Surface Contact Angle Research Articles

Study on the Wettability and Methane Desorption Characteristics of Coal under High Pressure with Different Surfactants.

In the process of coalbed methane extraction, due to the strong hydrophilicity of coal, the surface interaction force between water and the coal matrix is strong. The hydrophobic effect of the coal seam during drainage and pressure reduction is not significant, and adsorbed methane is difficult to desorb. In order to reduce the surface interaction force promoting methane desorption between water and coal, the surfactants NH766, G526, and D001 with a concentration of 0.1% were selected. A pressure of 12 MPa, which is close to that used for the on-site mining of coalbed methane in Baode, was selected as the experimental condition to simulate hydraulic fracturing of high fat coal, and the influence of different surfactants on methane desorption characteristics was analyzed. Combining contact angle experiments and infrared spectroscopy experiments, we explored the changes in wettability of the coal samples. We compared the changes in wettability and methane desorption characteristics and explored the similarities between these changes. The experimental results showed that after NH766 treatment, the content of oxygen-containing functional groups in coal rock decreased by 30%, and the contact angle of the coal matrix surface increased by 10°. Furthermore, its hydrophobicity was enhanced, and the desorption amount increased by 24%. In contrast, the oxygen-containing functional groups in coal rock after G526 and D001 treatments increased by 5% and 16%, respectively, and the contact angle of the coal matrix surface became smaller. Furthermore, its hydrophilicity was enhanced, and the desorption amount was reduced by 12.5% and 20%, respectively. NH766 reduces wettability and promotes methane desorption, and it can be applied to improve CBM extraction efficiency. G526 and D001 enhance wettability and inhibit methane desorption, which make them suitable for dust prevention and gas control in coal mines.

Turning Non-Sticking Surface into Sticky Surface: Correlation between Surface Topography and Contact Angle Hysteresis.

We present a surface modification technique that turns CuNi foam films with a high contact angle and non-sticking property into a sticky surface. By decorating with mesh-like biaxially oriented polypropylene (BOPP) and adjusting the surface parameters, the surface exhibits water-retaining capability even when being held upside down. The wetting transition process of droplets falling on its surface were systematically studied using the finite element simulation method. It is found that the liquid filled the surface microstructure and curvy three-phase contact line. Moreover, we experimentally demonstrated that this surface can be further applied to capture underwater air bubbles.

Experimental and DFT study of modified malachite with 2,5-dimercapto-1,3,4-thiadiazole and its response to sulfidization-xanthate behavior

Malachite is industrially recovered using sulfidization–xanthate flotation. However, due to the instability of the sulfidization effect, it is necessary to strengthen the sulfidization process. To this end, a 2,5-dimercapto-1,3,4-thiadiazole (DMTD) can modify the malachite surface for enhanced sulfidization. Analysis of the sulfidization products indicated that more of highly active Cu2S(Cu(I))species and polysulfides (Sn2−) were found, indicating that the DMTD-modified malachite surface facilitated the adsorption of S components and improved the surface reactivity. Analysis of the sulfidized surface revealed that DMTD and Na2S together increased the ionic strength of S, further confirming that the DMTD-modified malachite surface facilitates S adsorption. Density Functional Theory (DFT) simulates implicate that the intensified sulfidization of malachite surface is due to the resultant of Cu-S products with various degrees of binding and enhanced interactions between S and Cu atoms. Analysis of the sulfidization efficiency of malachite surface confirmed that the DMTD-modified surface adsorbed additional -S components. Changes in the surface potential and contact angle of malachite suggested that the DMTD-modified surface was higher hydrophobic owing to strong adsorption of xanthate. Flotation experiments confirmed that DMTD can improve the sulfidization-xanthate floatability.

