-fluorinated additive maintained its influence on ice adhesion strength even after numerous cycles. The interplay between material attributes, mechanical properties, and additive influences has been meticulously unraveled, charting a course for further advancements in the pursuit of robust icephobic coating.

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.

A Molecular Dynamics Analysis of the Thickness and Adhesion Characteristics of the Quasi-Liquid Layer at the Asphalt-Ice Interface.

The quasi-liquid layer (QLL), a microstructure located between ice and an adhering substrate, is critical in generating capillary pressure, which in turn influences ice adhesion behavior. This study employed molecular dynamics (MD) methods to obtain QLL thickness and utilized these measurements to estimate the adhesive strength between ice and asphalt. The research involved constructing an ice-QLL-asphalt MD model, encompassing four asphalt types and five temperature ranges from 250 K to 270 K. The QLL thickness was determined for various asphalts and temperatures using the tetrahedral order parameter gradient. Additionally, capillary pressure was calculated based on the QLL thickness and other geometric parameters obtained from the MD analysis. These findings were then compared with ice adhesion strength data acquired from pull-off tests. The results indicate that QLL thickness varies with different asphalt types and increases with temperature. At a constant temperature, the QLL thickness decreases in the order of the basal plane, primary prism plane, and secondary prism plane. Furthermore, the adhesion strength of the QLL diminishes as the temperature rises, attributed to the disruption of hydrogen bonds at lower temperatures. The greater the polarity of the asphalt's interface molecules, the stronger the adhesion strength and binding free energy. The MD simulations of the asphalt-ice interface offer insights into the atomic-scale adhesive properties of this interface, contributing to the enhancement in QLL property prediction and calibration at larger scales.

Precisely Controlled Polymerization of Two-Dimensional Conducting Polymers in Quasi-Liquid Layer Enables Ultrahigh Sensing Performance.

Gas sensors based on conducting polymers offer great potential for high-performance room temperature applications due to their cost-effectiveness, high-sensitivity, and operational advantage. However, their current performance is limited by the deficiency of control in conventional polymerization methods, leading to poor crystallinity and inconsistent material properties. Here, the quasi-liquid layer (QLL) on the ice surface acts as a self-regulating nano-reactor for precise control of thermodynamics and kinetics in the polymerization, resulting in a 7.62nm thick two-dimensional (2D) polyaniline (PANI) film matching the QLL thickness. The ultra-thin film optimizes the exposure of active sites, enhancing the detection of analyte gases at low concentrations. It is validated by fabricating a chemiresistive gas sensor with the 2D PANI film, demonstrating stable room-temperature detection of ammonia down to 10 ppt in ambient air with an impressive 10% response. This achievement represents the highest sensitivity among sensors of this kind while maintaining excellent selectivity and repeatability. Moreover, the QLL-controlled polymerization strategy offers an alternative route for precise control of the polymerization process for conducting polymers, enabling the creation of advanced materials with enhanced properties.

To be or not to be a hydrophobic matrix? the role of coating hydrophobicity on anti-icing behavior and ions mobility of ionic liquids

The demand for anti-icing coatings to endure extremely low temperatures is substantial. Despite the innovative pioneering research on the anti-icing potential of ionic liquids (ILs), the development of such coatings is still in its infancy. Our study investigates how matrix hydrophobicity influences mobility of ILs at subzero temperatures and, consequently, their anti-icing behavior. Wettability results highlight the key role of IL anion hydrophobicity. Dielectric spectroscopy distinguishes ion mobility in the coatings at low temperatures. We also investigate how varying crosslink density affects ion mobility by measuring the water absorbency. Higher mobility of released ILs from the coatings at subzero was confirmed by their presence in water solutions, validated with UV–vis spectroscopy, and resulted in increased ionic conductivity. Differential scanning calorimetry and experimental setups were employed to assess ice formation temperature, time, and ice adhesion strength. Notably, surfaces containing IL exhibited a remarkable reduction in ice formation temperature to –23.5 ℃ and achieved an exceptionally low ice adhesion strength (∼15 kPa), attributed to the formation of a quasi-liquid layer (QLL). Solid-state NMR spectroscopy provided confirmation of the existence of QLL at the interface. Ice adhesion strength of coatings was examined against accelerated weathering, icing/de-icing cycles, as well as endurance against frost formation under freeze–thaw. Our findings underscore the significance of selecting the right matrix with regards to hydrophobicity and ILs when designing coatings for subfreezing applications.

