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This paper focuses on the impact of elevated temperatures on the adsorptive and capillarity water retention mechanisms of unsaturated soils under constrained (constant volume) conditions. This topic is critical for simulating the thermo-hydraulic behavior of soils in hydrogeological or geotechnical applications, including climate change effects on near surface soils, energy piles or soil borehole thermal energy storage systems in unsaturated soil layers, and buffers for geological nuclear waste repositories. A nonisothermal soil water retention curve (SWRC) that separately considers the temperature-dependency of the key parameters governing adsorptive and capillarity water retention mechanisms and soil physical parameters (e.g., surface tension, contact angle, adsorption capacity, cation exchange capacity, mean cavitation suction, air entry value and equilibrium film thickness) was developed to provide insights into the impact of temperature on water retention over the full suction range. The nonisothermal SWRC was validated using experimental data on high plasticity clays, with a good prediction of temperature effects on adsorption and capillarity water retention mechanisms in constrained unsaturated soils. [ABSTRACT FROM AUTHOR]

The study aims to eliminate the effect of coalescing filter blocking due to on–off operation by changing the wetting properties of the non-woven fiberglass filter media through their chemical modification with the use of a polydimethylsiloxane (PDMS) solution in hexane and a few commercial products that give the surface oleophobic properties. The best results—high separation efficiency, no redispersion of droplets at the outlet, and low flow resistance—were obtained for materials coated by immersion in a 0.2% PDMS solution, for which a reduction in oleophilicity was found, but the material was not oleophobic and still moderately wetted with the test liquid. The corresponding static contact angle with the VG-46 rotary compressor oil measured on the flat borosilicate glass wafer made of the same material as the fiberglass media was equal to 54° for the PDMS dip-coated surface. Moreover, the good stability of the applied polymer on the material surface was confirmed by the SEM imaging, the FTIR analysis, and maintaining a high performance in multiple tests run for a single coalescing element. [ABSTRACT FROM AUTHOR]

In view of the limitation that the existing theoretical methods cannot reflect the influence of fiber wettability on permeability, the analytical expression of capillary pressure and the calculation formula of lateral dynamic permeability of fiber tow impregnation process were derived. The numerical simulation of the process of resin impregnated fiber tows was carried out by using a phase field method. The simulation results indicated that the numerical solution of the capillary pressure obtained by the phase field method was consistent with the analytical solution obtained from this paper. This proved the reliability of the developed method. The effects of fiber volume fraction and contact angle on the dynamic permeability were studied. The results indicated that this method could better characterize the effect of fiber wettability on the permeability and realize the dynamic prediction of the permeability at different impregnation radii. Compared to the existing permeability calculation methods, the developed method is more applicable and the calculation results are more accurate. [ABSTRACT FROM AUTHOR]

Synthesis of the MAX phase is most often conducted at high temperatures, and the synthesized mixture contains many contaminant phases that require removal. The discovery of efficient low-temperature methods for the synthesis of MAX phases and MXenes is the key to their mass application. This work reports a method for obtaining pure MAX-phase with composition of Cr 2 GaC using a microwave reactor without additional heating. Synthesis was performed under 2 torr vacuum in hydrogen and methane flows of 80 and 20 sccm, respectively. The power of the microwave generator was 500 W at a frequency of 4.5 GHz. The synthesis process consists of creating conditions for capillary interaction (contact angle much lower than 90°, tends to zero), dissolution of chromium substrate in liquid gallium and dissolution of carbon directly from the gas phase (H 2 –CH 4 plasma). The synthesized MAX phase does not contain any phase contaminations and has a thickness of several atomic layers and submicron lateral dimensions. Characterization of the phases was carried out using the transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), atomic-force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy methods. Diffraction methods show high purity of Cr 2 GaC phase synthesized by this method, which can be a good precursor for MXenes production. [ABSTRACT FROM AUTHOR]

Consider a system of two parallel solid cylinders of equal radius made of a homogeneous material. We study the stability of a liquid bridge of circular cylinder shape between both solid cylinders. It is proved that if the circular cylinder liquid is concave, then it is stable. If the circular cylinder liquid is convex, we establish conditions on the radius of the cylinder liquid and the contact angle that ensure that long convex circular cylinders are not stable. Estimates for the length of these convex cylinders are given. [ABSTRACT FROM AUTHOR]

We derive the ab initio equilibrium statistical mechanics of the gas–liquid–solid contact angle on planar periodic, monodisperse, textured surfaces subject to electrowetting. To that end, we extend an earlier theory that predicts the advance or recession of the contact line amount to distinct first-order phase transitions of the filling state in the ensemble of nearby surface cavities. Upon calculating the individual capacitance of a cavity subject to the influence of its near neighbors, we show how hysteresis, which is manifested by different advancing and receding contact angles, is affected by electrowetting. The analysis reveals nine distinct regimes characterizing contact angle behavior, three of which arise only when a voltage is applied to the conductive liquid drop. As the square voltage is progressively increased, the theory elucidates how the drop occasionally undergoes regime transitions triggering jumps in the contact angle, possibly changing its hysteresis, or saturating it at a value weakly dependent on further voltage growth. To illustrate these phenomena and validate the theory, we confront its predictions with four data sets. A benefit of the theory is that it forsakes trial and error when designing textured surfaces with specific contact angle behavior. [ABSTRACT FROM AUTHOR]

In the present study, nine fabrics have been tested for brackish water treatment with the aim of industrial application under the concept of zero liquid discharge (ZLD). Moisture content was determined, where it was observed that the lignocellulosic fabrics had a moisture content ranging from 2.5 to 8.5%. The wetting contact angle showed that the flax with polylactic acid (LPLA) was the most hydrophobic. The determination of the liquid absorption capacity showed that, of the synthetic fabrics, the one with the highest absorption, both in distilled water and in brackish water, was the polyester (PES) fabric with an absorption of 816% compared to its initial weight. In the natural fabrics, the highest absorption capacity was shown by the wet-laid without treatment (WL-WT) fabric for both distilled water and brackish water, although it required several cycles of operation to maintain this stable absorption. Exposure to brackish water improved the absorption capacity of all samples. Mechanical and thermal characterization showed that the synthetic fabrics were more resistant than the natural fabrics, although they may compete in terms of applicability. The capillarity study showed that the most hydrophilic fabrics completed the test the fastest. Finally, the composting degradation test showed that those fabrics with polylactic acid (PLA) content degraded faster in the first 14 days and thereafter the degradation of the lignocellulosic content showed a slower degradation until 112 days. The Bam fabric did not degrade during the course of the experiment. [ABSTRACT FROM AUTHOR]

