Liquid invasion into a porous medium is a phenomenon of great importance in both nature and technology. Despite its enormous importance, there is a surprisingly sparse understanding of the processes ...occurring on the scale of individual pores and of how these processes determine the global invasion pattern. In particular, the exact influence of the wettability remains unclear besides the limiting cases of very small or very large contact angles of the invading fluid. Most quantitative pore-scale experiments and theoretical considerations have been conducted in effectively two-dimensional (2D) micromodels and Hele-Shaw geometries. Although these pioneering works helped to unravel some of the physical aspects of the displacement processes, the relevance of 2D models has not always been appreciated for natural porous media. With the availability of X-ray microtomography, 3D imaging has become a standard for exploring pore-scale processes in porous media. Applying advanced postprocessing routines and synchrotron microtomography, researchers can image even slow flow processes in real time and extract relevant material parameters like the contact angle from the interfaces in the pore space. These advances are expected to boost both theoretical and experimental understanding of pore-scale processes in natural porous media.
Although negligible at large scales, capillary forces may become dominant for submillimetric objects. Surface tension is usually associated with the spherical shape of small droplets and bubbles, ...wetting phenomena, imbibition, or the motion of insects at the surface of water. However, beyond liquid interfaces, capillary forces can also deform solid bodies in their bulk, as observed in recent experiments with very soft gels. Capillary interactions, which are responsible for the cohesion of sandcastles, can also bend slender structures and induce the bundling of arrays of fibers. Thin sheets can spontaneously wrap liquid droplets within the limit of the constraints dictated by differential geometry. This review aims to describe the different scaling parameters and characteristic lengths involved in elastocapillarity. We focus on three main configurations, each characterized by a specific dimension: three-dimensional (3D), deformations induced in bulk solids; 1D, bending and bundling of rod-like structures; and 2D, bending and stretching of thin sheets. Although each configuration deserves a detailed review, we hope our broad description provides a general view of elastocapillarity.
Thermo- and soluto-capillarity: Passive and active drops Ryazantsev, Yuri S.; Velarde, Manuel G.; Rubio, Ramón G. ...
Advances in colloid and interface science,
September 2017, 2017-Sep, 2017-09-00, 20170901, Letnik:
247
Journal Article
Recenzirano
A survey is provided of a variety of problems where a passive or an active drop experiences directed motion consequence of the action of an external or internal agent or a combination of both. An ...active drop is capable of reacting by engendering autonomous, self-propelled motion in favor or against the agent. The phenomena involved offer diverse complexity but one way or another the drop motion finally rests on thermo- or soluto-capillarity hence on interfacial tension gradients. Accordingly, here a minimal mathematical framework underlying such drop motions is provided when direct external temperature or solute gradients, illumination, internal heat generation or surface chemical reaction are incorporated into the physico-chemical-hydrodynamics.
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•Review of hydrodynamics of passive and active drops/bubbles in host fluids.•Mathematical description of the motion of drops/bubbles due to interfacial tension gradients is itemized.•Force on active and passive drops/bubbles has been provided.•Classical and recent experiments on active and passive motion of drops/bubbles are described.
It is widely appreciated that surface tension can dominate the behavior of liquids at small scales. Solids also have surface stresses of a similar magnitude, but they are usually overlooked. However, ...recent work has shown that these can play a central role in the mechanics of soft solids such as gels. Here, we review this emerging field. We outline the theory of surface stresses, from both mechanical and thermodynamic perspectives, emphasizing the relationship between surface stress and surface energy. We describe a wide range of phenomena at interfaces and contact lines where surface stresses play an important role. We highlight how surface stresses cause dramatic departures from classic theories for wetting (Young-Dupré), adhesion (Johnson-Kendall-Roberts), and composites (Eshelby). A common thread is the importance of the ratio of surface stress to an elastic modulus, which defines a length scale below which surface stresses can dominate.
Developing fabric-based electronics with good wearability is undoubtedly an urgent demand for wearable technologies. Although the state-of-the-art fabric-based wearable devices have shown unique ...advantages in the field of e-textiles, further efforts should be made before achieving "electronic clothing" due to the hard challenge of optimally unifying both promising electrical performance and comfortability in single device. Here, we report an all-fiber tribo-ferroelectric synergistic e-textile with outstanding thermal-moisture comfortability. Owing to a tribo-ferroelectric synergistic effect introduced by ferroelectric polymer nanofibers, the maximum peak power density of the e-textile reaches 5.2 W m
under low frequency motion, which is 7 times that of the state-of-the-art breathable triboelectric textiles. Electronic nanofiber materials form hierarchical networks in the e-textile hence lead to moisture wicking, which contributes to outstanding thermal-moisture comfortability of the e-textile. The all-fiber electronics is reliable in complicated real-life situation. Therefore, it is an idea prototypical example for electronic clothing.
•Review of paper-based microfluidics.•Overview of current methods of fabrication.•Applications as diagnostic devices.•Limitations and opportunities.
