Liquid-filled Pores Research Articles

Mass Transport Regimes in a CO2R Gas Diffusion Electrode Pore with Coupled Microkinetics Model

Gas Diffusion Electrodes (GDEs) have arisen as a popular CO2 electrolyser configuration due to the improved mass transfer properties and higher current densities possible in comparison to a liquid-fed system. In this work, we aim to understand the mass transport regimes in a single liquid-filled pore of a GDE, i.e., an idealized model of the porous catalyst layer. In previous work, Butler-Volmer (BV) expressions have been used to model the CO evolution reaction and the Hydrogen Evolution Reaction (HER). In this study, we extend that in a few ways: (1) a MicroKinetic Model (MKM) of Au at the surface of the electrode is used instead of the BV expressions, (2) volume/steric effects are incorporated through the Generalized Modified Poisson-Nerst-Planck (GMPNP) equation, and (3) more reactions are considered in the electrolyte. By analyzing pores of varying sizes, following the size distribution measured by Focused Ion Beam Scanning Electron Microscopy (FIB/SEM) in a GDE from the literature, we assess conditions where concentration profiles are no longer effectively one-dimensional in the pore axis. We discuss how these three-dimensional mass transfer effects impact CO2 conversion efficiency. In such regimes, we describe why special treatment is required when calling BV expressions in macroscale pore-averaged models.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL release number: LLNL-ABS-858384.

Plant-inspired rearrangement of liquid in a porous structure for controlled swelling

Soft robots can adapt to dynamic environments without prior knowledge of their properties. Plants inspire mechanisms for counterbalancing dynamic loads by locally modulating compliance through anisotropic humidity-responsive materials and structures. In addition to well-known passive bilayers, plants may also actively control swelling. The combination of robust hygroscopic material-level response and simple electrical control makes active swelling particularly attractive for technological implementation. However, dynamic swelling demands the development and optimisation of congruent pumping solutions. This work suggests electrohydrodynamic pumping, enabled by highly reversible ion immobilisation at capacitive electrodes, as a particularly suitable low-pressure, high-area liquid displacement solution for active swelling. Local pore fill ratio (PFR) modulation is used as a measure for dynamic liquid displacement and swelling. A method for highly localised (10 μm membrane thickness) assessment of the dynamic variation of PFR in a 400 μm laminate undergoing cross-plane electrokinetic liquid displacement is developed. Two modes for transient PFR modulation were identified: electrokinetic ion transfer and diffusive solvent redistribution, pronounced at high and low voltage scan rates, respectively. The strategic combination of these modes enables various compliance-modulation scenarios. The system contains (within a cycle) a constant amount of liquid in an open network of liquid-filled pores. 30%–75% PFR yielded the highest dynamic PFR modulation: a high amount of empty pores is beneficial, yet a too-low PFR compromises the continuous liquid pathway necessary for electrokinetic pumping. The dynamic nature of internal liquid rearrangement was characterised by relatively fast electrokinetics-driven fluxes (6.3% PFR change in 80 s), followed by a slow equilibration of concentration and PFR. At high scan rates, PFR decreased at positive polarisation, while both positive and negative polarity yielded a similar decrease at low scan rates (5 mV s−1). Localised control over the swelling gradient enables the design of systems that morphologically adapt to complex dynamic loading conditions.

Lewis acidity and substituent effects influence aldehyde enolization and C–C coupling in beta zeolites

The Claisen-Schmidt condensation between propanal and benzaldehyde was used a model aldol reaction to assess the reactivity of tetravalent framework Lewis acid sites (Ti, Zr, Sn, Hf) in hydrophobic beta zeolites (M-*BEA) and determine rates of enolization and carbon–carbon (C–C) bond formation along with selectivities among cross- and self-condensation products. Rates of enolate formation during liquid phase reactions (393 K) span nearly 100-fold, depending on the identity of the metal heteroatom, and correlate with enthalpies for adsorption of pyridine in liquid-filled pores of M-*BEA, as measured by isothermal titration calorimetry. Comparisons among adsorption enthalpies suggest that tetrahedrally substituted Zr and Hf are more effective Lewis acids than Sn and Ti for coordinating aldehydes within these environments. Ratios of initial rates of C–C coupling between propanal and benzaldehyde compared to propanal self-condensation were less than unity for all M-*BEA catalysts. These selectivity patterns reflect the combination of electronic and steric effects imposed by the larger aromatic substituent at the carbonyl carbon atom and its concerted interactions with the Lewis acid site, which causes rates for nucleophilic attack of enolates to benzaldehyde to be far less than those to propanal.

