Narrow Results

For interface-tracking simulation of two-phase flows in various micro-fluidics devices, we examined the applicability of two versions of computational fluid dynamics method, NS-PFM, combining Navier-Stokes equations with phase-field modeling for interface based on the van der Waals-Cahn-Hilliard free-energy theory. Through the numerical simulations, the following major findings were obtained: (1) The first version of NS-PFM gives good predictions of interfacial shapes and motions in an incompressible, isothermal two-phase fluid with high density ratio on solid surface with heterogeneous wettability. (2) The second version successfully captures liquid-vapor motions with heat and mass transfer across interfaces in phase change of a non-ideal fluid around the critical point.

In this paper, the immiscible displacements in the different cavities are studied by the pseudo-potential lattice Boltzmann (LB) model. We first validate the model with a two-dimensional (2D) layered flow, and find that the numerical results agree well with the corresponding analytical solutions. Then, we perform some numerical simulations to study the immiscible displacements in the cavities, and focus on the effects of the surface wettability, capillary number and density ratio on the displacement efficiency. The numerical results show that the displacement efficiency increases with the increase of the capillary number at first and then presents a decrease with the capillary number when it is large enough. The increase of the contact angle θ₁ or decrease of the density ratio increases the displacement efficiency but decreases the critical capillary number. Finally, it is also found that both the size and geometry of cavity have a significant influence on the displacement efficiency.

This paper explores the impact of viscosity ratio and surface wettability on immiscible viscous fingering instability within a rectangular channel. Numerical investigations are conducted across a range of viscosity ratios (VR) from 0.0009 to 0.5 and wall wettability ($\theta$) from 15° to 150°. The volume of fluid (VOF) model is employed to track the development of finger-shaped instability at the fluid interface. Our results indicate that higher viscosity ratios lead to increased displacement efficiency. Additionally, we find the formation of necking at low VR, which diminishes at higher VR values. The finger-shaped pattern splits into two parts at a wettability of 15°; beyond this threshold, no such splitting occurs. Furthermore, a transition from hydrophilic to superhydrophobic wettability abolishes necking, resulting in enhanced displacement efficiency. Notably, as wettability shifts from hydrophilic to super hydrophobic, instability shifts toward the left side. These findings hold relevance for applications in drug delivery, clinical processes and oil recovery.

A new method of bonding diamond to metal with active solder has been developed. This method was then used for making micro-cutting wire saws capable of cutting composite materials with high hardness. This cutting process is an environmentally friendly process, as diamond grains loss and hence pollution is minimum. The active solder contained titanium hydride (TiH₂). Titanium hydride dissociates to atomic Ti and H at high temperatures improving wetting between the solder metal and diamond grains and hence high bonding strength can be obtained. An example of using the new wire for cutting a typical IC chip is given. We believe this environmentally friendly micro-cutting process will be widely used in the future.

The wetting behavior of Ti-78Cu and Ti-50Cu alloys on graphite has been investigated by the sessile drop method in high vacuum. The contact angle of Ti-Cu alloys on graphite is influenced by the wetting temperature. The wetting of Ti-78Cu and Ti-50Cu alloys on graphite is chemical wetting. The microstructure and composition of the interfacial zone of the wetting samples were analyzed by SEM, EDX and XRD. Microstructure and phase analysis reveals that inter-diffusions and interfacial reactions take place in the wetting process. The reaction products include TiC and the intermetallic compounds composed of Ti and Cu. The inter-diffusions and interfacial reactions contribute to the interfacial bonding.

Different time air plasma treatment was conducted on acrylonitrile–butadiene rubber (NBR) surface, the wettability and friction behavior of the samples surface were measured after two months of storage. The changes in surface composition and microstructure during storage process were observed by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), respectively. The results show that the wettability of modified surface has obvious “hydrophobic recovery” phenomenon in the storage process, and the range of contact angle increase is closely related to the plasma treatment time, mainly because the change in surface composition at various time treatment are different during storage; the frictional behavior of plasma-modified NBR surface has not exhibited a “recovery” phenomenon after two months of storage, and the friction coefficient of the surface treated for 4 min and 8 min were even smaller than those before storage, which is due to the smoother and lower roughness of the surface morphology after storage. This study demonstrates that air plasma treatment is a promising technique for improving the wettability and tribological properties of NBR rubber, but the proper treatment time is needed to make the surface have the best wetting and frictional behavior.

