Capillary Condensation Research Articles

Dynamics of a colloid-in-tube host-guest system.

Originated from supramolecular chemistry, the host-guest concept is generalized and appreciated across the fields of enzyme catalysis, biological channel conduction, and carbon nanotube transport, to name a few. Despite the extensive study of host-guest thermodynamics, it is still a fundamental challenge to directly measure its dynamics in real-space and real-time. Herein we approach such dynamics by direct imaging and tracking in a colloid-in-tube system, where self-assembled tubes are the hosts and sphere particles are the guests. The key difference from a previously reported static 1D confinement is that the present tubes are thermally actuated and capable of translations and rotations. It is the host tube thermal motions that impose a number of anomalies to guest particle dynamics including broadened distribution perpendicular to the tube, enhanced diffusion parallel to the tube phenomenologically resembling the rapid flow in ion channels or carbon nanotubes, and induced long-range particle-particle attraction analogous to capillary condensation. This work in the colloidal system is of wide implications for host-guest systems that are naturally embedded in thermal fluctuations such as transmembrane ion channels and carbon nanotube arrays in a soft matrix.

Bidirectional Light-Driven Ion Transport through Porphyrin Metal–Organic Framework-Based van der Waals Heterostructures via pH-Induced Band Alignment Inversion

Bidirectional Light-Driven Ion Transport through Porphyrin Metal–Organic Framework-Based van der Waals Heterostructures via pH-Induced Band Alignment Inversion

Condensation‐Assisted Separation of Alkanes by Silica Membranes with Wide Pore Size Distribution

AbstractPurification of gases by membranes can provide enormous energy savings. Inorganic membranes offer good stability and regenerability, but large margin manufacturing is limited. Silica membranes are an exception since they can be produced by coating with molecular precursors. However, such membranes do not have a defined pore structure, which limits their applicability in mass separation. Nevertheless, it is possible to fill the pores of silica membranes with condensate of a component to be separated from gas mixtures. In this work, this applicability of a micro‐mesoporous silica membrane was demonstrated exemplarily by the separation of n‐butane (C4) from mixtures containing methane (C1). The main result, which was supported by grand canonical Monte Carlo (GCMC) simulations, is that capillary condensation contributes significantly to the performance. The experimental results showed that the n‐butane separation efficiency (permeate flux and separation selectivity) through the silica membrane under the condensation conditions is excellent and thus can serve as a model for similar separation tasks.

Analysis of the Water Adsorption Isotherms in UiO-Based Metal–Organic Frameworks

The present work takes a detailed look at the adsorption of nitrogen gas and water vapor in six related zirconium-based metal–organic frameworks (UiO-66, UiO-66-NH2, UiO-67, UiO-67-NH2, UiO-68-Me4/PCN-57, and UiO-68-NH2). The work relates the role of defects, linker length, and linker functionality to the gas adsorption properties. The water adsorption isotherms showed no hysteresis consistent with capillary condensation. This suggests a node-based cluster growth mechanism is occurring. Analysis of the water adsorption isotherms illustrated that, prior to the water condensation step in the isotherm, each MOF adsorbed roughly one water molecule per zirconium center. As the linker length increases, the MOF becomes more hydrophobic. The amine functionality increases the hydrophilicity, but the effect of the functional group diminishes as the linker length increases. The latter point is illustrated by calculating the apparent contact angle between the pore wall and condensed water. The apparent contact angle increased from 54.0 to 83.1° from UiO-66 to UiO-68-Me4/PCN-57 and from 13.0 to 71.0° from UiO-66-NH2 to UiO-68-NH2. From this, the water isotherm was used to construct a pore size distribution consistent with the distribution determined from nitrogen gas adsorption. We further explored the amine-unfunctionalized MOFs for long-term water vapor exposure. Below the water condensation step, the MOFs showed no change in nitrogen gas adsorption capacity/surface area for 100 days.

Effects of a tiny particle trapped in a spherical cavity on fluid structure, contact density, and capillary condensation (a DFT approach)

The Modified Fundamental Measure Theory is exploited to investigate the effects of a mobile tiny particle, TP, trapped in a spherical pore on fluid structure, contact density, and capillary condensation. The decreasing and oscillatory behaviors for contact densities versus mobile TP size are observed respectively for hard sphere and Lennard Jones fluids. The capillary condensation of a Lennard Jones confined fluid is investigated in the presence of a mobile TP and compared with those in cases in which the TP is either absent or fixed at the pore center. The configurational chemical potential at which capillary condensation occurs for a fixed TP is smaller than that for a mobile one while both values are still smaller than that for a fluid confined in a spherical pore with no TP. Increasing the size of the mobile TP leads to a decrease in the configurational chemical potential (μ∗) at which capillary condensation occurs and in the coexistence curve width.