The comprehension of capillarity phenomenon is important in chemical, printing, and textile dyeing. The current paper provides an insight into the diffusion of direct dyes into cellulosic materials with regard to the change of fabric characteristics, dye structure, and bath composition. First, an experimental device was developed and series of experiments were carried out using cotton as textile fabric model and direct dyes (Direct Orange 39, Direct Red 79, and Direct Red 80) as wicking liquids. Data were analyzed based on the evolution of diffusion rate [D (cm2/s)] versus C/C0. Results exhibited that the capillary ascension of dyes depends on weft count, weave structure, yarn type, angle contact, wet agent, dye structure, and dye concentration. The D (cm2/s) values were much higher than for twisted yarn. The tortuosity lowered the diffusion of the dye along with fabrics. The rate of water transport increased with weft count and it became more important when the structure of fabric is more tightened. Both inter-yarn space and vertical position of the fabric limited the ascension of the liquid. In brief, along this study, we demonstrated that the proposed apparatus could provide a potential evaluation of wicking phenomenon along with textile materials.

We revisit the classical problem of calculating the pancake-like shape of a sessile drop at large Bond numbers. Starting from a formulation where drop volume and contact angle are prescribed, we develop an asymptotic scheme which systematically produces approximations to the two key pancake parameters, height and radius. The scheme is based on asymptotic matching of a 'flat region' where capillarity is negligible and an 'edge region' near the contact line. Major simplifications follow from the distinction between algebraically and exponentially small terms, together with the use of two exact integral relations. The first represents a force balance in the vertical direction. The second, which can be interpreted as a radial force balance on the drop edge (up to exponentially small terms), generalises an approximate force balance used in classical treatments. The resulting approximations for the geometric pancake parameters, which go beyond known leading-order results, are compared with numerical calculations tailored to the pancake limit. These, in turn, are facilitated by an asymptotic approximation for the exponentially small apex curvature, which we obtain using a Wentzel–Kramers–Brillouin method. We also consider the comparable two-dimensional problem, where similar integral balances explicitly determine the pancake parameters in closed form up to an exponentially small error. [ABSTRACT FROM AUTHOR]

Surfactants (i.e., solutes that reduce the surface tension of water) exist in the subsurface either naturally or are introduced to the subsurface due to anthropogenic activities (e.g., agricultural purposes, environmental remediation strategies). Surfactant-induced changes in surface tension, contact angle, density, and viscosity alter the water retention and conduction properties of the vadose zone. This research numerically investigates the effects of surfactants in the vadose zone by comparing the flow and transport of three different surfactant solutions, namely butanol, ethanol, and Triton X-100. For each surfactant case, surfactant-specific concentration-dependent surface tension, contact angle, density, and viscosity relationships were incorporated by modifying a finite element unsaturated flow and transport code. The modified code was used to simulate surfactant infiltration in the vadose zone at residual state under intermittent boundary conditions. The modelling results show that all three surfactant solutions led to unique and noteworthy differences in comparison to the infiltration of pure water containing a conservative tracer. Results indicate that surfactant infiltrations led to complex patterns with reduced vertical movement and enhanced horizontal spreading, which are a function of concentration-dependent surface tension, density, contact angle, viscosity and sorption characteristics. The findings of this research will help understanding the effects of surfactant presence in the subsurface on unsaturated flow and its possible links to future environmental problems. [ABSTRACT FROM AUTHOR]

We derive the ab initio equilibrium statistical mechanics of the gas–liquid–solid contact angle on planar periodic, monodisperse, textured surfaces subject to electrowetting. To that end, we extend an earlier theory that predicts the advance or recession of the contact line amount to distinct first-order phase transitions of the filling state in the ensemble of nearby surface cavities. Upon calculating the individual capacitance of a cavity subject to the influence of its near neighbors, we show how hysteresis, which is manifested by different advancing and receding contact angles, is affected by electrowetting. The analysis reveals nine distinct regimes characterizing contact angle behavior, three of which arise only when a voltage is applied to the conductive liquid drop. As the square voltage is progressively increased, the theory elucidates how the drop occasionally undergoes regime transitions triggering jumps in the contact angle, possibly changing its hysteresis, or saturating it at a value weakly dependent on further voltage growth. To illustrate these phenomena and validate the theory, we confront its predictions with four data sets. A benefit of the theory is that it forsakes trial and error when designing textured surfaces with specific contact angle behavior.

[Display omitted] Hypothesis : The migration of supercritical CO 2 (scCO 2) injected into underground reservoirs as part of carbon capture and storage is influenced by organic contamination affecting mineral wettability. Molecular dynamics (MD) simulations of relevant systems that incorporate representative organic solutes allow detailed investigation of changes in fundamental interfacial and capillary properties. Experiments : We use MD simulations to explore the effects of four organic solutes (quinoline, decanoic acid, coronene, sorgoleone) on the wettability of quartz by water in the presence of scCO 2. We examine the impacts of polar, alkyl, and aromatic moieties as well as fluid flow velocity at elevated temperatures and pressures. Findings : Organic molecules accumulate at the water-CO 2 interface, where they distribute according to their size and functional groups. Certain organics penetrate the adsorbed water film at the quartz-CO 2 interface, revealing two modes of hydrogen bonding between polar organic functional group, water, and quartz surface –OH groups. Interfacial energies and contact angles are minimally impacted by organic adsorption at the water-CO 2 interface, possibly due to simultaneous CO 2 desorption. Non-equilibrium MD simulations reveal that flow-induced redistribution of organic compounds modulates the radii of curvature of the advancing and receding water-CO 2 interfaces. Our results indicate that organic adsorption on water surfaces is likely ubiquitous during multi-phase flow in soils and sedimentary rocks, with implications for the mobilization and transport of organic compounds. [ABSTRACT FROM AUTHOR]

