Thin Water Film Research Articles

Superhydrophilic polymer modified galvanic array moisture sensor chip with stable/improved lifetime towards enhanced dew condensation detection

A stable, sensitive, and accurate moisture chip with long life time is always desired in practical applications. Therefore, it is very important to investigate several factors that affect these properties. In this context, an enhancement in the sensitivity and life time of galvanic array moisture chip used for dew condensation detection has been reported. The chip is capable of early prediction of dew condensation promptly and precisely. The sensing aptitude of the chip with the smallest electrode gap ~500 nm is very fast and can detect water molecules, even much before actual dew condensation occurs. Furthermore, through modification of the surface of the chip using modified superhydrophilic polymer coating, the output could be enhanced by ~2 orders than that of moisture chip without coating. The wettability was promoted by the coating and hence adsorption of water on the surface between the electrodes, generating galvanic current. It could increase the number and area of bridging water droplets between the electrodes, leading to an enhanced output. Interestingly, with the modified superhydrophilic polymer coating used in this study, a wide thin film of water was observed covering the whole surface of moisture chip, not easily observed otherwise. Optical images, contact angle measurement and output current results supported the fact that a moisture chip showed long term stability and excellent capacity towards detection of dew condensation. The life time of moisture chip with superhydrophilic surface is also comparatively long (time period for this study ~20 months).

Efficient milling and cutting of borosilicate glasses through a thin flowing water film with a picosecond laser

Direct laser ablation allows high-quality processing, precision, and cutting of complex shapes. Unfortunately, this technology is usually not considered as the primary candidate for cutting and milling of glasses due to low processing speeds. Thus, laser-based rear side drilling and crack generation techniques are chosen instead. However, we report on the milling and cutting of borosilicate glass plates with high average power and high pulse repetition rate picosecond laser. We optimised laser processing parameters for the efficient direct material ablation and employed water-assisted ablation to improve the ablation efficiency and the cutting speed of borosilicate glasses. The laser process was realised through a thin flowing water film, which was formed by spraying water mist on the surface of the workpiece. Firstly, we characterised thin water film parameters, such as film thickness, flow velocity, and defined a working area with constant processing conditions. Next, we optimised laser processing parameters for both processing environments: ablation through the thin water film and in air. Under optimal parameters, ablation through the thin water film was much more effective, increasing the cutting speed of 420 μm thick glass plates nearly ten times – from 0.52 to 5 mm/s. Furthermore, the morphology of the cuts was improved as well: cut wall roughness and edge chipping were reduced, spatter deposition was avoided in the vicinity of the cut. We investigated the milling of 130 to 1700 μm wide and 50 to 500 μm deep grooves with a maximum depth-to-width ratio of 3.8. Findings revealed that the ablation efficiency increase provided by the water layer did not depend on the depth or the width of the groove and remained constant. Therefore, it became possible to predict the ablation efficiency through the thin water film by knowing the ablation efficiency in air and an absolute ablation efficiency difference between two processing environments. • Efficient borosilicate glass milling and cutting in the air and through the water film was conducted with a picosecond laser. • Optimal laser fluence for efficient glass ablation was 40% higher than in air. • An absolute change in ablation efficiency between two environments did not depend on the transverse dimensions of the groove. • Water film improved ablation efficiency significantly, resulting in nearly 10 times higher cutting speed than in air.

Experimental Study of Unsteady Heat Transfer and Phase Changing Process Upon Impacting of Ice Crystals onto Heated Surfaces Pertinent to Aero-Engine Icing Phenomena

