Solid Surface Research Articles

Chemiresistive effect of p-type delafossite CuScO2 microsheets to gaseous alcohols.

The chemiresistive effect of an oxide significantly influences its electrical properties, which depend greatly on the interactions between the ambient gas molecules and the solid surface, including the gas adsorption and charge transfer still challenging to be clarified. In this work, we investigate the chemiresistive effect of the p-type delafossite CuScO2 microsheets by comparing their responses to various gaseous alcohols, which increase with an approximately linear relationship with the length of straight carbon chains from methanol to n-hexanol. A new mechanism is proposed to elucidate such a dramatic trend of observed chemiresistive change based on the first-principles calculations and test results. The increasing carbon chain length modulates the adsorption configuration and provides supplementary routes for electron transfer, which is assumed to account for the observed chemiresistive effect. This work may provide a novel perspective for the investigation and development of more advanced functional oxides for electrical applications.

Size-Dependent Ab Initio Atomistic Thermodynamics from Cluster to Bulk: Application to Hydration of Titania Nanoparticles.

Ab initio atomistic thermodynamics (AIAT) has become an indispensable tool to estimate Gibbs free energy changes for solid surfaces interacting with gaseous species relative to pressure (p) and temperature (T). For such systems, AIAT assumes that solid vibrational contributions to Gibbs free energy differences cancel out. However, the validity of this assumption is unclear for nanoscale systems. Using hydrated titania nanoparticles (NPs) as an example, we estimate the vibrational contributions to the Gibbs free energy of hydration (ΔGhyd(T,p)) for arbitrary NP size and degree of hydration. Comparing ΔGhyd(T,p) phase diagrams for NPs when considering these contributions (AIATnano) relative to a standard AIAT approach reveals significant qualitative and quantitative differences, which only become negligible for large systems. By constructing a size-dependent ΔGhyd(T,p) phase diagram, we illustrate how our approach can provide deeper insights into how nanosytems interact with their environments, with many potential applications (e.g., catalytic nanoparticles, biological colloids, nanoparticulate pollutants).

Sol-Gel Transition of a Thermo-Responsive Polymer at the Closest Solid Interface.

Thermo-responsive polymers are applied as surface modifications for the temperature switching of hydrophilic and hydrophobic properties through adsorption and grafting on solid substrates. The current understanding of the influence of polymer chains bound to the solid surface on the transition behavior of thermo-responsive polymers is rather restricted. In this study, we aim to elucidate the effect of the bound polymer chains at the interface on the thermo-responsive sol-gel transition behavior of aqueous methylcellulose (MC) solutions by employing a quartz crystal microbalance (QCM) to evaluate the shear modulus near the solid interface. When the sample thickness was thinner on the order of the millimeter scale, the sol-gel transition temperature evaluated by the cloud point decreased because the condensation of MC near the solid interface promoted the sol-gel transition. On the other hand, focusing on the closest solid interface on the nanometer scale by QCM, the sol-gel transition temperature increased when approaching the solid interface. Adsorption and interfacial interactions reduced the chain mobility and restrained the sol-gel transition by preventing MC chain aggregation. We demonstrated the physical properties evaluation at the closest interface between the thermo-responsive polymer and solid substrate by combining a simple analytical model of QCM and controlling the analytical depth of the QCM sensors. In conclusion, the mobility change of the bound polymer chains at the solid interface caused by adsorption and interfacial interactions must be considered when a thermo-responsive polymer is applied as in adsorbed or thin films on solid substrates for the functionalization of biomaterials.