In Situ Mapping and Local Negative Uptake Behavior of Adsorbates in Individual Pores of Metal-Organic Frameworks.

Herein, we report the adsorbate behavior in individual local pores of MIL-101, which is a metal-organic framework (MOF) with two heterogeneous mesopores and different metal sites, by combining adsorbate isotherms and in situ crystallography profiles. The in situ mapping shows that the substrate-adsorbate interaction affects the initial adsorption and pore condensation steps. The monolayer adsorption gradient changes greatly depending on the framework metal-adsorbate attraction force. Also, broad inflection points are found in adsorption isotherms, and the initial shape depends on the different metals. Besides, the capillary condensation at a pore draws adsorbates from other local pores. This leads to the local negative uptake behavior in individual pore isotherms. At higher pressure, they move to a larger space, whereas in a relatively low-pressure range the attraction force between the MOF framework and guest molecule influences the amount of rearranged guest molecules. Furthermore, the origin of the characteristic adsorption behavior based on the metals constituting the MOFs and the relative strength of substrate-adsorbate and adsorbate-adsorbate interactions are elucidated through the combined study of electron densities in pores, electron paramagnetic resonance spectroscopy spectra, and density functional theory and Monte Carlo simulations to uncover the previously veiled information on adsorption behavior.

High performance lithium-sulfur batteries using threedimensional hierarchical porous carbons to host the sulfur

Lithium-sulfur batteries are promising for future energy storage because of their high-energy density and low price. However, they have many problems, especially the large volume change during cycling and the shuttle effect of the soluble polysulfides. To solve these problems, a three-dimensional hierarchical porous carbon (3D-HPC) was investigated as the sulfur host of a lithium-sulfur battery. The 3D-HPC was prepared by a template method using polymethyl methacrylate and zinc oxide as the templates to form mesopores and macropores, respectively. The results showed that the interconnected macroporous channels and abundant large mesopores formed a three-dimensional conductive carbon network which is beneficial for electron/ion transfer and relieves the cathode volume change by the physical limiting effect. The pores alleviate the shuttle effect by the capillary condensation. A 3D-HPC-S composite used as the cathode has excellent electrochemical properties. The first discharge specific capacity of the 3D-HPC-S is 1314.6 mAh g−1 at 0.2 C with a sulfur loading of 70%. After 100 cycles, the capacity retention rate is 69.13%. At 0.5 C, the capacity retention rate after 200 cycles is 59.02% and the average coulombic efficiency is 98.16%.

Effects of Ethene Pressure on the Deactivation of Ni‐Zeolites During Ethene Oligomerization at Sub‐ambient Temperatures

AbstractNi cation sites exchanged onto microporous materials catalyze ethene oligomerization to butenes and heavier oligomers but also undergo rapid deactivation. The use of mesoporous supports has been reported previously to alleviate deactivation in regimes of high ethene pressures and low temperatures that cause capillary condensation of ethene within mesoporous voids. Here, we reproduce these prior findings on mesoporous Ni‐MCM‐41 and report that, in sharp contrast, reaction conditions that nominally correspond to ethene capillary condensation in microporous Ni‐Beta or Ni‐FAU zeolites do not mitigate deactivation, likely because confinement within microporous voids restricts the formation of condensed phases of ethene that are effective at solvating and desorbing heavier intermediates that are precursors to deactivation. Deactivation rates are found to transition from a first‐order to a second‐order dependence on Ni site density in Ni‐FAU zeolites with increasing ethene pressure, suggesting a transition in the dominant deactivation mechanism involving a single Ni site to one involving two Ni sites, reminiscent of the effects of increasing H2 pressure on changing the kinetic order of deactivation in our prior work on Ni‐Beta zeolites.

Water cluster in hydrophobic crystalline porous covalent organic frameworks

Progress over the past decades in water confinement has generated a variety of polymers and porous materials. However, most studies are based on a preconception that small hydrophobic pores eventually repulse water molecules, which precludes the exploration of hydrophobic microporous materials for water confinement. Here, we demonstrate water confinement across hydrophobic microporous channels in crystalline covalent organic frameworks. The frameworks are designed to constitute dense, aligned and one-dimensional polygonal channels that are open and accessible to water molecules. The hydrophobic microporous frameworks achieve full occupation of pores by water via synergistic nucleation and capillary condensation and deliver quick water exchange at low pressures. Water confinement experiments with large-pore frameworks pinpoint thresholds of pore size where confinement becomes dominated by high uptake pressure and large exchange hysteresis. Our results reveal a platform based on microporous hydrophobic covalent organic frameworks for water confinement.