A series of Cu–34Mn–6Ni–$x$Sn (wt.%) braze fillers that were used for brazing stainless steel (SS) were prepared. The microstructures, melting temperatures, wettability and mechanical properties of the braze fillers were investigated. An Sn-rich phase was formed in braze fillers with an Sn content above 6 wt.% (including) because of the segregation performance of Sn. The melting temperatures of braze fillers decreased markedly with an increase in Sn content. The addition of 6 wt.% Sn resulted in the highest wettability of braze fillers on the SS. With an increase in Sn content, the tensile strength and hardness increased, whereas the plasticity and toughness of the braze fillers decreased owing to the solid solution and segregation of Sn.

Wettability, porosity and mechanical properties of ultrasonic-aided laser reflow soldering lead-free solder Sn-3.0Ag-0.5Cu (SAC305) on Cu pad have been investigated at ultrasonic vibration (USV) of different power. The parameters of laser reflow soldering are determined by the wetting experiment, and the effects of different ultrasonic powers on the performance of the solder joint are studied. Results showed that USV can improve wettability without keyholes on top of the solder joint, and the contact angle between the solder joint and the substrate decreases first and then increases as the ultrasonic power increases. The cavitation effect caused by USV effectively reduces the porosity of the solder joints. When the ultrasonic power is 225 W, the porosity of the solder joint is reduced from the initial 13.2% to 5.2%. Through X-ray Diffraction (XRD) analysis of the solder joint matrix, all solder joints have diffraction peaks of $\beta$-Sn, Cu₆Sn₅ and Ag₃Sn, and the solder joints show higher diffraction peak intensity with USV treated. Furthermore, the solder joints prepared by ultrasonic-aided laser reflow soldering show better shear strength compared with laser reflow soldering.

Ag–26.7Cu–4.5Ti filler metals with different contents of SiC nanowires were prepared to analyze the effect of SiC nanowires on the microstructures, melting temperature, wettability, shear strength and fracture morphology of brazed joints. The results indicate that a small amount of SiC nanowires ($\le$0.1%) can refine the matrix microstructure and reduce the Cu–Ti intermetallic compounds, which can induce the increase of shear strength of brazed joints with 46.7% maximum amplitude, the ductile pattern is the main fracture mode for Ag–Cu–Ti–1.0 SiC brazed joints. Moreover, the SiC nanowires can improve the spreading are of Ag–Cu–Ti filler metals on steel substrate with a 9.4% increase amplitude, when the content of SiC nanowires is more than 0.1%, the wettability can be reduced obviously. The addition of SiC nanowires can show little effect on the melting temperature, which results in the same brazing temperature for Ag–Cu–Ti–$x$SiC filler metals. With the optimization content of SiC nanowires, the optimal content of SiC is 0.05–0.1%, excessive SiC addition with agglomeration can decrease the wettability and shear strength.

The apparent liquid permeability (ALP) of shale is challenging to be characterized due to complex wettability and nanopore size distribution. The nanopores in organic matter of shale are usually hydrophobic and the nanopores in inorganic matter are hydrophilic. The flow behaviors in these two different nanopores are quite different, and accurately predicting the ALP of shale is difficult. This paper proposes a fractal model for predicting the ALP of shale with dual wettability. The nonflowing boundary layer effect of water in inorganic pores and the slip effect in organic pores are considered, and the equations for describing the flow rate in single organic pore and inorganic pore are derived, respectively. With the assumption of the fractal distributions of organic pores and inorganic pores in shale, the analytical expression for predicting the ALP of shale is derived, and the key parameters influencing shale ALP are analyzed with sensitivity study. The research results show that the nonflowing boundary layer can reduce the ALP of inorganic pores, but slip effect will increase the ALP of organic pores. ALP of inorganic pores is affected by the thickness of nonflowing boundary layer, which is determined by the displacement pressure gradient, fluid viscosity, and pore size distribution. ALP of inorganic pores is more affected by contact angle and pore size distribution.

Lotus-leaf-like amorphous carbon (a-C) films were fabricated on glass and Si substrates by a magnetron sputtering system and fluorinated in carbon tetrafluoride plasma. The fluorinated films (a-C:F) had a maximum contact angle (CA) of about 162°, which is much larger than that of the nonfluorinated films (105°). Furthermore, the geometric microstructure and chemical composition of the a-C:F films were investigated by scanning electron microscopy and Fourier transform infrared spectrometry, respectively. The characterization results indicated that the CA on the surfaces of the a-C:F films can be improved remarkably by the plasma-fluorinated process. Such a-C:F films that combine superhydrophobicity with other properties may have many potential applications.