Dissolution behavior of mixed calcium‑cobalt carbonates at 25 °C in contact with different gas phases

The potential immobilization of cobalt in various environments can be achieved through the incorporation of Co into carbonate minerals, forming solid solutions of (Ca1-xCox)CO3. However, the thermodynamic properties of these minerals are not well-understood due to conflicting data from natural observations and experiments. In this work, a series of mixed calcium‑cobalt carbonates were prepared and their interaction with aqueous solution was investigated. Depending on the Co/(Ca + Co) mol ratio (XCo) of the mixed solution, ranging from 0.00 to 1.00, pure calcite, Co-bearing calcite, Co-bearing aragonite, Ca-bearing spherocobaltite and pure spherocobaltite were successively synthesized using a precipitation method. Upon dissolution of the Co-bearing solids (XCo = 0.10–1.00) in N2-degassed water (NW) and air-saturated water (AW), the Co concentration of the aqueous solutions increased gradually to a stable state of 0.017–0.191 and 0.018–0.186 mmol/L after 240–360 d dissolution, respectively. When the dissolution occurred in CO2-saturated water (CW), the Co concentration initially spiked to 0.372–2.258 mmol/L within 6 h ∼ 15 d and then decreased to a stable range of 0.030–0.559 mmol/L after 240–360 d. The Co/(Ca + Co) mol ratio in the aqueous solution (XCo2+,AS) was significantly lower than the Co/(Ca + Co) atomic ratio in the solids (XCo,SS), particularly when dissolved in NW and AW. During these dissolution processes in NW, AW and CW at 25 °C, the average log IAP values at the final stable state were determined as follows: for calcite (CaCO3), the values were −8.25 ± 0.03 in NW, −8.34 ± 0.11 in AW, and −8.10 ± 0.08 in CW; for spherocobaltite (CoCO3), they were −9.24 ± 0.26 in NW, −9.39 ± 0.23 in AW, and −9.38 ± 0.09 in CW. Furthermore, the log IAP values increased from those typical for calcite to −7.89 ± 0.01 ∼ −7.84 ± 0.10 for the solid with XCo,SS = 0.187 as XCo,SS increased, eventually aligning with those typical of spherocobaltite. Lippmann diagrams, constructed using the Guggenheim parameters a0 = 2.30 and a1 = 0.265 for the “subregular” calcite-spherocobaltite solid solutions [(Ca1-xCox)CO3] with a miscibility gap ranging from XCo,SS = 0.251 to 0.858, highlighted the “peritectic” point at XCo2+,AS = 0.0538 on the solutus. This analysis revealed that the solids dissolved non-stoichiometrically in water. Consequently, the Co-poor aqueous solution would reach equilibrium with the Co-rich calcite-structure phase at the solid surface.

Large-scale assessment of characteristic plant species on Eurasian saline and alkaline soda ecosystems

From an ecological standpoint, saline and alkaline habitats are considered as extreme environments for vascular plants because salinity and alkalinity serve as primary structuring factors that significantly influence the species richness of vegetation cover. The non-alkaline salinity stress on plants primarily results from interactions of NaCl, Na2SO4, and other neutral salts, whereas alkalinity stress is caused by NaHCO3 and Na2CO3, accompanied by an increase in pH. Some halophytes and salt-tolerant plants are well-adapted to such permanent abiotic stress. Surprisingly, they are able to survive and reproduce under environmental conditions of more than 200 mM NaCl concentration and are also able to live permanently in extreme conditions. The aim of this study was to identify characteristic and indicator plant species for permanently alkaline soda and non-alkaline saline wetland habitats, and to analyze the relationship between the chemical composition of water and the plant’s saturation index. Based on the obtained results we can conclude that plant species identified to live in high saline conditions may also grow under high alkaline conditions. Two groups were distinguished based on the salinity and alkalinity: “Saline group” includes all types of halophytes and halotolerant species, while “Soda group” includes obligate alkalophytes and alkalotolerant species. However, the diversity of plants in alkaline environment is bigger than in saline environment, and most of the halotolerant species grow in both alkaline soda and saline habitats. It is possible to identify three indicator species requiring alkaline soda habitats to live in (Aster tripolium, Puccinellia limosa, Suaeda pannonica) and three indicator species that dominantly grow in non-alkaline saline habitats (Juncus maritimus, Salicornia prostrata, Suaeda salsa). Different independent variables have been identified and analyzed to understand their influence on the species saturation index by calculating percentage of characteristic plant species of the entire region. It was identified that the plant saturation index has a significant positive relationship with the Mean Temperature of the Warmest Quarter, Topsoil Sand, and Clay fraction variables, and there is a significant negative relationship with the Solid Earth surface heat flow, as the heating can increase the extremity of the environment. Identification of indicator species of salinity and alkalization makes it possible to determine the type of soil, water bodies and habitats as a rapid biomonitoring method as a visual observation, without the use of expensive equipment and chemical laboratory tests.