Joint interpretation of gravity and airborne magnetic data along the Calama-Olacapato-Toro fault system (Central Puna, NW Argentina): Structural and geothermal significance

Here, we present new gravity and airborne magnetic geophysical data from a preliminary exploration along the western sector of the NW-striking Calama-Olacapato-Toro fault system. This area is located in the back-arc region of the Central Andes (NW, Argentina) and is considered as a high potential geothermal area within the Central Puna Energy Hub.The gravity and magnetic modelling was carried out with the aim of delineating geological structures that control the geothermal manifestations and estimate the geothermal field extent. Gravity data were separated into regional and residual components. Then, a 2-D gravity and magnetic modelling was carried out through the 2-D GM-SYS - Oasis Montaj software in order to build an inversion model that adjusts the residual gravimetric and magnetic anomalies observed on the surface. The resultant model was also fitted taking into consideration previous electrical resistivity studies, surface manifestations, geology, and geological structures. Bouguer anomalies are negative in the range of -411 to -304 mGal, while magnetic anomalies have a range of − 127 to 15 nT, in the central part of the study area. Hot springs correlate with low residual Bouguer and magnetic anomalies located on the Calama-Olacapato-Toro lineament, and are related to the alteration zone and the main damage zone. Gravity and magnetic inversion show low density and susceptibility contrast of rocks associated with volcano-sedimentary rocks filling a volcano-tectonic depression, limited by the Antuco and Pompeya N-S thrust faults, westward and eastward respectively. The low density and susceptibility contrast can be related to a combination of high temperatures and steam versus liquid-filled pores and fractures. Hence, this geological conceptual model based on the 2-D forward modelling of geophysical data, allows better knowledge and comprehension of hydrothermal fluids circulation in the middle of the Central Puna, in northwest Argentina.

Hybrid enzymatic CO2 capture process in intensified flat sheet membrane contactors with immobilized carbonic anhydrase

A hybrid enzymatic CO2 absorption process in an intensified flat sheet membrane contactor with immobilized human carbonic anhydrase II (hCA II) enzyme was proposed. In addition to be immobilized on the membrane surface, extra carbonic anhydrase enzyme was immobilized on the surface of magnetic nanoparticles (MNPs) dispersed in the liquid phase to reduce the mass transfer limitations and enhance the absorption process. This hybrid enzymatic process is beneficial to attain high CO2 absorption rates, even if a component of the enzymatic system, either the biocatalytic membrane or biocatalytic MNPs, does not operate appropriately. The improvement CO2 hydration in the presence of biocatalytic MNPs was more significant at lower CA loadings on membrane surface. Reusability of the biocatalytic membranes and biocatalytic MNPs was demonstrated by 10 absorption cycles and the intensified membrane contactor displayed stable operation for several hours. A multiscale mathematical model (under gas-filled or partially liquid-filled membrane pores conditions) was proposed to explore the behaviour of the intensified membrane contactor. Model simulations showed that the resistance to mass transfer in membrane wetted zones is overcame by the CO2 enzymatic absorption in these zones (catalyzed by enzyme immobilized in membrane pores) and possible by the absorption of CO2 in the presence of biocatalytic MNPs.

