Two-dimensional Pore Network Research Articles

Formation of Coronene Clusters in Concentration and Temperature Controlled Two-Dimensional Porous Network.

In this research, with the assistance of scanning tunneling microscopy (STM), we observed the two-dimensional (2D) self-assembly transition of a star-shaped oligofluorene derivative (StOF) from disordered structure to honeycomb network by adjusting StOF concentration in solution. By introducing guest molecules coronene (COR), we for the first time achieved novel triangle-shaped COR trimers on liquid/highly oriented pyrolytic graphite (HOPG) interface in both honeycomb network and the disordered structure. In thermal tests, the COR/StOF-disorder system underwent a structural conformation to form well-ordered ladder structures, while the COR/StOF-honeycomb system remained the perfect hexagonal network with COR trimers included in the cavities. Density functional theory (DFT) calculations have been employed to investigate the forming mechanism of the molecular nanoarrays. These studies are expected to enhance controlling on 2D self-assembly and provide a facial approach toward constructing on-surface molecular clusters.

Pore Network Simulations of Heat and Mass Transfer inside an Unsaturated Capillary Porous Wick in the Dry-out Regime

In this work, a two-dimensional pore network model is developed to study the heat and mass transfer inside a capillary porous wick with opposite replenishment in the dry-out regime. The mass flow rate in each throat of the pore network is computed according to the Hagen–Poiseuille law, and the heat flux is calculated based on Fourier’s law with an effective local thermal conductivity. By coupling the heat and the mass transfer, a numerical method is devised to determine the evolution of the liquid–vapor interface. The model is verified by comparing the effective heat transfer coefficient versus heat load with experimental observations. For increasing heat load, an inflation/deflation of the vapor pocket is observed. The influences of microstructural properties on the vapor pocket pattern and on the effective heat transfer coefficient are discussed: A porous wick with a non-uniform or bimodal pore size distribution results in a larger heat transfer coefficient compared to a porous wick with a uniform pore size distribution. The heat and mass transfer efficiency of a porous wick comprised of two connected regions of small and large pores is also examined. The simulation results indicate that the introduction of a coarse layer with a suitable thickness strongly enhances the heat transfer coefficient.

Interaction of droplets with porous structures: Pore network simulation of wetting and drying

ABSTRACTIn fluidized bed spray agglomeration, the time evolution of a liquid droplet deposited on a porous particle is of paramount importance for the success of the process. The combination of droplet penetration into the pores and evaporation, either directly from the droplet surface or from the surrounding wet pores, determines how long free liquid remains on the particle surface so that other particles can bind via liquid bridges. In this work, a two-dimensional pore network model that combines the algorithms of liquid migration and drying is developed to track the full droplet evolution, from its deposition on network surface to complete evaporation of the liquid. The influence of the pore structure for mono-modal and bi-modal networks with different spatial correlation of the pore size on the evolution of the liquid droplet is investigated. The effect of the liquid viscosity on the evolution of the droplet in the pore network is studied. Moreover, pore network simulations with multiple depositions of liquid droplets on the same network are presented as a rough approximation of spray agglomeration process.

A Quantitative Technique to Compare Experimental Observations and Numerical Simulations of Percolation in Thin Porous Materials

Quantitative validation of numerical simulations of percolation in porous media has always been challenging due to the stochastic nature of the material structure and morphology regardless of the numerical technique being used. In this article, we present a technique that allows for a quantitative comparison between numerical and experimental percolation. The experimental observations are of injection pressure and liquid intrusion within thin porous materials in a Hele-Shaw style test. The thin porous materials tested had a surface treatment such the contact angle was larger than \(90^{\circ }\) resulting drainage percolation. Flow rates were adjusted to encompass the range of capillary numbers for drainage flow patterns between the stable displacement and capillary fingering. In parallel to the experimental observations, a series of numerical simulations using a two-dimensional pore network model were performed mimicking the Hele-Shaw experiments. The material properties of the pore network realizations, pore size distribution, contact angle, and representative volume for the pore space were based on measurements of the porous materials tested. Boundary and initial conditions were matched between numerical simulations and experiments. To compare and validate the numerical simulation against the experiments, a new scaling of the dissipated energy during percolation in thin porous media was used. This scaling has been recently used to identify the transition between capillary fingering and stable displacement for drainage in different thin porous materials and provides a unique method for characterizing percolation in thin porous materials. Though the experiments and simulations presented in this article are for drainage, the technique described is equally applicable to imbibition. Excellent agreement is obtained between experiment and simulation with clear delineation between different types of thin porous materials.