Ice accretion on exposed surfaces of aero-engine components has been widely recognized as a significant hazard to aviation safety in cold weathers. Icing process due to the impingement of the supercooled water droplets suspended in the cloud onto the cold surfaces of inlet components of aeroengines have been studied extensively for decades. Since ice particles were believed to simply bounce off from the exposed surfaces of aero-engine components, ice crystals in the clouds were initially considered not to pose a threat to aviation safety. Therefore, the ice accretion process due to the impacting of ice crystals onto the surfaces of hot engine componentes has not been studied until recently. It has been found recently that, tiny ice particles in the cloud may be partial/full melting upon impacting onto the hot surfaces of aero-engine components, such as heated Inlet Guide Vanes (IGV) and various probes. The partially/fully melted ice crystals were found to stick onto the hot surfaces and form thin water film, which would intercept more oncoming ice particles and lead to significant ice accretion over the surfaces of the hot engine components. The ice crystal induced ice accumulation on the critical aero-engine components has been found to cause significant engine performance loss and erroneous data being read from the probes. In the present study, a series of experimental investigations were conducted to elucidate the underlying physics of the dynamic ice accretion process pertinent to ice crystal icing phenomena. A novel ice crystal icing test rig with the capacity of generating controllable amount of ice crystals and flying speed up to 100 m/s was developed in a temperature-controllable environment chamber for the ice crystal icing studies. By using a high-speed imaging system, a digital particle image velocimetry(PIV), and an Infrared (IR) thermal imaging system, a comprehensive experimental campaign was performed to characterize the transient impacting process of ice crystals, dynamic ice accretion and unsteady heat transfer process associated with the impacting of ice crystals onto heated surfaces, in comparison to those due to the impingement of supercooled water droplets. By using an ultra-sensitive force sensor and a high-speed image system, a comparative study is conducted to examine the differences in the transient impinging dynamics of single water droplets, supercooled water droplets, and ice crystals onto solid surfaces with different wettability and stiffness. By upgrading the unique Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) with additional ice crystal icing capability, a set of explorative studies are also conducted to examine the characteristics of the dynamic ice accretion processes over the heated surfaces of an aero-engine Inlet Guide Vane (IGV) model under both ice crystal icing and supercooled droplet icing conditions. The anti-/de-icing performance of a novel hybrid strategy by integrating icephobic coatings and minimized surface heating are also evaluated under both supercooled water droplet icing and ice crystal icing conditions. The new findings derived from the present studies are very helpful to gain further insights into the ice crystal icing phenomena for the development of more effective and robust anti-/de-icing strategies to ensure safer and more efficient aircraft/aero-engine operations in cold weathers.

Concurrent Enhancement of Conductivity and Stability in Water of Poly(3,4‐Ethylenedioxythiophene):Poly(Styrenesulfonate) Films Using an Oxetane Additive

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most used conducting polymer in organic electronics and bioelectronics owing to its high conductivity combined with high optical transparency and availability as a stable colloidal aqueous dispersion, that can be processed as a conducting ink to produce thin and flexible films and electrodes. In this work, water‐resistant films of PEDOT:PSS showing enhanced conductivity are prepared by solely adding one reagent, 3‐methyl‐3‐oxetanemethanol, to PEDOT:PSS aqueous dispersions. The stability of the resultant thin films in water is attributed to the covalent cross‐linking of benzene rings anchored in PSS chains to polyether chains originated from the polymerization of oxetane groups, as indicated by NMR studies. A phase‐segregation within the PEDOT:cross‐linked PSS film is suggested to facilitate charge transport within the PEDOT network and to be at the origin of the improved conductivity. When immersed in water, the films exhibit increased water‐resistance towards resuspension and delamination and exhibit an increase of conductivity, by two to three orders of magnitude, depending on the used raw PEDOT:PSS formulation. The method described in this work is advantageous in originating water‐stable and highly conducting thin films of PEDOT:PSS as it does not involve high temperatures nor strong acids.

Coupled Monte Carlo and Molecular Dynamics Simulations on Interfacial Properties of Antifouling Polymer Membranes.

