Imbibition Triggered by Capillary Condensation in Nanopores

Microporous Cobalt Ferrite with Bio-Carbon Loosely Decorated to Construct Multi-Functional Composite for Dye Adsorption, Anti-Bacteria and Electromagnetic Protection

Currently, facing electromagnetic protection requirement under complex aqueous environments, the bacterial reproduction and organic dye corrosion may affect the composition and micro-structures of absorbers to weaken their electromagnetic properties. To address such problems, herein, a series of CoFe2O4@BCNPs (cobalt ferrite @ bio-carbon nanoparticles) composites are synthesized via co-hydrothermal and calcining process. The coupling of magnetic cobalt ferrite and dielectric bio-carbon derived from Apium can endow the composite multiple absorption mechanisms and matched impedance for effective microwave absorption, attaining a bandwidth of 8.12 GHz at 2.36 mm and an intensity of -49.85 dB at 3.0 mm. Due to the ROS (reactive oxygen species) stimulation ability and heavy metal ions of cobalt ferrite, the composite realizes an excellent antibacterial efficiency of 99% against Gram negative bacteria of Escherichia coli. Moreover, the loose porous layer of surface stacked bio-carbon can promote the adsorption of methylene blue for subsequent eliminating, a high removal rate of 90.37% for organic dye can be also achieved. This paper offers a new insight for rational design of composite's component and micro-structure to construct multi-functional microwave absorber for satisfying the electromagnetic protection demand in complicated environments.

Consummating ion desolvation in hard carbon anodes for reversible sodium storage

Hard carbons are emerging as the most viable anodes to support the commercialization of sodium-ion (Na-ion) batteries due to their competitive performance. However, the hard carbon anode suffers from low initial Coulombic efficiency (ICE), and the ambiguous Na-ion (Na+) storage mechanism and interfacial chemistry fail to give a reasonable interpretation. Here, we have identified the time-dependent ion pre-desolvation on the nanopore of hard carbons, which significantly affects the Na+ storage efficiency by altering the solvation structure of electrolytes. Consummating the pre-desolvation by extending the aging time, generates a highly aggregated electrolyte configuration inside the nanopore, resulting in negligible reductive decomposition of electrolytes. When applying the above insights, the hard carbon anodes achieve a high average ICE of 98.21% in the absence of any Na supplementation techniques. Therefore, the negative-to-positive capacity ratio can be reduced to 1.02 for full cells, which enables an improved energy density. The insight into hard carbons and related interphases may be extended to other battery systems and support the continued development of battery technology.

Comparative evaluation of three materials used for fragment reattachment in uncomplicated crown fracture-An in vitro study using bovine teeth

BACKGROUND/AIMS

The recommended treatment for uncomplicated crown fractures is bonding the fractured fragment or the fragment reattachment. A paucity was identified regarding the studies comparing the efficacy of micro-hybrid and nanohybrid composites in fragment reattachment. Hence, the present study aimed to evaluate and compare three materials for bonding of fragments rehydrated by humidification in teeth with uncomplicated crown fractures.

MATERIAL AND METHODS

Eighty mandibular bovine incisors with similar dimensions and free of any structural deformities were fractured similar to the technique followed in previous studies. Fracture was simulated, fragments, and stumps were coded, stumps were stored in artificial saliva and the fragments were dehydrated at room temperature and pressure. They were randomly assigned to Group-1 (no rehydration), Group-2 (rehydrated and bonded by flowable nanohybrid composite-3M Filtek Supreme Syringe Flowable Composite Resin-A2, Sao Paulo, Brazil), Group-3 (rehydrated and bonded by flowable micro-hybrid composite- Ruby Flow, InciDental, England, United Kingdom), and Group-4 (rehydrated and bonded by light-cured Glass-Ionomer-Cement-Voco Ionoseal, Cuxhaven, Germany). The samples were subjected to a universal testing machine to evaluate the force required to fracture the bonded fragments.