Degradation mechanism of cuticular wax composition and surface properties of bamboo culm during storage

Cuticular wax on bamboo culm forms a kind of protective biointerface during growing and degrades after harvesting leading to the deterioration of surface quality and protection function during storage. The degradation mechanism of the cuticular wax and surface property of harvested bamboo culm during storage is still unclear. To understand it, the microstructure of cuticular wax on the harvested bamboo culm was characterized and composition content was analyzed by GC-MS as well as the contact angle and color of bamboo culm surface were tested after the bamboo culm was stored in four simulated seasons: spring, summer, autumn and winter. The results showed that the more wax deposited on bamboo culm surface during storage, and the thickness of cuticular wax increased. During storage, the content of alkanes, alcohols and total ketone in bamboo culm cuticular wax decreased as well as the contents of terpenoids and esters increased. This suggested that the degradation of cuticular wax on bamboo culm should be due to the hydrolysis of alkane into fatty acids and terpenoids.The surface contact angle of stored bamboo culm decreased and the color of bamboo culm changed. The contact angle of the stored bamboo culm surface reduced 12.24%, 25.53%, 9.76%, 1.85% compared with the fresh bamboo culm. The surface color of bamboo culm was related to the content of cuticular wax and weight loss of bamboo culm and was the joint function of weight loss and wax content change.

A new insight on a novel auxiliary collector 4-MBA synergize with BHA to enhance flotation of scheelite

The hydroxamic acid reagents are extremely pervasive in the collector of scheelite flotation. The high flotation cost is caused by its large dosage and high price. A novel auxiliary collector 4-methodybenzoicacid (4-MBA) was used in combination with benzohydroxamic acid (BHA) to optimize the flotation reagents system for scheelite in the study. A single 4-MBA has weak collection capacity for scheelite. Nevertheless, the combination of 4-MBA and BHA optimized the flotation system of scheelite by ensuring its recovery and reducing the reagent consumption. The results of solution surface tension and contact angle measurements showed that the surface tension of the mixed reagent solution is a relatively lower and the hydrophobicity of the scheelite surface is a relatively higher in the BHA and 4-MBA mixed reagent system. Additionally, a synergistic effect between BHA and 4-MBA on Pb2+ activated scheelite is revealed by the Zeta potential measurements, infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The addition of 4-MBA promoted the physical and chemical adsorption of BHA. The results of molecular dynamics simulation (MDS) further explained that the collector adsorption layer of the surface of scheelite (112) is more compact under BHA and 4-MBA mixed reagent system, which prevents the vertical entry of water phase and improves the hydrophobicity of scheelite. Finally, the bench-scale flotation experiment verified that the addition of 4-MBA enhanced scheelite flotation with BHA, and decrease the flotation cost of scheelite.

Investigation of the Influence of Machining Parameters and Surface Roughness on the Wettability of the Al6082 Surfaces Produced with WEDM.

Electrical Discharge Machining (EDM) is a non-conventional machining technique, capable of processing any kind of conductive material. Recently, it has been successfully utilized for producing hydrophobic characteristics in inherently hydrophilic metallic materials. In this work, Wire Electrical Discharge Machining (WEDM) was utilized for producing hydrophobic characteristics on the surface of the aluminum alloy 6082, and various parameters that can affect wettability were investigated. Adopting an orthogonal Taguchi approach, the effects of the process parameter values of peak current, pulse-on time, and gap voltage on the contact angles of the machined surfaces were investigated. After machining, all samples were observed to have obtained hydrophobic properties, reaching contact angles up to 132°. The peak current was identified as the most influential parameter regarding the contact angle, while the gap voltage was the less influential parameter. A contact angle variation of 30° was observed throughout different combinations of machining parameters. Each combination of the machining parameters resulted in a distinct surface morphology. The samples with moderate roughness values (3.4 μm > Sa > 5.7 μm) were found to be more hydrophobic than the samples with high or low values, where the contact angle was measured under 115°. In addition, the finite element modeling of the experimental setup, with parametric surfaces of uniform random and Perlin noise types of roughness, was implemented. Time dependent simulations coupling phase field and laminar flow for the modelingof the wetting of surfaces with different surface roughness characteristics showed that an increase in the Sa roughness and total wetted area can lead to an increase in the contact angle. The combination of experimental and computational results suggests that the complexity of the wettability outcomes of aluminum alloy surfaces processed with WEDM lies in the interplay between variations of the surface chemical composition, roughness, micro/nano morphology, and the surface capability of forming a composite air/water interface.

