Hydrophobic Pore Research Articles

The role of surface thermodynamics and kinetics in the removal of PFOA from aqueous solutions

Perfluorooctanoic acid (PFOA) has been extensively used as surfactant in industrial applications. Human exposure to PFOA through contaminated water has been linked to serious adverse health effects. In this work, the removal of PFOA from water in all-silica zeolites, which are hydrophobic materials with diverse pore geometries and exceptional hydrothermal stability, is studied. Molecular scale structure, dynamics, kinetics, and free energy landscapes associated with PFOA adsorption are characterized. Interfacial adsorption constitutes the rate limiting step and the adsorption of PFOA is orientation competitive. The PFOA orientation where the hydrophobic perfluorinated methyl group is adsorbed first on the zeolite surface is thermodynamically favored; whereas the adsorption kinetics is faster when the hydrophilic carboxyl group is adsorbed first. Furthermore, the adsorption of PFOA in deprotonated state in hydrophobic pores is thermodynamically prohibitive. Based on computed permeabilities in the pores and kinetic rates associated with the adsorption of PFOA from water, three zeolites, MTW, VET and GON, are estimated to exhibit several orders of magnitude better PFOA removal performance compared to the benchmark material, zeolite Beta (BEA).

In situ self-sacrificial synthesis of polypyrrole/biochar composites for efficiently removing short- and long-chain perfluoroalkyl acid from contaminated water

Efficient removal of perfluoroalkyl acids (PFAAs), especially short-chain ones, from contaminated water is of great challenge and is urgently called for so as to safeguard the ecosystem and human health. Herein, polypyrrole (PPy) functionalized biochar (BC) composites were innovatively synthesized by an in situ self-sacrificial approach to allow efficient capture of PFAAs with different chain lengths. Compared with conventional PPy-based composites synthesized by direct polymerization using FeCl3 as an oxidizing agent, PPy/BC composites were fabricated utilizing freshly generated Fe3+ as an oxidizing agent from self-sacrificial Fe3O4 for pyrrole monomers in situ polymerizing on BC. As a result, with the support of BC and gradual release of Fe3+, PPy overcame its tendency to aggregate and became uniformly dispersed on BC, and meanwhile, PPy could well tailor the surface chemistry of BC to endow its positively charged surface. Consequently, the composites exhibited strong sorption capacities of 3.89 and 1.53 mmol/g for short-chain perfluorobutanoic acid (PFBA) and perfluorobutane sulfonic acid (PFBS), 2.55 and 1.22 mmol/g for long-chain perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), respectively, which were superior to those of pristine BC, commercial activated carbon, and anion exchange resins reported. Additionally, they could effectively remove 17 different classes of per- and polyfluoroalkyl substances (PFAS) (removal >95%) from actual PFAS-contaminated water, and the spent sorbent could be well regenerated and reused at least 5 times. An integrated analysis indicated that such an outstanding PFAA sorption performance on PPy/BC composites could be mainly attributed to surface adsorption enhanced by electrostatic attractions (anion exchange interaction) with the traditional hydrophobic interaction and pore filling of less contribution, particularly for short-chain analogues. These results are expected to inform the design of BC with greater ability to remove PFAS from water and the new sorbent could help water facilities comply with PFAS regulations.

Role of polyamide microplastics as vector of parabens in the environment: An adsorption study

The prevalence of microplastics in the aquatic environment has become a global problem. Their capacity to adsorb pollutants may influence in their environmental fate, bioavailability, and toxicity to biota. This work provides a systematic study to characterize the role of polyamide (PA) as vector of parabens (PBs) in the environment. The effect of PA and influence of environmental factors in the adsorption process were investigated. The amount of PBs adsorbed onto 50μm PA at 30 mg/L of PBs follows the order: butylparaben (1.440 mg/g) > propylparaben (1.321 mg/g) > ethylparaben (0.995 mg/g) > methylparaben (0.543 mg/g), which is positively correlated with their log Kow and length of the ester alkyl chain. Physical adsorption forces such as hydrophobic interaction, pore filling and hydrogen bond dominated the adsorption mechanism The size of the PA particles has been resulted in a significant factor; a higher adsorption capacity was remarkable when decreasing PA particle size (from 10.3% for 3 mm to 79.5% for 50 μm (0.5 mg/L PBs)). The adsorption percentage increases with pH until the PBs pKa value and decrease significantly at pH>pKa values due to repulsion forces. Salinity increases adsorption capacity until at 2% NaCl content while the dissolved organic matter negatively affects and leads to low adsorption. Our results reveal that PBs were potentially adsorbed onto PA in real water matrices (average of 82% in tap water, 72% in surface water, 76% in effluent wastewater, and, 53% in influent wastewater (0.5 mg/L PBs)), which may have important environmental implications.