We use molecular simulation to study the wetting behavior of antifouling polymer-tethered membranes. We obtain the interfacial properties (e.g., contact angle) of water at various temperatures for five polymer membranes, including a base polysulfone (PSF) membrane and four other PSF membranes grafted with antifouling polymers (two poly(ethylene glycol) (PEG) tethers and two zwitterionic tethers). We implement a coupled Monte Carlo (MC)/molecular dynamics (MD) approach to determine the interface potentials of water on the membrane surfaces in an efficient manner. Within this method, short MC and MD simulations are performed in cycles to collect the surface excess free energy of a thin water film on polymer membrane surfaces. Simulation results show that the grafting of zwitterionic tethers provides a more significant enhancement in the hydrophilicity of the PSF membrane than that of the PEG tethers. Water completely wets the surface of zwitterionic polymer membranes.

Application and Mechanism of Superhydrophilic Surfaces for the Enhancement of CO2–H2O Absorption

In this work, superhydrophilic packings are employed to intensify the absorption process of CO2 with H2O. The results show that the improvement in absorption efficiency with a superhydrophilic surface in the falling film process was 1.7–2 times that for the untreated pristine plate and more than 10% in the packed tower. The enhancement of absorption is caused by the high attraction of the superhydrophilic surface to water, which evokes a stable but relatively thin water film, enlarging the wetted surface area with low water flow and holding more water on the surface with high water flow. The flooding point of the superhydrophilic packings increases by 20% and the water holdup improves by 1.2–1.4 times. The enhancement effect can be introduced by modifying the existing absorption correlation with the parameter of the wetted area ratio of the superhydrophilic surface to the unmodified surface. The intensification of the CO2/H2O adsorption process evoked by superhydrophilicity provides a useful strategy for packing reformation.

Investigating the Ubiquitous Presence of Nanometric Water Films on Surfaces

When we speak of nanometric water films on surfaces we are speaking about a truly ubiquitous phenomenon in nature. All surfaces exposed to ambient conditions are covered by a thin film of water that affects or mediates surface chemistry, general physical-chemical processes on surfaces, and even solid–solid interactions. We have investigated this phenomenon for over a decade by exploiting dynamic atomic force microscopy and have (1) described how these layers affect apparent height measurements, (2) analyzed the excitation of subharmonics, (3) investigated its effects on surface functionality over time (“aging”), (4) monitored and quantified the time-dependent wettability of several relevant surfaces such as highly oriented pyrolytic graphite and monolayer systems, and (5) developed high-resolution and highly stable modes of imaging. Here, we discuss these findings to elucidate the present and future of the field. We further provide a brief but general discussion of solvation and hydration layers in vacuum, liquid, and air that center around current controversies and discuss open possibilities in the field.

Probing the Interactions between Pickering Emulsion Droplets Stabilized with pH-Responsive Nanoparticles.

The presence and adsorption of particles at the oil/water interface play a critical role in stabilizing Pickering emulsions and affecting their bulk behavior. For water-in-oil (W/O) and oil-in-water (O/W) Pickering emulsions with pH-responsive nanoparticles, their interaction forces and stabilization mechanisms at the nanoscale have not been reported. Herein, the Pickering emulsions formed by oil/water mixtures under different pH values with bilayer oleic acid-coated Fe3O4 nanoparticles (Fe3O4@2OA NPs) were characterized using microscopy imaging and zeta potential and interfacial tension (IFT) measurements. The interaction forces between formed emulsion droplets were quantified using an atomic force microscope (AFM) drop probe technique. A W/O emulsion formed at pH 2 and 4 is mainly stabilized by the steric barrier formation of confined particle layers (with Fe3O4@2OA NPs and aggregates). At pH 9 and 11, an O/W emulsion is formed, and its stabilization mechanism is mainly due to relatively low IFT, strong electrostatic repulsion due to carboxyl groups, and steric repulsion from confined nanoparticles and aggregates, leading to a stable confined thin water film. Increasing the maximum loading force and dwelling time enhances the confinement of Fe3O4@2OA particles and aggregates at the oil/water interface. This work provides useful insights into the interaction and stabilization mechanisms of Pickering emulsions with stimuli-responsive interface-active particles.