Electrothermal-Assisted Photothermal Lubrication Surfaces for Continuous Anti-Icing/Deicing in Multiple Low-Temperature Environments.

Solving the problem of ice accumulation on solid surfaces is of great significance to the economic development of the country and the safety of people's lives. In this work, a coating with multifunctional photothermal/electrothermal solid-state lubrication (PEL) for anti-icing/deicing was prepared in layers based on the intrinsic properties of silicone oil and paraffin wax in combination with conductive graphite and multiwalled carbon nanotubes. Silicone oils and paraffins are used as lubricating media giving the coating excellent lubricity, which results in a water sliding angle (SA) of only 12° on the PEL surface. Meanwhile, PEL shows favorable static and dynamic ice resistance at low temperatures; at -10 °C, the freezing time of water droplets on the PEL surface is extended by at least 4 times compared to the bare substrate. Furthermore, PEL also offers highly efficient photothermal and electrothermal deicing performance, which can effectively remove the accumulated ice at a light intensity of 0.6 kW/m2 or an EPD of 0.1 W/cm2. Meanwhile, the synergistic deicing mechanism of photothermal and electrothermal was verified at -20 °C. Interestingly, the coating shows heat-assisted healing ability due to the phase change characteristic of paraffin wax, which allows the coating to regain lubricating properties after mechanical abrasion. Therefore, this work provides a reliable way for the design of stable all-weather anti-icing/deicing strategies at low temperatures.

Effect of physicochemical properties on critical sinking and attachment of respirable coal mine dust impacting on a water surface

Respirable coal mine dust (RCMD) inhalation is identified as the main cause of the resurgence of coal worker’s pneumoconiosis (CWP) since the mid-1990s. At present, the predominant dust control technology is the water spray system. However, in practice, the capture efficiency of RCMD by this technology is relatively low. To understand the capturing mechanism and develop improvement strategies, this research is focused on the surface chemistry study of RCMD and its impact on a water surface using a dynamic model. Proximate analysis, chemical, and mineral composition of a run-of-mine (ROM) coal sample from Appalachian region were analyzed using a proximate analyzer, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and X-ray Diffraction (XRD), respectively. Contact angles were measured by capillary rise test using the Washburn equation. Based on the dynamic model, the effects of particle size, density, contact angle, and surface tension on the critical sinking were investigated. It was pointed out in this work that reducing surface tension, in turn, decreases contact angle, which has been neglected in the literature. Regime maps for different minerals were created and showed that organic matter has the highest critical velocity due to its low density and high contact angle. Reducing water surface tension to the critical solid surface tension of coal around 30 mN/m could maximize the attachment efficiency. Scaling laws, constructed by force balance, led to the criteria of critical sinking: Ucr61-cosθ2D+1γlvρlR, i.e., Wecr121-cosθ2D+1. A semi-empirical formula for critical velocity was obtained by fitting the simulation data, Ucr=1.0961-cosθ2D+1γlvρlR. Attachment efficiency was defined and formulated as Pa=U02Ucr2=We0Wecr, establishing relationships between attachment efficiency and the physicochemical properties of RCMD and water droplets

The Formation of a Low-Carbon Steel/Ni-Cr-W Alloy Bimetallic Material via Liquid–Solid Compound Casting with a Laser Assisted Solid Surface

