Wetting Liquid Research Articles

Size matching effect on Wenzel wetting on fractal surfaces

Abstract Materials with fractal structures may show distinct features of wetting. Here we report the characteristics of wetting of liquid caps on fractal surfaces in the Wenzel wetting regime. It shows that the relationship between the apparent and Young’s contact angles is associated with the size-matching degree or discrepancy between the liquid caps and substrate. An explicitly fractal-dimension-and size-related equation is developed to bridge over the apparent contact angle and the Young’s contact angle, and validated by the experimental results of water wetting on nanostructured fractal surfaces reported in the literature. The features of the Wenzel wetting of liquid caps on fractal surfaces are also discussed. This work enables us to understand the wetting regimes on fractal surfaces, and may pave a path for the rational uses of fractal structures to control liquid wetting.

Wettability of coal by room temperature ionic liquids

ABSTRACT The wettability of room temperature ionic liquids (ILs) on coal structure was studied by measuring contact angle, water-retaining property, and FTIR spectra. The eight ILs utilized were [EMIm][BF4], [EMIm][NTf2], [PMIm][BF4], [BMIm][BF4], [HOEtMIm][BF4], [HOEtMIm][NTf2], [P4,4,4,1][MeSO4] and [P4,4,4,2][DEP]. The contact angle results showed that compared with distilled water, the contact angles of ILs decreased, indicating good wetting effect. However, different ILs showed different wetting effects. Among of them, the [HOEtMIm][NTf2] had the best wetting effect, the [P4,4,4,2][DEP] and [P4,4,4,1][MeSO4] were in the second place, and the worst one was [HOEtMIm][BF4]. The water-retaining experiments showed that the evaporation rate of coal containing ILs was slower and the water-retaining time was longer, indicating that the coal containing ILs had stronger resistance to moisture evaporation. The water-retaining property of [EMIm][BF4] was the best. The FTIR experiments showed that the main structure of coal was not changed but some structures changed by ILs treatment. The significant changes were the aliphatic hydrogen groups (1435 and 1371 cm−1), the C-O bond (1300–1000 cm−1) and the mineral structures (1032 and 472 cm−1). This study will provide a new development platform for the ILs used for coal dust prevention.

Inverse Opal Photonic Crystals as an Optofluidic Platform for Fast Analysis of Hydrocarbon Mixtures.

Most of the reported optofluidic devices analyze liquid by measuring its refractive index. Recently, the wettability of liquid on various substrates has also been used as a key sensing parameter in optofluidic sensors. However, the above-mentioned techniques face challenges in the analysis of the relative concentration of components in an alkane hydrocarbon mixture, as both refractive indices and wettabilities of alkane hydrocarbons are very close. Here, we propose to apply volatility of liquid as the key sensing parameter, correlate it to the optical property of liquid inside inverse opal photonic crystals, and construct powerful optofluidic sensors for alkane hydrocarbon identification and analysis. We have demonstrated that via evaporation of hydrocarbons inside the periodic structure of inverse opal photonic crystals and observation of their reflection spectra, an inverse opal film could be used as a fast-response optofluidic sensor to accurately differentiate pure hydrocarbon liquids and relative concentrations of their binary and ternary mixtures in tens of seconds. In these 3D photonic crystals, pure chemicals with different volatilities would have different evaporation rates and can be easily identified via the total drying time. For multicomponent mixtures, the same strategy is applied to determine the relative concentration of each component simply by measuring drying time under different temperatures. Using this optofluidic sensing platform, we have determined the relative concentrations of ternary hydrocarbon mixtures with the difference of only one carbon between alkane hydrocarbons, which is a big step toward detailed hydrocarbon analysis for practical use.

Study on the thermal stability of the NdBCO film in inducing the growth of REBa2Cu3Ox/Ag superconductor bulks

The NdBCO-film is a prominent seed in melt-growth of REBa2Cu3Ox (REBCO, RE = rear earth element) cryomagnets because of its extremely high thermal stability (TS), which, however evidently degraded, when Ag was added into NdBCO for improving its brittle nature, leading to fabrication failure. Here we clarified that film TS is caused by high wettability of the Ag-added liquid, governed by precursor composition of REBCO/Ag. We developed a novel film-seed/buffer-pellet/main-pellet construction to effectively strengthen film TS via wetting modification by exploiting Ba-rich buffer-pellets, and succeeded in growing high superconductivity NdBCO/Ag bulks. This new conception is broadly applicable for producing all REBCO/Ag cryomagnets.