Behavior of a water droplet impacting a thin water film

Behavior of a water droplet impacting a thin water film

Reactivity of Hydrogen-Related Electron Centers in Powders, Layers, and Electrodes Consisting of Anatase TiO2 Nanocrystal Aggregates.

Anatase TiO2 nanoparticle aggregates were used as model systems for studying at different water activities the reactivity of electron centers at semiconductor surfaces. The investigated surface conditions evolve from a solid/vacuum interface to a solid/bulk electrolyte interface. Hydrogen-related electron centers were generated either chemically—upon sample exposure to atomic hydrogen at the semiconductor/gas interface—or electrochemically—upon bias-induced charge accumulation at the semiconductor/electrolyte interface. Based on their corresponding spectroscopic and electrochemical fingerprints, we investigated the reactivity of hydrogen-related electron centers as a function of the interfacial condition and at different levels of complexity, that is, (i) for dehydrated and (partially) dehydroxylated oxide surfaces, (ii) for oxide surfaces covered by a thin film of interfacial water, and (iii) for oxide surfaces in contact with a 0.1 M HClO4 aqueous solution. Visible (Vis) and infrared (IR) spectroscopy evidence a chemical equilibrium between hydrogen atoms in the gas phase and—following their dissociation—electron/proton centers in the oxide. The excess electrons are either localized forming (Vis-active) Ti3+ centers or delocalized as (IR-active) free conduction band electrons. The addition of molecular oxygen to chemically reduced anatase TiO2 nanoparticle aggregates leads to a quantitative quenching of Ti3+ centers, while a fraction of ∼10% of hydrogen-derived conduction band electrons remains in the oxide pointing to a persistent hydrogen doping of the semiconductor. Neither trapped electrons (i.e., Ti3+ centers) nor conduction band electrons react with water or its adsorption products at the oxide surface. However, the presence of an interfacial water layer does not impede the electron transfer to molecular oxygen. At the semiconductor/electrolyte interface, inactivity of trapped electrons with regard to water reduction and electron transfer to oxygen were evidenced by cyclic voltammetry.

Development of Bile Direct Stent Having Antifouling Properties by Atmospheric Pressure Low-Temperature Plasma

Biomimetics (or biomimicry) is a field of technologies based on imitating various functions and properties of organisms. Waterproof products, which are inspired by lotus leaves with super-water-repellent fine structures, are a well-known example of biomimetics. The present study examined the surface structure of snail shells, which exhibit oil repellency (oleophobic property). Snail shells have nanoporous structures with nanoholes on the scale of 200–400 nm. When water enters these nanoholes, the surface is covered by thin water films. The oil can be repelled by the water film. These structures are known as superhydrophilic nanostructures. An earlier report discussed our efforts to create such nanostructures using a nanoimprinting method and assessed the feasibility of application to the inner walls of biliary stents. This involves a labor-consuming two-stage process involving creating nanostructures on a film surface, then rolling the film into a tube. In addition, the nanoimprinting mold made via electron beam lithography is costly and unsuitable for mass production.To overcome these issues, we sought to develop elemental technologies for providing antifouling properties to biliary stents, which are made of polyethylenes (PEs), by forming nanostructures directly on the inner surface, using atmospheric pressure low-temperature plasma. We formed nanostructures on the inner walls of PE tubes of varying diameters under varying plasma conditions. We then examined the resulting structures and effects of the antifouling properties thus imparted.

Material Removal and Wear Behaviour of Copper Thin Film in Ambient Air and Wet Environment by Nanoindenter