From Langmuir isotherm to Brunauer–Emmett–Teller isotherm

AbstractDeveloped for multilayer adsorption, the Brunauer–Emmett–Teller (BET) isotherm considers the adsorption of the first layer as an equilibrium chemical reaction between adsorbate molecules and adsorption sites and the adsorption of the second and subsequent layers as a condensation–evaporation process. Following the recent development of an activity‐based formulation for the Langmuir isotherm for monolayer adsorption, we present an activity‐based formulation for the BET isotherm in which species concentrations are replaced with species activities. Capturing the adsorbent surface heterogeneity for the adsorption of the first layer, the resulting thermodynamic BET isotherm is shown to accurately represent pure component adsorption isotherms over the relative pressure range of zero to unity or prior to the onset of capillary condensation. The thermodynamic BET isotherm should facilitate accurate estimation of monolayer adsorption capacity and the corresponding adsorbent surface area.

An Integrated Droplet Manipulation Platform with Photodeformable Microfluidic Channels.

Manipulating droplets by light in microscale allows precise control of microfluidics, liquid delivery, micromachines, and so on. Among these applications, microfluidic technology is of particular interest for miniaturization of the portable analysis systems, which require the integration of various liquid operations in one device. Here, a photodeformable microfluidic platform is constructed by combining Laplace pressure and capillary condensation to integrate the transportation, fusion, separation, and mixing of liquid slugs in one chip. The Laplace pressure, attributed to the photodeformation of the liquid crystal polymers, is generated to propel the slug. The capillary condensation is introduced by the delicate design of the fluid channels, allowing the fusion and separation of slugs without any connected microvalves. Catalytic oxidation reaction and protein detection processes are realized in the platform, which are amenable to a variety of miniaturized bio-medical applications, such as portable analysis and point of care testing.

Hygrothermal performance of a brick wall with interior insulation in cold climate: Vapour open versus vapour tight approach

Interior insulation of historic buildings is well-studied in Central Europe; however, their conclusions might not be directly applicable to colder climates. Heat, air and moisture (HAM) modelling can be a valuable tool for studying those solutions in different conditions. Recently, incorporating the capillary condensation redistribution (CCR) test into the material characterization process has shown to cause dramatic improvement in correlating hygrothermal modelling results to measurements in certain situations. It is also noteworthy, that the HAM modelling errors made using material data from conventional characterization process can be severely non-conservative. In this article a parametric study of a 51 cm thick mass masonry wall is undertaken to determine the effect of the improved material properties on the reliability of a vapour open ‘capillary active’ autoclaved aerated concrete (AAC) and calcium silicate (CaSi) interior insulation solutions and to compare them to a vapour tight insulation system. A 49-year real weather dataset from Estonia is used. The results show that compared to conventionally characterized material properties the CCR-optimized material data causes more critical conditions directly behind the interior insulation, while having a similar performance in the exterior part of the masonry. The differences occur close to the performance limits and highlight the importance of using the CCR test in material characterization process. The vapour tight and vapour open systems showed a very similar impact on the freeze-thaw cycles and on the maximum ice saturation of the exterior part of the masonry. The vapour open solutions perform better than the vapour tight PIR in terms of frost damage and possible mould growth behind the insulation – even though the advantage has been reduced when using the CCR-optimized material data. Regardless of the insulation solution, a case-specific approach is still required to avoid damaging the original wall and/or the added insulation system.

An atmospheric water electrolyzer for decentralized green hydrogen production

The necessity of ultrapure water and water-transport infrastructure pose grand challenges in renewable-energy-assisted water electrolysis to produce green hydrogen. Directly accessing atmospheric water should offer a decisive solution because it provides ∼13 trillion kiloliters of pure water at any given instant. We show that the central challenge for atmospheric water electrolysis is related to the water-sorption kinetics of the proton-conducting membrane where state-of-the-art membranes critically fail. A proof-of-concept atmospheric water electrolyzer is demonstrated with a graphene oxide proton-conducting membrane, which has nearly three times higher water-sorption kinetics and ten times higher hydration number than a Nafion membrane due to capillary water condensation and the abundant presence of hydrophilic functionalities. At a wind velocity of ∼50 km/h, this electrolyzer delivers nearly 18 mL/h/cm2 of green hydrogen directly from the feedstock of atmospheric water. Because this electrolyzer does not require water-transport infrastructure, it can be placed almost anywhere, which offers opportunities for decentralized green hydrogen production.

