Retraction Curve Research Articles

Defective Biomechanics and Pharmacological Rescue of Human Cardiomyocytes with Filamin C Truncations.

Actin-binding filamin C (FLNC) is expressed in cardiomyocytes, where it localizes to Z-discs, sarcolemma, and intercalated discs. Although FLNC truncation variants (FLNCtv) are an established cause of arrhythmias and heart failure, changes in biomechanical properties of cardiomyocytes are mostly unknown. Thus, we investigated the mechanical properties of human-induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) carrying FLNCtv. CRISPR/Cas9 genome-edited homozygous FLNCKO-/- hiPSC-CMs and heterozygous knock-out FLNCKO+/- hiPSC-CMs were analyzed and compared to wild-type FLNC (FLNCWT) hiPSC-CMs. Atomic force microscopy (AFM) was used to perform micro-indentation to evaluate passive and dynamic mechanical properties. A qualitative analysis of the beating traces showed gene dosage-dependent-manner "irregular" peak profiles in FLNCKO+/- and FLNCKO-/- hiPSC-CMs. Two Young's moduli were calculated: E1, reflecting the compression of the plasma membrane and actin cortex, and E2, including the whole cell with a cytoskeleton and nucleus. Both E1 and E2 showed decreased stiffness in mutant FLNCKO+/- and FLNCKO-/- iPSC-CMs compared to that in FLNCWT. The cell adhesion force and work of adhesion were assessed using the retraction curve of the SCFS. Mutant FLNC iPSC-CMs showed gene dosage-dependent decreases in the work of adhesion and adhesion forces from the heterozygous FLNCKO+/- to the FLNCKO-/- model compared to FLNCWT, suggesting damaged cytoskeleton and membrane structures. Finally, we investigated the effect of crenolanib on the mechanical properties of hiPSC-CMs. Crenolanib is an inhibitor of the Platelet-Derived Growth Factor Receptor α (PDGFRA) pathway which is upregulated in FLNCtv hiPSC-CMs. Crenolanib was able to partially rescue the stiffness of FLNCKO-/- hiPSC-CMs compared to control, supporting its potential therapeutic role.

Mechanism of long-range hydrophobic force based on cavitation of metastable liquid film

Hydrophobic force, a key driving force in colloid physicochemical system and biological macromolecular system, exhibits a distinct multi-scale effect. The prevailing scholarly consensus attributes long-range hydrophobic force to bubble bridging, facilitated by unstable liquid film cavitation, while short-range force is thought to arise from the reorganization of water molecules at the solid-liquid interface. However, a comprehensive theoretical study remains elusive. To further elucidate the mechanism of the long-range hydrophobic force based on unstable liquid film cavitation, we carry out systematic research on the long-range hydrophobic force between perfluorooctyl trichlorosilane hydrophobic particles and the surface, by utilizing atomic force microscopy (AFM) and molecular dynamics simulations. According to AFM force tests, the long-range hydrophobic force escalates incrementally with subsequent close contacts before reaching a plateau. On the tenth contact, the penetration curve exhibits a sudden jump to an adhesion distance of 502.01 nm. A distinct step in the retraction curve suggests the rupture of the cavitation bubble capillary bridge. Importantly, the classical capillary force mathematical model provides an effective fit for the penetration curve. Our calculations estimate the volume of the capillary bridge at 0.30 μm³, offering direct theoretical evidence of the unstable liquid film cavitation bubble capillary bridge. Further insights are gained from large-scale tensile molecular dynamics simulations by using GROningen MAchine for Chemical Simulations (GROMACS). The inherent correlation mechanism of the formation, evolution, and mechanical behavior of the cavitation bubble capillary bridge in the separation process of hydrophobic particles are further explored from a molecular perspective. The results demonstrate that the local pressure drop occurring at the moment of “jump-out” separation of the hydrophobic particles attracts nitrogen molecules to diffuse into the liquid film, thereby forming a cavitation bubble capillary bridge. Simultaneously, a jumping behavior is observed in the calculated spring potential curve at the moment of capillary bridge rupture. Finally, the influence of solution gas content on long-range hydrophobic force is investigated. There is a positive correlation between gas molecule content and both the growth rate of cavitation bubble capillary bridge volume and the length of capillary bridge stretch-rupture, further demonstrating the gas concentration dependence of long-range hydrophobic forces. In a word, revealing the long-range hydrophobic force mechanism based on the cavitation of unstable liquid film can enhance our understanding of the interaction between colloid physical chemistry and biological macromolecules. Meanwhile, hydrophobic force is the fundamental driving force of particle-bubble adhesion in mineral flotation system, and the revelation of its action mechanism has important guiding significance for regulating the actual mineral flotation process.