This paper aims to investigate the scratching behaviour of copper thin film in dry and wet environments by nanoindenter using conical indenter. The material removal mechanism of the complex chemical mechanical polishing (CMP) process is viewed as single abrasive scratch wear considering the effect of the wet environment. The experimental scratches are performed on Hysitron TI 980 Triboindenter in constant load mode as well as ramp load mode. The experimental results show that for a given force, the scratch depth in slurry environment sample is significantly larger than that in the DI water environment sample, due to the presence of soft passivation in the slurry environment. Consequently, the wear rate in the slurry environment is significantly larger than wear rates in the air and DI water environment. The wear rate in the slurry environment is five times larger than those in ambient air and DI water environments. A similar trend is reflected by the instantaneous specific energy evaluation for all conditions. In comparison to ambient conditions, the slurry environment requires 78% less and the DI water environment require 17% more instantaneous specific energy for unit volume material removal, at a given scratch depth. The ease of material removal in the slurry environment is supported by the significant decrease in Scratch hardness of the copper thin film sample passivated in the slurry environment. The progression of the coefficient of friction is studied concerning the nano deformation mechanism in the copper thin film in all environments. The stick-slip behaviour is observed for the copper thin film in wet environment. An explicit scratch hardness model with consideration of elastic recovery is developed for constant load mode scratching to access the scratch hardness of the copper thin film. The computed scratch hardness of copper thin film in ambient, DI water and slurry comes out to be 1.875 GPa, 1.948 GPa and 0.996 GPa respectively. X-ray photoelectron spectroscopy (XPS) analysis is performed to characterize the copper thin film surface before and after passivation in DI water and slurry. Results of this study of deformation during scratching of the passivation layer on copper thin film can be applied to develop and analyze the advanced node copper CMP process.

Analysis of mechanical properties of copper thin film in ambient, DI water and slurry environment by nanoindentation

ABSTRACT The nanomechanical properties of chemically altered wafer surface are critical for modelling the material removal in the chemical mechanical planarization (CMP). This paper investigates the nanomechanical properties of copper thin film on the silicon wafer and the reacted passivation layer in different environmental conditions by nanoindentation. The environmental conditions are ambient air, DI water and slurry environment at 45°C temperature. Nanoindentation test is performed on Hysitron TI980 triboindenter using standard Berkovich indenter. Experimental results show that the nanohardness and Young’s modulus of the copper thin film in the ambient environment are 1.72 GPa and 118.03 GPa, respectively. The passivation in DI water results in a slight increase in nano-hardness of copper thin film, on the other hand, a significant decrease in nano-hardness is observed after passivation in the slurry environment. The reduced values of hardness and young’s modulus in the slurry environment are in line with the chemical action of slurry in CMP. The estimated nano-hardness and modulus of the wafer contact surface after the chemical action of slurry are critical process parameters for the analysis and modelling of the advanced node (CMP) process.

A nature-inspired suspended solar evaporator for water desalination of high-salinity brines

• A water strider-inspired suspended solar evaporator (WSUSE) is fabricated. • The WSUSE shows stable suspending depth regardless of changed salinity. • Salt-resistance is achieved by confining a thin water film on the solar absorber. • High solar evaporation performance is realized even for concentrated brines. As an environmental-friendly and cost-effective technology, interfacial evaporation mediated by photo-thermal materials has shown great potential in solar desalination and wastewater treatment. However, salt accumulation or fouling on the surface of solar absorbers during water evaporation, especially in high-salinity brines, is seemingly inevitable for current solar evaporators, resulting in severely weakened steam generation performance as well as limited long-term use. Here, inspired by water strider, we demonstrate a new type of solar evaporator consisting of a hydrophobic frame, a hydrophilic solar absorber and a heat-insulation layer. Relying on the surface tension force generated by the hydrophobic frame, the solar evaporator can suspend stably just underneath water surface, enabling the confinement of a thin water film on solar absorber for salt-resistance and efficient energy utilization. More notably, the suspending depth is kept almost unchanged in different-salinity brines, achieving high evaporation rates (1.45 kg m -2 h - 1 and 1.35 kg m -2 h - 1 ) in highly concentrated salt solutions (15 wt% and 20 wt% NaCl) under one-sun illumination. No salt-accumulation is observed during the evaporation process till the limit of salt-saturation, and stable evaporation performance is achieved under dynamic water environment. With the merits of antifouling and excellent evaporation performances, the new concept of “suspended evaporators” provides great opportunities in solar-based water desalination and treatment, especially for high-salinity seawater or in closed-systems.

