Capillary Condensation Research Articles

Edge Contact Angle, Capillary Condensation, and Meniscus Depinning.

We study the phase equilibria of a fluid confined in an open capillary slit formed when a wall of finite length H is brought a distance L away from a second macroscopic surface. 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. 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 characterized by an edge contact angle. 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. We show that there is an additional continuous phase transition in the condensed liquidlike phase, associated with the depinning of each meniscus as they round the upper open edges of the slit. Finite-size scaling predictions are developed for these transitions and phase boundaries which connect with the fluctuation theories of wetting and filling transitions. 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.

Performance evaluation of hybrid oscillating heat pipe with carbon nanotube nanofluids for electric vehicle battery cooling

• The OHP charged with CNT nanofluids for EV battery cooling was experimentally tested. • The OHP charged with 0.2 wt% CNT nanofluid exhibited the best heat transfer performance. • The average temperature of battery pack could be 44.5 °C with a mean temperature difference of 0.8 °C. The development of highly-efficient, cost-effective and reliable cooling schemes of electric vehicle (EV) battery is still an urgent need for the massive commercialization of EVs. In this paper, a hybrid oscillating heat pipe (OHP) fabricated by a copper flat-plate evaporator with parallel circular channels side and a capillary copper-tube condenser has been developed to remove the heat generated by EVs battery for its safe operation during rapid charging/discharging process. The ethanol aqueous solutions of carbon nanotubes (CNTs) (or CNT nanofluids) were selected as working fluids at a volumetric filling ratio of 35%. The volume ratio of water–ethanol mixture is 1:1, and the mass concentration of CNTs varies in the range of 0.05 wt% to 0.5 wt%. Experimental results show that the vertical OHP charged with CNT nanofluids exhibited better start-up and heat transfer performance as compared with that of ethanol–water mixture. At the CNT concentration of 0.2 wt%, the average evaporator temperature and thermal resistance of the OHP could be reduced to 43.1 °C and 0.066 °C/W, respectively, at 56 W power input, which are 9.8 °C and 0.278 °C/W lower respectively than that of ethanol–water mixture. Correspondingly, the average temperature and maximum temperature difference of the battery pack could be maintained below 45 °C and 1 °C, respectively. The hybrid OHP charged with water–ethanol mixture-based CNT nanofluids provides a promising option for EV battery cooling.

Water distribution and adsorption behaviors of two typical coal gasification fine slags from Ningxia Region

In this study, the water distribution and adsorption behaviors of two typical coal gasification fine slag (GFS) samples with different moisture contents were studied. Both of the samples were collected from entrained-flow coal gasifiers with the same coal as feedstock from Ningxia Region. The GFS sample collected from a GSP gasifier (2.5–4.0 MPa, 1400–1750 °C), with lower moisture content, was named as GFS-L, and the sample collected from a Texaco gasifier (4.0–6.5 MPa, 1300–1400 °C), with higher moisture content, was GFS-H. As the water distribution and adsorption behaviors in GFS samples, largely depending on the pore structure, had not been extensively analyzed, this study was investigated by the means of nitrogen adsorption analysis, mercury intrusion porosimetry (MIP), low field nuclear magnetic resonance (LF NMR) and dynamic water vapor sorption analysis (DVS). Experimental results revealed that the surface area, pore volume and average pore diameter of GFS-L were all lower than those of GFS-H. The fractal dimension analysis results illustrated that the GFS-L sample had smoother surface but more complicated internal pore structure than the GFS-H sample. Accordingly, the moisture content in GFS-L (45.42%) was slightly lower than that in GFS-H (48.78%). Water distributed in macropores decreased significantly during dehydration process, whereas decrease of water in mesopores was not apparent. And negligible water was found in micropores. Moreover, it was found that the water adsorption behaviors in both of the GFS samples could be characterized by the monolayer adsorption and multilayer adsorption over the relative humidity (RH) range of 0–0.7. Beyond the RH range of 0.7, it was found that water adsorption in the GFS-H sample transitioned to the capillary condensation, leading to higher moisture content. This study is envisaged to provide some new insights into developing GFS dehydration technology.

Continuous Water Filling in a Graphene Nanochannel: A Molecular Dynamics Study.