Periodic Functionalization of Surface-Confined Pores in a Two-Dimensional Porous Network Using a Tailored Molecular Building Block

We present here the periodic functionalization of a two-dimensional (2D) porous molecular network using a tailored molecular building block. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, 1-isoDBA, having an isophthalic acid unit connected by an azobenzene linker to a C12 alkyl chain and five C14 chains, was designed and synthesized. After the optimization of monolayer preparation conditions at the 1,2,4-trichlorobezene (TCB)/graphite interface, scanning tunneling microscopy (STM) observation of the self-assembled monolayer of 1-isoDBA revealed the formation of extended domains of a porous honeycomb-type molecular network, which consists of periodically located nanowells each functionalized by a cyclic hexamer of hydrogen-bonded isophthalic acid units and those without functional groups. This result demonstrates that the present strategy based on precise molecular design is a viable route to site-specific functionalization of surface-confined nanowells. The nanowells of different size can be used for guest coadsorption of different guests, coronene COR and hexakis[4-(phenylethynyl)phenylethynyl]benzene HPEPEB, whose size and shape match the respective nanowells. STM observation of a ternary mixture (1-isoDBA/COR/HPEPEB) at the TCB/graphite interface revealed the site-selective immobilization of the two different guest molecules at the respective nanowells, producing a highly ordered three-component 2D structure.

Impact of NAPL architecture on interphase mass transfer: A pore network study

Interphase mass transfer in porous media is commonly modeled using Sherwood number expressions that are developed in terms of fluid and porous medium properties averaged over some representative elementary volume (REV). In this work the influence of sub-grid scale properties on interphase mass transfer was investigated using a two-dimensional pore network model. The focus was on assessing the impact of (i) NAPL saturation, (ii) interfacial area (iii) NAPL spatial distribution at the pore scale, (iv) grain size heterogeneity, (v) REV or domain size and (vi) pore scale heterogeneity of the porous media on interphase mass transfer. Variability of both the mass transfer coefficient that explicitly accounts for the interfacial area and the mass transfer coefficient that lumps the interfacial area was examined. It was shown that pore scale NAPL distribution and its orientation relative to the flow direction have significant impact on flow bypassing and the interphase mass transfer coefficient. This results in a complex non-linear relationship between interfacial area and the REV-based interphase mass transfer rate. Hence, explicitly accounting for the interfacial area does not eliminate the uncertainty of the mass transfer coefficient. It was also shown that, even for explicitly defined flow patterns, changing the domain size over which the mass transfer process is defined influences the extent of NAPL bypassing and dilution and, consequently, the interphase mass transfer. It was also demonstrated that the spatial variability of pore scale parameters such as pore throat diameters may result in different rates of interphase mass transfer even for the same pore size distribution index.

Two-Dimensional Nanoporous Networks Formed by Liquid-to-Solid Transfer of Hydrogen-Bonded Macrocycles Built from DNA Bases.

We present an approach that makes use of DNA base pairing to produce hydrogen-bonded macrocycles whose supramolecular structure can be transferred from solution to a solid substrate. A hierarchical assembly process ultimately leads to two-dimensional nanostructured porous networks that are able to host size-complementary guests.