Deconstructing electrode pore network to learn transport distortion

The central premise of porous electrodes is to make more surface area available for reactions. However, the convoluted pore network of such reactors exacerbates the transport of reacting species. Tortuosity is a measure of such transport distortion and is conventionally expressed in terms of porosity (the fraction of electrode volume occupied by liquid-filled pores). Such an approach is overly simplistic and falls short of accounting for spatial variabilities characteristic of electrode samples. These networks are defined by multiple features such as size distribution, connectivity, and pore morphology, none of which are explicitly considered in a porosity based interpretation, thus limiting predictability. We propose a recourse using a two-point correlation function that deconstructs the pore network into its essential attributes. Such a quantitative representation is mapped to the transport response of these networks. Given the explicit treatment of pore network geometry, this approach provides a consistent treatment of three-dimensionalities such as inhomogeneity and anisotropy. Three-dimensional (3D) tomograms of Li-ion battery electrodes are studied to characterize the efficacy of the proposed approach. The proposed approach is applicable to abstracting effective properties related to different transport modes in porous fluid networks.

Numerical analysis of meniscus dynamics in monolayer-wick dropwise condensation

The effect of hydrophobic monolayer sintered-particle wick on the growth and departure of droplets in dropwise condensation over a vertical surface is analyzed numerically using the minimum meniscus surface energy principle and the direct simulation of the meniscus and heat transfer through the partially liquid-filled pores. The condensate fills the pores, increases the capillary pressure, and joins with the menisci from adjacent pores, leading to a droplet formation. The droplet growth is supported by liquid supply from the adjacent pores until the critical droplet departure volume is reached. The heat transfer rate is controlled by the average meniscus thickness, and the droplet surface coverage. Based on these and the plain–surface limit (for very small and very large particle diameter dp), a threshold band of dp is predicted below which the dropwise condensation rate is slightly enhanced compared to the plain, hydrophobic surface. The analysis explains the existing experimental results (and new augmented experimental results) and the challenges in further enhancing the dropwise condensation with surface microstructures.

Bacteria-in-paper, a versatile platform to study bacterial ecology.

Habitat spatial structure has a profound influence on bacterial life, yet there currently are no low‐cost equipment‐free laboratory techniques to reproduce the intricate structure of natural bacterial habitats. Here, we demonstrate the use of paper scaffolds to create landscapes spatially structured at the scales relevant to bacterial ecology. In paper scaffolds, planktonic bacteria migrate through liquid‐filled pores, while the paper’s cellulose fibres serve as anchor points for sessile colonies (biofilms). Using this novel approach, we explore bacterial colonisation dynamics in different landscape topographies and characterise the community composition of Escherichia coli strains undergoing centimetre‐scale range expansions in habitats structured at the micrometre scale. The bacteria‐in‐paper platform enables quantitative assessment of bacterial community dynamics in complex environments using everyday materials.

Mass transport in porous media at the micro- and nanoscale: A novel method to model hindered diffusion

Abstract Mass transport in liquid-filled pores at the micro- and nanoscale can play an important role in applications such as membrane separations, chromatography, and catalytic processes. In this work, we use Brownian dynamics in order to describe the motion of spherical solute molecules at a pore-scale. The method can be used to calculate effective parameters intrinsically related to the porous medium such as the effective diffusivity and the hindrance factor for diffusion. The latter is calculated using a novel probabilistic model derived in the present study, which uses the Lennard-Jones potential to reproduce the hindering effect of the interaction between solute molecules and the wall atoms on the diffusivity. In addition, we introduce a fitting function that can be used to estimate the diffusive hindrance factor of a complex geometry when the pore size distribution of the porous network is known. Finally, a multiscale approach is presented and illustrated with an application example, whereby the hindrance factors of the micro- and nanoscale are used in the simulations of the mass transport at the larger scale.

Bio-inspired fabrication of asymmetric wettability Janus porous membrane for secure F-oil infused F-free-membrane filtration

Porous membranes, which consist of air-filled or liquid-filled pores, provide a gating strategy for tunable multiphase selectivity separation, and exhibit tremendous application potential in fields involving intelligent liquid management. Herein, we report the fabrication of a novel asymmetric wettability Janus porous membrane (JPM) based on bio-inspired models that integrate the air-gate floating mechanism and adhesive proteins secreted by mussels to attach to material-independent surfaces. The JPM fabricated through this novel and straightforward methodology has distinct hydrophobic-hydrophilic properties and interfacial compatibility. These features were engineered for F-oil (lubricant oil, Dupont Krytox 105) infused F-free JPM membrane filtration. The hydrophilic layer infused with high-surface-energy water acts as a perfect barrier (liquid gating) preventing invasion of the low-surface-energy F-oil which was infused in the hydrophobic surface, protecting the F-oil in the JPM. This is the first report regarding F-oil infused membrane filtration using the F-free-membrane, which can overcome the limitations of F-substrates for F-oil infused filtration.