The aim of this study was to develop a new manufacturing process for bimetallic materials by combining laser treatment with traditional casting methods. This process involves laser-treating nickel alloy-grade UNS 6230 plates to create a regular macro-relief on their surface. These treated plates are then placed in a sand mold, and molten non-alloy steel (S235JRG2) is poured into the mold to create bimetallic layered castings. The experimental procedure focuses on optimizing the melt-to-solid phase ratios and pouring temperatures to achieve a uniform microstructure and strong mechanical properties in the bimetals. The produced bimetallic castings are suitable for applications in the oil refining and chemical industries and heavy machinery sector. The quantitative results indicate that the optimized process parameters lead to a high-quality transition zone with minimal defects, characterized by the diffusion of alloying elements from the nickel alloy to the steel. The microstructure, chemical, and phase compositions were evaluated using XRD and SEM with EDS, confirming the formation of a robust metallurgical bond. Key findings include a significant improvement in the hardness and strength of the transition layer, with the optimal pouring temperature being 1600 °C. The resulting bimetallic materials demonstrate an improved performance in demanding industrial environments.

In Situ Visual Observation of Surface Energy-Controlled Heterogeneous Nucleation of Metal Nanocrystals.

Electrochemical growth of metal nanocrystals is pivotal for material synthesis, processing, and resource recovery. Understanding the heterogeneous interface between electrolyte and electrode is crucial for nanocrystal nucleation, but the influence of this interaction is still poorly understood. This study employs advanced in situ measurements to investigate the heterogeneous nucleation of metals on solid surfaces. By observing the copper nanocrystal electrodeposition, an interphase interaction-induced nucleation mechanism highly dependent on substrate surface energy is uncovered. It shows that a high-energy (HE) electrode tended to form a polycrystalline structure, while a low-energy (LE) electrode induced a monocrystalline structure. Raman and electrochemical characterizations confirmed that HE interface enhances the interphase interaction, reducing the nucleation barrier for the sturdy nanostructures. This leads to a 30.92-52.21% reduction in the crystal layer thickness and a 19.18-31.78% increase in the charge transfer capability, promoting the formation of a uniform and compact film. The structural compactness of the early nucleated crystals enhances the deposit stability for long-duration electrodeposition. This research not only inspires comprehension of physicochemical processes correlated with heterogeneous nucleation, but also paves a new avenue for high-quality synthesis and efficient recovery of metallic nanomaterials.

Interaction of Diisopropyl methyl Phosphonate (DIMP) with magnesium oxide at elevated temperatures

Diisopropyl Methyl Phosphonate (DIMP) is a liquid widely considered a surrogate for chemical warfare agents (CWA). Respectively, its interactions with different surfaces must be understood to predict the fate of CWA in various scenarios involving their release. Magnesium oxide (MgO) is a combustion product of metallized energetic materials and can serve as a model material for other common oxides. Thus, its interaction with DIMP is of both fundamental and practical interest. In this work, powders of MgO produced by different methods and having different surface areas and crystallite sizes were exposed to liquid DIMP and heated above the DIMP boiling point in a thermal analyzer. The residue remaining on the surface of different powders was quantified and examined using infrared spectroscopy. It was found that the mass of the residue scaled with the specific surface area determined based on the MgO crystallite sizes. The results suggest that the residue consists of P-CH3 molecular groups with the phosphorus attached to multiple surface oxygen anions. The residue was found to be discontinuous on smaller crystallites, but it could form a continuous monolayer on larger crystallites. The presence of Mg(OH)2 prevented interactions between DIMP and the solid surface.