Mechanoresponsive Tuning of Anisotropic Wetting on Hierarchically Structured Patterns

Here, we propose a simple mechanoresponsive system on patterned soft surfaces to manipulate both anisotropy and orientation of liquid wetting. On the poly(dimethylsiloxane) embedding line patterned structures, additional topographies, such as wrinkles and cracks, can be provided by applying compressive and tensile stress, respectively. This tunable hierarchy of structures with the different scales and directions of lines, wrinkles, and cracks allow the mechanoresponsive control of anisotropic wetting in a single platform. In addition, the wetting behavior on those surfaces is precisely investigated based on the concept of critical contact angle to overcome the ridges in a step flow.

An analysis on heterogeneous bubble nucleation around a nanoparticle based on density functional approach

Density functional analyses are performed to study bubble nucleation around a nanoparticle submerged in a supersaturated LJ/s fluid in this paper. Two heterogeneous nucleation modes, i.e. core-shell mode and spherical cap mode, are considered. The minimal free energy path (MFEP) of these two nucleation modes are obtained. Effects of particle wettability and supersaturation of the bulk liquid on heterogeneous nucleation are studied. It is found that the energy barrier of the spherical cap mode nucleation is lower than that of core-shell mode nucleation. However, the difference between energy barriers of the two heterogeneous nucleation modes approaches zero when the particle becomes strongly solvophobic. The disappearance of nucleation barrier is observed for strongly solvophobic particles at high supersaturation.

A two-angle model of dynamic wetting in microscale capillaries under low capillary numbers with experiments

ObjectivesAn accurate model of the dynamic contact angle θd is critical for the calculation of capillary force in applications like enhanced oil recovery, where the capillary number Ca ranges from 10−10 to 10−5 and the Bond number Bo is less than 10−4. The rate-dependence of the dynamic contact angle under such conditions remains blurred, and is the main target of this study. ExperimentsFeaturing with pressure control and interface tracking, the innovative experimental system presented in this work achieves the desired ranges of Ca and Bo, and enables the direct optical measurement of dynamic contact angles in capillaries as tiny as 40 × 20 (width × height) μm and 80 × 20 μm. The advancing and receding processes of wetting and nonwetting liquids were tested. FindingsThe dynamic contact angle was confirmed velocity-independent with 10−9 < Ca < 10−5 (contact line velocity V = 0.135–490 μm/s) and it can be described by a two-angle model with desirable accuracy. A modified two-angle model was developed and an empirical form was obtained from experiments. For different liquids contacting the same surface, the advancing angle θadv approximately equals the static contact angle θo. The receding angle θrec was found to be a linear function of θadv, in good agreement with our and other experiments from the literature.

Polymer-functionalized nanoparticles for improving oil displacement

This work focuses on the synthesis, functionalization, and characterization of magnetic nanoparticles to be used for improving the oil recovery in the oil exploitation industry. In this manuscript we explore three different types of hydrophobic/hydrophilic functionalization through a silanized particle: with styrene, with acrylic acid and with a copolymer of styrene and maleic acid. Further application of such nanoparticles dispersions (nanofluid) are discussed as the wetting and spreading behaviour of liquids on the solid surfaces change if the wettability of solid surface is altered. In order to investigate the influence of wettability alternation on enhancing oil recovery after nanofluid treatment, flushing oil experiment and contact angle measurement were conducted in our laboratory. The results indicated that nanofluid can produce a better flushing efficiency compared with brine solution, and the contact angles of oil phase increased from 13° to 37° after nanofluid treatment (0.005% w/w). We focus on the synthesis of magnetic iron oxide nanoparticles considering recovering possibility.

Tailoring surface wettability of TZP bioceramics by UV picosecond laser micro-fabrication

Controlled wettability of liquids on bioceramic surfaces has recently received widespread attention. Here, tunable wettability of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP, 3 mol% yttria) bioceramic surface was achieved by ultrafast laser micro-fabrication. Two surface microstructures, arc grooves and square pillar arrays, were designed based on the Wenzel and Cassie model, and then fabricated by 355 nm picosecond laser with high controllability and quality. The contact angle of the treated surface was tunable from superhydrophilicity (10°) to hydrophobicity (133°) by changing the microstructure characteristics with laser processing. The microstructures with uniform size, crack-free, smooth edges and alleviated taper were achieved. In addition, the laser-treated Y-TZP ceramic surfaces were biocompatible for cell adhesion and growth. The range of the optimized parameters was also determined based on the study of the interaction of the laser with the Y-TZP ceramics.

