Water Film Research Articles

Unravelling the main mechanism responsible for nocturnal CO2 uptake by dryland soils

Soil respiration, or CO2 efflux from soil, is a crucial component of the terrestrial carbon cycle in climate models. Contrastingly, many dryland soils absorb atmospheric CO2 at night, but the exact mechanisms driving this uptake are actively debated. Here we used a mechanistic model with heuristic approaches to unravel the underlying processes of the observed patterns of soil-atmosphere CO2 fluxes. We show that the temperature drop during nighttime is the main driver of CO2 uptake by increasing CO2 solubility and local water pH of a thin water film on soil particle surfaces, providing favourable conditions for carbonate precipitation. Our data demonstrate that the nocturnal inorganic carbon absorption is a common soil process, but often offset by biological CO2 production. The uptake rates can be impacted by different successional stages of biocrusts that consume or produce CO2 and modify the pH of the soil water film, which can be maintained by non-rainfall water inputs, such as pore space condensation. Annual estimates of nocturnal carbon uptake, based on in situ continuous measurements at the soil level in drylands are still very scarce, but fluxes of up to several tens of g C m−2 y−1 have been reported, potentially accounting for a considerable fraction of the global residual terrestrial carbon sink.

Oxyfl uorinated polyethylene terephthalate for liquid storage containers

The effectiveness of surface modification of polyethylene terephthalate with a mixture of fluorine and oxygen to reduce the permeability to water and aqueous ethanol solutions has been studied. We obtained a decrease in the permeability coefficient of the modified fi lm for water and ethanol solutions, the degree of decrease in the permeability coefficient depends on the chemical composition of the liquid. Oxyfluorination leads to the production of a modified fi lm with an increased liquid diffusion coefficient compared to the original fi lm, which is associated with the formation of local defects which is confirmed by micrographs made with of an atomic force microscope and by measuring the surface roughness of the original and modified films.

Atomistic exploration of unfrozen water film connection modes in CSH gel pores

Significant changes in concrete's internal structure profoundly affect its performance across varied environmental conditions. Concrete behaves differently in low-temperature environments compared to room temperature due to phase transitions and the freezing of pore water within its matrix. However, understanding the microstructure within cementitious material's gel pores under low-temperature conditions, especially the ice-water-matrix connection mode, has remained elusive. Our molecular dynamics simulations have unveiled that pore size and temperature wield a considerable influence on the connection mode within these gel pores. We have delved deeply into the melting process of ice crystals and the intricate nature of unfrozen water films (UWFs) across different temperatures and pore sizes. The results elucidate that pore size's impact on the connection mode largely hinges on whether gel pores of specific sizes can retain an intact ice layer. At lower temperatures, thinner UWFs emerge, revealing at the nanoscale a reduction in the layers of water molecules within the connection structure. Additionally, we have observed the pivotal role played by calcium ions and water-like molecules in substituting within the matrix's connection structure. These findings offer theoretical insights for construction practices in cold regions, enhancing our ability to predict concrete behavior under low-temperature conditions.

Water Dose influence to the ALD hafnium oxide process: Simulation and experiment

In this work, we report a two-dimensional gas-dynamic model for the formation of hafnium oxide from TDMAH and water during the atomic layer deposition (ALD) process. Application of the model is demonstrated by the example of water cycle, in which the monolayer of functional groups –OH is formed. The simulation results show that the duration of the water pulse affects the dynamics of surface coverage with the -OH groups. At short pulse durations, the resulting coverage of the film surface with -OH groups becomes incomplete and has heterogeneous distribution over the film surface, which is due to the design of the reaction chamber and regimes of gas supply. The amount of residual water vapor depends on the duration of the water pulse and pumping regimes. Experimental data show the influence of water pulse duration on the refractive index, which is related to the structure of the deposited layer (composition, morphology, etc.). Based on experimental data and modeling results, we explain the effect of water pulse duration on the refractive index by the change in reaction mechanisms depending on water amount in the chamber. With a lack of water, the incomplete monolayer of –OH groups is formed and a {HfO2-y} layer grows as a result of the monomolecular decomposition of the precursor. With an excess of water, we expect the implementation of multilayer adsorption of water, provoking the reaction of the precursor in the volume of the water film, leading to the formation of the product {HfO2+y}.

