Liquid-air Interface Research Articles

Double pattern improves the Schlieren methods for measuring liquid–air interface topography

Double pattern improves the Schlieren methods for measuring liquid–air interface topography

On-Chip Planar Interdigital Micro-Supercapacitors Based on Reduced Graphene Oxide with Superior Rate and Charge-Discharge Capabilities

Reduced graphene oxide (RGO) thin films were prepared on silicon substrates by a modified liquid-air interface self-assembly method and a hydroiodic acid reduction method. Planar on-chip micro-supercapacitors with interdigital structure electrodes (RGO-POMSs) were prepared by photolithography and gold sputtering on the electrode lugs. Area capacitance of interdigital RGO-POMSs was 51.72 μF cm−2. They also had 0.0072 μW h cm−2 of energy density and 59.78 μW cm−2 of power density. Due to the short ion transport path caused by interdigital electrodes, the charge discharge time constant of the device was only 0.029 ms, which could realize rapid charge discharge. In addition, they also had good cycle stability and could maintain 82% capacitance after 4500 cycles of charge and discharge. The cyclic voltammetry test showed that the device still worked well at the ultra-high scan rate of 10,000 V s−1. This showed that RGO-POMSs had considerable prospects in the research field of micro energy storage devices.

Ultrafast response planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots with both ultrahigh power and energy densities

Great results had been achieved in the research of graphene-based planar on-chip micro-supercapacitors. The performances of fabricated micro-supercapacitors had been greatly improved. However, the energy characteristics of graphene-based planar on-chip micro-supercapacitors are generally low due to few active sites of graphene. Nitrogen and oxygen co-doped graphene quantum dots have the nanometer size, more active sites, and rich edge defects, are conducive to ion adsorption and desorption, and can solve the above-mentioned disadvantages of graphene. In this article, all-solid-state planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots with both ultrahigh power and energy densities were fabricated by modified liquid–air interface self-assembly and photolithography for the first time. Planar on-chip electrodes were provided with a nanoscale thickness of 6 nm and an interdigital electrode width of 3 μm. Energy density of 11.49 mWh cm−3, power density of 41.42 W cm−3, and time constant of 3.16 μs were demonstrated. It should be emphasized that the above-mentioned energy density and power density are the highest for the planar on-chip micro-supercapacitors based on nitrogen and oxygen co-doped graphene quantum dots reported to date. The capacitance retention was 99% after 10000 cycles at 5000 V s−1.

All-solid-state planar on-chip micro-supercapacitors with excellent areal power performance at ultrahigh scan rates by photolithography

All-solid-state planar on-chip micro-supercapacitors (MSCs), as a new type of energy storage device, can be well integrated with micro-nano devices and exhibit good practical performance. Nitrogen and oxygen co-doped graphene quantum dots (GQDs), as one of the electrode materials for fabricating supercapacitors, exhibiting novel chemical/physical properties including nanometer-size, abundant edge defects, good conductivity and better surface grafting. In this article, the GQDs film was prepared by modified liquid–air interface self-assembly method and fabricated interdigital electrodes with electrode width and interdigital gap of 6 μm by simple photolithography technology. Electrochemical measurements revealed that the obtained GQDs electrodes for all-solid-state MSCs exhibited the areal power density of up to 0.107 mW cm−2 at the scan rate of 10,000 V s−1 and 95.6% capacitance after charging and discharging for 10,000 cycles. Specially, there was still the ultra-fast charging-discharging time (4.17 μs). The favorable performances make the GQDs film interdigital electrodes prepared by photolithography have good application prospects.

Surface and Calorimetric Behavior of N,N-Dimethylacetamide with n-Alkanols or 2-Alkanols

The surface tension at the liquid–air interface of eight binary mixtures formed by N,N-dimethylacetamide and n-alkanols (from methanol to 1-pentanol) or 2-alkanols (from 2-propanol to 2-pentanol) was studied at three different temperatures (283.15, 298.15, and 313.15 K) and a pressure of 0.1 MPa. Surface tension deviations were also calculated. Moreover, the excess molar enthalpies for all of these mixtures were measured at T = 298.15 K and a pressure of 0.1 MPa. Both deviation and excess functions were correlated with the mole fraction by means of the Redlich–Kister equation. The surface tension deviations are found to be positive for the system containing methanol, sigmoidal for ethanol and negative for the rest of the alkanols. With regard to excess molar enthalpies, negative values are found for the system containing methanol, sigmoidal values for ethanol, and positive values for the rest of the alkanols.