• A quasistatic modeling approach has been developed to model the dislodgment of a nonwetting droplet by a wetting slug. • A CFD analysis has been developed to provide a framework for validation of the developed model. • Very good match is obtained between the developed model and the CFD work, which builds confidence of the modelling approach. • Snapshots of the progression of the emergence of the droplet till its dislodgment are provided. • Data related to the changes of the pressure profile along the system are provided. The problem of ejection of a droplet from a pore opening into a reservoir appears in many fields including pharmaceutical, food, chemical, and several other industries. In this work, we are interested in investigating the onset of dislodgment of such an emerging droplet. A one-dimensional model is developed that describes the dynamics of this process under quasistatic assumptions. Fluid inertia, the dynamic nature of the contact angle, as well as the entrance and exit hydrodynamic effects are ignored. Fluid inertia may be important at the very early stage of the displacement process, after which its effect diminishes. It is hypothesized that the emerging droplet will dislodge the surface when the two contact lines associated with the two interfaces meet. The forces acting on this system include external pressures, viscous and capillary forces. The flow rate is influenced by the capillary pressure of the emerging nonwetting fluid when the advancing interface reaches the exit of the tube and starts to develop, then by the two interfaces when the wetting fluid starts to displace the wetting one. At the onset of dislodgment, the capillary pressure across the two interfaces equalizes. A computational fluid dynamics (CFD) study has been conducted to confirm the stated hypothesis and to provide a framework for the validation and verification of the developed model. The CFD model depicts the whole spectrum of processes involved from the start of injection of the nonwetting fluid towards the ejection of the droplet. The model, however, only considers the system when the wetting fluid starts to emerge from the exit of the tube into the reservoir. Comparisons between the model and the CFD analysis show a good match, which builds confidence in the modeling approach. Interesting results are obtained, particularly when the interfaces reach the exit of the tube. [Display omitted] [ABSTRACT FROM AUTHOR]

The comprehension of capillarity phenomenon is important in chemical, printing, and textile dyeing. The current paper provides an insight into the diffusion of direct dyes into cellulosic materials with regard to the change of fabric characteristics, dye structure, and bath composition. First, an experimental device was developed and series of experiments were carried out using cotton as textile fabric model and direct dyes (Direct Orange 39, Direct Red 79, and Direct Red 80) as wicking liquids. Data were analyzed based on the evolution of diffusion rate [D (cm2/s)] versus C/C0. Results exhibited that the capillary ascension of dyes depends on weft count, weave structure, yarn type, angle contact, wet agent, dye structure, and dye concentration. The D (cm2/s) values were much higher than for twisted yarn. The tortuosity lowered the diffusion of the dye along with fabrics. The rate of water transport increased with weft count and it became more important when the structure of fabric is more tightened. Both inter-yarn space and vertical position of the fabric limited the ascension of the liquid. In brief, along this study, we demonstrated that the proposed apparatus could provide a potential evaluation of wicking phenomenon along with textile materials. [ABSTRACT FROM AUTHOR]

Surface-active solutes that exist in the subsurface either naturally (humic acid) or as a result of anthropogenic activities (alcohols, surfactants, PFAS) alter the hydraulic and geotechnical properties of the unsaturated porous media. The alteration of properties is the result of concentration-dependent surface tension, and/or density, and the contact angle effects. These effects are manifested in the form of changes in water retention and conduction and changes in the suction component of the shear strength. Differences in the spatial distribution of these solutes in the subsurface result in capillary pressure gradients causing flow perturbations. Conceptual and numerical models to understand the effects of these solutes require concentration-dependent consideration of surface tension, density, and the contact angle effects on hydraulic and geotechnical properties of porous media. Capillary rise experiments have been carried out to either quantify the effect of surface-active solutes on the height of capillary rise or to determine the concentration-dependent contact angle changes due to salinity of the pore water. This paper provides a comprehensive review of the literature on capillary rise experiments and how they can potentially be used to characterize the hydraulic and geotechnical properties of unsaturated porous media affected by surface-active solutes. [ABSTRACT FROM AUTHOR]

Shales are mostly unexploited energy resources. However, the extraction and production of their hydrocarbons require innovative methods. Applications involving carbon dioxide in shales could combine its potential use in oil recovery with its storage in view of its impact on global climate. The success of these approaches highly depends on various mechanisms taking place in the rock pores simultaneously. In this work, properties governing these mechanisms are presented at technically relevant conditions. The pendant and sessile drop methods are utilized to measure interfacial tension and wettability, respectively. The gravimetric method is used to quantify CO2 adsorption capacity of shale and gas adsorption kinetics is evaluated to determine diffusion coefficients. It is found that interfacial properties are strongly affected by the operating pressure. The oil-CO2 interfacial tension shows a decrease from approx. 21 mN/m at 0.1 MPa to around 3 mN/m at 20 MPa. A similar trend is observed in brine-CO2 systems. The diffusion coefficient is observed to slightly increase with pressure at supercritical conditions. Finally, the contact angle is found to be directly related to the gas adsorption at the rock surface: Up to 3.8 wt% of CO2 is adsorbed on the shale surface at 20 MPa and 60 °C where a maximum in contact angle is also found. To the best of the author's knowledge, the affinity of calcite-rich surfaces toward CO2 adsorption is linked experimentally to the wetting behavior for the first time. The results are discussed in terms of CO2 storage scenarios occurring optimally at 20 MPa. [ABSTRACT FROM AUTHOR]

Considering the hydraulic hysteresis caused by the change of contact angle at the soil–capillary water interface during the drying–wetting processes, this note proposes a novel hysteretic water-retention model. Compared with the previous studies, the model can take into account two distinct mechanisms, i.e., capillarity and adsorption, separately. The capillarity instead of adsorption is related to the contact angle hysteresis. Based on the Young–Laplace equation and the conjugate point on the main drying–wetting curve, the scanning equation is determined for the capillary part. It is evident that the new model is able to capture the hydraulic hysteresis behavior by comparing against experimental data from the published literature. [ABSTRACT FROM AUTHOR]