Correlation between the Chemical Structure of (Meth)Acrylic Monomers and the Properties of Powder Clear Coatings Based on the Polyacrylate Resins.

This paper presents studies on the influence of the chemical structure of (meth)acrylic monomers on the properties of powder coatings based on polyacrylate resins. For this purpose, a wide range of monomers were selected-2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), n-butyl acrylate (nBA), tert-butyl acrylate (tBA), dodecyl acrylate (DA), ethyl acrylate (EA) and benzyl acrylate (BAZ)-for the synthesis of the polyacrylate resin. The average molecular mass and molecular mass distribution of the synthesized resins were measured by gel permeation chromatography (GPC). The glass transition temperature (Tg) and viscosity of polyacrylate resins were determined by using differential scanning calorimetry (DSC) and a Brookfield viscometer. These parameters were necessary to obtain information about storage stability and behavior during the application of powder clear coatings. Additionally, DSC was also used to checked the course of the low-temperature curing reaction between the hydroxyl group contained in the polyacrylate resin and the blocked polyisocyanate group derived from a commercial agent such as Vestanat B 1358/100. The properties of the cured powder clear coatings were tested, such as: roughness, gloss, adhesion to the steel surface, hardness, cupping, scratch resistance, impact resistance and water contact angle. The best powder clear coating based on the polyacrylate resin L_HEMA/6MMA/0.5nBA/0.5DA was characterized as having good scratch resistance (550 g) and adhesion to the steel surface, a high water contact angle (93.53 deg.) and excellent cupping (13.38 mm). Moreover, its crosslinking density (CD) and its thermal stability was checked by using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).

Impacts of Low Energy Argon Beam on Enhancing the Surface Wettability and Electrical Performance of CA/PANI Films

This work study the impacts of argon irradiation on surface wettability of CA/PANI using home made ion source with fluences (4 × 1014, 8 × 1014, and 12 × 1014 ions cm−2). The EDX, SEM and FTIR methods verified the successful fabrication of the composites. Surface wettability, contact angle, and work of adhesion were measured for the untreated and irradiated composites. Raising the ion flux from 4 × 1014 ions.cm−2 to 12 × 1014 ions.cm−2, it decreases the contact angle of CA/PANI from 62.1° to 43.4° and increases the surface free energy from 46.7 to 63.9 mJ m−2. The results showed that the CA/PANI changed after exposed to radiation, proving that the irradiated surface properties were improved. In addition, their electrical conductivity was tested in frequency of 50 to106 Hz. When subjected to 12 × 1014 ions.cm−2, the conductivity rose from 1.1 × 10−8 S cm−1 for CA/PANI to 6.5 × 10−7 S cm−1. The results showed that the irradiated CA/PANI had better electrical and surface properties, which is crucial for many devices including batteries and supercapacitors.

Fabrication of Superhydrophobic Coating (SiO<sub>2</sub>/PDMS) by a Simple Method

A simple and economical method for producing a superhydrophobic surface on a glass substrate is investigated. The surface composes of silica particles synthesized via a sol-gel method with an average particle size of 69.33 nm. Organosilan PDMS (FS-1200 silicon sealant) was used to reduce the surface energy of particles, which were then coated onto a glass substrate by dip coating. After coating, the substrate was dried for one hour at 60ºC in an oven to remove excess solvent. XRD, FE-SEM, FTIR, and contact angle (CA) measurement techniques were used to characterize silica particles and coated surfaces. The water contact angle (WCA) of pure SiO2 (NPs) was 86º indicating its hydrophilic qualities, while the contact angle of a superhydrophobic surface was 156º.