RESULTS

The highest median value of the force required to fracture was recorded for Group 2 (208.4 N) followed by Group 3 (195.2). The force required to fracture the bonded fragments was lowest in Group 4 (67.2 N) which was lower than the negative control (131.4 N). The differences between the observations in Groups 2 and 3 were not found to be statistically significant.

CONCLUSION

The nano and micro-hybrid composites showed greater force required to fracture than fragments bonded by LC-GIC. Dehydrated fragments bonded using nanocomposites performed better than rehydrated fragments bonded by using LC-GIC.

Nanoparticles exhibiting virus-mimic surface topology for enhanced oral delivery

The oral delivery of nano-drug delivery systems (Nano-DDS) remains a challenge. Taking inspirations from viruses, here we construct core-shell mesoporous silica nanoparticles (NPs, ~80 nm) with virus-like nanospikes (VSN) to simulate viral morphology, and further modified VSN with L-alanine (CVSN) to enable chiral recognition for functional bionics. By comparing with the solid silica NPs, mesoporous silica NPs and VSN, we demonstrate the delivery advantages of CVSN on overcoming intestinal sequential barriers in both animals and human via multiple biological processes. Subsequently, we encapsulate indomethacin (IMC) into the nanopores of NPs to mimic gene package, wherein the payloads are isolated from bio-environments and exist in an amorphous form to increase their stability and solubility, while the chiral nanospikes multi-sited anchor and chiral recognize on the intestinal mucosa to enhance the penetrability and ultimately improve the oral adsorption of IMC. Encouragingly, we also prove the versatility of CVSN as oral Nano-DDS.

Redesigning Natural Materials for Energy, Water, Environment, and Devices

The United Nations Framework Convention on Climate Change (UNFCCC) acknowledges that global cooperation is paramount to mitigate climate change and further warming. The global community is committed to renewable energy and natural materials to tackle this challenge for all humankind. The widespread use of natural materials is embraced as one such action to reach net-zero carbon emissions. Given the hierarchical framework and earth abundance, cellulose-based materials extend their negative carbon benefits to our daily products and accelerate our pace toward carbon neutrality. Here, we present an overview of recent developments of cellulose-based materials in upsurging applications in radiative cooling, thermal insulation, nanofluidics, and wearable devices. We also highlight various modifications and functionalized processes that transform massive amounts of cellulose into green products. The prosperous development of functionalized cellulose materials aligns with a circular economy. Expedited interdisciplinary fundamental investigations are expected to make fibrillated cellulose penetrate more into carbon downdraw at speed and scale.

Review of Waterproof Breathable Membranes: Preparation, Performance and Applications in the Textile Field

Waterproof breathable membranes (WBMs) characterized by a specific internal structure, allowing air and water vapor to be transferred from one side to the other while preventing liquid water penetration, have attracted much attention from researchers. WBMs combine lamination and other technologies with textile materials to form waterproof breathable fabrics, which play a key role in outdoor sports clothing, medical clothing, military clothing, etc. Herein, a systematic overview of the recent progress of WBMs is provided, including the principles of waterproofness and breathability, common preparation methods and the applications of WBMs. Discussion starts with the waterproof and breathable mechanisms of two different membranes: hydrophilic non-porous membranes and hydrophobic microporous membranes. Then evaluation criteria and common preparation methods for WBMs are presented. In addition, treatment processes that promote water vapor transmission and prominent applications in the textile field are comprehensively analyzed. Finally, the challenges and future perspectives of WBMs are also explored.

Electrospun Nanofibrous Membranes: A Versatile Medium for Waterproof and Breathable Application

Waterproof and breathable membranes that prevent liquid water penetration, while allowing air and moisture transmission, have attracted significant attention for various applications. Electrospun nanofiber materials with adjustable pore structures, easily tunable wettability, and good pore connectivity, have shown significant potential for constructing waterproof and breathable membranes. Herein, a systematic overview of the recent progress in the design, fabrication, and application of waterproof and breathable nanofibrous membranes is provided. The various strategies for fabricating the membranes mainly including one-step electrospinning and post-treatment of nanofibers are given as a starting point for the discussion. The different design concepts and structural characteristics of each type of waterproof and breathable membrane are comprehensively analyzed. Then, some representative applications of the membranes are highlighted, involving personal protection, desalination, medical dressing, and electronics. Finally, the challenges and future perspectives associated with waterproof and breathable nanofibrous membranes are presented.