The mechanical properties of lipid nanoparticles depend on the type of biomacromolecule they are loaded with.

For drug delivery systems, the mechanical properties of drug carriers are suspected to play a crucial role in the delivery process. However, there is a lack of reliable methods available to measure the mechanical properties of drug carriers, which hampers the establishment of a link between delivery efficiency and the mechanical properties of carriers. Lipid nanoparticles (LNPs) are advanced systems for delivering nucleic acids to target cell populations for vaccination purposes (mRNA) or the development of new drugs. Hence, it is crucial to develop reliable techniques to measure the mechanical properties of LNPs. In this article, we used AFM to image and probe the mechanical properties of LNPs which are loaded with two different biopolymers either pDNA or mRNA. Imaging the LNPs before and after indentation, as well as recording the retraction curve, enables us to obtain more insight into how the AFM tip penetrates into the particle and to determine whether the deformation of the LNPs is reversible. For pDNA, the indentation by the tip leads to irreversible rupture of the LNPs, while the deformation is reversible for the mRNA-loaded LNPs. Moreover, the forces reached for pDNA are higher than for mRNA. These results pave the way toward the establishment of the link between the LNP formulation and the delivery efficiency.

Mechanomics study of cardiomyocytes with filamin c truncations

Abstract Background Filamin C (FLNC) is expressed in cardiomyocytes, where it binds to actin and localizes to Z-discs, sarcolemma, and intercalated discs. Although FLNC truncation variants (FLNCtv) are an established cause of arrhythmias and heart failure (arrhythmogenic cardiomyopathy), the underlying mechanisms, in particular changes in mechanical properties of cardiomyocytes, are mostly unknown. Purpose In this study, we applied a biophysical approach to investigate the interaction between altered mechanical properties and biological response in human induced pluripotent stem cells–derived cardiomyocytes (hiPSC-CMs) carrying FLNCtv. Methods CRISPR/Cas9 genome-edited FLNC-/- hiPSC-CMs, a homozygous condition that is lethal in animal models, and FLNC+/- hiPSC-CMs, recapitulating the heterozygous human disease, were analyzed. Wild-type FLNC hiPSC-CMs were used as controls. Atomic Force microscopy (AFM) was used to perform single-cell force spectroscopy (SCFS) microindentation, to evaluate passive and dynamic mechanical properties. From the loading curves, two cell Young’s Moduli were calculated: E1, related to the compression of the plasma membrane and actin cortex, and E2, including the rest of the inner cell layers (cytoskeleton and nucleus). Cell adhesion was assessed using the retraction curve of the SCFS. Data were processed in terms of adhesion force (the highest value of the force exerted by the cell-surface contact to the cantilever during retraction) and work of adhesion (integrating the area under the retraction curve). Finally, FLNC-/- hiPSC-CMs were incubated with 1 µM Crenolanib (a PDGFRA signaling inhibitor) for 3 days, and the microindentation was performed again using DMSO-only-treated FLNC-/- cells as controls. Results The AFM indentation curve for the cells analyzed showed significant differences. Both elastic contributions (E1 and E2) show that wild-type FLNC iPSC-CMs are stiffer than both mutant FLNC+/- and FLNC-/- iPSC-CMs (see Figure upper panel). The adhesion showed the same trend as the elasticity: mutant FLNC iPSC-CMs showed a progressive decrease of work of adhesion as well as max adhesion force from the FLNC+/- to the FLNC-/- models. Rescue of the latter with Crenolanib showed to moderately increase their stiffness. Moreover, a qualitative analysis of the beating traces showed that FLNC+/- but mostly FLNC-/- display "irregular" small peaks, resembling those of delayed after depolarizations (see Figure lower panel). Conclusions We found that FLNCtv causes a decrease in cell stiffness which declines progressively from the heterozygous status, which is associated with FLNC haploinsufficiency, to the homozygous status, which lacks FLNC. This indicates a progressive softening of the cardiomyocytes, suggesting a damaged cytoskeleton. Crenolanib rescue suggests that the inhibition of PDGFRA signaling could partially restore such damage (see Figure upper panel - right corner).

