Recent developments in the area of plant‐based hydrogels are introduced, especially those derived from wood as a widely available, multiscale, and hierarchical source of nanomaterials, as well as ...other cell wall elements. With water being fundamental in a hydrogel, water interactions, hydration, and swelling, all critically important in designing, processing, and achieving the desired properties of sustainable and functional hydrogels, are highlighted. A plant, by itself, is a form of a hydrogel, at least at given states of development, and for this reason phenomena such as fluid transport, diffusion, capillarity, and ionic effects are examined. These aspects are highly relevant not only to plants, especially lignified tissues, but also to the porous structures produced after removal of water (foams, sponges, cryogels, xerogels, and aerogels). Thus, a useful source of critical and comprehensive information is provided regarding the synthesis of hydrogels from plant materials (and especially wood nanostructures), and about the role of water, not only for processing but for developing hydrogel properties and uses.
Inspired from nature, wood‐based and man‐made hydrogels are produced taking advantage of the properties and structure of elements present in the cell walls of plants, including (nano)celluloses. They endow new materials with features that include directionality, hierarchy, responsiveness, and function, all of which are associated to the composition and morphology of the building blocks.
Liquid-liquid phase separation and related phase transitions have emerged as generic mechanisms in living cells for the formation of membraneless compartments or biomolecular condensates. The surface ...between two immiscible phases has an interfacial tension, generating capillary forces that can perform work on the surrounding environment. Here we present the physical principles of capillarity, including examples of how capillary forces structure multiphase condensates and remodel biological substrates. As with other mechanisms of intracellular force generation, for example, molecular motors, capillary forces can influence biological processes. Identifying the biomolecular determinants of condensate capillarity represents an exciting frontier, bridging soft matter physics and cell biology.
Multiphase flows in porous media are important in many natural and industrial processes. Pore-scale models for multiphase flows have seen rapid development in recent years and are becoming ...increasingly useful as predictive tools in both academic and industrial applications. However, quantitative comparisons between different pore-scale models, and between these models and experimental data, are lacking. Here, we perform an objective comparison of a variety of state-of-the-art pore-scale models, including lattice Boltzmann, stochastic rotation dynamics, volume-of-fluid, level-set, phase-field, and pore-network models. As the basis for this comparison, we use a dataset from recent microfluidic experiments with precisely controlled pore geometry and wettability conditions, which offers an unprecedented benchmarking opportunity. We compare the results of the 14 participating teams both qualitatively and quantitatively using several standard metrics, such as fractal dimension, finger width, and displacement efficiency.We find that no single method excels across all conditions and that thin films and corner flow present substantial modeling and computational challenges.
Theorems on the existence and form of solutions of variational problems with circular symmetry, such as the deflection problem of an elastic plate and the capillarity problem, were obtained.
We consider the numerical solution of the partial differential equations governing multiphase flow in porous media. For highly nonlinear problems, the temporal discretization of choice is often the ...unconditionally stable fully implicit method. However, the nonlinear systems, often solved with Newton’s method, are difficult to solve. Thus, the computational cost is strongly dependent on the nonlinear convergence rate, and enhancing this convergence property is key to speed up subsurface flow simulation.
We focus on the case of spatially discontinuous capillary pressure between rock regions. To efficiently and accurately simulate the flow dynamics in heterogeneous porous media, the flux computation combines Implicit Hybrid Upwinding with transmission conditions between different rock regions. This leads to a scheme that correctly represents the trapping mechanisms while improving the nonlinear convergence.
We extend our previous results (Hamon et al., 2016 18) by generalizing the scheme to fully implicit coupled flow and transport to address realistic problems in multiple dimensions. The generalized scheme is supported by an analysis of its mathematical properties. Our multidimensional numerical examples, which range from buoyancy-driven flow with capillary barriers to viscous-dominated flow, demonstrate that the Implicit Hybrid Upwinding scheme improves the accuracy compared to the standard phase-based upwinding scheme, while leading to significant reductions in the number of nonlinear iterations in multiple dimensions.
This paper is devoted to the study of the existence of solutions of the capillary equation under the influence of an external potential leading to surface surgery.
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•A generalized model that considers the displacement of one fluid by another immiscible one is introduced.•Both wetting and nonwetting combinations are considered.•All combinations of ...pressure, gravity, capillarity, and friction forces are studied.•The model reduces to all special cases.•Comparisons with CFD simulations show very good agreement.