An experimental evaluation on revamping the productivity of solar PV panel using wind tunnel as an optimizer

At high working temperatures, the performance of the solar photovoltaic (PV) cells will be affected. With the increase in temperature of the PV cells, the conversion of solar radiation into electrical output will be decreased. The operating temperature of the PV cells is one of the prime factors for determining its electrical conversion efficiency. In order to get the maximum electrical output from the solar PV cells, the temperature should be maintained properly. In this experimental study, the temperature of the solar PV cells was maintained by cooling both sides of the PV panel simultaneously. The front surface of the PV panel is sprayed with a thin film of pot water and the rear side is attached with a fabricated duct that was connected into a wind tunnel blower. The mass flow rate of the moist air from the wind tunnel to the rear side of the PV is ranged between 0.1m/s to 0.5m/s. The performance characteristics of both the commercially available PV panel and the experimental PV panel (PVT Clay pipe panel) were compared. The results show that the PVT clay pipe panel has an electrical efficiency of about 11.72%, whereas the commercially available PV panel has only 9.77%. Also, the overall efficiency of the experimental PVT panel is 65.55% respectively.

Non-Immersion Ultrasonic Cleaning: An Efficient Green Process for Large Surfaces with Low Water Consumption

Ultrasonic cleaning is a developed and widespread technology used in the cleaning industry. The key to its success over other cleaning methods lies in its capacity to penetrate seemingly inaccessible, hard-to-reach corners, cleaning them successfully. However, its major drawback is the need to immerse the product into a tank, making it impossible to work with large or anchored elements. With the aim of revealing the scope of the technology, this paper will attempt to describe a more innovative approach to cleaning large area surfaces (walls, floors, façades, etc.) which involves applying ultrasonic cavitation onto a thin film of water, which is then deposited onto a dirty surface. Ultrasonic cleaning is an example of the proliferation of green technology, requiring 15 times less water and 115 times less power than conventional high-pressurized waterjet cleaning mechanisms. This paper will account for the physical phenomena that govern this new cleaning mechanism and the competition it poses towards more conventional pressurized waterjet technology. Being easy to use as a measure of success, specular surface cleaning has been selected to measure the degree of cleanliness (reflectance) as a function of the process’s parameters. A design of experiments has been developed in line with the main process parameters: amplitude, gap, and sweeping speed. Regression models have also been used to interpret the results for different degrees of soiling. The work concludes with the finding that the proposed new cleaning technology and process can reach up to 98% total cleanliness, without the use of any chemical product and with very low water and power consumption.

Polymer dewetting in solvent-non-solvent environment- new insights on dynamics and lithography-free patterning

HypothesisWe show that one may employ polymer dewetting in solvent-non-solvent environment to obtain lithography-free fabrication of well-defined nano- to micro- scale polymer droplets arrays from pre-patterned polymer films. The polymer droplet pattern may be converted to a series of hybrid organic–inorganic and inorganic well-defined nano-patterns by using sequential infiltration synthesis (SIS). In particular, we scrutinize the physical parameters which govern the dewetting of flat and striped polymer thin films, which is the key to obtaining our objective of lithography-free ordered nano-patterns. ExperimentsWe immerse polystyrene (PS) and polymethyl methacrylate (PMMA) thin films in water in the presence of chloroform vapors. We study the ensuing polymer dewetting dynamics and the pattern formation of nanospheres by employing in-situ light microscopy and scanning electron microscopy. We then investigate pattern formation by dewetting of polymer stripes, fabricated by directed solvent evaporation, and SIS of AlOx from vapor phase precursors, trimethyl aluminum (TMA) and H2O, within the nanosphere patterns. FindingsWe find that solvent- non-solvent environments render film dewetting rates, which are an order of magnitude faster than solvent vapor dewetting, and supports the formation of small solid polymer droplets, down to sub-100 nm droplet size, of large contact angles with the solid substrate. Pre-patterned polymer film stripes support the formation of highly ordered structures of polymer droplets, which are easily transformed to hybrid polymer-AlOx nanosphere patterns and templated AlOx nanosphere via SIS.