Computing the viscous effect in early-time drop impact dynamics

The impact of a liquid drop on a solid surface involves many intertwined physical effects, and is influenced by drop velocity, surface tension, ambient pressure and liquid viscosity, among others. Experiments by Kolinski et al. (Phys. Rev. Lett., vol. 112, no. 13, 2014b, p. 134501) show that the liquid–air interface begins to deviate away from the solid surface even before contact. They found that the lift-off of the interface starts at a critical time that scales with the square root of the kinematic viscosity of the liquid. To understand this, we study the approach of a liquid drop towards a solid surface in the presence of an intervening gas layer. We take a numerical approach to solve the Navier–Stokes equations for the liquid, coupled to the compressible lubrication equations for the gas, in two dimensions. With this approach, we recover the experimentally captured early time effect of liquid viscosity on the drop impact, but our results show that lift-off time and liquid kinematic viscosity have a more complex dependence than the square-root scaling relationship. We also predict the effect of interfacial tension at the liquid–gas interface on the drop impact, showing that it mediates the lift-off behaviour.

Large-Area Uniaxial-Oriented Growth of Free-Standing Thin Films at the Liquid-Air Interface with Millimeter-Sized Grains.

Manipulating materials at the atomic scale and assembling them into macroscopic structures with controlled dimensionalities and single-crystal quality are grand scientific challenges. Here, we report a general solvent evaporation method to synthesize large-area uniaxial-oriented growth of free-standing thin films at the liquid-air interface. Crystals nucleate at the solution surface and rotate into the same orientation under electrostatic interaction and then merge as large crystals and grow laterally into a large-area uniform thin film with millimeter-sized grains. The lateral dimension is confined only by the size of containers. The film thickness can be tuned by adjusting solvent evaporation rate (R) and solute diffusivity (D), and a characteristic length, , was derived to estimate the film thickness. Molecular dynamic (MD) simulations reveal a concentration spike at the liquid-air interface during fast solvent evaporation, leading to the lateral growth of thin films. The large-area uniaxial oriented films are demonstrated on both inorganic metal halides and hybrid metal halide perovskites. The solvent evaporation approach and the determination of key parameters enabling film thickness prediction are beneficial to the high throughput and scalable production of single crystal-quality thin film materials under controlled evaporation conditions.

Liquid free boundary in vertical gap subject to modulated rotation

The effect of rotation velocity modulation on the equilibrium shape of the liquid-air interface in a vertical slot gap rotating around a horizontal axis is studied experimentally. The case is considered when the modulation frequency coincides with the rotation frequency. It is found that in this case, velocity modulation leads to a violation of the axial symmetry of the interface formed by the centrifugal force of inertia. The displacement of the center of symmetry of the interface increases linearly with the amplitude of the velocity modulation and decreases quadratically with the speed of rotation. It is shown that the detected phenomenon is explained by the averaged effect of an external gravitational field on a fluid in a rotating frame of reference.

CFD based analysis of 3D printed nasopharyngeal swabs for COVID-19 diagnostics

Background and ObjectiveAdditive manufacturing of nasopharyngeal (NP) swabs using 3D printing technology presents a viable alternative to address the immediate shortage problem of standard flock-headed swabs for rapid COVID-19 testing. Recently, several geometrical designs have been proposed for 3D printed NP swabs and their clinical trials are already underway. During clinical testing of the NP swabs, one of the key criteria to compare the efficacy of 3D printed swabs with traditional swabs is the collection efficiency. In this study, we report a numerical framework to investigate the collection efficiency of swabs utilizing the computational fluid dynamics (CFD) approach. MethodsThree-dimensional computational domain comprising of NP swab dipped in the liquid has been considered in this study to mimic the dip test procedure. The volume of fluid (VOF) method has been employed to track the liquid-air interface as the NP swab is pulled out of the liquid. The governing equations of the multiphase model have been solved utilizing finite-volume-based ANSYS Fluent software by imposing appropriate boundary conditions. Taguchi's based design of experiment analysis has also been conducted to evaluate the influence of geometric design parameters on the collection efficiency of NP swabs. The developed model has been validated by comparing the numerically predicted collection efficiency of different 3D printed NP swabs with the experimental findings. ResultsNumerical predictions of the CFD model are in good agreement with the experimental results. It has been found that there prevails huge variability in the collection efficiency of the 3D printed designs of NP swabs available in the literature, ranging from 2 µl to 120 µl. Furthermore, even the smallest alteration in the geometric design parameter of the 3D printed NP swab results in significant changes in the amount of fluid captured. ConclusionsThe proposed framework would assist in quantifying the collection efficiency of the 3D printed designs of NP swabs, rapidly and at a low cost. Moreover, we demonstrate that the developed framework can be extended to optimize the designs of 3D printed swabs to drastically improve the performances of the existing designs and achieve comparable efficacy to that of conventionally manufactured swabs.