Water dynamics in calcium silicate hydrates probed by inelastic neutron scattering and molecular dynamics simulations

Calcium-silicate-hydrate (C-S-H) is a disordered, nanocrystalline material, acting as a primary binding phase in Portland cement. C-S-H and C-A-S-H (an Al-bearing substitute present in low-CO2 cement) contain thin films of water on solid surfaces and inside nanopores. Water controls multiple chemical and mechanical properties of C-S-H, including drying shrinkage, ion transport, creep, and thermal behavior. Therefore, obtaining a fundamental understanding of its properties is essential. We applied a combination of inelastic incoherent neutron scattering and molecular dynamics simulations to unravel water dynamics in synthetic C-(A)-S-H conditioned at five hydration states (from drier to more hydrated) and with three Ca/Si ratios (0.9, 1, and 1.3). Our results converge towards a picture where the evolution from thin layers of interfacial water to bulk-like capillary water is dampened by the structure of C-(A)-S-H. In particular, the hydrophilic Ca2+ sites organize the distribution of interfacial C-(A)-S-H water.

Computer simulation and modeling of glow discharge optical emission coded aperture elemental mapping

BackgroundElemental mapping (EM) yields necessary insights into mechanisms of interest in solid samples across multiple disciplines. There are several EM techniques available but long acquisition time is a common limitation. Glow discharge optical emission spectroscopy (GDOES) allows direct quantitative multi-EM at very high throughput (∼10 s s) when coupled to traditional hyperspectral imaging (HSI) techniques. However, GDOES consumes the sample via sputtering, such that traditional HSI sequential scanning requirements lead to loss of information/resolution, which is compounded for multi-EM and limits nanomaterials analysis. Thus, there is a need for faster HSI to enable GDOES multi-EM of nanoscale materials. ResultsHere, a new technique is described, Glow discharge Optical emission Coded Aperture elemental Mapping (GOCAM), that takes advantage of compressive coded aperture spectral imaging to enable multi-EM in a single camera exposure. In this first phase of development, computer model simulations were implemented to study the effects of coded aperture parameters on data fidelity, which showed the best fidelity is achieved at smaller mask element sizes and transmittance of 60 %. In addition, SeSCIGPU demonstrated the best fidelity performance compared to several compressed sensing reconstruction algorithms, including TwIST, GAP-TV, SeSCICPU, and ADMM-TV, as evaluated by studying the effects of varying the corresponding hyperparameters. SignificanceThis study shows GOCAM's feasibility and provides a starting point for the second phase hardware development currently underway. GOCAM's potential to allow multi-EM from solid surfaces in a fraction of a second will be particularly enabling for nanostructured materials characterization.

Liquid Springs for High‐Speed Contamination‐Free Manipulation of Droplets and Solid Particles

AbstractAccurate and flexible control of droplets is essential in many industrial applications, such as water harvesting, chemical assays, and biological detection. Magnetic force‐based methods have been broadly exploited to fulfill the goals due to the advantage of non‐contact, easy control, and long‐range navigation. Nevertheless, it still suffers from some challenges, such as sample fouling, and the paradox between the droplet efficient motion and the large volume. Here a ferrofluid‐based liquid spring to achieve contamination‐free and fast droplet transportation on non‐wetting solid surfaces is proposed. The liquid spring is based on the actuation of a ferrofluid droplet in an external uniform magnetic field. The actuation enables the liquid spring to propel tiny objects, including the non‐magnetic miscible droplets and water‐repellent solid particles, with adjustable motion velocity. Furthermore, the magnetic force, applied on the ferrofluid via an additional permanent magnet, makes it possible to navigate the liquid spring in a programmable way. With the aid of the liquid spring, the single or multiple droplets/solid particles advancing, on‐demand droplets coalescence, and out‐of‐plane droplet motion are achievable.

Microscopic behavior of heteroatom asphaltene in the multi-media model: The effect on heavy oil properties