Multiphase flow is important for many natural and engineered processes in subsurface geoscience. Pore‐scale multiphase flow dynamics are commonly characterized by an average balance of driving forces. However, significant local variability in this balance may exist inside natural, heterogeneous porous materials, such as rocks and soils. Here, we investigate multiphase flow in heterogeneous rocks with different wetting properties using fast laboratory‐based 4D X‐ray imaging. The mixed‐wet dynamics were characterized by displacement rates that differed over orders of magnitude between directly neighboring pores. While conventional understanding predicted strongly capillary‐dominated conditions, our analysis suggests that viscous forces played a key role in these dynamics, facilitated by a complex interplay between the mixed‐wettability and the pore structure. These dynamics highlight the need for further studies on the fundamental controls on multiphase flow in geomaterials, which is crucial to design, for example, groundwater remediation and subsurface CO2 storage operations. Plain Language Summary: The flow of multiple fluids through a porous material plays an important role in many industrial and natural processes such as rain infiltrating a dry soil or CO2 storage in the subsurface. At the pore‐scale, these flows are governed by forces which depend on the pore‐geometry and the relative affinities of the fluids with the solid (i.e., wettability). The rates at which fluids flow in geological reservoirs is in most cases considered to be very slow (in the order of tens of meters per year). At these slow flow rates, fluid displacements are thought to be controlled by capillary forces. However, much of our current understanding of multiphase flow stems from artificial samples with simplified geometries, while most natural geomaterials tend to be far more complex in terms of pore structure and wettability. We show that heterogeneous pore structures and wetting properties can lead to different mechanisms of fluid displacement compared to those observed in model materials due to local variations in the viscous‐capillary force balance. This implies that models commonly used to predict subsurface flow process such as geological CO2 storage that assume capillary forces to dominate may not adequately capture the dynamics at the pore‐scale. Key Points: The pore‐scale dynamics of multiphase flow in heterogeneous rocks were investigated using fast laboratory‐based 4D X‐ray microtomographyWe describe a pore‐scale displacement mechanism with displacement rates orders of magnitude slower than those in neighboring poresWe demonstrate that viscous forces could play a significant role even at very low global capillary numbers under mixed‐wet conditions [ABSTRACT FROM AUTHOR]

We propose a novel formulation of capillarity, which geometrically extends the Bosanquet equation to irregular geometries, taking the effect of inertia and the dynamic contact angle into account. The governing equation is an integrodifferential equation that is solved numerically and compared with computer simulations, experimental data, and other cases available in the literature. The numerical examples investigated in this work show that contrary to flat channels and tubes, inertial effects decay much slower in corrugated channels and tubes due to the walls' geometrical fluctuations. We also draw the paramount conclusion that the true solution for Jurin's height in irregular capillaries is path-dependent and highly sensitive to the initial conditions, and no single static-equilibrium solution can necessarily be attributed to the eventual position of the meniscus. Resulting from the non-linear dynamics, the multiple equilibria in the presence of gravity for irregular capillaries can only be analyzed if the effect of inertia is considered, which has largely been neglected in the literature thus far. [ABSTRACT FROM AUTHOR]

[Display omitted] Contact angle measurements alongside Young's equation have been frequently used to quantitatively characterize the wettabilities of solid surfaces. In the literature, the Wenzel and Cassie-Baxter models have been proposed to account for surface roughness and chemical heterogeneity, while precursor film models have been developed to account for stress singularity. However, the majority of these models were derived based on theoretical analysis or indirect experimental measurements. We hypothesize that sub-nanometer-scale in situ investigations will elucidate additional complexities that impact wettability characterization. To develop further insights into in situ wettability, we provide the first direct experimental observation of fluid-solid occupancies at three-phase contacts at sub-nanometer resolution, using environmental transmission electron microscopy. Considering the partially spreading phenomenon and capillarity, we provide an improved physics-based interpretation of measuring the sub-nanometer-scale contact angle at the inflection point of the fluid-fluid interface. The difference between this angle and the commonly-used apparent one measured at a lower resolution is also discussed. Furthermore, we provide direct experimental evidence for the density differences between the adsorbed wetting film and the bulk wetting phase. For the effect of surface roughness, the applicability of the Wenzel model is discussed based on the observed in situ solid-fluid occupancies. [ABSTRACT FROM AUTHOR]

Viscoelastic liquids could be used as potential substrates in the microfluidics paradigm. The theoretical and experimental investigation of an evaporating aqueous droplet, over a viscoelastic liquid substrate, could provide a fundamental perspective of the complex interplay amongst capillarity, viscosity, and elasticity, resulting in a wide array of intriguing dynamics, which could be important in several microscale processes. The evaporation dynamics of a water droplet atop an un-crosslinked polydimethylsiloxane film (polymeric liquid substrate) are examined using an optical goniometer and a laser scanning confocal microscopy, to discern the interfaces. The recorded videos were analyzed to estimate the contact angles, velocities, and other parameters of relevance. The viscoelasticity of the film, in conjunction with evaporation, triggered a self-propulsion in the droplet, leading to crumpling of the polymeric film, and finally culminating in the encapsulation of the water drop by the polymer. The evaporation caused a dynamic variation in both the radius and contact angle of the droplet. The physics of the hitherto unreported phenomena is explained via the development of a semi-analytical model, considering all the relevant forces. We postulate that this symbiotic and self-sustained dynamics would pave the path towards the comprehension of micro-swimmers and surface encapsulation, to name a few. [ABSTRACT FROM AUTHOR]

Plasma treatment is known as a new technology applied on textile surface allowing the modification of their chemical properties. In our study, we have activated a cotton fabric surface with air atmospheric plasma. The wettabilty measurements, in terms of water contact angle and capillarity, reveal the hydrophobic behavior of cotton surface after plasma treatment under the studied conditions. The water contact angle increases from 60° for the untreated sample to 128° after 1 week from plasma activation. The capillarity of the plasma-treated surface reaches 42% instead of 72% for the untreated one. The chemical, morphological and physical modifications of cotton surface were also investigated before and after plasma activation. [ABSTRACT FROM AUTHOR]