High-Resolution and Large-Sensing-Range Liquid-Level Sensor Based on Optical Frequency Domain Reflectometry and No-Core Fiber.

Liquid-level sensors are required in modern industrial and medical fields. Optical liquid-level sensors can solve the safety problems of traditional electrical sensors, which have attracted extensive attention in both academia and industry. We propose a distributed liquid-level sensor based on optical frequency domain reflectometry and with no-core fiber. The sensing mechanism uses optical frequency domain reflectometry to capture the strong reflection of the evanescent field of the no-core fiber at the liquid–air interface. The experimental results show that the proposed method can achieve a high resolution of 0.1 mm, stability of ±15 μm, a relatively large measurement range of 175 mm, and a high signal-to-noise ratio of 30 dB. The sensing length can be extended to 1.25 m with a weakened signal-to-noise ratio of 10 dB. The proposed method has broad development prospects in the field of intelligent industry and extreme environments.

All-solid-state planar on-chip micro-supercapacitors based on reduced graphene oxide with ultrahigh energy characteristics

Planar on-chip micro-supercapacitors are recognized as one of the most competitive energy sources for electronics. Here, we showed ultrahigh performance all-solid-state planar on-chip micro-supercapacitors with photolithographic interdigital electrodes based on modified liquid-air interface self-assembly technique. The electrode width which is narrower than other existing lithography is only on the order of 10° μm (electrode width is 4 μm and the gap width is 4 μm). Planar on-chip micro-supercapacitors prepared with reduced graphene oxide films as electrodes had the energy density of 124.4 mWh cm−3, the corresponding time constant of 2.15 μs and the displayed stack capacitance of 895.74 F cm−3. In addition, it exhibited excellent cycle stability with a capacitance retention of 98.9% after 10,000 cycles. The demonstrated planar on-chip micro-supercapacitors have a good application foreground in the preparation of high-performance integrated micro-devices.

Fabrication and Characterization of Planar on-Chip Micro-Supercapacitors Based on Nitrogen and Oxygen Co-Doped Graphene Quantum Dots by Modified Liquid-Air Interface Self-Assembly Method

Planar micro-supercapacitors stand out among micro/nano energy storage components for their high power, high energy, long life and fast time response. In this paper, all-solid-state planar on-chip micro-supercapacitors with high power characteristics were prepared by modified liquid-air interface self-assembly method, photolithography and sputtering gold. The nitrogen and oxygen co-doped graphene quantum dots electrode films are continuous and uniform, and the surface contains a large number of nitrogen and oxygen chemical bonds and functional groups. The finger width of the supercapacitors is 50 μm, the gap width is 50 μm and a number of electrode fingers is 100. In terms of performance, the supercapacitors had a very short time constant (2.16 μs), high power density (15.80 μW cm−2) and excellent cycle stability (94.5% capacity retention after 10000 cycles).