Dynamic air/liquid pockets for guiding microscale flow

Microscale flows of fluids are mainly guided either by solid matrices or by liquid–liquid interfaces. However, the solid matrices are plagued with persistent fouling problems, while liquid–liquid interfaces are limited to low-pressure applications. Here we report a dynamic liquid/solid/gas material containing both air and liquid pockets, which are formed by partially infiltrating a porous matrix with a functional liquid. Using detailed theoretical and experimental data, we show that the distribution of the air- and liquid-filled pores is responsive to pressure and enables the formation and instantaneous recovery of stable liquid–liquid interfaces that sustain a wide range of pressures and prevent channel contamination. This adaptive design is demonstrated for polymeric materials and extended to metal-based systems that can achieve unmatched mechanical and thermal stability. Our platform with its unique adaptive pressure and antifouling capabilities may offer potential solutions to flow control in microfluidics, medical devices, microscale synthesis, and biological assays.

Porosity estimation in kerogen-bearing shale gas reservoirs

Porosity is a fundamental petrophysical parameter in shale gas reservoirs that governs the space for hydrocarbon storage, and directly determines the free gas amount and absorbed gas capability. Technically, in kerogen-bearing shales, well-log derived porosity may yield inaccurate results as the porosity tools in response to both the kerogen and the liquid-filled pore spaces that are often undifferentiated. In this paper, we propose a new method for porosity estimation in kerogen-bearing shales, where porosity is assumed to be composed of both matrix porosity and kerogen porosity. The kerogen responses of density, sonic and neutron logs are first calculated from experimental data to calibrate porosity logs with the kerogen volume. The matrix porosity is then computed using the improved Wyllie equation based on the calibrated logging data with the kerogen influence removed. The kerogen porosity is estimated by a mass-balance relation based on the original total organic carbon (TOCo) and kerogen maturity characterized by the percentage of convertible organic carbon (Cc) and the transformation ratio (TR). Application of the new method to a shale gas reservoir in the Ordos Basin, China shows that the estimated porosity matches the core derived porosity satisfactorily well. Furthermore, the results also indicate that the shale kerogen porosity is relatively higher than the shale matrix porosity when the kerogen amount and maturity are high. The results of the study lead to a better understanding of the shale formation and thus contribute towards the better evaluation of shale gas reservoirs.

Extraterrestrial Soils and Space Agriculture

Extraterrestrial Soils and Space Agriculture

FAST: Size-Selective, Clog-Free Isolation of Rare Cancer Cells from Whole Blood at a Liquid-Liquid Interface.

Circulating tumor cells (CTCs) have great potential to provide minimally invasive ways for the early detection of cancer metastasis and for the response monitoring of various cancer treatments. Despite the clinical importance and progress of CTC-based cancer diagnostics, most of the current methods of enriching CTCs are difficult to implement in general hospital settings due to complex and time-consuming protocols. Among existing technologies, size-based isolation methods provide antibody-independent, relatively simple, and high throughput protocols. However, the clogging issues and lower than desired recovery rates and purity are the key challenges. In this work, inspired by antifouling membranes with liquid-filled pores in nature, clog-free, highly sensitive (95.9 ± 3.1% recovery rate), selective (>2.5 log depletion of white blood cells), rapid (>3 mL/min), and label-free isolation of viable CTCs from whole blood without prior sample treatment is achieved using a stand-alone lab-on-a-disc system equipped with fluid-assisted separation technology (FAST). Numerical simulation and experiments show that this method provides uniform, clog-free, ultrafast cell enrichment with pressure drops much less than in conventional size-based filtration, at 1 kPa. We demonstrate the clinical utility of the point-of-care detection of CTCs with samples taken from 142 patients suffering from breast, stomach, or lung cancer.