Water film-mediated photocatalytic oxidation of oxalate on TiO2

Water films on minerals under humid environment can be photocatalytic hotspots when exposed to sunlight or artificial sources of ultraviolet (and visible) radiation. In this study, we resolved the water film-mediated photocatalysis of oxalate adsorbed on TiO2 using in situ infrared spectroscopy. We found that 0.5 to 4 monolayer- (ML) thick water films enhanced the photodecomposition rates of oxalate under 21 kPa O2. We explained this through the combined actions of direct hole transfer, ligand-to-metal-charge transfer, as well as the production of hydroxyl radicals and reactive oxygen species. Rates were, however, substantially slower in the absence of O2 because charge recombination, together with water film-mediated charge localization, disrupted hole transfer and hydroxyl radical production. Our work adds insight into the impact of humidity on controlling important photocatalytic processes in nature (drying soils, atmospheric aerosols), and technology (water and air treatment).

Exploring magnetic properties and dynamic performance of magnetic-hydraulic double-floating journal bearing based on offset load

An innovative structural system of magnetic-hydraulic double-floating journal bearing is designed to improve the ability to resist offset loads. By considering the magnetic force to the water-lubricated journal bearing and the magnetic structure design, a force model of the innovative bearing is proposed. The magnetic force and water film force for the bearing are simulated by comparing the load-carry capacity of only water film force. Experimental results showed the load-carry capacity and stability test of the innovative bearing. The design of innovative bearing with the upper suction and lower magnetic repulsion based on the Halbach array can provide a larger supporting magnetic force. The axially non-uniform magnetic structure deployment can manipulate the changes of the magnetic force in the axial direction to hold the offset load. The test found that by comparing the traditional water-lubricated bearing, the bearing has a certain vibration suppression ability in the vertical direction. Under the test speed, the bearing stiffness hardly changes with the change of the speed, which also shows a slightly decreasing trend with the increase of the excitation frequency.

Simulation of phase change during the freezing of unsaturated porous media by using a coupled lattice Boltzmann model

PurposeThe purpose of this paper is to develop a coupled lattice Boltzmann model for the simulation of the freezing process in unsaturated porous media.Design/methodology/approachIn the developed model, the porous structure with complexity and disorder was generated by using a stochastic growth method, and then the Shan-Chen multiphase model and enthalpy-based phase change model were coupled by introducing a freezing interface force to describe the variation of phase interface. The pore size of porous media in freezing process was considered as an influential factor to phase transition temperature, and the variation of the interfacial force formed with phase change on the interface was described.FindingsThe larger porosity (0.2 and 0.8) will enlarge the unfrozen area from 42 mm to 70 mm, and the rest space of porous medium was occupied by the solid particles. The larger specific surface area (0.168 and 0.315) has a more fluctuated volume fraction distribution.Originality/valueThe concept of interfacial force was first introduced in the solid–liquid phase transition to describe the freezing process of frozen soil, enabling the formulation of a distribution equation based on enthalpy to depict the changes in the water film. The increased interfacial force serves to diminish ice formation and effectively absorb air during the freezing process. A greater surface area enhances the ability to counteract liquid migration.

Airflow Triggered Water Film Self-Sculpturing on Femtosecond Laser-Induced Heterogeneously Wetted Micro/Nanostructured Surfaces.

Liquid manipulation is essential for daily life and modern industry, and it is widely used in various fields, including seawater desalination, microfluidic robots, and biomedical engineering. Nevertheless, the current research focuses on the manipulation of individual droplets. There are a few projects for water film management. Here, we proposed a facile method of wind-triggered water film self-sculpturing based on a heterogeneous wettability surface, which is achieved by the femtosecond laser direct writing technology and femtosecond laser deposition. Under the conditions of various airflow velocities and water film thicknesses, three distinct behaviors of the water film were analyzed. As a result, when the water film thickness is lower than 4.9 mm, the self-sculpture process will occur until the whole superhydrophobic surface dewetting. Four potential applications are demonstrated, including encryption, oil containers, reconfigurable patterning, and self-splitting devices. This work provides a new approach for manipulating a water film of fluid control engineering.

Drought shifts soil nematode trophic groups and mediates the heterotrophic respiration

Abstract As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.