The adsorption behavior of dodecylamine and its effect on the wettability and corrosion of carbon steel in hydrochloric acid solution were studied. Polarization data suggest that inhibition of carbon steel corrosion is due to geometric blocking effect of adsorbed dodecylamine molecules on the metal surface, which leads to the formation of a monolayer on the metal. Phase images measured by tapping-mode atomic force microscopy (AFM) reveal different properties of the surface with and without various concentrations of dodecylamine. AFM force–distance curves indicate that sample surface exhibits adhesion characteristic after the adsorption of dodecylamine. Contact angle measurements show that dodecylamine reduces surface wettability obviously.

Laser surface melting is known to alter surface energy and wettability of a few engineering materials, but its effect on magnesium alloys has never been reported. Effort was made to study how Nd:YAG laser irradiation influenced surface energy of an AZ91D magnesium alloy. Contact angle measurement was carried out using three types of liquids to make it possible to calculate the surface energy quantitatively based upon the acid–base theory. The laser irradiation was found to enhance surface wettability significantly and lead to a drastic increase in surface energy from 25.82 to 40.78 mJ/m². The change in surface property was attributed to the laser-induced refinement of α-Mg and β-Mg₁₇Al₁₂ phases and enrichment of Al in the microstructure.

In this study, Sn-Ag-Ti ternary alloy has been used as the active solder to braze pure aluminum and graphite in atmospheric conditions using ultrasonic vibration as an aid. The authors studied the formation, composition and decomposition temperature of the surface oxides of the active solder under atmospheric conditions. In addition, the wettability of Sn-5Ag-8Ti active solder on the surface of pure aluminum and graphite has also been studied. The results showed that the major components presented in the surface oxides formed on the Sn-5Ag-8Ti active solder under ambient conditions are TiO, TiO₂, Ti₂O₃, Ti₃O₅ and SnO₂. Apart from AgO and Ag₂O₂, which can be decomposed at the brazing temperature (773 K), other oxides will not be decomposed. The oxide layer comprises composite oxides and it forms a compact layer with a certain thickness to enclose the melted solder, which will prevent the liquid solder from wetting the base metals at the brazing temperature. After ultrasonic vibration, the oxide layer was destroyed and the liquid solder was able to wet and spread out around the base materials. Furthermore, better wettability of the active solder was observed on the surface of graphite and pure aluminum at the brazing temperature of 773–823 K using ultrasonic waves. The ultrasonic wave acts as the dominant driving factor which promotes the wetting and spreading of the liquid solder on the surface of graphite and aluminum to achieve a stable and reliable brazed joint.

This paper describes a simple and economic approach for fabrication of surface wettability gradient on poly(butyl acrylate – methyl methacrylate) [P (BA–MMA)] and poly(butyl acrylate – methyl methacrylate – 2-hydroxyethyl methacrylate) [P (BA–MMA–HEMA)] films. The (meth)acrylate copolymer [including P (BA–MMA) and P (BA–MMA–HEMA)] films are hydrolyzed in an aqueous solution of NaOH and the transformation of surface chemical composition is achieved by hydrolysis in NaOH solution. The gradient wetting properties are generated based on different functional groups on the P (BA–MMA) and P (BA–MMA–HEMA) films. The effects of both the surface chemical and surface topography on wetting of the (meth)acrylate copolymer film are discussed. Surface chemical composition along the materials length is determined by XPS, and surface topography properties of the obtained gradient surfaces are analyzed by FESEM and AFM. Water contact angle system (WCAs) results show that the P (BA–MMA–HEMA) films provide a larger slope of the gradient wetting than P (BA–MMA). Moreover, this work demonstrates that the gradient concentration of chemical composition on the poly(meth) acrylate films is owing to the hydrolysis processes of ester group, and the hydrolysis reactions that have negligible influence on the surface morphology of the poly(meth) acrylate films coated on the glass slide. The gradient wettability surfaces may find broad applications in the field of polymer coating due to the compatibility of (meth) acrylate polymer.

A dynamic test method for the measurement of the underwater sliding properties of model boats has been developed. Surface-modified model boats were examined to assess how the surface wettability properties affect sliding. Along with the surface properties, the influence of the boat shape was considered. We studied various coatings in the contact angle range of 3–162${}^{\circ }$ with two model boat shapes. The hydrophobicity of the surfaces influenced the sliding speed of the model boat depending on the boat shape. The method is applicable to study sliding properties of model boats with different surfaces in variable flow conditions.