Improvement of LIBS signal stability for NaCl solution using femtosecond laser-induced water film

This paper studies the analysis of Na element concentration in NaCl aqueous solution using laser-induced breakdown spectroscopy (LIBS). The NaCl solution is transformed to a thin water film. The water film can provide a stable liquid surface, and overcome the disadvantage that laser focusing position cannot be fixed due to liquid level fluctuation (when nanosecond laser is used as the excitation light source, there is serious liquid splash phenomenon, which affects the signal stability). And, femtosecond pulse laser is used to excite the water film to produce the plasma, avoiding liquid splashing. The measured emission lines are Na (I) at 589.0 nm and 589.6 nm. The calibration curves of sodium are plotted by measuring different concentrations of NaCl solution. The linear correlation coefficients of Na (I) lines at 589.0 nm and 589.6 nm are 0.9928 and 0.9914, respectively. In addition, the relative standard deviation is also calculated; its range is from 1.5% to 4.5%. The results indicate that the combination of femtosecond laser and water film can significantly improve the signal stability for liquid analysis in LIBS.

Effect of Pore Structure on Slippage Effect in Unsaturated Tight Formation Using Pore Network Model

The gas slippage phenomenon under dry conditions has been investigated extensively both numerically and experimentally. However, very limited research has focused on gas slippage behavior under wet conditions. Unlike conventional formation, the influence of water on the gas transport process cannot be neglected in tight formations due to the comparable amount of thin water film attached along the rock surface. It is found experimentally that the gas slippage factor is positively related to water saturation if the water saturation is small, while it decreases with water saturation if it is larger than a critical value. Most of the existing models failed to capture the measured downtrend of the gas slippage factor with increasing water saturation, which resulted from water blocking or gas trapping phenomenon. In this work, a pore-scale network model is proposed to look at the water distribution characteristic and investigate the effect of water on the gas slippage factor. The proposed pore-scale model incorporates the capillary dominated multiphase fluid distribution, real gas effect, and gas transport mechanisms at pore scale. On the basis of our pore network model, the effect of pore structure characteristics including the frequency of mean pore radius, size of mean pore radius, aspect ratio, and coordination number on the gas slippage behavior are investigated and discussed in detail. Similar to previous experimental observations, the simulated gas slippage factor shows a non-monotonic increase trend with water saturation; it starts to decrease under high water saturation, and the critical water saturation depends on the pore structure factors. It increases with the mean pore radius and coordination number but decreases with the aspect ratio. We used the pore network model to investigate the effect of the water phase on the gas slippage behavior at the pore scale for the first time. It emphasized the predominance of water blocking and the gas trapping phenomenon in the estimation of the gas slippage factor at high water saturation.

Influence of the formwork removal by polarization on the facing aesthetics in reinforced concrete

Formwork removal by means of polarization offers an alternative solution to compensate for some of the disadvantages and risks of using mineral-based oil due to its petrochemical origin. This technique consists of applying an electrical current between the steel reinforcing bars and the metal formwork wall in order to obtain a thin water film at the concrete/formwork interface and allow for formwork removal. This paper focuses on the facing quality of the reinforced concrete and formwork surface at various temperatures for both conventional and self-compacting concretes. A series of experimental tests have been conducted in the laboratory to determine the optimal polarization parameters (voltage value, time and duration of its application). On-site tests were then performed to observe the scaling effect. Results indicate that the proposed polarization technique can indeed provide an effective means to separate the concrete from its formwork without requiring demoulding oil. Concrete mixtures implemented both in the laboratory and on-site display high-quality facing without the presence of any attachment points. A chromatographic analysis of the concrete pore solution and water transported by electro-osmosis shows that ion concentrations remain unaffected. This polarization approach can thus be used as an alternative to avoid the use of oils of a chemical or petrochemical origin.