Hygroscopic Porous Polymer for Sorption-Based Atmospheric Water Harvesting

Sorption-based atmospheric water harvesting (SAWH) holds huge potential due to its freshwater capabilities for alleviating water scarcity stress. The two essential parts, sorbent material and system structure, dominate the water sorption-desorption performance and the total water productivity for SAWH system together. Attributed to the superiorities in aspects of sorption-desorption performance, scalability, and compatibility in practical SAWH devices, hygroscopic porous polymers (HPPs) as next-generation sorbents are recently going through a vast surge. However, as HPPs' sorption mechanism, performance, and applied potential lack comprehensive and accurate guidelines, SAWH's subsequent development is restricted. To address the aforementioned problems, this review introduces HPPs' recent development related to mechanism, performance, and application. Furthermore, corresponding optimized strategies for both HPP-based sorbent bed and coupling structural design are proposed. Finally, original research routes are directed to develop next-generation HPP-based SAWH systems. The presented guidelines and insights can influence and inspire the future development of SAWH technology, further achieving SAWH's practical applications.

Pushing the limits of nanopore transport performance by polymer functionalization

Inspired by the design and performance of biological pores, polymer functionalization of nanopores has emerged as an evolving field to advance transport performance within the last few years. This feature article outlines developments in nanopore functionalization and the resulting transport performance including gating based on electrostatic interaction, wettability and ligand binding, gradual transport controlled by polymerization as well as functionalization-based asymmetric nanopore and nanoporous material design going towards the transport direction. Pushing the limits of nanopore transport performance and thus reducing the performance gap between biological and technological pores is strongly related to advances in polymerization chemistry and their translation into nanopore functionalization. Thereby, the effect of the spatial confinement has to be considered for polymer functionalization as well as for transport regulation, and mechanistic understanding is strongly increased by combining experiment and theory. A full mechanistic understanding together with highly precise nanopore structure design and polymer functionalization is not only expected to improve existing application of nanoporous materials but also opens the door to new technologies. The latter might include out of equilibrium devices, ionic circuits, or machine learning based sensors.

Digital holographic microscopy implementation for capillary filling measurements in nanoporous materials

We report the implementation of lensless off-axis digital holographic microscopy as a non-destructive optical analyzer for nano-scale structures. The measurement capacity of the system was validated by analyzing the topography of a metallic grid with ≈150nm thick opaque features. In addition, an experimental configuration of self-reference was included to study the dynamics of the capillary filling phenomena in nanostructured porous silicon. The fluid front position as a function of time was extracted from the holograms, and the typical square root of time kinematics was recovered. The results shown are in agreement with previous works on capillary imbibition in similar structures and confirm a first step towards unifying holographic methods with fluid dynamics theory to develop a spatially resolved capillary tomography system for nanoporous materials characterization.

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.

A minimally disruptive method for measuring water potential in planta using hydrogel nanoreporters

Gaps in our ability to document local water relations in leaves compromise our ability to build complete models of leaf and plant function and our understanding of ecophysiological phenomena, such as response and adaptation to drought. Macroscopically, leaf water potential has been shown to impact vegetative growth and yield, susceptibility to disease, and, in extreme drought, plant viability, making it a promising candidate trait to improve water-use efficiency in plants. In this paper, we present a nanoscale sensor (AquaDust) that provides minimally disruptive measurements of water potential in leaves of intact plants at high spatial and temporal resolution. This creates opportunities for improving our understanding of the mechanisms coupling variations in water potential to biological and physical processes.