In this work, various silver-based thin films were prepared by sputtering method with inclined substrates in the presence of shadowing object. The morphology and structural and optical properties of the prepared thin films were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS), respectively. The wettability of films was investigated by measuring contact angles of the films. The obtained results show that by increasing shadowing effect, a decrease in contact angle of the prepared samples is observed. Bruggeman homogenization simulation method was applied to describe the film structures. The theoretical part and simulation using Bruggeman homogenization confirm the experimental findings and show the best possible agreements. Finally, an increase in contact angle of the prepared thin films with high porosity and high surface roughness was observed. In films with silver–silver oxide compositions, the higher contribution of oxide part in the structure of the films leads to the hydrophilicity of the surface.

In the present paper, the surface modification of low-density polyethylene (LDPE) polymer is done by plasma-etching to tune its surface structure, wettability and optical behavior to make it useful for technical applications. For this purpose, two gasses (N${}_2)$ and (O${}_2)$ are used as the discharge precursors in a home-built plasma reactor. The plasma-treated LDPE surface etch-rate (control other surface properties) is high at the beginning and slows down as the treatment time increases due to surface restructuring. The etched surfaces are analyzed by scanning electron microscopy (SEM), which indicate greater surface changes due to O₂ plasma compared to that of N₂. Also, the surface hardness is slightly low at the first treatment time and increases rapidly at higher exposure durations. Besides, the friction coefficient is significantly changed by plasma treatment, suggesting the formation of cohesive surface skin. The obtained X-ray diffraction (XRD) patterns show that the plasma-treated LDPE samples suffer disordering and structural changes which increase with raising the treatment duration. Surface restructuring is attributed to the combined effects of active species (from plasma) bombardments and surface oxidation. Also, the surface chemistry changes are evaluated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy which reveals chain scission after N₂ plasma treatment. Whereas, the O₂ plasma-treated samples suffer surface oxidation and formation of polar groups which offer some surface oxidation coatings. Furthermore, the surface wettability has been determined by the sessile drop method and shows enhancement upon plasma treatment due to the combined influence of surface chemistry and morphology. Also, the surface free energy (SFE) and adhesion are found to increase with the plasma exposure time due to surface activation. The optical behavior of LDPE is studied using ultraviolet–visible (UV–Vis) spectrophotometer which indicates that the optical bandgap performance depends on the amorphous or crystalline nature of the polymer. Also, the conjugated carbon atoms were examined and correlated to the reduced bandgap. In conclusion, the studied home-built glow discharge plasma reactor could be utilized efficiently to tune polymer surface properties to be used in high technology applications.

Surface roughness and wettability, which characterize the texture formed on the implant surface, are critical features for the functionality of the implant. Laser texturing is a promising processing method because of the advantages it provides in creating a particular surface topography on the surface of a metallic implant material with a nanosecond pulsed laser beam. Different experimental combinations were created using a fiber pulsed marking device on the surface of AISI 316LVM implant material using the hatch strategy; textures depending on the scan speed, frequency, and hatch distance were created on the surface. The surface roughness and wettability evaluated the effects of parameters on the texture form. Based on the experimental and statistical results, while the scan speed was the most significant parameter affecting the wettability behavior and surface roughness, the hatch strategy and frequency also affected the surface roughness to some extent. Many textured surfaces showed super-hydrophilic behavior with a contact angle of $0^{\circ }$. It has been determined that surface textures with the same or close roughness values did not exhibit the same wettability behavior. The lowest surface roughness of 2 $\mu$m with a $132^{\circ }$ contact angle was obtained at a hatch strategy of $0^{\circ }$/$90^{\circ }$, a scan speed of 900 mm/s, a frequency of 100 kHz, and a hatch distance of 0.03 mm. Three-dimensional surface images show that while many craters formed the surface textures, overlapping consecutive beams and hatch strategies significantly affected the surface topography.

The surface microstructure and wettability of Al-1.0 at.% Cr alloy films obtained by ion-beam-assisted deposition on glass substrates have been investigated using atomic force microscopy, scanning electron microscopy and the sessile drop method. In the passive deposition regime, the surface roughness of the films increased from 8.9nm to 21.6nm with an increase in coating time from 3h to 9h. A quantitative analysis of the morphology evolution of the films during their growth was performed. The results revealed that Al-1.0 at.% Cr alloy films are hydrophilic. The mechanism of heterogeneous water wetting of Al-1.0 at.% Cr alloy films was considered, when the increasing surface roughness accounts for a decrease of hydrophilicity.