Insight on the stability of methane hydrate in montmorillonite slits by molecular dynamics simulations

The extent of interactions between clay surfaces and water molecules and their impact on hydrate stability in clay reservoirs have been a source of debate. This study employs molecular dynamics simulations to investigate the stability of methane hydrates in montmorillonite slits at various temperatures, focusing on the surface influence scale, bound water molecule distribution characteristics, and binding strength. The results reveal that hydrates in close proximity to the clay surface exhibit lower stability and higher decomposition susceptibility due to the hydrophilic nature of the surface, which leads to water molecule aggregation, driving methane molecules away during decomposition. Furthermore, we compare the charged and neutral tetrahedral layer surfaces of montmorillonite and find that the quasi-liquid layer on the neutral tetrahedral layer surface is thinner, with persisting semicage structures within the vacancies of the Si-O rings. These variations in surface influence range and binding strength can be attributed to intermolecular Coulomb interactions and charge redistribution at the interface. These research findings provide valuable molecular insights into the microscopic characteristics and behavior of hydrates within clay slits.

Phase change surfaces with porous metallic structures for long-term anti/de-icing application

HypothesisIce mitigation has received increasing attention due to the severe safety and economic threats of icing hazards to modern industries. Slippery icephobic surface is a potential ice mitigation approach due to its ultra-low ice adhesion strength, great humidity resistance, and effective delay of ice nucleation. However, this approach currently has limited practical applications because of serious liquid depletion in the icing/de-icing process. ExperimentsA new strategy of phase change materials (PCM)-impregnation porous metallic structures (PIPMSs) was proposed to develop phase changeable icephobic surfaces in this study, and aimed to solve the rapid depletion via the phase changeable interfacial interactions. FindingsEvaluation of surface icephobicity and interfacial analysis proved that the phase changeable surfaces (PIPMSs) worked as an effective and durable icephobic platform by significantly delaying ice nucleation, providing long-term humid tolerance, low ice adhesion strength of as-prepared samples (less than 5 kPa), and signally improved maintaining capacity of impregnated PCMs (less than 10 % depletion) after 50 icing/de-icing cycles. To explore the interfacial responses, phase change models consisting of the unfrozen quasi-liquid layer and solid lubricant layer at the ice/PIPMSs interfaces were established, and the involved icephobic mechanisms of PIPMSs were studied based on the analysis of interfacial interactions.

Gas production from hydrates by CH4-CO2 replacement: Effect of N2 and intermittent heating

Extraction of CH4 gas from Natural Gas Hydrates (NGHs) while storing CO2 by CH4-CO2 replacement method is a promising technique for achieving CO2 emission reduction and CH4 production. However, improving the kinetics and enhancing the replacement efficiency is the fundamental issue for efficient CH4 production and CO2 safe sequestration, which have become the bottlenecks in NGH extraction. In this work, the CO2 replacement characteristics and kinetics process were further elucidated. The effects of small molecule gas (N2) and intermittent heating on the CO2 replacement were quantitatively investigated. And the enhancement mechanism of N2 and intermittent heating on CO2 replacement were deeply analyzed. The results show that as the proportion of N2 increases, the CH4 recovery rate gradually increases, but the CO2 sequestration rate exhibits a pattern of initial increase followed by a decrease. In addition, the intermittent application of heat has been shown to effectively enhance the replacement performance of pure CO2 in porous media. A thicker quasi-liquid layer forms when the temperature of hydrate reservoir approaches the freezing point, making it easier for CO2 gas to form hydrates. Additionally, when intermittent heating is combined with CO2 + N2 replacement, it results in a more significant promotion of CH4 recovery.

Probing the instability of surface structure on solid Hydrates: A microscopic perspective through experiment and simulation

The surface structural characteristics of clathrate hydrates play a significant role in mass transfer, interfacial properties, and mechanical stability during the hydrate growth process. However, the microstructure of hydrate surfaces remains unclear and controversial. In this study, a modified Atomic Force Microscopy (AFM) system was employed to confirm the presence of a quasi–liquid layer (QLL) on the solid tetrahydrofuran (THF) hydrate surface. Subsequently, sensitivity analyses were conducted on factors affecting the instability (fluidity) of QLL, including relative position, inclination angle, environmental temperature, and surface morphology. The results indicate that higher temperatures enhance the instability of the QLL surface, and altering the slope of the hydrate surface leads to an increase in the average thickness of the QLL due to the driving forces of gravity and surface tension, resulting in increased fluidity. Additionally, the surface morphological structure formed by Oswald ripening in polycrystalline THF hydrates affects the thickness of QLL. Furthermore, molecular dynamics simulations reveal that water molecules on the hydrate surface exhibit a multilayered structure, with the QLL region near the gas phase showing greater instability, while the region closer to the hydrate exhibits solid–phase characteristics, consistent with experimental findings.