Leaf water potential is a critical indicator of plant water status, integrating soil moisture status, plant physiology, and environmental conditions. There are few tools for measuring plant water status (water potential) in situ, presenting a critical barrier for developing appropriate phenotyping (measurement) methods for crop development and modeling efforts aimed at understanding water transport in plants. Here, we present the development of an in situ, minimally disruptive hydrogel nanoreporter (AquaDust) for measuring leaf water potential. The gel matrix responds to changes in water potential in its local environment by swelling; the distance between covalently linked dyes changes with the reconfiguration of the polymer, leading to changes in the emission spectrum via Förster Resonance Energy Transfer (FRET). Upon infiltration into leaves, the nanoparticles localize within the apoplastic space in the mesophyll; they do not enter the cytoplasm or the xylem. We characterize the physical basis for AquaDust’s response and demonstrate its function in intact maize (Zea mays L.) leaves as a reporter of leaf water potential. We use AquaDust to measure gradients of water potential along intact, actively transpiring leaves as a function of water status; the localized nature of the reporters allows us to define a hydraulic model that distinguishes resistances inside and outside the xylem. We also present field measurements with AquaDust through a full diurnal cycle to confirm the robustness of the technique and of our model. We conclude that AquaDust offers potential opportunities for high-throughput field measurements and spatially resolved studies of water relations within plant tissues.

Wettability-defined droplet imbibition in ceramic mesopores

Wettability-defined liquid infiltration into porous materials in nature and several industrial applications is of fundamental interest. Direct observation of wetting-controlled imbibition in mesopores is anticipated to deliver important insights into the interplay between nanoconfined liquid movement and nanoscale wettability. We present a systematic study of water imbibition into mesoporous silica thin films with wetting properties precisely adjusted through chemical functionalization. We observe the liquid infiltration, resulting in an imbibition ring around the water droplet, by top-view imaging using a camera with collimated coaxial illumination. With decreasing hydrophilicity, the maximum imbibition area around the droplet decreases, accompanied by a simultaneous change in the imbibition kinetics and imbibition mechanism. Initially, the imbibition kinetics follow a modified Lucas-Washburn law that considers a strong influence of evaporation. However, with increasing imbibition time after reaching constant imbibition ring dimensions, the imbibition area starts to increase again, causing a deviation from the applied model. This observation is ascribed to water-mediated surface activation at the imbibition front, leading to a slightly increased wettability, which is also confirmed by water adsorption measurements. Furthermore, recently described spontaneous condensation-evaporation imbalances that cause oscillations of the imbibition front could be verified and were studied with regard to changing wetting properties. By increasing the contact angle of the material and therefore the partial pressure needed for capillary condensation, the amplitude of the imbibition front oscillations decreases. These results provide insights into the wettability-defined complex movement of water in mesoporous structures, which has practical implications, e.g., for nano/microfluidic devices and water purification or harvesting.

Capillary condensation under atomic-scale confinement

Capillary condensation of water is ubiquitous in nature and technology. It routinely occurs in granular and porous media, can strongly alter such properties as adhesion, lubrication, friction and corrosion, and is important in many processes used by microelectronics, pharmaceutical, food and other industries^1-4. The century-old Kelvin equation⁵ is frequently used to describe condensation phenomena and has been shown to hold well for liquid menisci with diameters as small as several nanometres^1-4,6-14. For even smaller capillaries that are involved in condensation under ambient humidity and so of particular practical interest, the Kelvin equation is expected to break down because the required confinement becomes comparable to the size of water molecules^1-22. Here we use van der Waals assembly of two-dimensional crystals to create atomic-scale capillaries and study condensation within them. Our smallest capillaries are less than four ångströms in height and can accommodate just a monolayer of water. Surprisingly, even at this scale, we find that the macroscopic Kelvin equation using the characteristics of bulk water describes the condensation transition accurately in strongly hydrophilic (mica) capillaries and remains qualitatively valid for weakly hydrophilic (graphite) ones. We show that this agreement is fortuitous and can be attributed to elastic deformation of capillary walls^23-25, which suppresses the giant oscillatory behaviour expected from the commensurability between the atomic-scale capillaries and water molecules^20,21. Our work provides a basis for an improved understanding of capillary effects at the smallest scale possible, which is important in many realistic situations.