Smoothed particle hydrodynamics based numerical study of hydroplaning considering permeability characteristics of runway surface

The presence of water films on a runway surface presents a risk to the landing of aircraft. The tire of the aircraft is separated from the runway due to a hydrodynamic force exerted through the water film, a phenomenon called hydroplaning. Although a lot of numerical investigations into hydroplaning have been conducted, only a few have considered the impact of the runway permeability. Hence, computational problems, such as excessive distortion and computing efficiency decay, may arise with such numerical models when dealing with the thin water film. This paper presents a numerical model comprising of the tire, water film, and the interaction with the runway, applying a mathematical model using the smoothed particle hydrodynamics and finite element (SPH-FE) algorithm. The material properties and geometric features of the tire model were included in the model framework and water film thicknesses from 0.75 mm to 7.5 mm were used in the numerical simulation. Furthermore, this work investigated the impacts of both surface texture and the runway permeability. The interaction between tire rubber and the rough runway was analyzed in terms of frictional force between the two bodies. The SPH-FE model was validated with an empirical equation proposed by the National Aeronautics and Space Administration (NASA). Then the computational efficiency of the model was compared with the traditional coupled Eulerian-Lagrangian (CEL) algorithm. Based on the SPH-FE model, four types of the runway (Flat, SMA-13, AC-13, and OGFC-13) were discussed. The simulation of the asphalt runway shows that the SMA-13, AC-13, and OGFC-13 do not present a hydroplaning risk when the runway permeability coefficient exceeds 6%.

A novel multifunctional carboxymethyl cellulose packaging film with encapsulated lemon oil for quality enhancement of cherry tomato and baby spinach leaves

This is the first report on fabricating an active edible film based on CMC and lemon essential oil (LEO) micro/nanocapsules for packaging cherry tomatoes and baby spinach leaves. LEO extracted by hydrodistillation from lemon peels was efficiently encapsulated by oil-in-water emulsification method using high dextrose equivalent maltodextrin (MD) as the sole wall material, yielding physically stable MD-LEO micro/nanocapsules with potent cytotoxicity against Caco-2 cells, and antimicrobial activity against foodborne pathogens. Incorporating LEO micro/nanocapsules into CMC confirmed by SEM/FTIR analyses, significantly improved the film's water vapor permeability by 37.50%, increased its thermal stability by 25 ℃, and reduced its moisture content/water absorption. The transparent film demonstrated strong DPPH radicle scavenging activity, UV-blocking ability, low moisture, enhanced tensile strength, and soil biodegradability (96.84%) within 14 days. Direct application of the novel film as a single-layer overwrap to cherry tomatoes and spinach leaves stored at abusive temperature for up to 4 days revealed good prospects of preserving physical appearance, preventing water/texture loss, maintaining pH, and inhibiting growth of aerobic mesophilic/E. coli O157:H7 populations by 0.65 and 1.0 log units, respectively, highlighting that CMC is an optimal vehicle for encapsulated LEO. The data emphasizes the significant contribution of the novel film to active packaging of minimally processed fresh produce and its potential to compete with inert plastic films dominating food markets. Extending the film's applicability range to other pertinent food systems may promote industrial interest for production upscaling as a commercially viable postharvest preservation strategy to meet the demands of sustainable packaging industry in Egypt.

Impact dynamics of non-spherical droplets on a thin water film

A droplet impinging on a liquid film finds numerous applications in diverse scientific fields. Although studies have primarily focused on spherical droplets, a droplet can present both spherical shape and non-spherical shape at the moment of impact. In the present study, the impact dynamics of a non-spherical droplet on a thin liquid film is investigated experimentally. The results show that, under the same film thickness and Weber number conditions, the splashing and deposition regimes are different for different droplet shapes such as prolate, sphere, and oblate. It is found that the splashing threshold (Ksp) is changed according to the shape of the droplet. Under the same condition when a spherical droplet is in the deposition mode, an oblate droplet is more likely to splash and form secondary droplets, while a prolate droplet is more splash-resistant even at higher Weber numbers. A modified theoretical model for crown radius evolution is developed. The predictions of theoretical model are found to agree well with the experimental results for spherical and non-spherical droplets. Moreover, at the same Weber number, a prolate droplet has a relatively higher maximum crown height than those of an oblate droplet and a spherical droplet.

In Situ Real-Time Atomic Force Microscopy Observations of Chain Mobility at Polymer/Water Interfaces of Poly(methyl methacrylate), Poly(2-hydroxyethyl methacrylate), and Poly(2-methoxyethyl methacrylate) Films in Water.