Paper-based microfluidics is the branch of ...microfluidics involving devices made out of paper, or other porous membranes, that wick fluids by capillary action. Paper-based microfluidic devices have several advantages over conventional microfluidic devices including simpler fabrication, lower cost, easier disposal, and the ability to operate without pumps or other supporting equipment. The most common application of paper-based microfluidic devices is in the development of point-of-care (POC) diagnostic devices, which could eliminate the need for costly and time-consuming laboratory-based analytical procedures. This review provides an overview of current methods of fabricating paper-based microfluidic devices, examples of applications of these devices, a discussion of their current limitations, and an outlook on their future.
This paper presents a literature review and experimental results on the effect of high incorporation levels of fly ash (FA) and recycled concrete aggregates (RCA), individually and jointly, on the ...pore system of concrete that remarkably influences its durability. For that purpose, apart from an extensive literature review, three tests were performed, including electrical resistivity (ER) test, which indirectly measures the interconnected porosity of concrete, and water absorption (WA) by capillarity and immersion tests that both depend on the pores number and size but in a different way. A comparison between the experimental results and the literature is also presented to show the main findings and the research needs. The results show that WA increases and ER decreases with increasing incorporation level of RCA, and the opposite occurs with the addition of FA for both tests. The reduction percentage of WA was higher in mixes with both RCA and FA when compared to the sum of reductions in mixes with only RCA or FA. Thus, it is advisable to produce concrete with both mentioned non-traditional materials in terms of WA and ER of concrete. In addition, the benefit of incorporating of FA and RCA in concrete increased even more when superplasticizers was used.
Smart textile has been an attractive and promising issue in the field of artificial intelligent system. As the critical component of smart textile, the energy storage textiles are tending toward the ...directions of lightweight, portable, wearable and flexible. Developing flexible and wearable supercapacitors (SCs) has become a promising strategy to achieve seamless integration to garment. Herein, the planar flexible all-solid SC model was proposed in our work based on the graphene-and-MnO2-deposited fibrous nonwoven fabric. Graphene nanosheets and MnO2 were deposited on the prepared cellulose nonwoven fabric via capillarity-assisted assembly coating method and in-situ chemical growth method respectively. The assembled graphene/MnO2 SC exhibits good electric conductivity, excellent flexibility, a high specific capacitance of 138.8 mF/cm2, outstanding cycle life and bending properties of remaining 87.6% of the initial capacitance under 180° bending angles for 1000 cycles. The effect of the substrate texture structure (nonwoven and woven structure) was also investigated. To demonstrate the application of our all-solid SC, three devices connected in series could easily light six LED with a logo of “smiling”. The assembled GMNF-SC can be acted the reasonable energy storage candidates for the wearable devices with the seamless integration to garment.
•The hydrophilic cellulose nonwoven fabric is selected as the flexible substrate.•The capillarity-assisted assembly is applied to deposit graphene nanosheets.•The in-situ growth method is applied to deposit MnO2 nanoparticles.•The all-solid SC exhibits good performance due to the big specific area.
Nanometre-scale pores and capillaries have long been studied because of their importance in many natural phenomena and their use in numerous applications. A more recent development is the ability to ...fabricate artificial capillaries with nanometre dimensions, which has enabled new research on molecular transport and led to the emergence of nanofluidics. But surface roughness in particular makes it challenging to produce capillaries with precisely controlled dimensions at this spatial scale. Here we report the fabrication of narrow and smooth capillaries through van der Waals assembly, with atomically flat sheets at the top and bottom separated by spacers made of two-dimensional crystals with a precisely controlled number of layers. We use graphene and its multilayers as archetypal two-dimensional materials to demonstrate this technology, which produces structures that can be viewed as if individual atomic planes had been removed from a bulk crystal to leave behind flat voids of a height chosen with atomic-scale precision. Water transport through the channels, ranging in height from one to several dozen atomic planes, is characterized by unexpectedly fast flow (up to 1 metre per second) that we attribute to high capillary pressures (about 1,000 bar) and large slip lengths. For channels that accommodate only a few layers of water, the flow exhibits a marked enhancement that we associate with an increased structural order in nanoconfined water. Our work opens up an avenue to making capillaries and cavities with sizes tunable to ångström precision, and with permeation properties further controlled through a wide choice of atomically flat materials available for channel walls.
Multiphase flow in porous media is important in many natural and industrial processes, including geologic CO₂ sequestration, enhanced oil recovery, and water infiltration into soil. Although it is ...well known that the wetting properties of porous media can vary drastically depending on the type of media and pore fluids, the effect of wettability on multiphase flow continues to challenge our microscopic and macroscopic descriptions. Here, we study the impact of wettability on viscously unfavorable fluid–fluid displacement in disordered media by means of high-resolution imaging in microfluidic flow cells patterned with vertical posts. By systematically varying the wettability of the flow cell over a wide range of contact angles, we find that increasing the substrate’s affinity to the invading fluid results in more efficient displacement of the defending fluid up to a critical wetting transition, beyond which the trend is reversed. We identify the pore-scale mechanisms—cooperative pore filling (increasing displacement efficiency) and corner flow (decreasing displacement efficiency)—responsible for this macroscale behavior, and show that they rely on the inherent 3D nature of interfacial flows, even in quasi-2D media. Our results demonstrate the powerful control of wettability on multiphase flow in porous media, and show that the markedly different invasion protocols that emerge—from pore filling to postbridging—are determined by physical mechanisms that are missing from current pore-scale and continuum-scale descriptions.
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