Preparation of hydrophobic and fire-retarding poly(lactic acid)/graphene oxide foams for oil/organic solvents absorption

Petroleum leakage, oil spill and toxic organic solvent emissions have become a global water contamination issue. To solve this problem, it is a promising solution to develop a simple and green strategy to prepare environmentally friendly and high absorption capacity absorbents from biodegradable polymers. Herein, in this work, PLA was used as the matrix to prepare the foam absorbent. Firstly, the flame retardant methoxy-phosphonitrilic trimer (HEPCP, FR) was synthesized. Then PLA composite foams were produced by melting PLA with FR, and mixing with GO through a freezing-dry method. The results showed that FR-PLA/5GO foam self-extinguished immediately when removing the ignition source, due to the fact that the incorporation of GO further improve the fire retardancy of FR-PLA foam. The porosity and the water contact angle of FR-PLA/5GO were gradually increased up to 94.0% and 127.4°, showing a lightweight, highly hydrophobic and homogeneous pore structure. Then the FR-PLA/5GO foam was used as the oil/organic solvent absorbent, which reached the saturated adsorption capacity within 10 s due to the high hydrophobicity and porosity. Meanwhile, the absorbent showed good recyclability, and the FR-PLA/5GO foam still maintained > 75.0% of its original capacity after 10 cycles of the evaporation−adsorption procedure. This work provides a method for developing a biodegradable absorbent for the oil/organic contaminant.

Percolation transitions of spontaneous imbibition in fractional-wet porous media

Percolation transition is an important scientific question for characterizing complex two-phase flow phenomena in fractional-wet porous media composed of different wetting grains. Recent studies have shown significant transitions of fluid distribution and pressure system in fractional-wet porous media by changing wettability proportion. However, very few studies have systematically investigated controlling factors of percolation transition in spontaneous imbibition. Additionally, there is a lack of comprehensive knowledge and experimental observations about imbibition recovery and dynamic imbibition phenomena (including imbibition time, imbibition rate, and induction time) in fractional-wet porous media. In this study, these knowledge gaps are filled through a series of water imbibition experiments for fractional-wet artificial porous media with different water-wet proportions, three pore diameters, and two wettability heterogeneities. The results show that pore diameter and wettability heterogeneity are influential factors for percolation transition. Decreasing water-wet proportion results in the emergence of induction time, as well as the absences of transition and late imbibition stage, small pore radius enhances these negative impacts. Under strong wettability heterogeneity, relationship of water-wet proportion and imbibition recovery follows the classical percolation theory containing two percolation transitions. Small pore diameter retards percolation transitions, and weakens fluid displacements of the transition stage and late stage in the partial imbibition. Moreover, effects of water-wet proportion on dynamic imbibition phenomena exhibit exponential relationship resulted from transition of pathway type. Additionally, through decreasing wettability heterogeneity, three percolation transitions and an optimal imbibition ability are achieved, thus hydrophilization of hydrophobic pore is advantageous for water imbibition. These intriguing findings can broaden current knowledge about spontaneous imbibition in fractional-wet porous media.

A Molecular Dynamics Study Employing Bimetallic Co–CuHAB Nanosheets for Seawater Desalination

Bimetallic MOFs, which contain two different types of metal nodes within their porous structures, have emerged as a novel class of materials that exhibit tunable properties, rendering them suitable for various applications. In this research, molecular dynamics (MD) simulations are conducted to assess the performance of 2D Hexaaminobenzene (HAB)-derived MOF membranes in reverse osmosis seawater desalination. The membranes display different Co:Cu metal node ratios and degrees of offset nanosheets, and their ion rejection rates and water flux values are compared. In particular, their behaviors are explained through the corresponding radial distribution functions, density distributions, and interaction energy values. Our findings reveal that of the four MOF membranes studied, CuHAB exhibits the best performance in terms of water flux. In addition, the pore diameter of the MOFs is dependent on the ratio of the Co and Cu nodes inside their respective MOF membranes. To achieve high water flux, it is recommended for the membranes to have large hydrophobic pores, while the membrane must display poor salt adsorption to prevent salt ions from permeating through. It is also observed that Co nodes exhibit greater affinity toward the O atoms of the water molecules and the Cl– ions than the Cu nodes. Due to the hydrophobic nature of the small CoHAB pores, offsetting the nanosheets that constitute the membranes can improve salt rejection but show no significant effect on water flux. Overall, this study shows that MD simulations can effectively determine the optimal ratio of metal nodes in bimetallic 2D MOF membranes to achieve desirable water flux values and ensure excellent salt rejection.