Designing Self-floating Anisotropic Macroporous Hydrogel by Step Emulsification and Buoyancy-assisted Microfluidics

Macroporous hydrogel with self-floating properties shows promising applications in gastric drug delivery, water purification and air–liquid interface cell culture. Microfluidic bubble templating is an emerging routine to produce macroporous hydrogel. However, current methods are in lack of the control over the anisotropy and porosity. Here, we describe new developments for the buoyancy-assisted microfluidic fabrication of anisotropic hydrogel products by templating from bubbles formed using step emulsification. The step emulsification method generates bubbles with exceptional precision which enables convenient tailoring the internal porosity of the hydrogel particles. Further design over the device structure and the buoyancy during the drop formation produces irregular hydrogel products such as macroporous fibers and core/shell beads. The anisotropic hydrogel beads provide pressure-responsive swimming behaviors and controllable release of the carried cargos. They are proved to be competent as carriers for culture of bronchial epithelial cells on air–liquid interfaces.

In-situ formation of fluorophore cross-linked micellar thick films and usage as drug delivery material for Propranolol HCl

Polyethylene glycol monomethyl ether–block-poly(glycidyl methacrylate)-block-poly[2-(diethylamino)ethyl methacrylate] triblock copolymer was synthesized to prepare self-assembled micron sized films via a novel approach named as “phase separated micellar self assembly method”. Liquid-air interface self assembly method via slow solvent evaporation was used to obtain micellar films. Cross-linking of polymer films was carried out by diffusion of fluorophore cross-linker into polymer solution from subphase. In-situ micellar formation was triggered via driven forces such as molecular interactions and slow evaporation of solvent. Thiazolo[5,4-d]thiazole based cross-linker fluorophores containing alkali subphases were used to prepare highly fluorescent cross-linked micellar films. Micellar morphologies of the films were characterized with SEM while the cross-sections of fluorophore cross-linked films were observed with TEM analysis to examine diffusion of the dye as nano-sized particles into the polymer film. Convenience and usability of the micellar films as drug delivery material were demonstrated with Propranolol HCl release via UV–Vis spectroscopic studies. Optical properties of the films before and after drug release were determined via photoluminescence spectroscopy to be able to sense the completion of the drug release process. Swelling and shrinkage properties of the films were also determined in different pH values. These highly fluorescent polymer films have great potential as drug delivery materials and biomedical sensing applications.

Evaporation of confined droplet between parallel chips with varying gap at room temperature

A theoretical study and experimental validation of the evaporation of a droplet confined between two parallel square chips with a free-standing top chip over a water meniscus is presented in this article. The analytical model describes the surface area of a negatively curved liquid–air interface, and the evaporation model was thus solved for this case. The dynamics of decreasing the gap between the two parallel chips show a linear dependency in time at room temperature. Two main regimes are observed in this case, the constant wetted area regime and the varying wetted area regime. The theoretical study was lastly validated through experiments.

Interfacial Flows and Interfacial Shape Modulation Controlled by the Thermal Action of Light Energy

The review covers the research on thermocapillary convection caused by the thermal action of laser radiation in single-layer and bilayer liquid systems of capillary thickness. The advantages of using optical radiation are the instantaneous delivery of thermal energy to a place on demand (a bulk phase, interfaces); low radiation power required; concentrating heat flux on a spot of a few micrometers; the production of arbitrary spatial distributions of radiation intensity; and, as a result, corresponding thermal fields at a liquid interface and their fast reconfiguration. Thermocapillary stresses at the liquid interfaces lead to the transfer of the liquid and a change in the shape of the interface, in accordance with the distribution of the light-induced thermal field. Studies concerned with the methods of non-destructive testing of liquid media and solids, which are based on a photothermocapillary signal emitted by a laser-induced concave deformation of a thin layer, are considered. Features of thermocapillary deformation of a liquid–air interface caused by local heating of thin and thick (exceeding the capillary length) layers are demonstrated. A part of the review addresses the results of the study of thermocapillary rupture of films in the heating zone and the application of this effect in semiconductor electronics and high-resolution lithography. The works on the light-induced thermocapillary effect in bilayer (multilayer) liquid systems are analyzed, including early works on image recording liquid layer systems, liquid IR transducers, and nonlinear optical media.