Determination of the rate-dependent adhesion of polydimethylsiloxane using an atomic force microscope

A JKR (Johnson-Kendall-Roberts) formalism is used to extract the Young modulus, the contact radius, and the energy release rate simply from the retraction curve of a borosilicate glass colloidal probe from a polydimethylsiloxane (PDMS) surface using an atomic force microscope. PDMS samples ranged from perfectly elastic to those with incipient viscoelasticity. The dependence of the release rate energy with the crack speed is verified using a fracture mechanics-based method.

Maturation of Neural Cells Leads to Enhanced Axon-Extracellular Matrix Adhesion and Altered Injury Response

Although it is known that stronger cell-extracellular matrix interactions will be developed as neurons mature, how such change influences their response against traumatic injury remains largely unknown. In this report, by transecting axons with a sharp atomic force microscope tip, we showed that the injury-induced retracting motion of axon can be temporarily arrested by tight NCAM (neural cell adhesion molecule) mediated adhesion patches, leading to a retraction curve decorated with sudden bursts. Interestingly, although the size of adhesion clusters (~0.5–1 μm) was found to be more or less the same in mature and immature neurons (after 7- and 3-days of culturing, respectively), the areal density of such clusters is three times higher in mature axons resulting in a much reduced retraction in response to injury. A physical model was also adopted to explain the observed retraction trajectories which suggested that apparent adhesion energy between axon and the substrate increases from ~0.12 to 0.39 mJ/m2 as neural cell matures, in good agreement with our experiments.

Applicability of cavity-throat connecting model for estimating the hydraulic conductivity of fine-grained soils: a geometrical and mathematical approach

Determining the hydraulic conductivity of low permeable fine-grained soils is difficult and time-consuming. This work develops a new method with an eye to the pore morphology to correlate hydraulic conductivity with pore-size distribution (PSD) parameters obtained from mercury porosimeter data. In order to realize this method, calculating percolation loss along the flow paths in pore channels and quantifying the spatial morphology of pore channels by proposing a cavity-throat connecting model is necessary. In order to establish the standard process of the new method, a kind of sedimentary mucky clay with regular dual-structural PSD has been collected. The samples are divided into three series: (a) vibrated with variable frequencies; (b) frozen at variable temperatures and unfrozen, making the freezing-thawing effect as the variable; and (c) remolded with different water contents. The PSD of freeze-dried samples at the end of each process is obtained by mercury intrusion porosimetry. After that, the method is demonstrated with application to 12 series of fine-grained soils. Deduced from mercury porosimeter data, the volume-based PSD curves of fine-grained soils are bimodal, due to the presence of inter-aggregate and intra-aggregate pores. Two important hypotheses have been proposed: (i) one is that in the smaller pore scales, the experimental extrusion curve controlled by the hysteresis loop has a really approximate part compared to the theoretical overall retraction curve, making the experimental extrusion curve characterize the pore cavity size approximately, and (ii) the pore system consists of a series of multistage cavity-throat connections. Accumulating the effects of single connection on the percolation can be used to measure the overall effects of pore system on the percolation. Based on fluid-driven path analysis of percolation, the pore system is quantified by a series of cavity-throat connections and the percolation loss has been derived to estimate the hydraulic conductivity. The permeable parameter (κ) representing the overall effects of pore connections on the hydraulic conductivity (K) is suited to correlate the microstructure and hydraulic conductivity by the linear relationship with the fixed slope in semilogarithmic coordinate for the fine-grained soils. It is the destruction and recombination of cavity-throat connections that are dominant during the treatments like freezing, remolding, and reinforcing.