Interfacial wave of the gas-liquid two-phase flow in unsaturated reservoir pores

Unsaturated reservoir pores exist widely in porous self-lubricating materials for the continuous consumption of lubricant. The complex gas-liquid two-phase flow behavior in the pores significantly affects the self-lubricating performance. In this paper, the two-phase flow model in unsaturated pores was established based on the Couple Level Set and Volume of Fluid method. Two kinds of porous materials with significantly different wettability, stainless steel and polytetrafluoroethylene (PTFE), were concerned. The two-phase flow behaviors were investigated to reveal the flow mechanism in the unsaturated pores. The different flow behaviors caused by the wettability of materials were quantitative characterization. Results show that, the gas rises with a convex interface in the stainless steel pore, and the bubble is generated after the contact line is pinned on the edge of the pore at 35 ms. While in the PTFE pore, the gas rises with a concave interface. And the gas profile changes from concave to convex after the contact line is pinned at 32 ms. In the two pores, the gas-liquid interface fluctuates periodically. In the hydrophilic stainless steel pore, the fluctuation amplitude decreases and finally tends to be stable with the increase of time. In the hydrophobic PTFE pore, the interface has constant fluctuation amplitude for the attraction between gas and the hole wall. The fluctuation of the gas-liquid interface has an important influence on the flow state of the lubricant film. The results help to clarify the two-phase flow mechanism within unsaturated pores, and provide guidance for the self-lubrication design of the porous materials.

Structure of dimeric lipoprotein lipase reveals a pore adjacent to the active site

Lipoprotein lipase (LPL) hydrolyzes triglycerides from circulating lipoproteins, releasing free fatty acids. Active LPL is needed to prevent hypertriglyceridemia, which is a risk factor for cardiovascular disease (CVD). Using cryogenic electron microscopy (cryoEM), we determined the structure of an active LPL dimer at 3.9 Å resolution. This structure reveals an open hydrophobic pore adjacent to the active site residues. Using modeling, we demonstrate that this pore can accommodate an acyl chain from a triglyceride. Known LPL mutations that lead to hypertriglyceridemia localize to the end of the pore and cause defective substrate hydrolysis. The pore may provide additional substrate specificity and/or allow unidirectional acyl chain release from LPL. This structure also revises previous models on how LPL dimerizes, revealing a C-terminal to C-terminal interface. We hypothesize that this active C-terminal to C-terminal conformation is adopted by LPL when associated with lipoproteins in capillaries.

Mechanistic insights into the role of nanoparticles towards the enhanced performance of thin-film nanocomposite membranes

Thin-film nanocomposite (TFN) membranes are promising in improving water treatment due to their high permeability and selectivity. However, little is known about the mechanism by which nanoparticles enhance their performance. In this study, we prepared two series of TFN membranes containing ∼40 nm-sized zeolitic imidazolate framework (ZIF-8) nanoparticles, one with a hydrophobic porous form and the other with a nonporous amorphous form (aZIF-8). The TFN membranes containing 0.15 w/v% ZIF-8 exhibited a 100% increase in water permeance while maintaining a similar NaCl rejection (98.38%) compared to thin-film composite (TFC) membranes used in brackish water reverse osmosis (BWRO). In contrast, adding the same amount of aZIF-8 resulted in almost no water permeance enhancement. By comparing the physicochemical properties of the two materials and the two series of membranes, we found that the only difference was the presence or absence of internal hydrophobic pore structures. We proposed that the hydrophobic internal pores of nanoparticles served as extra water channels while preventing the passage of NaCl during BWRO.

