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Partial filling of mixed ferrite (Ni0.5Zn0.5Fe2O4; NZFO) nanoparticles into the amorphous carbon nanotubes (aCNTs) cavity is achieved by simple mixing of the aqueous dispersions of the two (aCNTs and NZFO) at room temperature. The process of incorporation of the nanoparticles into the aCNT cavity is solely mediated by the capillary action of the liquid. NZFO nanoparticles were homogeneously dispersed in the aqueous solution but after mixing they are sparsely distributed into the aCNT channel as a result of the capillary action. The encapsulation of the nanoparticles into the aCNTs amorphous shield was established by means of X-ray diffraction, transmission electron microscopy, Fourier transformed infrared spectroscopy, and Raman spectroscopic analysis. Such entrapment of the nanoparticles causes the composite nanotubes superparamagnetic in nature with blocking temperature (T B) at 15 K. However, compared to the powder NZFO nanoparticles, T B appears more sharply and at relatively lower temperature. Low filling density and the spatial confinement of the nanoparticles lessen the inter-particle interactions and the polydispersity within the NZFO nanoparticles which are manifested in their altered magnetic behavior.

The authors prove the existence and the linear stability of small amplitude time quasi-periodic standing wave solutions (i.e. periodic and even in the space variable x) of a 2-dimensional ocean with infinite depth under the action of gravity and surface tension. Such an existence result is obtained for all the values of the surface tension belonging to a Borel set of asymptotically full Lebesgue measure.

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. The physical principles of capillarity, including how capillary forces can influence biological processes, are discussed.

Soft materials that are subjected to large deformations exhibit an extremely rich phenomenology, with properties lying in between those of simple fluids and those of elastic solids. In the continuum description of these systems, one typically follows either the route of solid mechanics (Lagrangian description) or the route of fluid mechanics (Eulerian description). The purpose of this review is to highlight the relationship between the theories of viscoelasticity and of elasticity, and to leverage this connection in contemporary soft matter problems. We review the principles governing models for viscoelastic liquids, for example solutions of flexible polymers. Such materials are characterized by a relaxation time λ, over which stresses relax. We recall the kinematics and elastic response of large deformations, and show which polymer models do (and which do not) correspond to a nonlinear elastic solid in the limit λ → ∞. With this insight, we split the work done by elastic stresses into reversible and dissipative parts, and establish the general form of the conservation law for the total energy. The elastic correspondence can offer an insightful tool for a broad class of problems; as an illustration, we show how the presence or absence of an elastic limit determines the fate of an elastic thread during capillary instability.

We consider the full irrotational water waves system with surface tension and no gravity in dimension two (the capillary waves system), and prove global regularity and modified scattering for suitably small and localized perturbations of a flat interface. An important point of our analysis is to develop a sufficiently robust method, based on energy estimates and dispersive analysis, which allows us to deal simultaneously with strong singularities arising from time resonances in the applications of the normal form method and with nonlinear scattering. As a result, we are able to consider a suitable class of perturbations with finite energy, but no other momentum conditions. Part of our analysis relies on a new treatment of the Dirichlet-Neumann operator in dimension two which is of independent interest. As a consequence, the results in this paper are self-contained.

The manipulation of small amounts of liquids has applications ranging from biomedical devices to liquid transfer. Direct light-driven manipulation of liquids, especially when triggered by light-induced capillary forces, is of particular interest because light can provide contactless spatial and temporal control. However, existing light-driven technologies suffer from an inherent limitation in that liquid motion is strongly resisted by the effect of contact-line pinning. Here we report a strategy to manipulate fluid slugs by photo-induced asymmetric deformation of tubular microactuators, which induces capillary forces for liquid propulsion. Microactuators with various shapes (straight, ‘Y’-shaped, serpentine and helical) are fabricated from a mechanically robust linear liquid crystal polymer. These microactuators are able to exert photocontrol of a wide diversity of liquids over a long distance with controllable velocity and direction, and hence to mix multiphase liquids, to combine liquids and even to make liquids run uphill. We anticipate that this photodeformable microactuator will find use in micro-reactors, in laboratory-on-a-chip settings and in micro-optomechanical systems. A light-actuated liquid crystal polymer material system precisely manipulates liquid drops through capillary forces, and can be formed into a variety of shapes. Light-controlled manipulation of liquid movement Liquid droplets confined within a conical capillary tube — for instance in a microfluidic device — will travel spontaneously towards the narrower end, owing to differences in curvature pressure at either end of the droplet. Now, Yanlei Yu and colleagues have designed a tubular, light-actuated, liquid crystal polymer system that can induce such asymmetric morphologies to reversibly manipulate liquid drops through capillary forces. This method of light-controlled liquid movement does not suffer from contact-line pinning, and is shown to work with a range of liquids and mixtures to achieve propulsion with controllable velocity and direction, and mixing of multiphase liquids through microactuators of various shapes (straight, 'Y'-shaped, serpentine and helical).

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 equation 5 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. In the tiniest of capillaries, barely larger than a water molecule, condensation is surprisingly predictable from the macroscopic Kelvin condensation equation, a coincidence partially owing to elastic deformation of the capillary walls.

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.

The urgency of addressing water scarcity and exponential population rise has necessitated the use of sustainable desalination for clean water production, while conventional thermal desalination processes consume fossil fuel with brine rejection. As a promising solution to sustainable solar thermal distillation, we report a scalable mangrove-mimicked device for direct solar vapor generation and passive salt collection without brine discharge. Capillarity-driven salty water supply and continuous vapor generation are ensured by anti-corrosion porous wicking stem and multi-layer leaves, which are made of low-cost superhydrophilic nanostructured titanium meshes. Precipitated salt at the leaf edge forms porous patch during daytime evaporation and get peeled by gravity during night when saline water rewets the leaves, and these salt patches can enhance vaporization by 1.6 times as indicated by our findings. The proposed solar vapor generator achieves a stable photothermal efficiency around 94% under one sun when treating synthetic seawater with a salinity of 3.5 wt.%. Under outdoor conditions, it can produce 2.2 L m −2 of freshwater per day from real seawater, which is sufficient for individual drinking needs. This kind of biomimetic solar distillation devices have demonstrated great capability in clean water production and passive salt collection to tackle global water and environmental challenges. Conventional desalination processes generate clean water and reject brine to sea, which is harmful to the aquatic life. Here, the authors propose a low- cost scalable and foldable mangrove-mimetic device for solar thermal distillation and passive salt collection without brine discharge.

Nanometre-scale graphitic capillaries with atomically flat walls are engineered and studied, revealing unexpectedly fast transport of liquid water through channels that accommodate only a few layers of water. Tunable nanometre-sized capillaries Artificial nanometre-sized capillaries have enabled new research and led to the emergence of nanofluidics, but surface roughness in particular makes it very challenging to exactly control their dimensions. Andre Geim and colleagues now show that van der Waals assembly can produce narrow and smooth capillaries that have atomically flat top and bottom graphite sheets, separated by spacers made from a precisely controlled number of graphene layers. Water transport through the channels, which range in height from a single atomic plane to dozens of them, is unexpectedly fast and speeds up further in channels that accommodate only a few layers of water. The fabrication method is expected to give access to a wide range of capillaries with atomically precise sizes, and with permeation properties that are tunable by the choice of two-dimensional material used for creating the channel walls. Nanometre-scale pores and capillaries have long been studied because of their importance in many natural phenomena and their use in numerous applications 1 . 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 2 , 3 , 4 . 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 5 , with atomically flat sheets at the top and bottom separated by spacers made of two-dimensional crystals 6 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.