Particle detachment from fluid interfaces: theory vs. experiments.

Microparticle adsorption and self-assembly at fluid interfaces are strongly affected by the particle three-phase contact angle θ. On the single-particle level, θ can be determined by several techniques, including colloidal-probe AFM, the gel-trapping technique (GTT) and the freeze-fracture shadow-casting (FreSCa) method. While GTT and FreSCa provide contact angle distributions measured over many particles, colloidal-probe AFM measures the wettability of an individual (specified) particle attached onto an AFM cantilever. In this paper, we extract θ for smooth microparticles through the analysis of force-distance curves upon particle approach and retraction from the fluid interface. From each retraction curve, we determine: (i) the maximal force, Fmax; (ii) the detachment distance, Dmax; and (iii) the work for quasistatic detachment, W. To relate Fmax, Dmax and W to θ, we developed a detailed theoretical model based on the capillary theory of flotation. The model was validated in three different ways. First, the contact angles, evaluated from Fmax, Dmax and W, are all close in value and were used to calculate the entire force-distance curves upon particle retraction without any adjustable parameters. Second, the model was successfully applied to predict the experimental force-distance curve of a truncated sphere, whose cut is positioned below the point of particle detachment from the interface. Third, our theory was confirmed by the excellent agreement between the particle contact angles obtained from the colloidal-probe AFM data and the ensemble-average contact angles measured by both GTT and FreSCa. Additionally, we devised a very accurate closed-form expression for W (representing the energy barrier for particle detachment), thus extending previous results in the literature.

Interfacial separation of a mature biofilm from a glass surface – A combined experimental and cohesive zone modelling approach

A good understanding of the mechanical stability of biofilms is essential for biofouling management, particularly when mechanical forces are used. Previous biofilm studies lack a damage-based theoretical model to describe the biofilm separation from a surface. The purpose of the current study was to investigate the interfacial separation of a mature biofilm from a rigid glass substrate using a combined experimental and numerical modelling approach. In the current work, the biofilm–glass interfacial separation process was investigated under tensile and shear stresses at the macroscale level, known as modes I and II failure mechanisms respectively. The numerical simulations were performed using a Finite Volume (FV)-based simulation package (OpenFOAM®) to predict the separation initiation using the cohesive zone model (CZM). Atomic force microscopy (AFM)-based retraction curve was used to obtain the separation properties between the biofilm and glass colloid at microscale level, where the CZM parameters were estimated using the Johnson–Kendall–Roberts (JKR) model. In this study CZM is introduced as a reliable method for the investigation of interfacial separation between a biofilm and rigid substrate, in which a high local stress at the interface edge acts as an ultimate stress at the crack tip.This study demonstrated that the total interfacial failure energy measured at the macroscale, was significantly higher than the pure interfacial separation energy obtained by AFM at the microscale, indicating a highly ductile deformation behaviour within the bulk biofilm matrix. The results of this study can significantly contribute to the understanding of biofilm detachments.

Experimental and modelling studies of the kinetics of mercury retraction from highly confined geometries during porosimetry in the transport and the quasi-equilibrium regimes

Mercury porosimetry is a widely used method for pore structural characterisation but, often, half of the data obtained in any given experiment, in the form of the retraction curve, is simply not used. This may be because mercury retraction is significantly less well understood than intrusion, and thus it is more difficult to extract reliable information. In this work, detailed studies have been made of the retraction process from mesoporous materials, with non-random heterogeneities in their void structure, to obtain fundamental knowledge that could form the basis of methods to reliably extract accurate pore space descriptors from the retraction curve. In one material the initiation of retraction was found to be independent of the experimental time-scale because it was governed by the rapid equilibration of the narrowing of mercury necks, and subsequent snap-off of mercury connections at a small number of pore intersections. This scenario has been validated by simulations of quasi-equilibrium mercury retraction on structural models obtained from magnetic resonance images. In another material, the slow relaxation of entrapped mercury was followed by integrated gas sorption experiments and SAXS. This process was also simulated using Monte-Carlo methods. It was found that the temporal evolution of the remaining pore size distribution was sensitive to the initial configuration of entrapped mercury ganglia, and could thus be used to validate specific models of mercury entrapment for particular amorphous materials.