Experimental Investigation of Calcium Carbonate Precipitation and Crystal Growth in One- and Two-Dimensional Porous Media

Visualization experiments using one-dimensional (1-D) porous media made of Plexiglas and two-dimensional glass porous networks were conducted to obtain qualitative and quantitative information concerning the precipitation and crystal growth of CaCO3 under varying flow and concentration conditions. Supersaturated solutions were prepared by mixing sodium bicarbonate and calcium chloride solutions before the pore networks. Nucleation and crystal growth were assumed to occur within the porous media. Changes in the initial and final solution composition were monitored. At low initial supersaturation values (SRinitial), a few crystals were observed within the flow channels and crystal growth took place exclusively on the newly formed crystals. As the SRinitial increased, more crystals were formed along the flow channels and new crystallites were continuously formed during the course of the experiments. Nucleation and crystal growth were not uniform. The crystal growth rates depended on the initial value of SR a...

A microscopic particle image velocimetry method for studying the dynamics of immiscible liquid–liquid interactions in a porous micromodel

The development of an experimental protocol to investigate the flow field produced by the interaction of two immiscible liquids flowing through a porous network is reported. The experimental protocol allows simultaneous quantification of the velocity distribution in a multi-liquid system based on the microscopic particle image velocimetry technique. The experimental challenges associated with this unique application are discussed, including two-liquid imaging and interface tracking, and solutions that couple refractive index matching and fluorescent signal separation are described. The technique was applied to both single- and two-liquid flows in a two-dimensional pore network comprising a staggered array of circular pillars wherein the flow was driven by a steady pressure gradient. Both drainage and imbibition were considered herein with a focus on fluid–fluid front migration and effects owing to the passage of the interface. The velocity distribution obtained for these two-liquid-phase flow scenarios revealed several peculiarities when compared to the reference case of single-liquid-phase flow. In particular, the instabilities associated with the interfacial processes propagate downstream and perturb the flow field, resulting in dramatic differences from the regular and periodic flow paths typical of steady-state, single-phase flow. Additionally, the passage of the interface does not restore previous flow patterns, but instead yields complex preferential flow paths that mutually interact with residual trapped pockets of fluid. Such dynamical events must be quantified in order to properly model the pore-scale physics central to fully understanding the wealth of practical applications represented by this model flow system.

Synthesis, Crystal Structure of Two-Dimensional Porous Network [Zn(dmbdc)(py)]·NMP}2n (py = Pyridine, NMP = N-Methyl-pyrrolidone, H2dmbdc = 2,5-Dimethylbenzenedicarboxylic Acid)

Synthesis, Crystal Structure of Two-Dimensional Porous Network [Zn(dmbdc)(py)]·NMP}2n (py = Pyridine, NMP = N-Methyl-pyrrolidone, H2dmbdc = 2,5-Dimethylbenzenedicarboxylic Acid)

On-surface synthesis of a two-dimensional porous coordination network: Unraveling adsorbate interactions

We present a detailed experimental and theoretical characterization of the adsorption of the perylene derivative 4,9-diaminoperylene-quinone-3,10-diimine (DPDI) on Cu(111) and compare it to its threefold dehydrogenated derivative 3deh-DPDI, which forms in a surface reaction upon annealing. While DPDI itself does not give rise to long-range ordered structures due to lack of appropriate functional groups, 3deh-DPDI acts as an exoligand in a Cu-coordinated honeycomb network on Cu(111). The main focus of this work lies on the analysis of intermolecular and molecule-substrate interactions by combining results from scanning tunneling microscopy, x-ray photoelectron spectroscopy, x-ray standing wave measurements, and density functional theory. We show, in particular, that the interactions between metal atoms and organic ligands effectively weaken the molecule-surface interactions for 3deh-DPDI leading to an increase in molecule-substrate distances compared to the DPDI precursor. Our experimental findings also shed light on the applicability of current theories, namely van der Waals corrections to density functional theory.

Cellulose films: designing template-free nanoporous cellulose films on semiconducting surfaces.

In this work, we report the preparation of ultrathin submicro- and nanoporous cellulose films onto Si (100). The effect of different experimental conditions of preparation on the film surface morphology was studied, namely the role of the film casting method (spin- versus dip-coating), solvent (toluene or tetrahydrofuran), substrate pretreatment (hydrophilicity degree), and regeneration procedure with HCl vapors (two consecutive dips followed by regeneration or regeneration after each dip). The surface morphological structures presented in this work were never obtained before without the use of templates. A rather regular two-dimensional pore network was obtained onto the less hydrophilic Si substrate (contact angle≅68°), after two consecutive dips (with an intercalary rotation of 180º) in trimethylsilyl cellulose diluted in toluene and regeneration at the end. All the surfaces were characterized by atomic force microscopy.