A fractal effective permeability model for dual-wet porous Media

Recent studies have shown that the pores of some unconventional rocks can be categorized into hydrophilic pores that boarded by inorganic minerals such as quartz and hydrophobic pores that within the organic matter. The rock which consists of both hydrophilic and hydrophobic pores shows a dual-wettability behavior. The previously-proposed imbibition transient analysis technique has been applied in characterizing the pore size distribution of the dual-wet rocks by analyzing comparative oil and water imbibition data. On the basis of the determined pore size distribution, a fractal model for estimating effective permeability of the dual-wet rock was proposed. The proposed model, together with the imbibition transient analysis technique, is able to estimate effective permeability of the dual-wet rocks by using imbibition data. The proposed model can also estimate the effective permeability of hydrophilic pores and hydrophobic pores. The proposed model takes injection pressure, wettability behavior and pore size distribution of the dual-wet rock into the consideration. Our sensitivity analyses show that injection pressure affects effective permeability and hydrophobic permeability by controlling the water saturation within hydrophobic pores. The rock with higher volumetric fraction of hydrophilic pores tends to have higher hydrophilic permeability and lower hydrophobic permeability. By keeping the porosity constant, effective permeability decreases as the volumetric fraction of small pores increases. Cited as: Shi, Y., Guo, Y., Dehghanpour, H., Song, H. A fractal effective permeability model for dual-wet porous media. Advances in Geo-Energy Research, 2023, 8(2): 100-111. https://doi.org/10.46690/ager.2023.05.04

Confined Water Cluster Formation in Water Harvesting by Metal-Organic Frameworks: CAU-10-H versus CAU-10-CH3.

Several metal-organic frameworks (MOFs) excel in harvesting water from the air or as heat pumps as they show a steep increase in water uptake at 10-30 % relative humidity (RH%). A precise understanding of which structural characteristics govern such behavior is lacking. Herein, CAU-10-H and CAU-10-CH3 are studied with H, CH3 corresponding to the functions grafted to the organic linker. CAU-10-H shows a steep water uptake ≈18 RH% of interest for water harvesting, yet the subtle replacement of H by CH3 in the organic linker drastically changes the water adsorption behavior to less steep water uptake at much higher humidity values. The materials' structural deformation and water ordering during adsorption with in situ sum-frequency generation, in situ X-ray diffraction, and molecular simulations are unraveled. In CAU-10-H, an energetically favorable water cluster is formed in the hydrophobic pore, tethered via H-bonds to the framework μOH groups, while for CAU-10-CH3, such a favorable cluster cannot form. By relating the findings to the features of water adsorption isotherms of a series of MOFs,it is concluded that favorable water adsorption occurs when sites of intermediate hydrophilicity are present in a hydrophobic structure, and the formation of energetically favorable water clusters is possible.

Metal‐Organic Frameworks with Rod Yttrium Secondary Building Units

AbstractWe report a new hydroxamate‐based yttrium MOF, named MOF‐419 [Y(HCOO)(BDH)], with rod‐SBUs. The compound was synthesized employing chelating construction of benzene‐1,4‐hydroxamate (BDH2−) linkers, and the use of formic acid as the modulator was found to be crucial for the formation of rod‐shaped SBUs. MOF‐419 shows permanent porosity and has a BET surface area of 1130 m2/g. Its hydrophobic pore environment and gas sorption properties were demonstrated through the combination of single crystal X‐ray diffraction and nitrogen, carbon dioxide, and water sorption experiments. We envision that these results will aid the study and understanding of rod MOFs with chelating linkages.

Ultra-Fast Preparation of Large-Area Graphdiyne-Based Membranes via Alkynylated Surface-Modification for Nanofiltration.

Graphdiynes (GDYs), two-dimensional graphene-like carbon systems, are considered as potential advanced membrane material due to their unique physicochemical features. Nevertheless, the scale-up of integrated GDY membranes is technologically challenging, and most studies remain at the theoretical stage. Herein, we report a simple and efficient alkynylated surface-mediated strategy to prepare hydrogen-substituted graphdiyne (HsGDY) membranes on commercial alumina tubes. Surface alkynylation initiates an accelerated surface-confined coupling reaction in the presence of a copper catalyst and facilitates the nanoscale epitaxial lateral growth of HsGDY. A continuous and ultra-thin HsGDY membrane (∼100 nm) can be produced within 15 min. The resulting membranes exhibit outstanding molecular sieving together with excellent water permeances (ca. 1100 L m-2 h-1 MPa-1 ), and show a long-term durability in cross-flow nanofiltration, owing to the superhydrophilic surface and hydrophobic pore walls.

Hydrophobic gating in bundle-crossing ion channels: A case study of TRPV4.