The interfacial behaviour of singlepoly(N,N-dimethylacrylamide) chains as a function of pH

We have studied the pH-dependent conformational behaviour ofpoly(N,N-dimethylacrylamide) (PDMAc) at silicon and gold surfaces using single-moleculeforce spectroscopy and a quartz crystal microbalance (QCM). Despite the pHdependence, nuclear magnetic resonance and titration experiments demonstrate thatPDMAc is not a weak polybase. The interaction between single chains and asilicon surface (with native oxide layer intact) in aqueous solution was investigatedusing force spectroscopy. Single-molecule force measurements were performedusing thiol-functionalized PDMAc and gold-coated AFM cantilevers. The forces ofinteraction between PDMAc and the native oxide-coated silicon surface varywith the pH. The shape of the retraction curve for low pH solution includes agreater number of ‘train’ conformations, which suggests a stronger interactionwith the surface relative to the surrounding media at low pH. The adsorptionbehaviour of PDMAc, from liquid onto silicon surfaces, was monitored using aQCM, which shows greater PDMAc adsorption onto silicon at low pH. The forcespectroscopy and QCM investigations confirm that the PDMAc chain is moreextended and stiffer in low pH solution. We attribute the pH-dependent behaviourto an increased number of hydrogen bonding sites on the silicon surface at lowpH.

Dynamic and Thermo-Mechanical Properties of Some Specialty Fluoroelastomers for Low Tg Seal Materials

The viscoelastic behaviour of three different low Tg fluoroelastomer materials belonging to the class of Fluorosilicones (FVMQ), Perfluoropolyether-hydrosilanes (Sifel™) and Perfluoropolyether-polyurethanes (FEU) was investigated. Materials considered were high hardness rubbers and were characterized by dynamic-mechanical analysis (DMA), thermo-mechanical analysis (TMA), and swelling tests in Fuel C and other solvent mixtures. DMA spectra in dynamic scan allowed the determination of Tg and other minor intensity relaxation phenomena. Thermo-mechanical analysis was used to measure the thermal expansion coefficient αL and the low temperature retraction curve Re(T) in creep and recovery experiments with different test conditions. Highly diversified behaviours were observed, apparently related to polymer Tg and damping in the rubbery plateau. Swelling measurements showed a better performance for the two perfluoropolyether samples than for fluorosilicones.

Nano-mechanical exploration of the surface and sub-surface of hydrated cells of Staphylococcus epidermidis