Novel dual-layer ZIF-71/PH-PSF electrospun nanofiber for robust membrane distillation

Membrane distillation (MD) is a promising technology for the treatment of hypersaline dyeing wastewater. However, commercial membranes still have limitations such as low permeate flux, membrane fouling, and membrane wetting issue in MD process. Herein, a dual-layer MD membrane was fabricated with a polysulfone (PSF) bottom layer and a poly(vinylidene fluoride-co-hexafluoropropylene) (PH) hydrophobic surface layer incorporated with ZIF-71 nanoparticles. The addition of ZIF-71 was optimized based on the results of surface morphology, contact angle, and MD performance. The incorporation of ZIF-71 nanoparticles into PH nanofiber membranes, along with their dual-layer structure, has led to notable improvements in both permeate flux and rejection performance. The fouling resistance of membrane was further evaluated with model dyeing wastewater as feed solution, which contained four types of dyes and heavy metal antimony. The MD performance of the optimized membranes was also measured with real dyeing wastewater as feed solution. The dual-layer membrane decorated with ZIF-71 nanoparticles significantly outperformed the pristine membrane in treating real dyeing wastewater, exhibiting potential for practical applications. Finally, the underlying mechanism on the improved permeate flux and rejection was elucidated systematically.

Synthesis of zeolite‐derived blue nanopigment and its modification for hydrophobic coating on ceramic tile

AbstractThis study presents the successful synthesis of a vibrant blue nanopigment derived from the metastable structure of Na‐heulandite zeolite. Employing ion exchange and coprecipitation methods with cobalt and zinc ions, followed by thermal treatment at 1100°C, resulted Co‐willemite and gahnite phases, confirmed by x‐ray diffraction and Rietveld refinement. Optical analyses verified the blue coloration, with cobalt ion transitions evident. CIE L* a* b* colorimetric analysis placed the pigment in the blue region (L* = 49.19, b* = −22, a* = −11). Application to ceramic tiles, followed by sodium dodecyl sulfate (SDS) modification, produced a nearly superhydrophobic surface (contact angle 140°, sliding angle 8°), attributed to the nano–micro structure and SDS–silica interaction. Field emission‐scanning electron microscopy images confirmed the pattern‐like surface with small patterns. These findings indicate potential self‐cleaning capabilities when exposed to dirt or water, highlighting the research's promise in enhancing ceramic functionality.

Comparison of surface tension, density, viscosity and contact angle of ethyl oleate to those of ethanol and oleic acid

Taking into account extensive practical application of ethyl oleate (EO) some of its physicochemical properties were determined and compared to those of ethanol (ET) and oleic acid (OA). For this purpose the surface tension, density, viscosity and contact angle of EO, ET and OA were measured. The contact angle was measured on the polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), steel and glass in the solid–liquid–air system. Based on the results of the surface tension and contact angle of ET, EO and OA on PTFE and PMMA the Lifshitz-van der Waals component as well as electron-acceptor and electron-donor parameters of the acid-base component of surface tension of these liquids were determined. For this determination the van Oss et al. method was applied. This method was carefully analyzed in terms of its usefulness for the systems studied by us. The components and parameters of the ET, EO and OA surface tension were analyzed with regard to their molecular structure. Based on the molecular structure and on the length of bonds and contact angle between them the size of the molecules and their contactable area were determined.