A terahertz transmission imaging based approach for liquid alcohol wettability investigation

By using terahertz time-domain spectroscopy (THz-TDS), the transmission spectral images of a series of aliphatic monohydric liquid alcohols were investigated in this work. The image gray value indicated the non-uniform distribution of the liquid. After noise reduction, the depth distribution was computed from the image content, which depended on the wettability of the container surface by the liquid. Then the volume of the liquid crept up to the container surface was compared quantitatively. Our result showed that the surface wettability of the PS container surface by the liquids increased with the alcohol alkyl chain increasing, which was verified by the contact angle of the liquid and the surface. The study indicated that the THz image might offer a potential technique for detecting the wettability of liquid directly without an additional contact angle experiment.

Wettability and morphology of liquid gallium on graphene surface

Liquid gallium and its alloy with low melting point, low toxic and high electrical conductivity are used extensively in burgeoning microfluidic and flexible electronic devices. The key to producing these devices is to effectively control the wettability and morphology of liquid metal on the solid interface in different manufacturing processes. Based on the Lennard-Jones (L-J) potential describing the solid-liquid interaction, the wettabilities of liquid gallium film on the smooth and rough graphene surfaces are effectively investigated by molecular dynamics simulation which is an available and powerful option in this field. Different regimes of wetting are discovered by changing the depth of the L-J potential, and the stable contact angle increases with Ga-C potential depth decreases. The results show that the equilibrium contact angle and the retraction velocity increase with the decrease of the L-J potential between the gallium and graphene, showing that some properties change from complete wetting to hydrophilic and to hydrophobic. The L-J potential depth obtained from the simulation results can be effectively employed to describe the interaction between the liquid gallium and the substrate because the resulting wetting angle is extremely close to the experimental value. When employing the most appropriate L-J potential, it is found that although the initial retraction velocity increases with the proportional decrease of the thickness of the liquid Ga film, there are a few of differences in equilibrium contact angle and final retraction velocity in virtue of the competition between the surface tension of the Ga film and Ga-C interaction. It means that for the wetting state the film thickness is not the crux for changing the equilibrium contact angle and retraction velocity based on a similar conversion of potential energy into kinetic energy. Finally, we investigate the effects of the L-J potential on three rough surfaces which are patterned into three types of nanopillars with different top morphologies respectively. Specifically, it is shown that in spite of similar surface roughness, the wetting morphologies of liquid gallium deposited on various nano-textured graphene surfaces range from hydrophobic to dewetting state, suggesting that not only the roughness but also the morphology of surface can exert an available influence on the wettability of liquid. The wetting transition between the wetting and dewetting state can be achieved dynamically by adjusting the morphologies of nanopillars involved although we still need to go into more detail on the configurable way to fulfill the changing requirements.

Short timescale wetting and penetration on porous sheets measured with ultrasound, direct absorption and contact angle.

In this study the short timescale penetration and spreading of liquids on porous sheets is investigated. Three measurement techniques are evaluated: ultrasonic liquid penetration measurement (ULP), contact angle measurement (CA) and scanning absorptiometry (SA). With each of these techniques liquid penetration as well as surface wetting can be measured. A quantitative comparison between the methods is carried out. For our studies we are using model liquids with tuneable surface tension, viscosity and surface energy which are the governing parameters for pore flow according to the Lucas–Washburn equation. Scanning absorptiometry turns out to be an adequate tool for direct measurement for liquid penetration. Ultrasonic liquid penetration showed a stable correlation (R2 = 0.70) to SA and thus also gives a suitable indication on the liquid penetration behaviour. Absorption of individual microliter drops measured in the CA instrument showed different results than the other two measurements. For characterisation of the wetting behaviour the measurement techniques gave substantially different results. We thus conclude that ULP and SA do not capture the wetting behaviour of liquids on paper in the same way as conventional contact angle measurement, it is unclear if their results are meaningful. Finally we are proposing two parameters indicating a combination of liquid penetration and wetting, the slope of the contact angle over time dθ/dt and a contact angle calculated from SA. These two parameters are moderately correlated, supporting the idea that they are indeed capturing a combination of liquid penetration and wetting. While our investigations are restricted to paper, we believe that the methods investigated here are generally applicable to study liquid absorption in thin porous media like microfluidic paper based analytical devices, thin porous storage media, membranes and the like. Our findings are highlighting the importance to have a match in timescale (time for penetration and wetting) and size scale (liquid amount supplied) between the testing method and the actual use case of the material, when analyzing wetting and penetration on porous materials.