Polymer materials are widely used in water or in contact with an aqueous environment. However, evaluating the chain mobility, a crucial parameter, at a polymer-water interface is challenging. In this study, we, for the first time, observed poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(2-methoxyethyl methacrylate) (PMEMA) film surfaces in water via in situ real-time atomic force microscopy (AFM) in tapping mode and quantified the chain mobility. The average displacement between adjacent images (nm/8.75 min) was evaluated using particle image velocimetry. The displacement of PMMA, which has a high bulk glass-transition temperature (Tg) (108 °C) and exhibits limited water absorption, was low both in air (0.54 nm/8.75 min) and water (0.86), while PHEMA, which has a high bulk Tg (99 °C) and exhibits high water absorption, exhibited low mobility in air (0.40) but two orders of magnitude higher mobility in water (60). PMEMA, which has a low bulk Tg (14 °C) and exhibits limited water absorption, already started to move in air (4.5), and its mobility moderately increased in water (20). These behaviors were reasonable, considering the bulk Tg and water absorption characteristics of the polymers. Further, the chain mobility in water was compared with that of dried samples at high temperatures in air. The mobility of PMMA, PHEMA, and PMEMA in water corresponded to that of the dried samples observed in air below the surface Tg (97 °C) for PMMA, at ∼125 °C for PHEMA, and at ∼35 °C for PMEMA. In situ real-time AFM analysis of polymer materials in water is an effective method for evaluating the chain mobility at the polymer/water interface.

Experimental investigation of limit parameters of direct contact condensation in the heat exchanger for waste heat recovery

In the present study, a suitable composition of parameters has been obtained to provide an efficient process of cooling flue gas with complete condensation of water vapour from air-water vapour mixture on a water film in co-current upward flow in the tube of the direct contact heat and mass exchanger. The results showed that the value of the irrigation density depends on the velocity of the air-water vapour mixture and the initial vapour content and should be calculated from an empirical equation. The active pipe height depends on the velocity of the air-water vapour mixture and the initial vapour content and should also be calculated from an empirical equation. For example, if the initial vapour content of the air-water vapour mixture is 11%, the velocity of the mixture is 20.8 m/s the height of the channel should not exceed 0.460 m. The value of the water heating limit temperature increases from 46◦C to 62◦C with a change in the initial vapour content from 11% to 30%. The present experimental results could be helpful in the design of direct contact heat and mass exchangers for waste heat recovery.

Anomalous Adsorption of PFAS at the Thin‐Water‐Film Air‐Water Interface in Water‐Unsaturated Porous Media

AbstractPer‐ and poly‐fluoroalkyl substances (PFAS) are interfacially‐active contaminants that adsorb at air‐water interfaces (AWIs). Water‐unsaturated soils have abundant AWIs, which generally consist of two types: one is associated with the pendular rings of water between soil grains (i.e., bulk AWI) and the other arises from the thin water films covering the soil grains. To date, the two types of AWIs have been treated the same when modeling PFAS retention in vadose zones. However, the presence of electrical double layers of soil grain surfaces and the subsequently modified chemical potential of PFAS at the AWI may significantly change the PFAS adsorption at the thin‐water‐film AWI relative to that at the bulk AWI. Given that thin water films contribute to over 90% of AWIs in the vadose zone under many field‐relevant wetting conditions, it is critical to quantify the potential anomalous adsorption of PFAS at the thin‐water‐film AWI. We develop a thermodynamic‐based mathematical model to quantify this anomalous adsorption. The model couples the chemical equilibrium of PFAS with the Poisson‐Boltzmann equation that governs the distribution of electrical potential in a thin water film. Our model analyses suggest that PFAS adsorption at thin‐water‐film AWI can deviate significantly (up to 82%) from that at bulk AWIs. The deviation increases for lower porewater ionic strength, thinner water film, and higher soil grain surface charge. These results highlight the importance of accounting for the anomalous adsorption of PFAS at the thin‐water‐film AWI when modeling PFAS fate and transport in the vadose zone.

Particulate filtration by cryogenic condensation using a high efficiency Stairmand cyclone separator

This paper describes the synergy of a high-efficiency Stairmand cyclonic separator and the phenomenon of condensation generated by the low temperatures of the mixture of liquid nitrogen and ethanol, to increase the separation efficiency on particles with diameters of 1 μm, 45 μm, 75 μm, 150 μm and 250 μm. The cyclone separator adds the phenomenon of condensation, generating a film of liquid water on its internal walls. The film of liquid water causes a loss of kinetic energy in the particles, reducing their speed and becoming stuck. Al2O3 particles and pozzolana rock particles are used to perform the particle separation experimental tests. A computational fluid dynamics analysis using the second order RSM model is incorporated to describe the fluid dynamic behavior of the particles within the separator cyclone. The results in computational fluid dynamics show the agglomeration of larger diameter particles near the internal walls. Using condensation as a phase change generated by cryogenic mixing results in an overall particle separation efficiency of 76.00 %, standing for an increment of 70.14 % in comparison to a conventional high-efficiency Stairmand separator cyclone.Technological innovation: Particles, filtration, separation, condensation, cryogenic.