The high viscosity and surface adsorption of heavy oil pose significant challenges for its exploration. Asphaltenes, the most polar and heaviest components of crude oil, play a crucial role in these properties. Heteroatom asphaltenes (A-X, S-Y) exhibit stronger interaction energy compared to non-heteroatom asphaltenes A-C. The self-assembly of A-X/S-Y forms ordered "reinforcement-cement" aggregates, whereas A-C aggregates are more chaotic. The presence of heteroatoms, particularly the sulfur atom in the side chains, may significantly influences asphaltene aggregation structures. The diffusion coefficient of heteroatom asphaltene in oil droplet is smaller than that of A-C, and these heteroatom compound can bind other oil components, reducing the overall fluidity. Notably, the adsorption energy of asphaltenes on solid surfaces exceeds their interaction energy. Surface aggregation of A-X/S-Y is more dispersed compared to A-C adsorption system. Additionally, the existence of heteroatom asphaltenes can shorten the distance between oil droplets and the solid surface by 16.20 Å compared with non-heteroatom system. These phenomena, caused by A-X/S-Y, further complicate the detachment of crude oil components from surfaces. This study aims to share some new insights into the micro-mechanisms of heteroatom asphaltenes self-assembly and the behavior in the oil-sludge process, which may contribute to the theoretical foundation for the targeted and efficient exploitation of heavy oil.

Tannin-on-protein adlayers: Secondary adsorption quantified by quartz crystal microbalance with dissipation monitoring (QCM-D)

The quartz crystal microbalance with dissipation monitoring (QCM-D) technique allows to detect adsorption and mechanical characteristics of protein adsorption layers at solid surfaces, including subsequent secondary adsorption of additional species interacting with the proteins. Here, we study the secondary adsorption of two different classes of tannins - hydrolysable vs. condensed - onto a β-lactoglobulin base layer using QCM-D in a protein/tannin adlayer configuration. Sequential flow experiments of protein solutions, tannin solutions and neat solvent or buffer are used to distinguish reversible from desorption-resistant layer formation, evaluate the viscoelastic characteristics the layers, and map protein/tannin interactions in view of their structural properties and origin. We find that for the majority of tannins, secondary layer structural changes (detected via a change in the dissipation factor) occur before significant mass adsorption (detected via the resonance frequency shift). In contrast, simultaneous onset of structural change and adsorbed mass within an observation window of 100 ms was only found for certain hydrolysable tannins. We use these data to build adsorption maps and group the tannins according to their adlayer properties, providing a physical basis for an improved understanding of the organoleptic perception of tannins and polyphenols, in particular with respect to attributes such as ‘astringency’ and ‘lingering’. Moreover, these maps provide insight into the capacity of different tannins to modify the mechanical properties of protein adsorption layers.

Propulsive performance of a heaving and pitching foil with large amplitudes in unsteady ground effect

To reveal the effect of ground on the force behavior, propulsion performance, and vortex dynamics of a flapping foil, we numerically study a flapping foil actuated by combined heaving and pitching motions with large amplitudes near a solid ground surface. The instantaneous forces in both streamwise and cross-stream directions undergo a sudden drop during upstroke in close ground effect. The time-averaged thrust is enhanced by the ground but varies non-monotonically with ground distance at high foil oscillating frequencies. Three force regimes are identified in lift production, giving rise to two equilibrium altitudes of zero lift, one stable and another unstable. Moreover, we propose a simple scaling law model by a path-length-based Strouhal number and ground effect for thrust and power performance of a large-amplitude flapping foil. The results of the model are consistent with numerical results and previous experimental studies. The vortex dynamics in the wake structure are largely affected by ground proximity; in particular, the formed vortex pairs and their orientations are sensitive to their initial relative positions. Different sources and mechanisms of satellite vortex formation are then discussed. The ground exerts little effect on the phase angles that optimize the propulsive efficiency. This study is expected to provide new insights into the development and maneuvering of flapping foil-based propulsive systems.

Design of electrical energy harvesting devices utilizing air bubbles sliding along a fluoropolymer immersed in water

Recent research has shown that it is possible to utilize contact electrification combined with electrostatic induction to harvest electrical energy from the mechanical motion of air bubbles sliding along a charged solid surface immersed in water. The working principle of these devices is simple, but the design is usually complicated as transduction efficiency depends on a number of interdependent parameters. Here we propose a simple analytical model and demonstrate how it can be used to determine the optimal energy per bubble for a given resistive load. The model allows one to estimate the optimal energy harvested per bubble in terms of polymer thickness, electrode separation and load resistance. It is shown that the model provides a good fit to experimental data. The model may be used as an initial step when designing energy harvesting devices utilizing air bubbles sliding along a solid surface.