Mechanism of self-recovery of hydrophobicity after surface damage of lotus leaf

The surfaces of lotus leaves with micro- and nano-waxy cuticle structures are superhydrophobic and possess a self-healing ability to regain hydrophobicity after damage. Inspired by this phenomenon, the problem of water-repellent coatings used in natural environments failing to perform after damage can be solved if these coatings are endowed with rapid self-repair and self-growth functions. However, there has been almost no exploration into the hydrophobicity self-repair process in lotus leaves. The changes in surface morphology during the hydrophobicity recovery process are not understood. There is a lack of research on the hydrophobicity recovery in lotus leaves. In this study, the damage and recovery experiments on lotus leaf surfaces were carried out in an artificial climate chamber, and the water repellency recovery process and typical water repellency roughness parameters regained time were obtained. Upon analyzing the differences in the recovery process of different damage types, the recovery mechanism after lotus leaf surface damage was obtained. Finally, it was found that the microscopic roughness determined the static contact angle (WCA) of the lotus leaf surface, and the nanoscopic roughness determined the rolling angle (SA). The dual factors of the recovery of the extruded epidermal tissue and the regeneration of the epidermal wax crystals determined the hydrophobicity recovery process in damaged lotus leaves.

Scale-dependent wetting behavior of bioinspired lubricants on electrical discharge machined Ti6Al4V surfaces

The relationships between the geometric features of material surfaces and topographically related phenomena, such as wetting, change with the scale of observation. In these studies, multiscale analyzes allow characterizing the relationships between electrical discharge machining parameters, complex surface topographic structures and contact angles. Importantly, it was possible to indicate the best scales for observing the phenomena of lubricant flow on electro-discharged surfaces and to identify key geometric parameters of the surface affecting the contact angle. This paper proposes scale-dependent contact angle analyzes of electro-discharge machined Ti6Al4V alloy for biomedical implant applications. Liquids imitating synovial fluid in joints were used as lubricants. The research focuses on comparing the impact of discharge energy on surface microtexture, chemical composition, contact angle and surface free energy. The analysis of the lubrication behavior on micro-textured surfaces in contact mechanics co-determines the tribological properties. The research results confirm the effectiveness of modeling the specific wettability of implant surfaces with bioinspired lubricants.

Study on effect of magnetization on wetting characteristics of water with different ions to coal dust

Coal dust is a significant problem in underground coal mining, and more economical and effective methods are needed to control coal dust. Magnetized water dust removal technology is considered to be an effective method to solve the problem of high concentration dust. In order to further understand the role of ions in magnetic fields in water, the optimal magnetic field parameters for solutions containing various ions were determined by surface tension and contact angle measurements. The wettability experiments have shown that the optimal magnetization effect can be obtained by placing NaCl solution with the concentration of 0.04 mol/L in the 150mT magnetic field for 120 s at room temperature. Subsequently, the influence of various ions in water on the wettability of coal was investigated using a combination of FTIR testing and Zeta potential experiments. The results showed that the order of the influence intensity of different ions on the wettability of water was Na+ > Mg2+ > Ca2+ when the Cl– content was 0.04 mol/l, and Cl– > CO32– > SO42– when the Na+ content was 0.04 mol/L. Furthermore, Lorentz forces can influence various ions, accelerating their migration and enhancing their accessibility to water clusters. Different ions exert force on the dipoles within water molecules, which can promote or suppress hydrogen bond cleavage. When the number of hydrogen bond breaks rises, it leads to an increase in the wetting properties of the solution. The research findings provide a theoretical foundation for the use of magnetization technology in dust suppression with mist spray in underground coal mines.

The soybean lecithin-cyclodextrin-vitamin E complex nanoparticles stabilized Pickering emulsions for the delivery of β-carotene: Physicochemical properties and in vitro digestion