Low dimensional materials especially carbon materials hold high promise in the fields of water purification, mineral separation, energy harvesting/conversion, and so on. The fluidic devices fabricated by direct synthesis, lithography, or self-assembly of low dimensional materials provide opportunities for exploring the novel properties and applications of nanoconfined transport. Here, continuous filling of water and acetone molecules into a graphene nanochannel is investigated. A stairlike nonlinear dependence of the number of filling water molecules on interlayer distance d is found when d < 1 nm due to the existence of out-plane layered and in-plane ordered monolayer structure, while near-linear dependence is found for acetone because of the freely rotating configurations along with varying d during the filling process. The entropy, potential energy, and free energy of the confined system during the continuous filling are analyzed to understand the structural evolution of water. The energy-costs are discussed depending on the structure evolution of water during the filling, which is crucial to understanding the swelling and capillary condensation widely existing in the angstrom/nanometer-scale separation membranes.

Spontaneous spreading of nanodroplets on partially wetting surfaces with continuous grooves: Synergy of imbibition and capillary condensation

The wetting behavior of nanodroplets deposited on hydrophilic textured surfaces with discontinuous and continuous grooves was investigated by many-body dissipative particle dynamics. For surfaces with discontinuous grooves, the apparent contact angle (θa) can be described by the Wenzel model with an effective area ratio. However, for surfaces with continuous grooves, θa of nanodroplets depends on roughness topology, and spontaneous spreading of nanodroplets can take place even for partially wetting surfaces (θY > 0). That is, the partial-to-total wetting transition can occur on hydrophilic surfaces as surface textures change from discontinuous to continuous grooves. The dynamics of the spreading can be characterized by the apparent radius and groove radius (Rg). While the former is time-invariant at early stage, the latter follows the power law Rg ~ t1/4. This spreading of nanodroplets along continuous grooves can be explained from the synergy of spontaneous imbibition into continuous grooves, arrest by sharp edges, and capillary condensation for resuming the flow.

Core-Shell Microcapsules from Unpurified Legume Flours.

Plant-based ingredients are key building blocks for future sustainable advanced materials. Functionality is typically higher for highly purified plant-based ingredients, but this is at the expense of their sustainability value. Here, a method is introduced for creating a soft functional material, with structural elements ranging from the nanometer to the millimeter scale, directly from legume flours. Globulins from soy and pea flours are extracted in their native state at acidic pH and mixed with gum arabic, resulting in liquid–liquid phase separation into a dilute phase and a viscoelastic complex coacervate. Interfacial tensions of the coacervates, determined via AFM-based probing of capillary condensation, are found to be very low (γ = 48.5 and 32.3 μN/m for, respectively, soy and pea), thus promoting the deposition of a shell of coacervate material around oil droplets. Despite the complex nature of the starting material, the dependence of interfacial tensions on salt concentrations follows a scaling law previously shown to hold for model complex coacervates. Curing of the coacervate material into a strong and purely elastic hydrogel is shown to be possible via simple heating, both in bulk and as a shell around oil droplets, thus providing proof of principle for the fabrication of precise core–shell microcapsules directly from legume flours.

The Functioning of The Hybrid Integrated Partially Solar-Vapor-Compression Fridge

The main purpose of our research is to increase the utilization of solar thermal energy to supply a refrigerator with vapor compression and reduce the refrigeration power needed for cooling. Combined Hybrid Solar - the vapor- compression refrigerating unit has been built and operates under Mutah University's environment in Jordan. The systems were made up of a capillary tube, condenser, evaporator, and collector. The vapor-pressure refrigerator was incorporated with the classic water-solar system to minimize the compressor's duty and to reduce power consumption in heating the amount of water held in the pipe to be sent along the tube outside the evaporator. After that, it will be returned to the compressor, But at a lesser temperature, to minimize compressor workload and enhance cooling performance. Before the compressor was developed, a solar collector system had been created to maximize its temperature before reaching the compressor to improve C.O.P, and the difference in temperature was remarkable. The vapor-compression refrigerator unit was powered by many generators: solar collector that has been discharged, photovoltaic system, flat plate solar collector. Two groups of tests have been performed experimentally on the partial solar compression refrigerator integrated into a hybrid system. First in the vapor compression refrigerator only, and the second in the Hybrid solar compression refrigerator incorporated. Total sunlight and different temperatures, current, and voltage were measured for many months each hour of the day. The performance coefficient was determined found 2.019, 2.432 respectively. Many auxiliary instruments are utilized to measure the temperature in irradiation networks, voltage, and night-time current every hour.