A model for elucidating the contributions of meso- and macropores to water sorption and strain in cementitious materials

Hardened cement paste and concrete have a wide pore size distribution. Micro-, meso- and macropores can contribute to water sorption isotherms. Modifying a model for Vycor glass, we describe the impact of meso- and macropores in cementitious materials on sorption, swelling and shrinkage by varying relative humidity. Swelling and shrinkage isotherms can be compared with experimental data for autoclaved aerated concrete (AAC). Apart from delayed capillary condensation due to metastable adsorbed films, trapped water in the pore network promotes the appearance of enlarged hysteresis loops in plots of linear strain versus relative humidity. The model is potentially capable of predicting the contributions of meso- and macropores to the humidity-dependent strain in ordinary Portland cement paste (OPC). But in this case a comparison with experimental results turns out to be more difficult, because sorption in slit-like micropores associated with low pressure hysteresis is the main source of the observed strain in OPC.

Capillary condensation and depinning transitions in open slits.

We study the low-temperature phase equilibria of a fluid confined in an open capillary slit formed by two parallel walls separated by a distance L which are in contact with a reservoir of gas. The top wall of the capillary is of finite length H while the bottom wall is considered of macroscopic extent. This system shows rich phase equilibria arising from the competition between two different types of capillary condensation, corner filling, and meniscus depinning transitions depending on the value of the aspect ratio a=L/H and divides into three regimes: For long capillaries, with a<2/π, the condensation is of type I involving menisci which are pinned at the top edges at the ends of the capillary. For intermediate capillaries, with 2/π<a<1, depending on the value of the contact angle the condensation may be of type I or of type II, in which the menisci overspill into the reservoir and there is no pinning. For short capillaries, with a>1, condensation is always of type II. In all regimes, capillary condensation is completely suppressed for sufficiently large contact angles which is determined explicitly. For long and intermediate capillaries, we show that there is an additional continuous phase transition in the condensed liquid-like phase, associated with the depinning of each meniscus as they round the upper open edges of the slit. Meniscus depinning is third-order for complete wetting and second-order for partial wetting. Detailed scaling theories are developed for these transitions and phase boundaries which connect with the theories of wedge (corner) filling and wetting encompassing interfacial fluctuation effects and the direct influence of intermolecular forces. We test several of our predictions using a fully microscopic density functional theory which allows us to study the two types of capillary condensation and its suppression at the molecular level for different aspect ratios and contact angles.

Adsorption of water on carbon materials: The formation of “water bridge” and its effect on water adsorption

Water adsorption is very important for the modifications and applications of carbon materials. Some interesting phenomena in the process of water adsorption are still difficult to explain, and this necessitated our study. X-ray diffraction and X-ray photoelectron spectroscopies were used to characterize the structure and surface chemical properties of the carbon materials (namely graphite, activated carbon and coal). The water adsorption on carbon materials was analyzed by adsorption isotherms, and molecular simulation was used to explore the adsorption mechanisms. The results indicate that different structures and surface chemical properties of the carbon materials led to different adsorption isotherms. Graphite exhibited a Type III adsorption isotherm due to its compact structure and fewer oxygen-containing functional groups. The adsorption isotherms of activated carbon and coal conformed to the Type IV adsorption isotherm, but they presented dissimilar hysteresis loops. The “water bridge” was one of the important factors that affected water adsorption, and it was generated from the adsorption and charge transfer of water molecules induced by adjacent oxygen-containing functional groups on the surface. The strong hydrogen bond network formed by the interconnection of “water bridge” enhanced the water adsorption, capillary condensation, “ink bottle” effect, and adsorption/desorption hysteresis.

Water vapor diffusion models in asphalt mortar considering adsorption and capillary condensation