Functionalized multiscale visual models to unravel flow and transport physics in porous structures

The fluid flow, species transport, and chemical reactions in geological formations are the chief mechanisms in engineering the exploitation of fossil fuels and geothermal energy, the geological storage of carbon dioxide (CO₂), and the disposal of hazardous materials. Porous rock is characterized by a wide surface area, where the physicochemical fluid-solid interactions dominate the multiphase flow behavior. A variety of visual models with differences in dimensions, patterns, surface properties, and fabrication techniques have been widely utilized to simulate and directly visualize such interactions in porous media. This review discusses the six categories of visual models used in geological flow applications, including packed beds, Hele-Shaw cells, synthesized microchips (also known as microfluidic chips or micromodels), geomaterial-dominated microchips, three-dimensional (3D) microchips, and nanofluidics. For each category, critical technical points (such as surface chemistry and geometry) and practical applications are summarized. Finally, we discuss opportunities and provide a framework for the development of custom-built visual models.

Nucleation of Capillary Bridges and Bubbles in Nanoconfined CO2

Using molecular simulation, we examine the capillary condensation and the capillary evaporation of CO₂ in cylindrical nanopores. More specifically, we employ the recently developed μV T-S method to determine the microscopic mechanism associated with these processes and the corresponding free energy profiles. We calculate the free energy barrier for capillary condensation and identify that the key step consists in the nucleation of a liquid bridge of a critical size. Similarly, the free energy maximum found for the capillary evaporation process is found to correspond to the nucleation of a vapor bubble of a critical size. In addition, we assess the impact of the strength of the wall-fluid on the height of the free energy barrier and on the critical size of liquid bridges (condensation process) and vapor bubbles (evaporation process). We observe that the height of the free energy barrier increases with the strength of the wall-fluid interactions. Finally, we build a theoretical model, based on capillary theory, to rationalize our findings. In particular, the simulation results reveal a linear scaling of the free energy barrier with the critical size, in excellent agreement with the theoretical predictions.

Adsorption and Capillary Condensation-Induced Imbibition in Nanoporous Media

Multiphase flow phenomena in nanoporous media are encountered in many science and engineering applications. Shales, for example, possessing complex nanopore networks, have considerable importance as source rocks for unconventional oil and gas production and as low-permeability seals for geologic carbon sequestration or nuclear waste disposal. This study presents a theoretical investigation of the processes controlling adsorption, capillary condensation, and imbibition in such nanoporous media, with a particular focus on understanding the effects of fluid-fluid and fluid-pore wall interaction forces in the interconnected nanopore space. Building on a new theoretical framework, we developed a numerical model for the multiphase nanoporous flow and tested it against water vapor uptake measurements conducted on a shale core sample. The model, which is based on the density functional approach, explicitly includes the relevant interaction forces among fluids and solids while allowing for a continuum representation of the porous medium. The experimental data include gravimetrically measured mass changes in an initially dry core sample exposed to varying levels of relative humidity, starting with a low relative humidity (rh = 0.31) followed by a period of a higher relative humidity (rh = 0.81). During this process, water vapor uptake in the dry core is recorded as a function of time. Our model suggests that, under low rh conditions, the flow within the shale sample is controlled by adsorption- and diffusion-type processes. After increasing the rh to 0.81, the uptake of water vapor becomes more significant, and according to our model, this can be explained by capillary condensation followed by immiscible displacement in the core sample. It appears that strong fluid-pore wall attractive forces cause condensation near the inlet, which then induces water imbibition further into sample.

Comparative evaluation of fracture resistance using two rehydration protocols for fragment reattachment in uncomplicated crown fractures

BACKGROUND/AIMS

Uncomplicated crown fracture is the most common traumatic dental injury. The International Association of Dental Traumatology has recommended fragment reattachment as the best method for restoring uncomplicated crown fractures of permanent teeth. Dehydration can affect fracture resistance after reattachment. However, a standard protocol for rehydration is still lacking. Hence, the aim of this study was to design a humidification chamber and assess its efficacy for improving the rehydration of tooth fragments and increasing fracture resistance after reattachment.