The surface of hydrated cells of Staphylococcus epidermidis has been probed using an atomic force microscope. While local force measurements over the surface of bacteria reveal a heterogeneous chemical surface, with heterogeneous mechanical properties, different kinds of force curves appear with high frequency, and are thought to provide information on features contributing strongly to the overall mechanical and surface behaviour of the cell. Force curves often present two different mechanical regimes, being the first one (outer) of about 48 nm thick, and presenting a local relative elasticity of about 0.08 N/m, which is about a third of the relative elasticity of the inner part of the cell wall, harder, with a relative elasticity of about 0.24 N/m, in water. Both regimes appears as straight lines in the force versus distance curves (the 'corresponding' stress-strain curves in contact mechanics), but hysteresis is observed between the approach and the retraction line in the inner regime, indicating a degree of viscoelasticity. No viscoelasticity is observed in the outer regime, however, which presents quite linear and juxtaposed approach-retraction lines. These kinds of force curves do not present measurable pull-off forces nor snap-in forces, which indicates an almost null interaction between tip and bacterial surface, which could be in agreement with the measured very high hydrophobicity of this strain. Another kind of force curve has been observed recurrently, showing peaks in the retraction curves. Adhesive pull-off forces were measured giving an average of about 2 nN. Interestingly, however, these force curves appear only when quite irregular and wavy retraction curves are present, from the very beginning of its trace (maximum indentation). This leads us to think that these pull-off forces measured by our AFM do not give information on surface forces-unbinding events at the surface of the bacteria, but could be related to events at the sub-surface of the cell surface. Oscillations seen in the retraction curve in the portion corresponding to the contact with the bacteria surface could be due to rupture phenomena within the multilayered cell wall architecture expected in Gram-positive bacteria as Staphylococcus epidermidis, which could result in local irreversible deformations of the cell surface. Imaging with a sharp tip in contact mode sometimes leads to surface damage. Force curves recorded over damaged parts of the cell surface showed a completely different behaviour, in many cases with two well-defined high-adhesion peaks, and also interestingly, with snap-in forces of about 0-2 nN, which seems to indicate a completely different electrical/hydrophobicity state only a few nanometers down from the surface. Similar indentation effects can occur in the contact of a bacterial cell with a solid surface, even when showing only atomic-molecular-scale roughness, thus interacting not only with the very surface of the cell, especially when soft layers are present in the outer. Our results highlight the importance of the cell surface mechanical properties and their interplay with purely surface properties when analyzing cell-material interaction, and show the AFM as a useful method for investigating this.

TOMOGRAPHY OF MACRO-MESO-PORE STRUCTURE BASED ON MERCURY POROSIMETRY HYSTERESIS

Mercury porosimetry (MP) hysteresis loop scanning (SHL) data are used in the deduction of pore structure tomography diagrams. Macro and/or meso-pore structure tomography refers to the tracing of intrinsic pore size distributions (psd) of pore structure sections corresponding to specified volume saturation levels. Tomography information may be proved a useful tool e.g., to elucidate mass transfer, heterogeneous reaction phenomena, eic. The contribution of the present work is the simulation of the MP - scanning data, based on the random corrugated pore structure model (CPSM), reported elsewhere and the generation of the pertinent pore structure tomography spectra (i.e., a set of local, as regards saturation, intrinsic psd). The CPSM model has been applied to carry out parametric studies for the generation of theoretical loop scanning diagrams and the construction of the pertinent tomography plots. Additionally the CPSM model have been successfully used in curve fitting applications by using experimental MP hysteresis loop scanning data, taken from literature or produced in this work, and the deduction of the respective tomography diagrams. Part 1 of this work is devoted to pore structure tomography accruing from MP loop scanning along the penetration line while Part II deals with loop scanning along the retraction curve and the derivation of the respective pore structure tomography spectrum. Overall, the CPSM model simulates satisfactorily MP loop scanning data and yields credible pore structure tomography information.

TOMOGRAPHY OF MACRO-MESO-PORE STRUCTURE BASED ON MERCURY POROSIMETRY HYSTERESIS LOOP SCANNING Part II: MP Hysteresis Loop Scanning Along the Overall Retraction Line

The concept of macro-meso-pore structure tomography based on mercury porosimetry hysteresis loop scanning along the retraction curve (MP-SHL-R) is introduced. The random corrugaled pore structure (CPSM) model is used in the simulation of the present loop-scanning variant. The CPSM predicted, distribution (VT) of trapped mercury, reported elsewhere, is employed in the definition of a retraction line‘free of entrapment’(Vr) and hence, a ‘nominal’ MP hysteresis loop scanning (MP-SHL-R(A’)) is constructed. The CPSM model have been used in MP-SHL-R(N)) scanning cycles applications to deduce the relevant intrinsic pore size distributions. These psds drawn on a 2-D and/or 3-D plots, that constitute the pore structure tomography, are compared graphically to those obtained by MP hysteresis loop scanning along the penetration line (Part I), Further the CPSM model, as applied in Part II, has been successfully used in regression trials of experimental MP hysteresis loop scanning data and generated the respective tomography spectra. It is concluded that given an MP overall penetration-retraction experimental data, the CPSM model can be best fitted over these data and hence achieve sensible predictions of pore structure tomography based on both MP scanning modes.