In this work, soybean lecithin (LC) was used to modify β-cyclodextrin (β-CD) with hydrophobic fat chains to become amphiphilic (LC-CD), and vitamin E (VE) was encapsulated in former modified β-CD complexes (LC-CD-VE), the new Pickering emulsions stabilized by LC-CD-VE and LC-CD complexes for the delivery of β-carotene (BC) were created. The surface tension, contact angle, zeta potential, and particle size were used to assess the changes in complexes nanoparticles at various pH values. Furthermore, LC-CD-VE has more promise as Pickering emulsion stabilizer than LC-CD because of the smaller particle size (271.11 nm), proper contact angle (58.02°), and lower surface tension (42.49 mN/m). The interactions between β-cyclodextrin, soybean lecithin, and vitamin E were confirmed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and thermogravimetric analysis (TGA). The durability of Pickering emulsions was examined at various volume fractions of the oil phase and concentrations of nanoparticles. Compared to the emulsion stabilized by LC-CD, the one stabilized by LC-CD-VE showed superior storage stability. Moreover, for the delivery of BC, Pickering emulsions stabilized by LC-CD and LC-CD-VE can outperform bulk oil and Tween 80 stabilized emulsions in terms of UV light stability, storage stability, and bioaccessibility. This work could offer fresh perspectives on stabilizer alternatives for Pickering emulsion delivery systems.

Molecular simulation of the effect of anionic surfactant on methane diffusion in coal

Coal seam water injection is one of the important means of coal mine disaster prevention and control, which helps to reduce gas concentration. Anionic surfactants can change the hydrophilicity of coal to enhance the wetting effect of coal seam water injection and inhibit the diffusion of methane. However, the research on the effect of surfactants on the diffusion process of methane is still relatively weak. In order to explore the influence mechanism of anionic surfactant on coal surface wettability and methane diffusion from a microscopic point of view. Using wiser coal model and two commonly used anionic surfactants, sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS), the surfactant/water interface configuration, water/coal contact angle configuration and coal seam methane diffusion configuration were constructed. The interfacial stability of surfactant and water was discussed, and the wetting modification effect of surfactant on coal surface and the law of gas diffusion were analyzed. Finally, by studying the microscopic properties of each molecule in the simulation system, the adsorption mode of surfactants, the hydrophilicity of polar groups, the number of hydrogen bonds and the change of the pore volume in the coal seam system were analyzed, and the wetting modification mechanism of surfactants on coal surface and the inhibition effect of methane diffusion were discussed. The results show that with the increase of surfactant concentration, the interface formation energy is constantly enhanced, and the absolute value of electrostatic energy gradually increases, making the effect between surfactant and water stronger. The contact angle of coal surface under the action of SDS surfactant is the smallest, which is 36.230°, indicating that SDS surfactant has the best effect on the wettability of coal surface. The amount of methane diffusion in the surfactant action system decreased significantly compared with the pure water system, and the distribution of methane in the coal seam increased, indicating that the interaction between methane and coal is enhanced under the action of surfactant. With the increase of surfactant concentration, surfactant molecules are easier to spread on the surface of coal seam, and the wettability of coal surface increases. The research results can provide some research ideas and reference significance for anionic surfactants in the prevention and control of coal mine gas disasters.

The Wetting Characteristics and Microscopic Wetting Mechanism of Coal under High-Pressure Nitrogen Environment

The wettability of coal is an important factor influencing hydraulic stimulation. Field-trial data has proven that high-pressure N2 injection plays a positive role in increasing the coalbed methane (CBM) production rate. For the purpose of investigating the mechanism by which N2 promotes the gas rate, multiple experiments were conducted sequentially on the wettability of anthracite under different N2 pressures. Testing of the coal surface contact angle was conducted under 0.1–8 MPa nitrogen pressure using a newly built contact angle measuring device. The coal samples were collected from the Xinjing Coal Mine in the Qinshui Basin, China. The test results revealed that the contact angle increased with increasing N2 pressure. That is, the contact angle was 77.9° at an N2 pressure of 0.1 MPa and gradually increased to 101.4° at an infinite N2 pressure. In contrast, the capillary pressure decreased with an increasing N2 pressure, from 0.298 MPa to −0.281 MPa. The relationship between contact angle and N2 pressure indicated that the wettability was reversed at a N2 pressure of 5.26 MPa, with a contact angle of 90° and a capillary pressure of 0 MPa. The capillary pressure reversed to a negative value as the N2 pressure increased. At the microlevel, a high N2 pressure increases the surface roughness of coal, which improves the ability of the coal matrix to adsorb N2, forming the gas barrier that hinders the intrusion of water into the pores of the coal matrix. The results of this study provide laboratory evidence that high-pressure N2 injection can prevent water contamination and reduce the capillary pressure, thus benefiting coalbed methane production.