Many transmembrane (TM) ion channels regulate ion permeation by forming bundle crossing of the pore-lining TM helices when deactivated. The resulting physical constriction is generally believed to serve as the “gate” and impose the major free energy barrier to ion permeation. On the other hand, many ion channels have been observed contain inner pores that are highly hydrophobic and can undergo spontaneous dewetting transitions. The resulting “vapor” region can block ion flow even in the absence of physical constriction. However, it is not clear whether such hydrophobic gating mechanism could be involved in channels with bundle-crossing in the deactivated state. Using atomistic simulations, we show that the human TRPV4 (hTRPV4) channel in the bundle-crossing closed state can readily undergoes hydrophobic dewetting transition and forms a vapor region in the lower pore region. Importantly, free energy analysis reveals that the major barrier for ion permeation is not located at the most constricted site, but within the vapor region. Furthermore, a single hydrophilic mutation I715N in the lower pore region significantly increases pore hydration without affecting the physical opening near bundle crossing; yet it largely removes the free energy barrier of ion permeation in hTRPV4, consistent with a previous experimental study showing that I715N leads to a constitutively conductive channel. Therefore, hTRPV4 is a hydrophobic gating channel despite the presence of bundle-crossing in the deactivated state. We anticipate that hydrophobic gating may play a key role in other bundle-crossing ion channels with hydrophobic inner pores.

Cryo-EM structures of the TolQ membrane protein in complex with inner membrane protein partner TolR from the opportunistic pathogen Acinetobacter baumannii provide information on structure and stoichiometry.

TolQ-TolR-TolA is an energy-transducing inner-membrane sub-complex conserved across Gram-negative bacteria. It maintains connection with periplasmic TolB-Pal sub-complex in an energy-dependent manner through TolA protein spanning the periplasm. Utilizing proton motive force (PMF), Tol-Pal complex contributes to the integrity of outer membrane and the whole cell envelope. TolQ remains the only part of Tol-Pal complex with unknown structure up to now. To address this, we determined 3.02 and 3.34 Å cryo-electron microscopy (cryo-EM) structures of the integral inner-membrane protein TolQ and in complex with TolR, respectively from Acinetobacter baumannii. A. baumannii is one of the most dreaded and clinically important Gram-negative pathogens causing a broad-spectrum nosocomial infection mainly among debilitated patients admitted to intensive care units. Our structural analysis revealed that TolQ forms a pentamer with a channel-like hydrophobic trans-membrane pore slightly shifted above the membrane opening into a large negatively charged cytoplasmic chamber which is in common with the closest TolQ-TolR paralogs ExbB-ExbD and MotA-MotB. We validated observed structural features of TolQ by prior functional data. According to our analysis the most functionally detrimental point mutations mapped on structure are localized inside the channel. Obtained structures suggest that two trans-membrane domains of TolR dimer fit inside TolQ channel in TolQ-TolR complex forming a proton-flow pathway for PMF utilization. Cryo-EM structures solved in this work were funded in whole or in part with Refeyn Travel Grant and U.S. federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under contract No. HHSN272201700060C (Center for Structural Genomics of Infectious Diseases (CSGID); http://csgid.org).

Integrated interfacial design of covalent organic framework photocatalysts to promote hydrogen evolution from water

Attempts to develop photocatalysts for hydrogen production from water usually result in low efficiency. Here we report the finding of photocatalysts by integrated interfacial design of stable covalent organic frameworks. We predesigned and constructed different molecular interfaces by fabricating ordered or amorphous π skeletons, installing ligating or non-ligating walls and engineering hydrophobic or hydrophilic pores. This systematic interfacial control over electron transfer, active site immobilisation and water transport enables to identify their distinct roles in the photocatalytic process. The frameworks, combined ordered π skeletons, ligating walls and hydrophilic channels, work under 300–1000 nm with non-noble metal co-catalyst and achieve a hydrogen evolution rate over 11 mmol g–1 h–1, a quantum yield of 3.6% at 600 nm and a three-order-of-magnitude-increased turnover frequency of 18.8 h–1 compared to those obtained with hydrophobic networks. This integrated interfacial design approach is a step towards designing solar-to-chemical energy conversion systems.