Dynamic capillarity commonly exists for multiphase flow in porous media, during which fluid viscosity varies and has strong influence. Displacement experiments are conducted on water‐wet, fractured tight rock at in situ pressure and temperature of an oil reservoir via a specially designed apparatus to investigate the effects of fluid viscosity on the dynamic capillarity. The dynamic effect in the matrix is examined through the measurement and calculation of capillary pressure, the dynamic coefficient, and the fluid flow behavior. The results show that with a higher oil viscosity: (a) both the steady and the dynamic capillary pressures reverse their directions more quickly and behave as larger resistances in the matrix; (b) the difference between the steady and the dynamic capillary pressures becomes around 5%‐19% more significant; (c) water saturation changes more slowly corresponding to the lower water relative permeability, while oil relative permeability quickly becomes lower than that during the basic displacement process; and (d) the dynamic coefficient becomes 2‐3 times higher, and the dynamic contact angle becomes 10%‐25% larger, showing a more variable interface. A contact angle advancement coefficient is proposed to identify the significance of contact angle advancement and the competition between capillary pressure and viscous force. The findings of this study can help for better understanding of multiphase flow in tight reservoirs and enhancing oil recovery. [ABSTRACT FROM AUTHOR]

• Surfactants are crucial for enhancing oil recovery in challenging reservoirs by lowering IFT and altering wettability. • Achieving optimal surfactant conditions requires a delicate balance between IFT reduction and capillarity maintenance. • Cationic, anionic, and zwitterionic surfactants were tested for their effects on IFT and wettability. • Pore-scale and Darcy-scale simulations validate experimental results, aiding surfactant screening and optimization. Surfactant treatments play a crucial role in formation cleaning and wettability alteration for reservoirs characterized by low porosity and permeability. One effective approach to enhance oil recovery in such formations is spontaneous imbibition (SI) driven by capillarity, which enables surfactants to infiltrate tight rock matrices. Through the reduction of oil/water interfacial tension (IFT), surfactants effectively diminish residual oil saturation, leading to improved oil recovery. However, excessive IFT reduction can hinder capillarity, resulting in inefficient surfactant penetration. On the other hand, forced imbibition (FI) does not rely on capillarity for surfactant penetration, and thus, improved recovery is primarily driven by IFT reduction. Consequently, achieving the optimal surfactant conditions necessitates a delicate equilibrium between IFT reduction and maintaining adequate capillarity to facilitate surfactant penetration. In this study, we explored the performance of three surfactant types (cationic, anionic, and zwitterionic) for oil recovery through SI and FI experiments, assessing their effects at both Darcy and pore scales. All tested surfactants successfully lowered IFT as anticipated but exhibited distinct impacts on wettability, as indicated by contact angle measurements. Consequently, the use of SI in Amott cell experiments did not yield favorable oil recovery improvements in Berea rock compared to the water baseline. Pore-scale assessments using Micro-CT revealed that the surfactants disrupted the connectivity of the oil phase within the rock, leading to reduced SI efficiency. In contrast, distinct recovery trends emerged with FI. To replicate the experimental results, we conducted pore-scale and Darcy-scale simulations, which serve as valuable tools for surfactant screening and optimization. This study underscores the importance of balancing IFT reduction and wettability alteration in surfactant screening to achieve optimized recovery efficiency based on the predominant recovery mechanisms. [ABSTRACT FROM AUTHOR]

• The influence of capillarity and viscosity on the change of flow paths during water flooding in porous media is systematically investigated. • A novel particle-tracing-based approach is developed to extract the flow path during two-phases displacement in porous space. • Pore-scale direct numerical simulation is conducted to explore the dynamic distribution of water-oil phases and changes of flow paths in a real rock medium. Pore-scale direct numerical simulations were conducted to explore the changes of flow paths and dynamic distribution of water-oil phases during two-phase displacement in porous media. Three contact angles, i.e., 45°, 90°, and 135°, correspond to water-wet, intermediate-wet, and oil-wet rock surfaces, respectively. The medial axis within complex pore channels is obtained using a grid-based method. Subsequently, a novel particle tracking-based approach is proposed to extract the flow paths during two-phase displacement. The results show that when water enters a porous medium filled with oil, the distribution of oil phase flow paths is uniform, indicating that all oil phases are movable. As water continues to be injected, some water-oil interfaces stop at pores or throats due to capillary force, causing the flow paths through these locations to disappear. In oil-wet and intermediate porous media, capillary forces always act as resistance; therefore, the water-oil interfaces stop at the throat channels. Interestingly, under water-wet conditions, the water-oil interface can reverse, and the capillary force presents resistance, resulting in the interfaces being blocked at enlarging areas, usually from throats to pores. Once breakthrough occurs, preferential flow paths for pure water are established, resulting in a rapid decrease of flow paths with moving water-oil interfaces under oil-wet and intermediate-wet conditions, while movement continues in a water-wet medium. Due to the typically lower viscosity of water than oil, the viscous force decreases as water saturation increases. As water injection continues, the water in some channels gradually displaces oil, resulting in differences in flow rates between oil-filled and water-filled channels. This study provides a method for identifying the changes in flow paths during two-phase displacement in porous media and gives potential benefits for designing strategies to improve oil recovery. [Display omitted] [ABSTRACT FROM AUTHOR]

The capillary effect caused by the confinement in porous media leads to strongly differences in the physical properties and phase equilibrium of the fluids apart from the bulk phase. A joint model was established for investigating the capillary effect by combining Young-Laplace equation and the square-well chain-like fluid with variable well-width range (SWCF-VR) equation of state. The Young-Laplace equation supplies a simple way to relate the capillarity with the bulk properties, and the SWCF-VR equation was able to accurately describe the equilibrium of fluid in bulk phase compared with the Peng–Robinson equation. The model could predict well the phase equilibrium when comparing with experimental data in bulk, and consequently the results for confined fluids. The model was verified by experimental and computer simulation data. Further, the binary adjustable parameters of SWCF-VR EOS used in this study could be updated once the experimental data in confined situation are reported. In addition, the model could be used for complex component when experimental data are unavailable since the four parameters of EOS could be predicted. Image 1 • The SWCF-VR EOS was firstly combined with Young-Laplace equation to describe the fluid behavior in confined phase. • The joint model was verified by experimental data and computer simulation results. • The constant contact angle was proposed and the confined effect at different compositions for mixtures was considered. • The joint model was applied for the methane and gasoline in tight shale. [ABSTRACT FROM AUTHOR]