Dynamic wetting of imidazolium-based ionic liquids on gold and glass.

Many of the applications of ionic liquids rely on their bulk properties or their solvation abilities. However, it is their interactions with solid surfaces that underpin many of their potential applications in advanced technologies. Whether it is as lubricants for wind turbines or as electrolytes in supercapacitors, there are many areas where ionic liquids can provide an improvement in performance relative to more commonplace liquids. However, there are some barriers to their implementation in such applications. Foremost of these is the lack of systematic studies of their interactions with solid surfaces as well as neglecting the effect of the absorbed water on wetting. The present study explores the dynamic wetting of three ionic liquids (with a different length of hydrocarbon chain in the cation) on gold and glass substrates, both of which are relevant for nano- and micromechanical machine applications, under well-controlled environmental conditions. The form of data capture (Wilhelmy plate) allows for a direct analysis using analytical expressions for the two dominant approaches for dynamic wetting: the hydrodynamic and molecular kinetic models. All ionic liquids yield data that are described best by the molecular kinetic model. Substrate-ionic liquid and water-ionic liquid interactions contribute to the mechanisms involved in the wetting process.

Characterization of Novel Carbon Foam Corrugated Structured Packings with Varied Corrugation Angle

AbstractCarbon foam was utilized to develop corrugated structured packing in distillation for the first time. The hydrodynamics and mass transfer performance of CFP‐400X and CFP‐500W with 60 and 75° corrugation angle were determined by total reflux experiments. The results indicate that increasing the corrugation angle will improve the capacity but decrease the mass transfer efficiency. Comparisons among CFP‐400X, SCFP‐500X, BX‐500, and B1‐500X were made with respect to the performance of hydrodynamics and mass transfer. CFP‐400X shows advantages in terms of capacity and efficiency compared with the other two metal packings. SCFP‐500X exhibits a higher mass transfer efficiency than CFP‐400X because of its superior wettability of test liquid which is supported by the liquid flow behavior experiment.

A study on heat transfer characteristics of inclined copper sintered wick heat pipe using surfactant free CuO and Al 2 O 3 nanofluids

In this study, the experimental investigation is conducted on the heat transfer characteristics of inclined copper sintered wick heat pipes using surfactant free CuO and Al2O3 nanofluids. The morphology and size of CuO and Al2O3 nanoparticles kept remains same as well as the effects of mass concentrations at an optimum inclination angle of 45° are studied. Interestingly, the addition of nanoparticles in a base fluid reduces the difference between the surface and vapour temperature of the heat pipe. The thermal resistance of the heat pipe has showed a decreasing trend with the inclusion of nanoparticles and their concentration. The reduction in thermal resistance is achieved viz. 20.13%, 49.64% and 28.22%, for CuO nanofluids and 14.55%, 26.07% and 39.67% for Al2O3 nanofluids respectively. The overall thermal conductivity of heat pipe has produced a maximum value of 584.23 W/m°C for CuO nanofluid heat pipe at 1.0 wt.% with 45° inclination. The heat pipe is operated with DI water which produced only 69.08 W/m°C. The thermal efficiency of the heat pipe filled with CuO nanofluid has obtained the maximum performance of 30.42% at the optimum weight fraction of 1.0 wt.%, whereas Al2O3 nanofluid heat pipe reaches its maximum value of 26.17% for the mass concentration of 1.5 wt.%. The thermal performance of heat pipe is enhanced through the addition of nanoparticles which reduced the surface tension of working fluid. Due to this process the solid–liquid wettability has increased. The inclination of the heat pipe has improved the higher on-set of liquid film over the condenser surface area as well as will increase the rate of heat removal in the condenser section.