Low-energy atomic and molecular hydrogen ion interaction with low-work function electride 12CaO · 7Al2O3

To efficiently generate H− ions from positive atomic or molecular hydrogen beams injected onto a solid surface, it has been suggested to use a material with a low-work function as the target material. However, it is not clear under what conditions the most efficient H− production is realized for incident beam parameters or reflection angles. Therefore, we studied the interaction between low-energy atomic and molecular hydrogen beams (less than 1 keV/nucleon) with a low-work function electride 12CaO⋅7Al2O3 (C12A7). The production ratio of H− to H+ ions from the C12A7 electride was much higher than Mo targets with higher work functions, especially at smaller incident and smaller reflection angles. The H− to H+ production ratio slightly increased as the incident energies were decreased, but there was no significant difference between the electride and Mo targets. These results indicate that smaller incident angles and lower beam energies of the incident hydrogen beam are favorable for the enhancement of the production ratio of H− to H+ ions in C12A7. The higher production ratio appeared at the vertical beam energies less than on the order of 100 eV, where quantum mechanical processes may become important.

Liquefaction efficiency study of heterogeneous condensation of methane-ethane binary gas mixtures with different component contents

Natural gas is a mixture of hydrocarbons. During the liquefaction of natural gas, the mixed gas undergoes heterogeneous condensation on the surface of the heat exchanger. Currently, the heterogeneous condensation mechanism of mixed gases is not fully understood, and the influence of component content on the liquefaction efficiency is not clear. Therefore, the molecular dynamics simulation was employed to investigate the heterogeneous condensation process of methane-ethane binary mixed gas on a solid surface. The characteristics of condensation nucleation cluster growth was explored and the variations in temperature, density, heat flux, and liquefaction rate were analyzed. The impact of ethane on methane condensation was also discussed. The results indicate that increasing wettability enhances surface nucleation quantity and shortens nucleation time, resulting in a 3.6- times increase in heat flux. The addition of ethane gas in the system promotes condensation nucleation, which increases the liquefaction rate by 60 % when x = 20 % compared to the pure methane system. However, for methane gas, ethane only benefits the liquefaction of methane molecules in the initial nucleation stage. As the mixture in the system enters the cluster growth stage, component migration in the mixed gas leads to a lower liquefaction rate compared to pure methane gas.

An analysis of the contact time of nanodroplets impacting superhydrophobic surfaces with square ridges

Reducing the contact time between liquid droplets and solid surfaces is important in numerous engineering applications. Mechanisms for reducing the contact time have been extensively studied. However, there is still a lack of systematic research on the mechanisms governing the changes in the contact time of nanodroplets impacting superhydrophobic surfaces with square ridges. Additionally, there has been relatively little examination of the differences between nanodroplets and macroscopic droplets in this scenario. In this work, we investigate the impact of nanodroplets on both superhydrophobic planes and superhydrophobic surfaces with square ridges. When nanodroplets impact a superhydrophobic plane, we find that the droplet contraction time determines the total contact time. When nanodroplets impact superhydrophobic surfaces with square ridges, we find for the first time that the critical factor determining its contact time is the detachment time of the droplet from the square ridges as it lifts off. Compared to millimeter-sized droplets, nanodroplets exhibit stronger adhesion to solid surfaces. Additionally, we propose for the first time that nanodroplets are more resistant to deformation and splitting. We define the Weber number (We) at which the droplet rebounds as the critical rebound Weber number (We), and use this to evaluate the effect of square ridges on improving droplet rebound. We observe that a moderate increase in the square ridge height is beneficial to reducing the contact time. By altering the square ridge width, we find that a narrower ridge is more favorable for reducing the contact time and for facilitating droplet splitting.