MATERIALS AND METHODS

Sixty mandibular bovine incisors with similar dimensions and free of any structural deformities were fractured and randomized into five groups: Group I, Control Group (sound teeth); Group II (dehydrated for 24 hours); Group III (rehydrated in distilled water for 15 minutes); Group IV (rehydrated in a humidification chamber for 15 minutes); and Group V (restored with composite). A humidification chamber was designed and used for rehydration for 15 minutes in Group IV. Fragments in Group III were immersed in distilled water for 15 minutes. Reattachment procedures and materials remained the same in all groups. Fracture resistance was tested in a universal testing machine, and statistical analysis was done by Stata-14.

RESULTS

The Control Group with sound teeth (Group I) exhibited a maximum value of 282 ± 10.32 N, while Group II (fragment reattached without rehydration) had the least fracture resistance, 49.75 ± 5.2 N. Rehydration by means of the humidification chamber protocol (Group IV) resulted in significantly higher fracture resistance (150.54 ± 6.49 N) than in Group III (rehydration by means of immersion).

CONCLUSIONS

Fracture resistance after fragment reattachment was significantly affected by the rehydration of fragments for 15 minutes in the humidification chamber. Fragment reattachment after rehydration showed better fracture resistance than the composite restorations.

Adsorption, Desorption, and Crystallization of Aqueous Solutions in Nanopores

Probing nanoconfined solutions in tortuous, mesoporous media is challenging because of pore size, complex pore connectivity, and the coexistence of multiple components and phases. Here, we use optical reflectance to experimentally investigate the wetting and drying of a mesoporous medium with ∼3-nm-diameter pores containing aqueous solutions of sodium chloride and lithium chloride. We show that the vapor activities (i.e., relative humidities) that correspond to optical features in the isotherms for solutions can be used to deduce the thermodynamic state of a nanoscopic solution that undergoes evaporation and crystallization upon drying and condensation and deliquescence when increasing the relative humidity. We emphasize specific equilibrium states of the system: the onset of draining during desorption and the end of filling during adsorption as well as percolation-induced scattering and crystallization. We find that theoretical arguments involving classical thermodynamics (a modified Kelvin-Laplace equation and classical nucleation theory) explain quantitatively the evolution of the optical features and thereby the state of the solution as a function of imposed vapor activity and solute concentration.

How Solutes Modify the Thermodynamics and Dynamics of Filling and Emptying in Extreme Ink-Bottle Pores

We investigate the filling and emptying of extreme ink-bottle porous media-micrometer-scale pores connected by nanometer-scale pores-when changing the pressure of the external vapor, in a case where the pore liquid contains solutes. These phenomena are relevant in diverse contexts, such as the weathering of building materials and artwork, aerosol formation in the atmosphere, and the hydration of soils and plants. Using model systems made of vein-shaped microcavities interconnected by a mesoporous matrix, we show experimentally that the presence of a nonvolatile solute shifts the condensation and evaporation transitions and in a way that is consistent with a modified Kelvin-Laplace equation that takes into account the osmotic pressure of the solution. Emptying occurs far below saturation, when the Kelvin stress, mediated by the large curvature of the liquid-vapor interfaces in the nanopores, is negative enough to induce spontaneous bubble nucleation in the microveins. Filling, on the other hand, occurs close to equilibrium (i.e., at saturation, p_sat for pure water and p_s < p_sat for a solution), driven by the weak capillary pressure of the liquid-vapor interface in the microveins. Interestingly, solutes allow the system to reach situations where the vapor is supersaturated with respect to the solution ( p_s < p < p_sat). We show that in that latter situation, a condensation layer covers the outer surface of the porous system, preventing the generation of Kelvin stresses but inducing osmotic stresses and flows that are vapor pressure-dependent. The timescales and dynamics reflect these different driving forces: emptying proceeds through discrete, stochastic nucleation events with very fast, unsteady bubble growth associated with a poroelastic relaxation process, while filling occurs collectively in all veins of the sample through a slower steady-state process driven by a combination of osmosis and capillarity. The dynamics can however be rendered symmetrical between filling and emptying if bubbles pre-exist during emptying, a case that we explore using cycling of the vapor pressure around equilibrium.