Spontaneous imbibition (SI) is a capillary-driven flow process, in which a wetting fluid moves into a porous medium displacing an existing non-wetting fluid. This process likely contributes to the loss of fracking fluids during hydraulic fracturing operations. It has also been proposed as a method for an enhanced recovery of hydrocarbons from fractured unconventional reservoirs. Numerous analytical and numerical approaches have been employed to model SI. Invariably, these idealize a fracture as the gap formed between parallel flat surfaces. In reality, rock fracture surfaces are rough over multiple scales, and this roughness will influence the contact angle and rate of fluid uptake. We derived an analytical model for the early-time SI behavior within a fracture bounded by parallel impermeable surfaces with fractal roughness assuming laminar flow. The model was tested by fitting it to experimental data for the SI of deionized water into air-filled rock fractures. Twenty cores from two rock types were investigated: a tight sandstone (Crossville) and a gas shale (Mancos). A simple Mode I longitudinal fracture was produced in each core by compressive loading between parallel flat plates using the Brazilian method. Half of the Mancos cores were fractured perpendicular to bedding, while the other half were fractured parallel to bedding. The two main parameters in the SI model are the mean separation distance between the fracture surfaces, x ̄ , and the fracture surface fractal dimension 2 ≤ D < 3. The x ̄ was estimated for each core by measuring the geometric mean fracture aperture width through image analysis of the top and bottom faces, while D was estimated inversely by fitting the SI model to measurements of water uptake obtained using dynamic neutron radiography. The x ̄ values ranged from 45 μ m to 190 μ m, with a median of 93 μ m. The SI model fitted the height of uptake versus time data very well for all of the rock cores investigated; medians of the resulting root mean squared errors and coefficients of determination were 0.99 mm and 0.963, respectively. Estimates of D ranged from 2.04 to 2.45, with a median of 2.24. Statistically, all of the D values were significantly greater than two, confirming the fractal nature of the fracture surfaces. Future research should focus on forward prediction through independent measurements of D and extension of the existing SI model to late times (through the inclusion of gravity) and fractures with permeable surfaces. [ABSTRACT FROM AUTHOR]

Liquid water transportation through textiles plays an important role in comfort properties. Transport mechanism takes place from liquid's first behavior when get in touch with fabric to last behavior when evaporated to atmosphere. Wetting phenomena has been carried out by liquid and air interface with textile materials. Basically wetting is physical interaction of fabric with liquid, air and their surface energies results into wicking. Wicking is unconstrained liquid movement, driven by capillarities. Capillarity deals with the penetration ability of liquid into fine pores of fibre to travel along its walls. Wetting, wicking and capillarity are influential parameters to relate the fluid transport in textile fibrous media. This paper is focused on wetting, contact angle, wicking and capillarity, executes in measuring comfort and liquid moisture transport behavior of fabric. [ABSTRACT FROM AUTHOR]

We outline a low-order Lagrangian model for the inertial dynamics of spreading and imbibition of a spherical liquid cap on a plane featuring independent cylindrical capillaries without gravity. The analysis predicts the relative roles of radial and axial kinetic energy, reveals the critical Laplace number beyond which the drop oscillates, and attributes the exponent of the initial power-law for contact patch radius vs. time to the form of capillary potential energy just after the liquid sphere touches the plate. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5474-5481, 2017 [ABSTRACT FROM AUTHOR]

We consider a family of nonlocal capillarity models, where surface tension is modeled by exploiting the family of fractional interaction kernels $$|z|^{-n-s}$$ , with $$s\in (0,1)$$ and n the dimension of the ambient space. The fractional Young's law (contact angle condition) predicted by these models coincides, in the limit as $$s\rightarrow 1^-$$ , with the classical Young's law determined by the Gauss free energy. Here we refine this asymptotics by showing that, for s close to 1, the fractional contact angle is always smaller than its classical counterpart when the relative adhesion coefficient $$\sigma $$ is negative, and larger if $$\sigma $$ is positive. In addition, we address the asymptotics of the fractional Young's law in the limit case $$s\rightarrow 0^+$$ of interaction kernels with heavy tails. Interestingly, near $$s=0$$ , the dependence of the contact angle from the relative adhesion coefficient becomes linear. [ABSTRACT FROM AUTHOR]

Due to their compactness and independence of exterior energy sources, capillary microsystems are increasingly used in many different scientific domains, from biotechnology to medicine and biology, chemistry, energy and space. Obtaining a capillary flow depends on channel geometry and contact angle. A general condition for the establishment of a spontaneous capillary flow in a uniform cross section channel has already been derived from Gibbs free energy. In this work, we consider spontaneous capillary flows (SCF) in diverging open rectangular channels and suspended channels, and we show that they do not flow indefinitely but stop at some location in the channel. In the case of linearly diverging open channels, we derive the expression that determines the location where the flow stops. The theoretical approach is verified by using the Surface Evolver numerical program and is checked by experiments. The approach is extended to sudden enlargements, and it is shown that the enlargements can act as stop and trigger valves. [ABSTRACT FROM AUTHOR]

When a capillary is half-filled with liquid and turned to the horizontal, the liquid may flow out of the capillary or remain in it. For lack of a better criterion, the standard assumption is that the liquid will remain in a capillary of narrow cross-section, and will flow out otherwise. Here, we present a precise mathematical criterion that determines which of the two outcomes occurs for capillaries of arbitrary cross-sectional shape, and show that the standard assumption fails for certain simple geometries, leading to very rich and counterintuitive behavior. This opens the possibility of creating very sensitive microfluidic devices that respond readily to small physical changes, for instance, by triggering the sudden displacement of fluid along a capillary without the need of any external pumping. [ABSTRACT FROM AUTHOR]

An analytical model was developed to predict the infiltration of a non-wetting liquid into a sharp-cornered channel with rough walls. The distance from the liquid meniscus to the corner and the liquid radius of curvature predicted by the model are a function of contact angle, corner angle, head height and surface roughness. Measurements of these lengths were made in a model experiment as a function of liquid head height. The results of the experiments suggest that the analytical model accurately predicts the wetting limit of corner sharpness. [ABSTRACT FROM PUBLISHER]