Removing optical artifacts in near-field scanning optical microscopy by using a three-dimensional scanning mode

We demonstrate a method of acquiring near-field scanning optical microscopy data that allow for the construction of three different types of images from one data set: topographic, constantgap, and constant-height. This data set includes the topographic features of the surface and the optical response at various heights above the sample surface. Comparisons are made between the images recorded in this format and both conventional, constant-gap mode images, and pseudoconstant-height mode images constructed using a single retraction curve. Zmotion artifacts are identified by analyzing the optical intensity for a given image as a function of the sample topography. Using this procedure it is shown that significant z-motion artifacts exist in the constant-gap images of gold particles immobilized on a glass slide. These artifacts are avoided by constructing constant-height images.

Mercury intrusion and retraction in model porous media

Chamber-and-throat pore networks etched in glass (or plastic) are often used as model porous media to study the pore-scale mechanisms and their cooperative effects on macroscopic transport coefficients of important multiphase processes, such as hydrocarbon recovery from rock reservoirs, pollution of soils and aquifers by liquid organic wastes, etc. Such models have special built-in characteristics, notably, small pore depth (compared to the pore widths and diameters), equivalent capillary diameter that is nearly equal to the pore depth and has small variation and small chamber to throat equivalent capillary diameter ratio. Given that all these features strongly affect the various multiphase transport processes that are studied experimentally in model porous media, it is necessary to take them into account quantitatively. The present work develops a 2-D network mercury intrusion–retraction simulator that is adapted to the specific geometrical and topological characteristics of model pore networks. Based on experimental observations, the mercury meniscus motion in chambers and throats during intrusion and the mercury disconnection events during retraction are analyzed at pore-scale. Mercury intrusion or retraction in chamber-and-throat networks is simulated as a sequence of flow events occurring at progressively increasing or decreasing external pressures, respectively. It is found that the location and the degree of hysteresis of mercury intrusion-retraction curves are determined primarily by the depth of pores and the values of contact angles. The pressure of residual air may influence the high pressure region of intrusion curve and the low pressure region of retraction curve. Mercury retraction from the pore network is carried out through cluster growth, over a narrow pressure region and the residual mercury saturation is low because of the strong dependence of capillary pressures of retraction from pore chambers on the local fluid topology. The simulator predicts the experimental capillary pressure curves of two glass models satisfactorily; furthermore, the simulated patterns of mercury intrusion–retraction are in agreement with corresponding experimental ones. The experimentally validated simulator provides a reliable tool for the thorough characterization of the structure and the prediction of the capillary properties of model porous media as well as of real porous media with similar pore scale characteristics.

APPLICATION OF A STOCHASTIC NETWORK PORE MODEL TO A CATALYST PELLET

Abstract A previously developed stochastic two-dimensional network pore structure model has been applied directly to a nickel/alumina commercial catalyst pellet. A technique has been devised to determine the pore diameter distribution function of cylindrical pore segments for any prescribed network dimension which will exactly replicate the experimentally observed mercury penetration curve for the pellet in the method of mercury porosimetry. This stochastic network representation for the catalyst pellet pore structure is superior to the classical parallel bundle model since it incorporates the element of pore interconnectivity. The model has been extended to investigate the phenomena occurring during the accumulation of a foulant deposit (e.g. coke in hydrocarbon catalysis) for the pore structure determined for a 10 × 10 set of network elements for the pellet under study. The analysis shows how the build-up of a deposit causes physical blocking of the smaller pores at quite low accumulations of foulant which results in inaccessibility of parts of the interior pore structure. This necessarily results in only partial filling of the pore structure with deposit, with a tendency for greater accumulation towards the pellet exterior. This kind of behaviour is not possible with the parallel bundle model. A detailed comparison of the two pore models in respect of accessible interior volume at various foulant accumulations is presented. The derived network model based upon the penetration curve gives an independent prediction of the mercury porosimeter retraction curve which is in reasonably close agreement with the experimental result, thus confirming the probable utility of the model in predicting and correlating other macroscopic properties of the catalyst pellet.