Waterproof and Breathable Electrospun Nanofibrous Membranes

Waterproof and breathable (W&B) membranes combine fascinating properties of resistance to liquid water penetration and transmitting of water vapor, playing a key role in addressing problems related to health, resources, and energy. Electrospinning is an efficient and advanced way to construct nanofibrous materials with easily tailored wettability and adjustable pore structure, therefore providing an ideal strategy for constructing W&B membranes. In this review, recent progress on electrospun W&B membranes is summarized, involving materials design and fabrication, basic properties of electrospun W&B membranes associated with waterproofness and breathability, as well as their applications. In addition, challenges and future trends of electrospun W&B membranes are discussed.

Directional Water Collection in Nanopore Networks

The development of artificial nanosystems that mimic directional water-collecting ability of evolved biological surfaces is eagerly awaited. Here we report a new type of addressable water collection that is induced by coupling both vapor gradients, like a road drawn, and the temperature-tuned condensation in nanopores as step signals. What distinguishes the motion described here from the motions reported earlier is the fact that neither bulk liquid infiltration nor displacement of droplet is required. Instead, the motion results from a scanned water capture because of the temperature-dependent condensation command acting on the vapor pressure gradient track originated by a droplet without a bulk fluidic connection with a mesoporous film. This novel working principle demands only a small-range surface temperature control, which was entirely generated by a thermoelectric cell integrated to the mesoporous substrates. The strategy opens the route to achieving precise control over wetting location (from a few to hundreds of micrometers) and hence over the direction of water collected by these widely employed nanomaterials. Furthermore, as water is collected from condensation into the pores, the system naturally involves purification and subsequent delivery of clean water, which provides an added value to the proposed strategy.

Spontaneous water adsorption-desorption oscillations in mesoporous thin films

Understanding fluid transport and phase changes in nanopore structures is of great interest to many application fields, from energy conversion to water harvesting. This work discusses the spontaneous oscillations of the water saturation of mesoporous thin films, in the zone adjacent to a sessile water drop, at ambient conditions. The wetting-front dynamics onto the film is described by considering three coexisting phenomena: infiltration from the water drop, condensation from air vapor, and evaporation to the ambient. It was found that the oscillations follow spontaneous condensation-evaporation imbalances, which are governed by the hysteretic character of the adsorption-desorption behavior of the mesoporous material. The outcomes of this work provide insights on the complex interplay between water and nanopore structures, which has practical implications for the handling of humid microenvironments in lab-on-a-chip technology, as well as for many processes that take part of the cycle of water in nature.

Enhanced Oxygen Solubility in Metastable Water under Tension

Despite its relevance in numerous natural and industrial processes, the solubility of molecular oxygen has never been directly measured in capillary-condensed liquid water. In this article, we measure oxygen solubility in liquid water trapped within nanoporous samples, in metastable equilibrium with a subsaturated vapor. We show that solubility increases two fold at moderate subsaturations (relative humidity ∼0.55). This evolution with relative humidity is in good agreement with a simple thermodynamic prediction using properties of bulk water, previously verified experimentally at positive pressure. Our measurement thus verifies the validity of this macroscopic thermodynamic theory to strong confinement and large negative pressures, where significant nonidealities are expected. This effect has strong implications for important oxygen-dependent chemistries in natural and technological contexts.