Quantum corrections to molecular dynamics simulations of specific heat capacities of thin ices: Role of adsorption and quasi-liquid layers at interfaces

The thermodynamic properties of ice under confined conditions are significantly different from those of bulk, and their mechanisms are of great significance in many fields. In this work, we analyze thin ice under three different configurations, including freestanding, attached, and nanoconfined thin ice. The molecular dynamics method is employed to calculate the specific heat capacity of ice through the energy fluctuation formula, and quantum corrections are made to the simulations. The ice thickness is varied in the range of 28.57 Å–121.43 Å to explore its effect on the specific heat capacity at constant volume. The results show that the specific heat capacities of the thin ice are significantly higher than that of the bulk ice, with a tendency to increase and then decrease to a constant, and the maximum values of the specific heat capacities of the freestanding thin ice, the attached thin ice, and the nanoconfined thin ice decrease in order. The ice-copper plate interface and the ice-vacuum interface rearrange the surrounding ice molecules, which in turn form the adsorption layer and the quasi-liquid layer, respectively. Analysis of the vibrational density of states of the thin ice shows that the interface effect and the size effect play a competing role when it is smaller than a critical thickness and they play a synergistic role when it is larger than the critical thickness. This work reveals the important effects of interfacial and size effects on the specific heat capacities of thin ice and contributes to a better understanding of the thermophysical properties of ice in different configurations in fields such as atmospheric science and biology.

Surface premelting of ice far below the triple point

Premelting of ice, a quasi-liquid layer (QLL) at the surface below the melting temperature, was first postulated by Michael Faraday 160 y ago. Since then, it has been extensively studied theoretically and experimentally through many techniques. Existing work has been performed predominantly on hexagonal ice, at conditions close to the triple point. Whether the same phenomenon can persist at much lower pressure and temperature, where stacking disordered ice sublimates directly into water vapor, remains unclear. Herein, we report direct observations of surface premelting on ice nanocrystals below the sublimation temperature using transmission electron microscopy (TEM). Similar to what has been reported on hexagonal ice, a QLL is found at the solid-vapor interface. It preferentially decorates certain facets, and its thickness increases as the phase transition temperature is approached. In situ TEM reveals strong diffusion of the QLL, while electron energy loss spectroscopy confirms its amorphous nature. More significantly, the premelting observed in this work is thought to be related to the metastable low-density ultraviscous water, instead of ambient liquid water as in the case of hexagonal ice. This opens a route to understand premelting and grassy liquid state, far away from the normal water triple point.

Characterization of the quasi-liquid layer on gas hydrates with molecular dynamics simulations

Understanding the properties of the surficial quasi-liquid layer (QLL) is a prerequisite in proper handling of gas hydrates, a potential alternative future energy resource. Despite of its critical importance, the characterization of QLL has long been known to be highly challenging. In this work, the evolution of QLL during hydrate decomposition was systematically investigated by Molecular Dynamics simulations. Using the instant displacement of water molecules as a measure of the fluidity of the molecular layer adjacent to hydrate surfaces, QLL thickness was accurately measured using the dynamic properties of water molecules for the first time. The QLL thickness obtained by this new molecular dynamics-based approach takes amorphous water molecules close to hydrate surfaces into account, which was often ignored in the previous results based on the static structural order parameters. The variation of QLL thickness throughout the hydrate decomposition process at different temperatures and pressures was then evaluated. The thickness of QLL was found to increase with elevated temperature and pressure, owing to the varied changes of the amorphous and hydrate-like molecular content in this important layer. The results regarding the dynamics of the QLL with molecular resolution improved the current understanding on the stability of gas hydrate and shed new light on the physical fundamentals relevant to future hydrate exploration as well as anti-hydrate materials design.

Deposition freezing, pore condensation freezing and adsorption: three processes, one description?

Abstract. Heterogeneous ice nucleation impacts the hydrological cycle and climate through affecting cloud microphysical state and radiative properties. Despite decades of research, a quantitative description and understanding of heterogeneous ice nucleation remains elusive. Parameterizations are either fully empirical or heavily rely on classical nucleation theory (CNT), which does not consider molecular-level properties of the ice-nucleating particles – which can alter ice nucleation rates by orders of magnitude through impacting pre-critical stages of ice nucleation. The adsorption nucleation theory (ANT) of heterogeneous droplet nucleation has the potential to remedy this fundamental limitation and provide quantitative expressions in particular for heterogeneous freezing in the deposition mode (the existence of which has even been questioned recently). In this paper we use molecular simulations to understand the mechanism of deposition freezing and compare it with pore condensation freezing and adsorption. Based on the results of our case study, we put forward the plausibility of extending the ANT framework to ice nucleation (using black carbon as a case study) based on the following findings: (i) the quasi-liquid layer at the free surface of the adsorbed droplet remains practically intact throughout the entire adsorption and freezing process; therefore, the attachment of further water vapor to the growing ice particles occurs through a disordered phase, similar to liquid water adsorption. (ii) The interaction energies that determine the input parameters of ANT (the parameters of the adsorption isotherm) are not strongly impacted by the phase state of the adsorbed phase. Thus, not only is the extension of ANT to the treatment of ice nucleation possible, but the input parameters are also potentially transferable across phase states of the nucleating phase at least for the case of the graphite/water model system.

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.