• Pressure drop in a homogeneous channel is larger than in heterogeneous channel. • The pressure drop decreases with an increase of channel heterogeneity. • Droplet behavior in fractionally-wet channel is different to homogeneous channel. • The fluid-fluid menisci often form saddle-shaped interfaces. This study presents droplet dynamics due to capillarity-wettability interaction through a constricted capillary channel. Previous research has investigated the droplet motion in a constricted capillary channel with a two-dimensional geometry and uniform wettability to determine the critical pressure necessary for the droplet to pass through the constriction, but did not consider the change of pressure as the droplet crosses through a constricted geometry. To explore the dynamic behavior of droplet motion across a constriction, a direct numerical simulation of a droplet in a three-dimensional fractionally-wet constricted channel is performed where we have two different contact angles on opposing faces of the constriction. The results show that the fractional wettability condition significantly affects the evolution of fluid-fluid and fluid-solid interfaces, pressure drop, and displacement patterns. We show that droplet dynamics in a fractionally-wet channel do not necessarily follow the same behavior as in a uniform capillary channel and cannot be predicted using uniform wettability surfaces depicted by an average contact angle. In particular, the pressure difference needed to push the droplet through the restriction with fractional wettability is lower than that for a uniform channel with a constant contact angle representing the less favorable wettability state. The fluid-fluid meniscus often forms saddle-shaped interfaces with curvature of opposite sign in orthogonal directions. Moreover, the effects of droplet size, capillary number, viscosity ratio, and constriction shape are elucidated. The pressure difference increases with droplet size and capillary number. Triangular cross-sections can be accessed at a lower pressure because of wetting layer flow. [ABSTRACT FROM AUTHOR]

We investigate in this work how the presence of an occlusion affects the dynamics of the wetting front of a liquid film draining down a vertical surface. This numerical study is developed in the context of the lubrication approximation. Through a parametric study, we show that depending on the asymptotic film thickness and the fluid properties, there exists a critical substrate contact angle below which separation of the contact line from the occlusion wall is observed which results in the appearance of a dry zone in the wake of the occlusion. In analogy with external aerodynamics, we also show that a sharp corner in the occlusion can induce this contact line separation. Our numerical results also highlight the importance of the occlusion wettability on the morphology of the wetting front suggesting a possible mechanism to control and mitigate the often undesirable fingering instability. [ABSTRACT FROM AUTHOR]

In extreme weather conditions and activity levels of human subjects, evaporation of sweat is critical for maintaining the sensorial and thermal comfort. Fabrics, from which clothes worn next to the skin are made, play an important role in facilitating the transfer of body liquid perspiration away from the skin to the environment through the mechanisms of capillary flow and evaporation. This work is a theoretical and experimental investigation of water flow characteristics of yarns with relevance to their structure geometry and constituent fiber chemistry.A theoretical model to predict the capillary flow of liquid water through yarns was proposed. The model is based on the Kozeny–Carman equation, which represents interfiber pores in terms of the hydraulic radius theory. Cotton, polyester and cotton/polyester yarns were produced by systematically varying different production parameters, including fiber type, yarn twist, yarn linear density and blend ratio. Plain knitted fabrics were produced and yarns taken from the produced fabrics were tested for horizontal linear flow of liquid water. The experimental results showed a strong correlation with the estimated results based on the theoretical model. The model predicts that as the ratio of interfiber pore space area to the total fiber perimeter within yarn increases, the flow rate is expected to increase. [ABSTRACT FROM PUBLISHER]

• Novel embedded-domain phase-field model to study morphological evolution within bimetallic nanoparticles. • Role of solute segregation on surface energies and contact angle. • Role of contact angle, particle size and diffusion on the formation of Janus and core-shell structures in bimetallic nanoparticles. [Display omitted] Bimetallic nanoparticles (BNPs) exhibit diverse morphologies such as core-shell, Janus, onion-like, quasi-Janus, and homogeneous structures. Although extensive effort has been directed towards understanding the equilibrium configurations of BNPs, kinetic mechanisms involved in their development have not been explored systematically. Since these systems often contain a miscibility gap, experimental studies have alluded to spinodal decomposition (SD) as a likely mechanism for the formation of such structures. We present a novel phase-field model for confined (embedded) systems to study SD-induced morphological evolution within a BNP. It initiates with the formation of compositionally modulated rings as a result of surface directed SD, and eventually develops into core-shell or Janus structures due to coarsening/breakdown of the rings. The final configuration depends crucially on contact angle and particle size - Janus is favored at smaller sizes and higher contact angles. Our simulations also illustrate the formation of metastable, kinetically trapped structures as a result of competition between capillarity and diffusion. [ABSTRACT FROM AUTHOR]

Realization of simultaneous hydrophilizing and wrinkle-proofing effects on a cotton fabric is not impossible. This work proves that these objectives can be reached by using adequate multifunctional compounds: Tetronic 701 (T), chitosan (CS) and monochlorotriazine-β-cyclodextrin (MCT-β-CD). These were applied by means of three pad-dry-cure type treatments. We have studied, at first, the influences resulted after each stage in order to establish the optimum working fields. The results of the FTIR, XPS, XRD, DSC and TGA analyses confirmed the proposed mechanism. By applying the multiple linear regression as a statistical analysis of the data produced after the third treatment stage, one could determine the quantitative influences produced by the concentrations of the three multifunctional agents on the following parameters: taking-in degree, wrinkle recovery angles (WRA), breaking strength, durability test, immersion time, contact angle, and capillarity. [ABSTRACT FROM AUTHOR]

Highlights: [•] The metallic characteristic of galvanized steel surface determined the wettability. [•] Zn should not be a driving force for spreading. [•] Zn may be a factor for the contact angle hysteresis. [Copyright &y& Elsevier]

Abstract: One-way wicking (microfluidic diode) behaviors of a range of IPA–water mixtures on internally structured PDMS-based open micro-channels were experimentally demonstrated and quantified. The open microfluidic channels, each internally decorated with an array of angled fin-like-structure pairs, were fabricated using a combined photolithography and soft molding procedure. Propagations of wetting fluids were found to be much more impeded on the fin-tilting direction, or the hard wicking direction, comparing to the opposite direction, or the easy wicking direction. This asymmetric wicking behaviors were attributed to the structure-induced direction-dependent Laplace pressure. Two key parameters – the contact angle of the wicking fluid and the tilting angle of the fin-like structures – were studied. The effects of preferential evaporation and wetting instability were also investigated. The findings of this study are expected to provide a better understanding of how fluids interact with micro-scaled structures and to offer a new way of manipulating fluids at the micron and nanometer scales. [Copyright &y& Elsevier]