Site-specific bonding of copper adatoms to pyridine end groups mediating the formation of two-dimensional coordination networks on metal surfaces

We study the formation of a coordination network consisting of the organic pyridine-based 2,4,6-tris(4-pyridine)-1,3,5-triazine (T4PT) species and Cu atoms on Cu(111) and Ag(111) metal surfaces. Using scanning tunneling microscopy, we find that the organic molecule T4PT forms stable two-dimensional porous networks on the surface of Cu(111) and, by codeposition of Cu atoms, also on the Ag(111) crystal, in which Cu atoms are twofold coordinated by T4PT molecules. X-ray absorption spectroscopy measurements of the metal-organic network Cu--T4PT on Ag(111) accompanied by density-functional theory calculations show that the nitrogen atoms of the pyridine end groups of the T4PT molecules are the active sites in coordinating the Cu adatoms. X-ray magnetic circular dichroism experiments reveal that the Cu atom in such a metal-organic motif is in a low-valent ${d}^{10}$ state and has no magnetic moment.

Feasibility study of using microfluidic platforms for visualizing bubble flows in electrolyzer gas diffusion layers

In this study, microfluidic platforms were used to visualize air bubble transport in two-dimensional (2D) representations of gas diffusion layers (GDLs) to gain insight into how the geometric features of the GDL impact multiphase flow in polymer electrolyte membrane (PEM) electrolyzers. Two-dimensional porous networks were designed using volumetric pore space information, including average porosity and average throat size obtained from micro-computed tomography (micro CT) visualizations. Microfluidic chips were fabricated to represent felt, sintered powder, and foam GDLs and used to simulate the transfer of oxygen bubbles generated at the catalyst layer, through the GDL towards the flow channels of a PEM electrolyzer. The results of this work indicate that the use of microfluidic platforms for evaluating PEM electrolyzer GDLs is highly promising.

Structural Diversity of Two Novel Complexes of Co(II) withbis-Triazole Ligand: from One-Dimensional Chain to Two-Dimensional Porous Network

Structural Diversity of Two Novel Complexes of Co(II) with<i>bis</i>-Triazole Ligand: from One-Dimensional Chain to Two-Dimensional Porous Network

Structural diversity of two novel complexes of Co(II) with bis-triazole ligand: From one-dimensional chain to two-dimensional porous network

Using two novel bis-triazole ligands, 2,6-bis(1,2,4-triazole-4-yl)pyridine (L1) and 1,6-bis(1,2,4-triazole-1-yl)hexane (L2), one novel one-dimensional (1D) chain polymer [Co(NCS)2(L1)2] n (I) and one two-dimensional (2D) coordination polymer [Co(NCS)2(L2)2] n (II) have been synthesized and structurally characterized. The crystal crystallizes in the triclinic system for I, space group $$P\bar 1$$ , a = 7.879(6), b = 8.830(7), c = 9.837(8)A, α = 70.230(11)°, β = 115.474(6)°, γ = 85.591(12)°, Z = 1. The crystal crystallizes in the mo-noclinic system for II, space group $$P\bar 1$$ , a = 7.879(6), b = 8.830(7), c = 9.837(8) α = 70.230(11)°, β = 115.474(6)°, γ = 85.591(12)°, Z = 1. The structural diversity of these two new Co(II) complexes vary from 1D chain to 2D porous supramolecular network, which may be ascribed to ligand directing effects under similar synthetic conditions (L1 contains rigid pyridine spacers while L2 contains flexible hexane spacers).