Membranes for Continuous Nonenergized Air Freshener Perfume Delivery

Membrane-based liquid air fresheners are attracting significant market interest because of their small size and ability to allow continuous delivery of perfume compounds without the need of external energy sources. However, the air freshener membranes that enable the nonenergized delivery are rarely reported in the literature except in patents. For the first time, we investigated a commercial air freshener membrane systematically to provide thorough characterizations of the membrane materials, morphology, and pore information. The interaction between a model perfume containing four compounds and the membrane was also studied through liquid wetting and contact angle measurements. Long-term tests to track the air freshener revealed that the perfume release rate was dependent on the perfume reservoir composition in a controlled external environment. Lastly, perfume transport through the membrane was investigated for the correlation of membrane properties and liquid flux through the membrane. This pioneering ...

Sol–gel deposition of silica nanospheres onto polymeric separators for improved performance of Li-ion batteries

Abstract This work presents an efficient sol–gel method to coat SiO 2 nanopheres onto tri-layered polymeric separators for Li-ion batteries, consisting of Li 4 Ti 5 O 12 (LTO) anode/Li cathode. The surface density of silica nanospheres with diameter of 300–500 nm is chosen as controlling factor in affecting the electrochemical performance and thermal stability of Li-ion batteries. The SiO 2 deposition on the polymeric separators exhibits not only an enhanced thermal and dimensional stability but also an improved rate capability and inner resistance. The excellent performance originates from the formation of robust skeleton to stabilize the separators, allowing a superior insulation and mass transport barrier against volatile compounds generated during thermal decomposition process. An appropriate amount of SiO 2 nanospheres still features a highly porous structure, imparting favorable liquid wettability, high mass uptake of electrolyte, and superior ionic conductivity. Accordingly, the sol–gel deposition method is believed to attract interests for applications in Li-ion batteries due to its simplicity, effectiveness, and multi-functionality.

Measurement of contact angles at room temperature in high magnetic field.

The contact angle (CA) goniometer adaptable to a superconducting magnet was developed based on the sessile drop method. The goniometer mainly consisted of the sampling system, the supporting system, and the image acquisition system. Some improvements were taken to avoid the effects of the magnetic field (MF) on the CA measurement. As an example, the CAs of water on two substrates of silica and polymethyl methacrylate (PMMA) were measured using the goniometer. The results with and without a MF showed a good repeatability and reliability. Additionally, the MF was found to reduce the CA of water, which probably stemmed from the change of the surface tension in the MF. The CA goniometer will become an important tool which is used to study the wettability of liquids on a solid in the MF.

External-Field-Induced Gradient Wetting for Controllable Liquid Transport: From Movement on the Surface to Penetration into the Surface.

External-field-responsive liquid transport has received extensive research interest owing to its important applications in microfluidic devices, biological medical, liquid printing, separation, and so forth. To realize different levels of liquid transport on surfaces, the balance of the dynamic competing processes of gradient wetting and dewetting should be controlled to achieve good directionality, confined range, and selectivity of liquid wetting. Here, the recent progress in external-field-induced gradient wetting is summarized for controllable liquid transport from movement on the surface to penetration into the surface, particularly for liquid motion on, patterned wetting into, and permeation through films on superwetting surfaces with external field cooperation (e.g., light, electric fields, magnetic fields, temperature, pH, gas, solvent, and their combinations). The selected topics of external-field-induced liquid transport on the different levels of surfaces include directional liquid motion on the surface based on the wettability gradient under an external field, partial entry of a liquid into the surface to achieve patterned surface wettability for printing, and liquid-selective permeation of the film for separation. The future prospects of external-field-responsive liquid transport are also discussed.

Thermoresponsive Mobile Interfaces with Switchable Wettability, Optical Properties, and Penetrability.

Liquid-based mobile interfaces, in which liquids are being utilized as structural long-term components, have shown their multifunctionality in materials science, such as the hydration layer of polyelectrolyte brushes used for artificial implants, stabilized lubricants for antibiofouling, anti-icing, self-cleaning, optical control, and so forth. However, these currently available systems do not usually show a response to environmental stimuli. Here, we describe a strategy for preparing thermoresponsive mobile interfaces made from novel silicone-based lubricants that display lower critical solution temperature and demonstrate their capabilities on controlling in situ water wetting and dewetting, thermo-gating penetration, and optical properties. These properties allow the mobile films to form a kind of erasable recording platforms. We foresee diverse applications in liquid transport, wetting and adhesion control, and transport switching.