Abstract: Liquid droplet deposition on solid surfaces has an important role in the industrial and research activities. The behaviour of such deposit is influenced by volume and interfacial phenomena and involves a large number of mechanisms such as gravity effect, mass transfer, capillary forces, and wetting. For the case of metal deposition the analysis of the problem is more complex because of the importance of thermal effects, involving steep gradients and phase changes. A unique experimental approach is presented in order to study the evolution of the spreading of a large drop of liquid metal called “macro-drop”. The objective of this work is to supply qualitative and quantitative information during the deposit of liquid metal in relation with process parameters. The overall shape of the macro-drop, especially its spreading and contact angles are studied in detail. The gradual spreading of the macro-drop is mainly governed by mass and heat transfers. The initial rapid spreading is due to kinetic energy of depositing droplets and direct arc heating on the solid target. All experimental results are analysed in the light of process parameters to identify the physical mechanisms involved and appreciate their effects on the behaviour of such a macro-drop. [Copyright &y& Elsevier]

Abstract: In this study, CHF characteristics in pool boiling according to CuO nanoparticles deposition characteristics are investigated compared with that of pure water. The deposition characteristics are controlled by using in-house prepared CuO nanofluids in two ways such as one-step method of pulsed laser ablation in liquid (PLAL) and two-step method of particles dispersion. Morphology of CuO nanoparticles in shape and size is analyzed by TEM while SEM images are obtained to observe the deposition structures on heated surfaces. Also, contact angle and capillary height for deposition layer on the surfaces after pool boiling experiments are measured to investigate the surface wettability. Rayleigh–Taylor instability wavelength on the surface with respect to a unified CHF enhancement mechanism is measured indirectly by a condensation method. [Copyright &y& Elsevier]

We propose a new method which combines experiments with numerical calculations to determine the capillary constant and the capillary contact angle. We measure the ascent of the liquid at the interior and at the exterior of a circular transparent tube. In contrast to known methods we do not assume that the contact angle is known. Assuming the interior contact angle is equal to the exterior angle, we find the capillary constant of the given liquid from the fact that the surface tensions of the interior and the exterior surfaces are equal. Dipping a cylindrical wire with constant circular cross section into a liquid with known surface tension we can determine the contact angle between the given liquid and the material from which the wire is made. [ABSTRACT FROM AUTHOR]

Abstract: Owing to contact angle hysteresis, the contact angle that a sessile drop adopts on a surface can be quite different depending on the process of drop formation. This is particularly noticeable for receding contact angle because it is most susceptible to the details of the measuring method. We performed low-rate dynamic contact angle experiments with steadily moving contact lines and millimeter-size drops in the very low-capillary number regime. We employed a quadratic volumetric flow rate (V ∝ t 3) to achieve the steady motion of contact lines such as happens in the Wilhelmy balance. The values of receding contact angle provided with the quadratic flow rate were stable and time-independent over a larger area of the polymer surfaces studied. Next, we monitored receding sessile drops with equal initial volume but different static contact angle on the same surface. This procedure allowed us to scan the contact angle hysteresis range up to the minimum observable value of contact angle. We probed with distilled water the different response of surfaces of polymer (PMMA, PC and PTFE) and metal oxide (titanium). We found two behaviors according to the substrate employed: a constant value of receding contact angle regardless of the static contact angle and a decrease of receding contact angle as the static contact angle decreased. [Copyright &y& Elsevier]

Abstract: Capillary rise is the basis of some methods that are widely applied for the determination of contact angles as well as wettabilities of small particles. The equivalent hydraulic radius r d in the Classical Washburn equation is assumed to be particle-specific. But it seems that r d is not always constant when the type of liquids is different. The new equation with the pressure increment and the hydrostatic effects are theoretically derived based on the Washburn equation, so contact angles of small particles can be measured experimentally independently of r d. The result shows the validity of the proposed method, and therefore, it becomes possible to accurately measure the wettability of small particles. [Copyright &y& Elsevier]

The contact angle is a sensitive parameter often used to define wettability. With the increasing movement toward smaller liquid volumes in many biochemical applications, a key challenge lies in how to perform measurements in the retainer holding the reagent for rapid evaluation and limited material loss. Here, we report a simple and robust method to determine the contact angle of small volumes using the microscopic imaging of a capillary meniscus that requires only the radius and meniscus height information. An error analysis of the measurement finds the method to be highly accurate. We also uncovered that illumination delivered from the liquid end of the capillary lights up the interface, thereby facilitating the measurement. [ABSTRACT FROM AUTHOR]

Abstract: A method for the numerical simulation of the dynamic response of the contact angle is presented and its development discussed. The proposed method was developed within a level-set framework by modelling forced capillary flows and it is based on the introduction of a force function to capture the balance of forces in the contact region between solid boundaries and a diffuse free-surface fluid interface. The proposed approach allows the system to define its own dynamic contact angle and its own contact line dynamics, without introducing numerical discontinuities such as locally prescribed angles or slip-length. The method was developed through numerical testing and comparisons with experimental and empirical models reported in the literature. These showed the validity of the proposed approach, which was able to reproduce the experimental correlation between the capillary number and the dynamic contact angle reported by [R.L. Hoffman, Study of advancing interface. 1. Interface shape in liquid–gas systems, J. Colloid Interf. Sci. 50 (1975) 228–241]. By using a single constitutive model for the force function, the simulation results of the dynamic contact angle showed an excellent agreement with the values predicted by Jiang’s empirical equation [T.S. Jiang, O.H. Soo-Gun, J.C. Slattery, Correlation for dynamic contact angle, J. Colloid Interf. Sci. 69 (1979) 74–77] through different material properties and flow speeds. The proposed approach also demonstrated the ability to work with meshes of low resolution. [Copyright &y& Elsevier]