Fischer-Tropsch synthesis: Effect of solvent on the H2–D2 isotopic exchange rate over an activated nickel catalyst

The effect of solvent on the hydrogen-deuterium isotopic homomolecular exchange rate over a 26.4% Ni/Al2O3 catalyst was investigated using a plug flow reactor at room temperature (23°C) and at atmospheric pressure. In this study, two different molecular weight solvents were tested: n-pentane (MW¯(average molecular weight)=72), and n-hexadecane (MW¯=226). At dry (without addition of solvent) and n-pentane solvent addition conditions, similar amounts of H2 and D2 are consumed and the concentration of the HD produced is two times the consumption of H2 or D2. Thus, these conditions exhibited around 100% exchange with the formation of H2:HD:D2 having a 1:2:1 ratio. With n-hexadecane solvent, the initial exchange rate was approximately 45%, but the exchange rate decreased with time and reached a steady state rate after 60min on-stream. The lower exchange rate of the n-hexadecane solvent might be due to the limited mobility of reactant molecules in the liquid-filled pores of the catalyst. The exchange rate of the catalyst is decreased with increasing molecular weight and density of the solvent. An isotopic partitioning preference was not observed for the nickel catalyst under various co-fed solvents, and similar findings were observed in our previous work (Catalysis Letters 143 (2013) 1368–1373).

CO2 Removal in Packed-Bed Columns and Hollow-Fiber Membrane Reactors. Investigation of Reactor Performance

The CO2 absorption performance of hollow-fiber membranes and conventional packed-bed column reactors under similar operating conditions was evaluated. Two-scale, nonisothermal, steady-state models were used to simulate the reactors behavior. The membrane reactor model accounts for CO2 diffusion in gas-filled membrane pores, CO2 and amine diffusion accompanied by chemical reaction in liquid-filled membrane pores, and CO2 and amine diffusion accompanied by chemical reaction in the liquid film zone surrounding the inside membrane wall. The packed-bed column reactor model interconnects a two-fluid 2D hydrodynamic platform with 2D mass and energy transport equations in the gas and liquid phases and nonlinear differential equations governing diffusion and reaction in the liquid film. In the absence of membrane wetting, the hollow-fiber membrane reactor outperforms the packed-bed column reactor with similar volume and specific surface area. This is not the case under membrane wetting conditions, when at low spec...

Elucidating Li/O2 Battery Performance By Comparing Cell-Level Models with Experiments