Physicochemical Understanding of the Impact of Pore Environment and Species of Adsorbates on Adsorption Behaviour

AbstractFor a better design of adsorbents, it is important to know the intermolecular interaction among adsorbates and host material, leading to improved guest selectivity and uptake capacity. In this study, we demonstrate the influence of the interaction among adsorbates and substrate, controlled by the pore environment and species of adsorbates, on the adsorption behaviour. We report the unique CO2 adsorption behaviour of MOF‐205 due to distinct pore geometry. The precise analysis through gas‐adsorption crystallography with molecular simulation shows that capillary condensation of CO2 in MOF‐205 occurs preferentially in the large dodecahedral pore rather than the small tetrahedral pore, because the interaction of CO2 with MOF‐205 framework is weaker than that among CO2 molecules, while Ar and N2 are sequentially filled into two different pores of MOF‐205 according to their size. Comparison of the materials with different pore environments reveals that the relative strength of the adsorbate–adsorbate and adsorbate–substrate interaction gives rise to different shapes of isotherms.

Physicochemical Understanding of the Impact of Pore Environment and Species of Adsorbates on Adsorption Behaviour.

For a better design of adsorbents, it is important to know the intermolecular interaction among adsorbates and host material, leading to improved guest selectivity and uptake capacity. In this study, we demonstrate the influence of the interaction among adsorbates and substrate, controlled by the pore environment and species of adsorbates, on the adsorption behaviour. We report the unique CO2 adsorption behaviour of MOF-205 due to distinct pore geometry. The precise analysis through gas-adsorption crystallography with molecular simulation shows that capillary condensation of CO2 in MOF-205 occurs preferentially in the large dodecahedral pore rather than the small tetrahedral pore, because the interaction of CO2 with MOF-205 framework is weaker than that among CO2 molecules, while Ar and N2 are sequentially filled into two different pores of MOF-205 according to their size. Comparison of the materials with different pore environments reveals that the relative strength of the adsorbate-adsorbate and adsorbate-substrate interaction gives rise to different shapes of isotherms.

The Effect of Topology on Phase Behavior under Confinement

This work studies how morphology (i.e., the shape of a structure) and topology (i.e., how different structures are connected) influence wall adsorption and capillary condensation under tight confinement. Numerical simulations based on classical density functional theory (cDFT) are run for a wide variety of geometries using both hard-sphere and Lennard-Jones fluids. These cDFT computations are compared to results obtained using the Minkowski functionals. It is found that the Minkowski functionals can provide a good description of the behavior of Lennard-Jones fluids down to small system sizes. In addition, through decomposition of the free energy, the Minkowski functionals provide a good framework to better understand what are the dominant contributions to the phase behavior of a system. Lastly, while studying the phase envelope shift as a function of the Minkowski functionals it is found that topology has a different effect depending on whether the phase transition under consideration is a continuous or a discrete (first-order) transition.

Facile preparation of ordered mesoporous Nb,Ta-MCM-41 by hydrothermal direct synthesis using columbite ore as metal source

– The current study aims to prepare an Nb,Ta-containing ordered mesoporous catalyst MCM-41, using hydrated mixed oxide of niobium and tantalum, extracted from the columbite ore processing, as an alternative source of these metals. Direct hydrothermal synthesis was employed to incorporate the metals into the molecular sieve structure using the TEOS + sodium silicate mixture as silica source and varying Nb and Ta content in terms of Si/Me (Me = Nb and Ta) molar ratios of 60, 30 and 15 to evaluate the influence of the charge of these metals on both structural formation and properties of the material. The material was characterized by XRD, SEM, TEM, N2 adsorption, UV–Vis-DRS, and FTIR investigations to the incorporation of the metal into the MCM-41 framework. The techniques employed proved the successful replacement of Si atoms by metallic cations of Nb and Ta. The catalyst showed good structural order preservation and surface area (>600 m2 g-1) with mesoporous behavior with capillary condensation even at a higher metal load. This research signifies a successful procedure of a novel bimetallic mesoporous material with promising properties for several applications using an abundant ore as a metal source.

Vapor Condensation and Coating Evaporation Are Both Responsible for Soot Aggregate Restructuring.

Fresh soot is made of fractal aggregates, which often appear collapsed in atmospheric samples. A body of work has concluded that the collapse is caused by liquid shells when they form by vapor condensation around soot aggregates. However, some recent studies argue that soot remains fractal even when engulfed by the shells, collapsing only when the shells evaporate. To reconcile this disagreement, we investigated soot restructuring under conditions ranging from capillary condensation to full encapsulation, also including condensate evaporation. In these experiments, airborne fractal aggregates were exposed to vapors of wetting liquids, and particle size was measured before and after coating loss, allowing us to isolate the contribution from condensation toward restructuring. We show the existence of three distinct regions along the path connecting the initial fractal and final collapsed aggregates, where minor restructuring occurs already at zero vapor supersaturation due to capillary condensation. Increasing supersaturation increases the amount of condensate, producing a more notable aggregate shrinkage. At even higher supersaturations, the aggregates become encapsulated, and subsequent condensate evaporation leaves behind fully compacted aggregates. Hence, for wetting liquids, minor restructuring begins already during capillary condensation and significant restructuring occurs as the coating volume increases. However, at this time, we cannot precisely quantify the contribution of condensate evaporation to the full aggregate compaction.