Halogen‐free boron‐based hybrid system for enhancing flame retardancy, mechanical and thermal properties of epoxy

AbstractThis study aims to increase the flame retardancy of epoxy‐based composites by using various flame retardants together with colemanite filler (CLM), which is a very mineral‐rich boron type. As a flame retardant, aluminum hydroxide (Al(OH)3) and boron‐containing compounds: borax (BRX) and natural minerals (tincal (TNC) and colemanite (CLM)), as well as barium metaborate (BaMB) synthesized by us were used. Scanning electron microscopy (SEM), x‐ray powder diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), contact angle (CA), and particle size analysis were used to characterize the composites and additives. All boron compounds increased the thermal stability of the composites. Except for the ER/CLM‐BaMB composite, other composites' surface contact angles were over 90°. In terms of both combustion and thermal properties, the best CLM‐BaMB‐Al(OH)3‐TNC ratio was determined as 15:5:15:15. The tensile strength, self‐extinguishing time, estimated and experimental Limited Oxygen Index (LOI) values for this composite were determined as 96 MPa, 65 s, 29.6%, and 25%, respectively. In addition, ANOVA was applied to determine the effect of hybrid filler type and different weight ratios on the mechanical properties of composites.

Using X-ray computed tomography and pore-scale numerical modeling to study the role of heterogeneous rock surface wettability on hydrogen-brine two-phase flow in underground hydrogen storage

Underground hydrogen storage (UHS) is receiving increasing attention to address the challenges in hydrogen storage. A crucial aspect of UHS is understanding the transport of hydrogen in subsurface porous media. In this work, hydrogen core flooding experiments were conducted in a sandstone sample and then the pore-scale distribution of hydrogen and brine was visualized using high-resolution X-ray micro-computed tomography (micro-CT). After CT image processing, we measured the surface contact angles (CAs) on rock surfaces and found that the measured CAs followed a log-normal distribution. To investigate the influence of rock surface wettability on the transport properties in the hydrogen-brine-sandstone system, the lattice Boltzmann (LB) method was used to simulate two-phase flows with different surface CA distributions; hydrogen-brine relative permeability and capillary pressure curves through the primary drainage, imbibition, and secondary drainage processes were obtained by LB simulations. X-ray CT scanning showed that hydrogen resided in both large pores and small pores and pore throats after the primary drainage process (i.e., hydrogen displacing brine), whereas after the imbibition process (i.e., brine displacing hydrogen) hydrogen stayed primarily in large pores where the capillary pressure barriers were low. The LB two-phase flow modeling illustrated that water’s relative permeability increased whereas hydrogen’s relative permeability decreased when the core flooding moved from primary drainage to imbibition; in contrast, when the core flooding moved from imbibition to secondary drainage, water’s relative permeability decreased whereas hydrogen’s relative permeability increased. Decreasing the surface CA increased the capillary pressure and reduced the hydrogen residual rate, which indicates high hydrogen retrievability and thus is favorable for UHS practice. The change in CA’s standard deviation did not cause noticeable changes in water’s relative permeability curves, whereas it resulted in noticeable changes in hydrogen’s relative permeability curves. This work is the first study that utilizes X-ray micro-CT scanning and pore-scale multiphase flow modeling to quantitatively and comprehensively investigate hydrogen-brine two-phase flow properties under different rock surface wettability distributions. The research findings from this study will advance the understanding of hydrogen transport in an underground storage system and provide essential data for large-scale field studies in UHS.