Comparative study on distribution characteristics of anionic dispersants in coal water slurry

The anionic dispersants, i.e., sodium lignosulfonate (SLF), naphthalene sulfonate formaldehyde (NSF) and sodium polystyrene sulfonate (PSS), were commonly used to prepare a high concentrated coal water slurry (CWS). In order to reveal the distribution characteristics of the dispersants in CWS system and their adsorption behaviors on coal particle surface, the adsorption experiments, surface tension measurements, contact angle measurements and XPS analysis were conducted in this study. The saturation adsorption amount of dispersants on the coal surface was SLF > NSF > PSS. The fitting results showed that the three anionic dispersants were all monolayer adsorption with a chemical reaction or electron exchange. Surface tension measurements indicated that most SLF molecules were still dissolved in the liquid phase because of the lowest adsorption quantity and packing densities at the liquid-air interface. Contact angle measurements suggested that the hydrophilic groups of the dispersants were stretched to the solution. The adsorbed layer thickness of coal with different dispersants was uniform with the adsorption amount on the coal-liquid interface, which was opposed to the order of the adsorption amount on the liquid-air interface. It was concluded that there were competitive adsorptions between the liquid-air interface and the coal-liquid interface.

Analytical and numerical study of capillary rise in sinusoidal wavy channel: Unveiling the role of interfacial wobbling

Capillary rise is ubiquitous in engineering applications and natural phenomena. In straight channels, the dynamics of capillary rise have been thoroughly investigated and are well understood. However, for nonuniform channels of varying radius, the dynamics remain largely unclear. In this study, the capillary rise in a sinusoidal wavy channel is investigated both analytically and numerically. Specifically, the capillary rate-of-rise of water in sinusoidal channels with different contraction frequencies and amplitudes is derived based on the principle of energy conservation. The change in capillary velocity and height over time is further validated by two-phase flow simulations based on the conservative level-set method. The results reveal a strong viscous dissipation in the interfacial region resulting from the wave-like wobbling motion of the liquid–air interface, constituting more than 50% of the total viscous dissipation when the channel profile changes rapidly. Failing to account for this interfacial effect will result in significant overestimations of the capillary velocity and erroneous predictions of the capillary rise curve, typically more than 4 times difference in the capillary velocity and more than 2.5 times difference in the time taken to arrive at the maximum height.

Adhesion behavior and deposition morphology of cement grout flowing through granular materials

The liquid distribution of unsaturated wet granular media composed of granular materials and Newtonian fluid has been in detail studied. However, when a granular material is mixed with a certain amount of Bingham fluid, the effect of rheological properties of Bingham fluid on the deposition morphologies is not clearly explored. In this study, the adhesion rules of fresh cement grout flowing through granular materials without considering the filtration effect is investigated, and the deposition morphologies of cement grout in random packing of spheres is observed with the help of X-ray microtomography device. The results show that the deposition mechanism of cement grout is significantly dependent on its yield stress. The cement grout spontaneously forms open structures with large liquid–air interface. The morphologies of cement grout within cemented granular materials vary with grout content. With the increase of the yield stress of cement grout, neighbouring smaller clusters gradually touch each other and coalesce into more complex structure, and the largest cluster can contain almost all the cement grout.

Structural Diversity in Multicomponent Nanocrystal Superlattices Comprising Lead Halide Perovskite Nanocubes.

Nanocrystal (NC) self-assembly is a versatile platform for materials engineering at the mesoscale. The NC shape anisotropy leads to structures not observed with spherical NCs. This work presents a broad structural diversity in multicomponent, long-range ordered superlattices (SLs) comprising highly luminescent cubic CsPbBr3 NCs (and FAPbBr3 NCs) coassembled with the spherical, truncated cuboid, and disk-shaped NC building blocks. CsPbBr3 nanocubes combined with Fe3O4 or NaGdF4 spheres and truncated cuboid PbS NCs form binary SLs of six structure types with high packing density; namely, AB2, quasi-ternary ABO3, and ABO6 types as well as previously known NaCl, AlB2, and CuAu types. In these structures, nanocubes preserve orientational coherence. Combining nanocubes with large and thick NaGdF4 nanodisks results in the orthorhombic SL resembling CaC2 structure with pairs of CsPbBr3 NCs on one lattice site. Also, we implement two substrate-free methods of SL formation. Oil-in-oil templated assembly results in the formation of binary supraparticles. Self-assembly at the liquid–air interface from the drying solution cast over the glyceryl triacetate as subphase yields extended thin films of SLs. Collective electronic states arise at low temperatures from the dense, periodic packing of NCs, observed as sharp red-shifted bands at 6 K in the photoluminescence and absorption spectra and persisting up to 200 K.