Temperature Enhanced Backwash

Decentralized drinking water treatment is limited by supply of service, consumables, spare parts and in particular, power. Therefore, gravity-driven dead-end ultrafiltration is applied to purify surface water with high suspended solid loading. To obtain high flux in the long term, an effective membrane backwash is mandatory. Also, disinfection and cleaning is required regularly. Here we propose a new process coping with these particular challenges in decentralized water production: Temperature Enhanced Backwash. Herein, the membrane is backwashed at elevated temperature and corresponding steam pressure. A mathematical description of the Temperature Enhanced Backwash reveals that membrane pores are filled predominantly with liquid phase, irrespectively of whether membranes are charged with saturated steam or boiling liquid. A steam - water mixture is discharged at the module outlet suggesting evaporation at the end of the pores. This evaporation at membrane - fluid interface supposedly creates high volume fluxes shearing off potential fouling layers. Combined with gravity-driven filtration, the overall process potentially can cope with highly intermittent electrical power supply or even its absence. The methodology shows competitive cleaning efficacy compared to mechanical backwashing as demonstrated experimentally using silica nanoparticles, humic acid and river water.

Capillary Condensation in 8 nm Deep Channels

Condensation on the nanoscale is essential to understand many natural and synthetic systems relevant to water, air, and energy. Despite its importance, the underlying physics of condensation initiation and propagation remain largely unknown at sub-10 nm, mainly due to the challenges of controlling and probing such small systems. Here we study the condensation of n-propane down to 8 nm confinement in a nanofluidic system, distinct from previous studies at ∼100 nm. The condensation initiates significantly earlier in the 8 nm channels, and it initiates from the entrance, in contrast to channels just 10 times larger. The condensate propagation is observed to be governed by two liquid-vapor interfaces with an interplay between film and bridging effects. We model the experimental results using classical theories and find good agreement, demonstrating that this 8 nm nonpolar fluid system can be treated as a continuum from a thermodynamic perspective, despite having only 10-20 molecular layers.

Geo-material surface modification of microchips using layer-by-layer (LbL) assembly for subsurface energy and environmental applications

A key constraint in the application of microfluidic technology to subsurface flow and transport processes is the surface discrepancy between microchips and the actual rocks/soils. This research employs a novel layer-by-layer (LbL) assembly technology to produce rock-forming mineral coatings on microchip surfaces. The outcome of the work is a series of 'surface-mimetic micro-reservoirs (SMMR)' that represent multi-scales and multi-types of natural rocks/soils. For demonstration, the clay pores of sandstones and mudrocks are reconstructed by representatively coating montmorillonite and kaolinite in polydimethylsiloxane (PDMS) microchips in a wide range of channel sizes (width of 10-250 μm, depth of 40-100 μm) and on glass substrates. The morphological and structural properties of mineral coatings are characterized using a scanning electron microscope (SEM), optical microscope and profilometer. The coating stability is tested by dynamic flooding experiments. The surface wettability is characterized by measuring mineral oil-water contact angles. The results demonstrate the formation of nano- to micro-scale, fully-covered and stable mineral surfaces with varying wetting properties. There is an opportunity to use this work in the development of microfluidic technology-based applications for subsurface energy and environmental research.

Microfluidic and nanofluidic phase behaviour characterization for industrial CO2, oil and gas

Microfluidic systems that leverage unique micro-scale phenomena have been developed to provide rapid, accurate and robust analysis, predominantly for biomedical applications. These attributes, in addition to the ability to access high temperatures and pressures, have motivated recent expanded applications in phase measurements relevant to industrial CO₂, oil and gas applications. We here present a comprehensive review of this exciting new field, separating microfluidic and nanofluidic approaches. Microfluidics is practical, and provides similar phase properties analysis to established bulk methods with advantages in speed, control and sample size. Nanofluidic phase behaviour can deviate from bulk measurements, which is of particular relevance to emerging unconventional oil and gas production from nanoporous shale. In short, microfluidics offers a practical, compelling replacement of current bulk phase measurement systems, whereas nanofluidics is not practical, but uniquely provides insight into phase change phenomena at nanoscales. Challenges, trends and opportunities for phase measurements at both scales are highlighted.