Highly Robust Microporous Metal‐Organic Frameworks for Efficient Ethylene Purification under Dry and Humid Conditions

AbstractTwo C2H6‐selective metal‐organic framework (MOF) adsorbents with ultrahigh stability, high surface areas, and suitable pore size have been designed and synthesized for one‐step separation of ethane/ethylene (C2H6/C2H4) under humid conditions to produce polymer‐grade pure C2H4. Experimental results reveal that these two MOFs not only adsorb a high amount of C2H6 but also display good C2H6/C2H4 selectivity verified by fixed bed column breakthrough experiments. Most importantly, the good water stability and hydrophobic pore environments make these two MOFs capable of efficiently separating C2H6/C2H4 under humid conditions, exhibiting the benchmark performance among all reported adsorbents for separation of C2H6/C2H4 under humid conditions. Moreover, the affinity sites and their static adsorption energies were successfully revealed by single crystal data and computation studies. Adsorbents described in this work can be used to address major chemical industrial challenges.

Highly Robust Microporous Metal-Organic Frameworks for Efficient Ethylene Purification under Dry and Humid Conditions.

Two C2 H6 -selective metal-organic framework (MOF) adsorbents with ultrahigh stability, high surface areas, and suitable pore size have been designed and synthesized for one-step separation of ethane/ethylene (C2 H6 /C2 H4 ) under humid conditions to produce polymer-grade pure C2 H4 . Experimental results reveal that these two MOFs not only adsorb a high amount of C2 H6 but also display good C2 H6 /C2 H4 selectivity verified by fixed bed column breakthrough experiments. Most importantly, the good water stability and hydrophobic pore environments make these two MOFs capable of efficiently separating C2 H6 /C2 H4 under humid conditions, exhibiting the benchmark performance among all reported adsorbents for separation of C2 H6 /C2 H4 under humid conditions. Moreover, the affinity sites and their static adsorption energies were successfully revealed by single crystal data and computation studies. Adsorbents described in this work can be used to address major chemical industrial challenges.

Fluorescent azobenzene-confined coiled-coil mesofibers.

Fluorescent protein biomaterials have important applications such as bioimaging in pharmacological studies. Self-assembly of proteins, especially into fibrils, is known to produce fluorescence in the blue band. Capable of self-assembly into nanofibers, we have shown we can modulate its aggregation into mesofibers by encapsulation of a small hydrophobic molecule. Conversely, azobenzenes are hydrophobic small molecules that are virtually non-fluorescent in solution due to their highly efficient photoisomerization. However, they demonstrate fluorogenic properties upon confinement in nanoscale assemblies by reducing the non-radiative photoisomerization. Here, we report the fluorescence of a hybrid protein-small molecule system in which azobenzene is confined in our protein assembly leading to fiber thickening and increased fluorescence. We show our engineered protein Q encapsulates AzoCholine, bearing a photoswitchable azobenzene moiety, in the hydrophobic pore to produce fluorescent mesofibers. This study further investigates the photocontrol of protein conformation as well as fluorescence of an azobenze-containing biomaterial.

Experimental validation of a coupling concept for drop formation and growth onto porous materials by high-resolution X-ray imaging technique

Droplets formed on the hydrophobic surface of a porous medium exposed to a cross-flowing gas stream have a strong influence on the mass, momentum, and energy exchange across the porous interface, being of importance in several physical systems and engineering applications, like fuel cells. However, the fluid displacement front is highly complex at the pore-scale, since it is characterized by the surface wettability and a contact angle variation along the triple line. Furthermore, the droplet formation is affected by the pore geometry and the surface wettability. These result in a challenging multi-phase scenario with controversial literature, and few studies consider the detailed mechanism of droplet formation on the surface of the porous medium. In this work, two multi-scale simulations for the emerging water droplet from a single hydrophobic capillary pore opening into the gas phase are validated by a benchmark experiment with the help of a high-resolution X-ray imaging technique to characterize the droplet growing. A three-domain approach (gaseous free flow, interface and porous medium, FIP) was compared with a two-domain approach (based on a free-flow and the porous medium, FP). Whereas the three-domain approach introduces two sets of coupling conditions, one for the free flow-interface and one for the interface-porous medium, the two-domain approach introduces only one set of coupling connections for describing the interaction between the domains. In both approaches, droplet formation and growth alter the coupling conditions between the domains. While the FIP approach treats the porous medium as a continuous matter, it is resolved discretely with the help of a pore network in the FP approach. Both approaches show good agreements with the experimental observations and high correspondences for the drop volume, radii and contact angle evolution. The proposed models provide a base for future developments and help to gain a better insight about the impact of the droplet formation on the interface in a coupled free flow-porous medium system.