Soil-water retention curve model for fine-grained soils accounting for void ratio–dependent capillarity

This paper presents a soil-water retention curve (SWRC) model for fine-grained soils. Compared with existing studies, the proposed model accounts for the distinct roles of the volume change of soils on capillarity and adsorption mechanisms. The capillary water is described by a relation that includes the characteristics of the pore-size distributions as parameters, while the absorbed water is modeled by a novel proposition that both considers the phenomenon of capillary condensation and allows for the decoupling between the degree of capillary and adsorptive saturation. Based on this feature, the void ratio effects are considered in a way in which they only affect capillary water, i.e., consistent with how volume change influences soil microstructures. The relative contributions of void ratio effects and hydraulic hysteresis on the path- and history-dependence of a SWRC in Sr–s–e space, where Sr is degree of saturation, s is matric suction, e is void ratio, for deformable unsaturated soils are examined. The significance of discriminating the effects of volume change on capillary and adsorptive water is illustrated by applying the SWRC model to computing the shear strength of unsaturated soils with different void ratios. The model performance is assessed by comparing against test data reported for four types of fine-grained soils in the literature and those tested for natural loess in this work.

Water retention curve model based on micro-pore filling and capillary condensation theories

Water retention curve model based on micro-pore filling and capillary condensation theories

Biofilm addition improves sand strength over a wide range of saturations

Bio-mediated ground improvement is an attractive alternative to traditional admixtures for strength improvement of shallow surfaces because it is environmentally friendly. Since biofilms contain extracellular polymeric substances (EPS), they can be considered as an alternative to current technologies to improve soil strength. EPS containing biofilms are porous materials with charged surfaces, and therefore adsorption and capillary condensation can result in water retention. Currently, most of the literature work only tested soil improvement under the dry condition. Therefore, the influence of water retention by biofilms on the strength of improved soil remains unclear. Our goal is to evaluate the strength of a biofilm-enhanced sand over a wide range of saturations and explain the trends through the suction stress characteristic curve (SSCC), which quantifies interparticle adsorptive, capillary, and cementation forces as a function of saturation. We used homogenized anaerobic granule biofilms from an existing upflow anaerobic sludge blanket reactor and mixed it with sand to test the strength of a poorly-graded sand in a wide range of saturations, S (between 0.02 S and 0.74 S). We found that biofilm treatment of sand increases soil strength through cementation over a wide range of saturations and through adsorptive forces among sand, biofilm surfaces, and water molecules at low saturations (S < ~0.3). Our results suggested that homogenized biofilms mixed with sand can be used to improve the strength of sand over a wide range of saturations.

Revisiting the Nature of Adsorption and Desorption Branches: Temperature Dependence of Adsorption Hysteresis in Ordered Mesoporous Silica.

To gain a deeper understanding as to the nature of the adsorption hysteresis due to capillary condensation of nitrogen in ordered mesoporous silicas, we calculated the temperature dependences of the activated condensation, equilibrium transition, and activated desorption pressures for nitrogen in spherical and cylindrical silica pores with several different pore sizes on the basis of semimacroscopic continuum models. The results clearly indicate that the models capture the exact nature of capillary condensation and evaporation phenomena of a fluid in cagelike and cylindrical mesopores. The temperature dependences of the adsorption hysteresis of nitrogen measured confirm previous theoretical predictions for cylindrical pores: for the ordered mesoporous silicas with cylindrical mesopores at least greater than ∼7 nm in diameter, the capillary condensation takes place via a nucleation process followed by a growth process of a bridging meniscus at pressures higher than the equilibrium transition, while the capillary evaporation takes place via a receding meniscus from pore ends at the equilibrium. For SBA-15 and MCM-41 with smaller mesopore sizes, on the other hand, the capillary condensation takes place close to the equilibrium transition pressures, while the capillary evaporation takes place at pressures lower than the equilibrium, owing to single pore blocking due to corrugation of the cylindrical pores. We discuss the effect of curvature on surface tension in capillary condensation, as well as the relation between a change in the mechanisms of adsorption and desorption and the pore corrugation in the cylindrical pores.

Polymer-Infiltrated Nanoparticle Films Using Capillarity-Based Techniques: Toward Multifunctional Coatings and Membranes.