Water vapor diffusion persistently and extensively existing in asphalt pavement is one of the important contributors to moisture-induced damage. Non-Fickian diffusion of water vapor in asphalt mortar has not been deeply understood due to the lack of quantitative characterization of water molecular transport in micropores affected by the adsorption and capillary condensation. The objective of this study is to establish diffusion models considering the effects of the adsorption and capillary condensation and quantitatively characterize the dependence of diffusion coefficient on the humidity and sample thickness. The diffusion characteristics of water vapor in asphalt mortar with various thicknesses under various humid conditions were investigated using a standard wet cup method. The results suggest that in the steady diffusion the measured mass loss of diffusive water vapor linearly increases with time. The apparent diffusion coefficients determined by the first Fick’s law demonstrate a nonlinear rapid reduction from 51.45×10–9 m2/s to 12.66×10–9 m2/s while the relative humidity varies from 22% to 95%. The diffusion coefficient nonlinearly decreases from 40.92×10–9 m2/s to 24.71×10–9 m2/s while the sample thickness increases from 3.62 mm to 16.34 mm. The molecular transports in gaseous flow, surface flow, and capillary condensate flow were introduced to formulate the effects of adsorption and capillary condensation. Combining the measured adsorption isotherm of water vapor in asphalt mortar, a diffusion model considering adsorption was derived and quantitatively characterizes the diffusion coefficients varying with the relative humidity. The dependence on relative humidity is attributed to the thickening of adsorbed water film in high humidity that changes the diffusivities in gaseous flow and surface flow. Another diffusion model considering capillary condensation was established to formulate the thickness-dependent diffusion coefficients in asphalt mortar. The dependence on the sample thickness is explained as the variable ratio of the diffusion in capillary condensate flow to the overall diffusion in a thick sample. This study provides a feasible approach to quantifying the environment-dependent diffusion characteristics and promotes the understanding of non-Fickian diffusion of water vapor in asphaltic materials.

Effects of surface roughness on the kinetic interface-sensitive tracer transport during drainage processes

Porous media surface roughness strongly influences the transport of solutes during drainage due to the formation of thick water films (capillary condensation) on the surface of the porous medium. For interfacially-reacted, water-based solutes, these water films increase both the solute production at the fluid-fluid interface, due to the increased number of fluid-fluid interfaces, and the loss of the solute due to retention in the water films. This study applied a pore-scale, direct numerical simulation with the phase-field method-based continuous solute transport model to simulate the reactive transport of the kinetic interfacial sensitive tracer. The study is implemented during primary drainage in a 2D slit with rough solid walls, where the fractal geometries of the solid surfaces were generated numerically. The moving interfacial area is found to be changing non-monotonically with the root mean square of surface roughness. With increasing root mean square roughness, the average film thickness increases linearly, whereas the film-associated interfacial area per smooth surface area converges to a value slightly larger than one. The retention of the solute mass produced by the moving meniscus in the water film is observed, and this is described by a film-associated mobile mass retention term. An implicit relation between the mobile interfacial area and the solute mass in flowing zones is found. Finally, it is found that the film-associated mobile mass retention term is linearly related to the root mean square roughness.

Digital image correlation–based analysis of hygroscopic expansion in Herrnholz granite

Groundwater-induced deformation of natural rock slopes is typically interpreted to be related to changes in pore pressure. Rock, however, is a porous medium that has been shown to expand on contact with water. Here, we present insights into surface deformation of free-standing 115 × 65 × 35 mm granite prisms with water continuously infiltrating from the upper surface over 16 – 24 hours under ambient laboratory environmental conditions. Digital image correlation analysis indicates a mean extensional strain due to wetting of approximately (4 – 4.7) × 10 −4 , equivalent to an internal pressure of 40 – 47 MPa, assuming linear-elastic material behaviour. Nanoscale adsorption theory indicates the contribution from adsorption of water onto free surfaces may be 18.4 MPa, while capillary condensation generates pressure up to 30.9 MPa. It is likely a majority of strains is the result of water entering micro pores with radius less than 5 nm, which account for 1.16% of the porosity. Our relatively simple experimental setup may serve as a useful tool for analyzing moisture-induced deformation in a range of geological materials.

Highly Efficient Multiscale Fog Collector Inspired by Sarracenia Trichome Hierarchical Structure.

Fog harvesting through bionic strategies to solve water shortage has drawn considerable attention. Recently, an ultrafast fog harvesting and transport mode was identified in Sarracenia trichome, which is mainly attributed to its superslippery capillary force induced by its unique hierarchical microchannel. However, the underlying effect of hierarchical microchannel‐induced ultrafast transport on fog harvesting and the multiscale structural coupling effect on highly efficient fog harvesting are still great challenges. Herein, a bionic Sarracenia trichome (BST) with an on‐demand regular hierarchical microchannel is designed using a one‐step thermoplastic stretching approach on a glass fiber bundle. The BST is engineered to harbor major channels confined by an inner gear pattern along with junior microchannels that are automatically assembled by the glass fiber monofilaments. The BST shows enhanced capillary condensation and fog harvesting performance, in part due to its coupling effect with a Janus membrane (JM). Hence, a highly efficient multiscale fog collector is developed, in which a gradient high‐pressure field is purposely formed to improve by threefold fog harvesting performance compared with a single‐scale structure. This easy manufacturing and low‐cost fog collector may represent a useful tool for harvesting fog water for production and living and pave the way for further investigations.