Pore-Scale Simulations of Gas Displacing Liquid in a Homogeneous Pore Network Using the Lattice Boltzmann Method

A lattice Boltzmann high-density-ratio model, which uses diffuse interface theory to describe the interfacial dynamics and was proposed originally by Lee and Liu (J Comput Phys 229:8045–8063, 2010), is extended to simulate immiscible multiphase flows in porous media. A wetting boundary treatment is proposed for concave and convex corners. The capability and accuracy of this model is first validated by simulations of equilibrium contact angle, injection of a non-wetting gas into two parallel capillary tubes, and dynamic capillary intrusion. The model is then used to simulate gas displacement of liquid in a homogenous two-dimensional pore network consisting of uniformly spaced square obstructions. The influence of capillary number (Ca), viscosity ratio (\(M\)), surface wettability, and Bond number (Bo) is studied systematically. In the drainage displacement, we have identified three different regimes, namely stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number, viscosity ratio, and Bond number. Gas saturation generally increases with an increase in capillary number at breakthrough, whereas a slight decrease occurs when Ca is increased from \(8.66\times 10^{-4}\) to \(4.33\times 10^{-3}\), which is associated with the viscous instability at high Ca. Increasing the viscosity ratio can enhance stability during displacement, leading to an increase in gas saturation. In the two-dimensional phase diagram, our results show that the viscous fingering regime occupies a zone markedly different from those obtained in previous numerical and experimental studies. When the surface wettability is taken into account, the residual liquid blob decreases in size with the affinity of the displacing gas to the solid surface. Increasing Bo can increase the gas saturation, and stable displacement is observed for \(Bo>1\) because the applied gravity has a stabilizing influence on the drainage process.

Experimental Investigation of Drying in a Model Porous Medium: Influence of Thermal Gradients

In this study, isothermal and non-isothermal drying experiments with imposed constant temperature gradients have been conducted in a two-dimensional square pore network of borosilicate glass (SiO2) with interconnected etched channels. In experiments with temperature decreasing from the open surface of the pore network, a travelling stabilized gas-liquid region could be established, while in isothermal experiments with uniform temperature faster breakthrough and an extended two-phase zone were observed. Both findings are in good agreement with pore network simulations. However, numerical underestimation of drying rates (especially in the second period of drying) indicates that liquid films might play a major role in the experimental pore networks, even in the presence of thermal gradients.

Bis[μ-2,5-bis-(pyridin-2-yl)-1,3,4-thia-diazole-κ(4) N (2),N (3):N (4),N (5)]bis-[(nitrato-κO)silver(I)] tetra-hydrate.

The self-assembly of an angular 2,5-bis­(pyridin-2-yl)-1,3,4-thia­diazole ligand (L) with silver nitrate (AgNO3) produced a new dinuclear silver(I) coordination complex, [Ag2(C12H8N4S)2(NO3)2]·4H2O, which crystallizes with two Ag atoms bridged by two L ligands. The Ag atom is surrounded by four N atoms of L and by one O from the nitrate anion defining a distorted square pyramid. The atoms comprising the dication are nearly coplanar, with an r.m.s. deviation of 0.1997 Å. Mol­ecules are linked by C—H⋯O and O—H⋯O hydrogen bonds through nitrate anions and water mol­ecules, forming a two-dimensional porous network. The overall structure involves stacking of Ag complex layers along the b axis. The cohesion in the three-dimensional architecture is ensured by O⋯Ag inter­actions.

Molecular Multistate Systems Formed in Two-Dimensional Porous Networks on Ag(111)

Host–guest interactions in porous supramolecular structures have been studied on surfaces using scanning tunneling microscopy, with anticipation of biochemical and sensor applications, but limited to cases of van der Waals interactions and hydrogen bonds. Here, we studied the intermolecular structures of 4,4″-dibromo-p-terphenyl molecules self-caged in porous supramolecular structures with halogen bonds on Ag(111). The caged molecules hopped among six different configurations at higher than 50 K, showing a propeller-like pattern. At 30 K, they stayed at one of six states that were stabilized with Br···Br halogen bonds and Br···H hydrogen bonds with energy gains of 225, 197, and 163 meV, as revealed by our density functional theory calculations. The self-caged structure provides a model system to simulate multistate supramolecular memories.