Polymer-infiltrated nanoparticle films (PINFs) are a new class of nanocomposites that offer synergistic properties and functionality derived from unusually high fractions of nanomaterials. Recently, two versatile techniques,capillary rise infiltration (CaRI) and solvent-driven infiltration of polymer (SIP), have been introduced that exploit capillary forces in films of densely packed nanoparticles. In CaRI, a highly loaded PINF is produced by thermally induced wicking of polymer melt into the nanoparticle packing pores. In SIP, exposure of a polymer-nanoparticle bilayer to solvent vapor atmosphere induces capillary condensation of solvent in the pores of nanoparticle packing, leading to infiltration of polymer into the solvent-filled pores. CaRI/SIP PINFs show superior properties compared with polymer nanocomposite films made using traditional methods, including superb mechanical properties, thermal stability, heat transfer, and optical properties. This review discusses fundamental aspects of the infiltration process and highlights potential applications in separations, structural coatings, and polymer upcycling-a process to convert polymer wastes into useful chemicals.

Sub-nanometer confinement enables facile condensation of gas electrolyte for low-temperature batteries

Confining molecules in the nanoscale environment can lead to dramatic changes of their physical and chemical properties, which opens possibilities for new applications. There is a growing interest in liquefied gas electrolytes for electrochemical devices operating at low temperatures due to their low melting point. However, their high vapor pressure still poses potential safety concerns for practical usages. Herein, we report facile capillary condensation of gas electrolyte by strong confinement in sub-nanometer pores of metal-organic framework (MOF). By designing MOF-polymer membranes (MPMs) that present dense and continuous micropore (~0.8 nm) networks, we show significant uptake of hydrofluorocarbon molecules in MOF pores at pressure lower than the bulk counterpart. This unique property enables lithium/fluorinated graphite batteries with MPM-based electrolytes to deliver a significantly higher capacity than those with commercial separator membranes (~500 mAh g−1 vs. <0.03 mAh g−1) at −40 °C under reduced pressure of the electrolyte.

Diffusion‐to‐Imbibition Transition in Water Sorption in Nanoporous Media: Theoretical Studies

AbstractThe ability to predict multiphase fluid transport in nanoporous rocks such as shales is critical for many geoscience applications, for example unconventional hydrocarbon production, geologic carbon sequestration, and nuclear waste disposal. When the pore sizes approach nanoscales, the impact of the molecular interaction forces between fluids and solids becomes increasingly important. These forces can alter macroscopic fluid phase behavior and control transport. Recent experimental studies have shown that capillary condensation and subsequent imbibition of liquid water can occur in hydrophilic nanoporous media even if the vapor phase is at a critical relative humidity (rhcrit) well below vapor saturation. This study presents a theoretical investigation of the processes controlling adsorption, capillary condensation and imbibition in nanoporous media, using the square‐gradient classical density functional theory. The proposed theoretical model explicitly includes the relevant interaction forces among fluids and solids in macroscopic porous media. Application of the model to a relative‐humidity‐controlled water adsorption experiment is presented to demonstrate the impact of water‐pore wall attractive forces on multiphase water behavior in a hydrophilic silicon nanoporous medium. The model represents well the measured time‐dependent evolution of the water imbibition front inside the nanoporous medium and also explains the diffusion‐like water transport regimes observed at rh &lt; rhcrit and the imbibition‐like flow regimes observed at rh &gt; rhcrit. The study furthermore gives an insight on hysteresis phenomenon in adsorption and desorption isotherms.

Moisture-Assisted Formation of High-Quality Silver Nanowire Transparent Conductive Films with Low Junction Resistance

Silver nanowire (AgNWs) transparent conductive film (TCF) is considered to be the most favorable material to replace indium tin oxide (ITO) as the next-generation transparent conductive film. However, the disadvantages of AgNWs, such as easy oxidation and high wire-wire junction resistance, dramatically limit its commercial application. In this paper, moisture treatment was adopted, and water was dripped on the surface of AgNWs film or breathed on the surface so that the surface was covered with a layer of water vapor. The morphology of silver nanowire mesh nodes is complex, and the curvature is large. According to the capillary condensation theory, water molecules preferentially condense near the geometric surface with significant curvature. The capillary force is generated, making the wire-wire junction of AgNWs mesh bond tightly, resulting in good ohmic contact. The experimental results show that AgNWs-TCF treated by moisture has better conductivity, with an average sheet resistance of 20 Ω/sq and more uniform electrical properties. The bending test and adhesion test showed that AgNWs-TCF treated by moisture still exhibited good mechanical bending resistance and environmental stability.