Elucidating Li/O2 Battery Performance by Comparing Cell-Level Models with Experiments Jing Liu, Lucas D. Griffith, and Charles W. MonroeChemical Engineering Department, University of Michigan A viable rechargeable lithium/oxygen battery would impact transportation markets dramatically, by expediting the development of highway-capable full-electric vehicles with ranges comparable to gasoline-powered automobiles. Even conservative estimates show that Li/O2 electrochemistry could support batteries with energy densities four times greater than present-day lithium-ion technology [1]. This talk will focus on theoretical and experimental research we have undertaken to elucidate design factors and reaction mechanisms that control the rate capabilities and energy capacities of Li/O2 cells. In a metal/oxygen battery cell, the positive electrode comprises a liquid-permeated, electronically conductive porous solid, which poses many of the main barriers that limit its performance. During discharge, lithium ions and dissolved O2 diffuse through the liquid phase to meet at the solid surface, where they receive an electron and precipitate the Li2O2 discharge product. We have performed systematic experiments to illustrate how Li/O2 cell capacities, voltage responses, and discharge-product morphologies vary with respect to discharge current. Some representative first-discharge voltage vs. capacity data is shown in Figure 1; scanning electron microscopy and X-ray diffraction were also performed to provide more detailed characterization. Experimental results suggest several possible mechanisms that could limit capacity and affect the rate capability of the system. For instance, discharge-product formation may shrink – or even block – liquid-filled pores, decrease the surface area available for charge transfer, or introduce interfacial resistances to charge (electronic) or material (ionic/molecular) exchange. The relative importance of hypothesized performance-limiting processes can be illustrated by multicomponent, multiphase transport modeling. We therefore developed a PDE-based cell model that accounts for the three distinct phases comprising the positive electrode, as well as the individual components that constitute each phase. Figure 1 shows that simulations can produce discharge-voltage curves that agree both qualitatively and quantitatively with experiments, displaying a ‘voltage plateau’ before ‘sudden death’ of the cell. The oxygen, porosity and reaction distributions in the positive electrode at various discharge levels reveal key characteristics of electrodes and electrolytes that could be tailored to improve the capacities and power capabilities of Li/O2 batteries. The model is used to probe three hypothetical reaction mechanisms, which involve distinct product morphologies and electron-transfer sites. To achieve consistency with experimental data, it appears that the discharge-product layer must have electronic conductivity several orders of magnitude higher than bulk lithium peroxide, supporting the notion that the discharge product does not wholly prevent electrons from reaching dissolved reactants [2]. The product also appears to allow charge transport over length scales longer than the proposed electron-tunneling mechanism [3] permits. At high rates, the ‘sudden death’ of voltage in Li/O2 cells is explained by macroscopic oxygen-diffusion limitations in the positive electrode; at low rates, sudden death occurs as a consequence of pore clogging by the discharge product. [1] J. Christensen, P. Albertus, R.S. Sanchez-Carrera, T. Lohmann, B. Kozinsky, R. Liedtke, J. Ahmed, and A. Kojic, Journal of the Electrochemical Society 159 (2011) R1-R30. [2] M.D. Radin and D.J. Siegel, Energy & Environmental Science 6 (2013), 2370-2379. [3] V. Viswanathan, K.S. Thygesen, J.S. Hummelshøj, J.K. Nørskov, G. Girishkumar, B.D. McCloskey, and A.C. Luntz, The Journal of Physical Chemistry Letters 4 (2013), 556-560. Figure 1

Materials science: gating mechanism under pressure.

Liquid-filled pores in membranes have been designed to reversibly open and close, allowing only particular fluids through at given pressures. This enables tunable and gated separations of mixtures of immiscible fluids. See Letter p.70

Nutrient Transport in Soils Amended with Biochar: A Transient Model with Two Stationary Phases and Intraparticle Diffusion

We present the development of a rate model that simulates nutrient transport in soils amended with biochar. The model considers two stationary adsorbent phases (biochar and soil), axial dispersion, interphase mass transfer, and intraparticle diffusion. Langmuir isotherms govern the local equilibria between the solute diffusing in the liquid-filled pores and adsorbed on the pore surfaces of biochar and soil particles. We demonstrate that addition of biochar can effectively slow nutrient transport through the soil if the biochar/soil ratio and crucial biochar properties (such as its adsorption capacity and affinity to the sorbate) are carefully matched to the soil properties (water velocity and soil type) and the amount of rainfall or irrigation. Simulations can also track the spatial and temporal evolution of nutrient concentration profiles, information that is essential for analyzing and interpreting experimental data. The new model can be a valuable tool for fine-tuning the production and use of biochar.

A mechanistic model for drug release in PLGA biodegradable stent coatings coupled with polymer degradation and erosion.

Biodegradable poly(d,l-lactic-co-glycolic acid) (PLGA) coating for applications in drug-eluting stents has been receiving increasing interest as a result of its unique properties compared with biodurable polymers in delivering drug for reducing stents-related side effects. In this work, a mathematical model for describing the PLGA degradation and erosion and coupled drug release from PLGA stent coating is developed and validated. An analytical expression is derived for PLGA mass loss that predicts multiple experimental studies in the literature. An analytical model for the change of the number-average degree of polymerization [or molecular weight (MW)] is also derived. The drug transport model incorporates simultaneous drug diffusion through both the polymer solid and the liquid-filled pores in the coating, where an effective drug diffusivity model is derived taking into account factors including polymer MW change, stent coating porosity change, and drug partitioning between solid and aqueous phases. The model is used to describe in vitro sirolimus release from PLGA stent coating, and demonstrates the significance of simultaneous sirolimus release via diffusion through both polymer solid and pore space. The proposed model is compared to existing drug transport models, and the impact of model parameters, limitations and possible extensions of the model are also discussed.