Displacing one fluid by another immiscible with it is a phenomenon of greatest importance and exists in various applications from large scale oil productions to small scale microfluidics. Modeling this phenomenon is crucial, particularly, with respect to estimating penetration rates. Although considerable amounts of research works have been conducted to understand the physics involved in this phenomenon, they remain adherent to particular applications. This includes, for example, imbibition scenarios in which a wetting fluid imbibes inside a capillary tube even without the need to initiate the penetration. On the other hand, drainage scenarios, in which a nonwetting fluid displaces a wetting one, requires such initiation by providing external boosting. There are several external factors that influence the rate at which the meniscus advances inside a capillary tube. The most common such forces include pressure force, capillary force, and gravity force. Several of the modeling approaches have considered the case in which the displaced fluids are gases (e.g., air), particularly in applications related to infiltration studies in porous media. This allowed researchers to ignore the frictional resistance of the displaced fluid and only considers the other denser fluid. However, there exists other applications in which this is not correct and it may not be appropriate to ignore the displaced fluid. In this work, a new generalized model is introduced that accounts for all the physics involved in this process and also does not ignore the displaced fluid. For validation, it is shown that the derived model reduces to all the special cases for which analytical solutions exist, (including that of a single-phase flows). Furthermore, comparisons with computational fluid dynamics simulation (CFD) of drainage/imbibition scenarios show very good match with the results of the derived model, which builds confidence in the modeling approach.
Moisture and water transport in clay bricks are essential contributing factors towards brick decay in buildings. Experimental work is reported comparing water absorption and porosity of handmade and ...solid fired clay bricks from Paraguay. Their respective porosities were estimated by gravimetric test and, their pore distribution, degree of anisotropy and morphology were examined by SEM. Although it was found that both samples have a common composition (XRD), a higher degree of porosity was found in handmade bricks, which also absorb water at a higher rate accelerating the decay process. Experimental data is reported on the exponential kinetics behavior of water absorption similar to the one observed in capillary tubes, but with an additional diffusive process. A phenomenological model is proposed for water absorption in both types of bricks which compared with the standard model of water absorption available in the literature, produces a better representation of the experimental data.
Although interstitial fluid (ISF) contains biomarkers of physiological significance and medical interest, sampling of ISF for clinical applications has made limited impact due to a lack of simple, ...clinically useful techniques that collect more than nanoliter volumes of ISF. This study describes experimental and theoretical analysis of ISF transport from skin using microneedle (MN) patches and demonstrates collection of >1 μL of ISF within 20 min in pig cadaver skin and living human subjects using an optimized system. MN patches containing arrays of submillimeter solid, porous, or hollow needles were used to penetrate superficial skin layers and access ISF through micropores (μpores) formed upon insertion. Experimental studies in pig skin found that ISF collection depended on transport mechanism according to the rank order diffusion < capillary action < osmosis < pressure-driven convection, under the conditions studied. These findings were in agreement with independent theoretical modeling that considered transport within skin, across the interface between skin and μpores, and within μpores to the skin surface. This analysis indicated that the rate-limiting step for ISF sampling is transport through the dermis. Based on these studies and other considerations like safety and convenience for future clinical use, we designed an MN patch prototype to sample ISF using suction as the driving force. Using this approach, we collected ISF from human volunteers and identified the presence of biomarkers in the collected ISF. In this way, sampling ISF from skin using an MN patch could enable collection of ISF for use in research and medicine.
The development of flexible lithium–sulfur (Li–S) batteries with high energy density and long cycling life are very appealing for the emerging flexible, portable, and wearable electronics. However, ...the progress on flexible Li–S batteries was limited by the poor flexibility and serious performance decay of existing sulfur composite cathodes. Herein, we report a freestanding and highly flexible sulfur host that can simultaneously meet the flexibility, stability, and capacity requirements of flexible Li–S batteries. The host consists of a crisscrossed network of carbon nanotubes reinforced CoS nanostraws (CNTs/CoS-NSs). The CNTs/CoS-NSs with large inner space and high conductivity enable high loading and efficient utilization of sulfur. The strong capillarity effect and chemisorption of CNTs/CoS-NSs to sulfur species were verified, which can efficiently suppress the shuttle effect and promote the redox kinetics of polysulfides. The sulfur-encapsulated CNTs/CoS-NSs (S@CNTs/CoS-NSs) cathode in Li–S batteries exhibits superior performance, including high discharge capacity, rate capability (1045 mAh g–1 at 0.5 C and 573 mAh g–1 at 5.0 C), and cycling stability. Intriguingly, the soft-packed Li–S batteries based on S@CNTs/CoS-NSs cathode show good flexibility and stability upon bending.
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