A cationic type long-lasting drag-reduction agent based on reduced interfacial water film thickness for enhanced injection in low-permeability reservoirs

In water injection development of low-permeability reservoirs, the elevated flow resistance between the rock surface and the injected water results in enhanced injection pressure. Reducing the thickness of interfacial water film to expand flow radius is a new thought to achieve a decrease in injection pressure. In this work, a hydroxyl-containing cationic surfactant tetradecyl methyl dihydroxy-ethyl ammonium bromide (HTTAB) was designed and synthesized. The introduction of hydroxyl groups enhances the binding to the negatively-charged rock surface. HTTAB can modify the strong hydrophilic rock surface to a hydrophobic state, with the water contact angle increasing from 20.2° to 110.3°. HTTAB shows excellent drag-reducing effect, maintaining a drag reduction rate of over 30 % even after 30 PV of flushing. Particle Image Velocimetry (PIV) experiments show that after HTTAB adsorption, the interfacial slip velocity and centerline velocity can increase by 1.67 times and 33.66 % respectively, and the flow radius expands significantly. In addition, the thickness of the interfacial water film is obtained using Atomic Force Microscope (AFM). The results show that the thickness of the interfacial water film is reduced significantly from 79.42 nm to 8.85 nm. This study provides important guidance for the design of drag-reducing agents and the understanding of interfacial drag-reduction behavior.

Effect of aircraft tire wear on water spray and water displacement drag

During an aircraft taxiing on a water-contaminated runway, the worn tires with shallower grooves will significantly deteriorate the safety of take-off and landing. The hydrodynamics generated by the tire-water-pavement interaction is numerically studied using the coupling method of Smoothed Particle Hydrodynamics and Finite Element Method. By comparing a completely worn tire with a new tire, the effects of tire wear on water spray and water displacement drag are analyzed. With the increasing tire speed and water film depth, the water spray composed of bow wave and side plume increases, and the water displacement drag decomposed of wave- and film-generated components also increases. The effects of tire wear depend on the relative height of tire grooves to the water film depth. For the shallow water film with a depth smaller than the grooves height, the water spray and water displacement drag of new tire is much smaller than those of worn tire, because the groove drainage effect can work very well. While for the deep water film that completely floods the grooves, the water spray and water displacement drag of new tire are similar with those of worn tires, because the groove drainage effect cannot be fully utilized.

Effect of surface water on wollastonite carbonation: Activated dissolution and mass transfer

Carbonation of non-hydraulic calcium silicate to produce cement represents a crucial strategy for mitigating carbon emissions in the cement industry. However, the dissolution rate of Ca2+ is the main constraint on the reaction kinetics. In this study, the carbonation of wollastonite (CS) was investigated, with an emphasis on the role of water in the Ca2+ dissolution process. Firstly, we investigated carbonation performance of CS and its influencing factors. Results revealed a significant impact of the water-to-solid (w-s) ratio on carbonation. In the carbonate products, we observed that the dissolution of Ca2+ adsorbed on the particle surface, referred to as “pseudocrystalline replacement”, which can serve as supplementary cementitious material. Additionally, this observation signifies the accordance of Ca2+ dissolution with the electric double layer (EDL) theory. Subsequently, we quantitatively assessed the influence of w-s ratio on carbonation using kinetic models. Based on EDL theory and the kinetic model, we categorized water film effect into three stages and determined the influence of water film thickness on the rate-determining factors of CS carbonation. This provides theoretical support for preparation of CS-based cement. Interestingly, we found that reaction rate constant varies with changes in the w-s ratio, indicating a catalytic role of water. Further analysis using density functional theory demonstrated that the free water combined with the O/Ca sites on CS to form hydroxylated surfaces, thereby decreasing and increasing the abilities of the local and neighboring sites, respectively, to absorb H2CO3. These findings provide a theoretical foundation for the curing method of low-carbon cements and offer a methodology for the preparation of supplementary cementitious materials.

A New Water Film Depth Prediction Model for Pavement Surface Drainage

The prediction of the water film depth (WFD) on the road surface can help with road skid resistance research and reduce the risk associated with driving on rainy days. At present, there are many empirical and analytical models based on drainage length, slope, rainfall intensity and other parameters. Considering the influence of road surface runoff and starting from the Reynolds number formula of road surface water flow, a new road surface WFD calculation formula that considers the movement state of laminar water flow is derived. The results show that the changing trends of various parameters in the prediction model (drainage length, rainfall intensity, road slope) affecting WFD are consistent with those of the existing model. It is also found that the initial water film depth, initial speed of rainwater, and rainfall angle have little impact on WFD. The predicted value of the model has a suitable matching degree compared with the classical empirical model, which provides a new approach to the prediction of road water film depth.