Narrow Results

Pool boiling from a super-water-repellent (SWR) and polytetrafluoroethylene (PTFE) surface with checkered and spotted patterns has been studied experimentally. The heat transfer surfaces are copper with the SWR coating of checkered and spotted patterns and TiO₂-coated surface with PTFE spotted patterns. The domain of SWR and PTFE acts as nucleation sites and, therefore, bubble nucleation starts at very low superheating. In lower heat flux, bubbles with uniform size are generated on the SWR or PTFE domain of the heat transfer surface. These bubbles depart from the heat transfer surface when the contact line reaches the boundary of SWR or PTFE domain. Nucleate boiling with this surface was enhanced by seven times compared with the normal copper surface. The best was the spotted PTFE surface coated on TiO₂ superhydrophilic surface.

In the non-ideal gas lattice Boltzmann equation (LBE), the intermolecular forces between solid and fluid can be represented by the inclusion of the wall free energy in the expression of the total free energy. We derived and investigated three types of polynomial (linear, quadratic, and cubic) wall free energy based boundary conditions for the non-ideal gas LBE method. Static cases with a liquid drop sitting on solid surfaces are examined. All the proposed boundary conditions are able to predict the equilibrium states very well in the range of moderate contact angles by incorporating the potential form of the intermolecular forces and the bounce-back rule that guarantees mass conservation. Simulations with different boundary conditions are carried out and the results are compared concerning the accuracy as well as the applicability of different polynomial boundary conditions.

We present here an analysis of the regularity of minimizers of a variational model for epitaxially strained thin-films. The regularity of energetically-optimal film profiles is studied by extending previous methods and by developing new ideas based on transmission problems. The achieved regularity results relate to both the Stranski-Krastanow and the Volmer-Weber modes, the possibility of different elastic properties between the film and the substrate, and the presence of the surface tensions of all three involved interfaces: film/gas, substrate/gas, and film/substrate. Finally, geometrical conditions are provided for the optimal wetting angle, i.e. the angle formed at the contact point of films with the substrate. In particular, the Young–Dupré law is shown to hold, yielding what appears to be the first analytical validation of such law for a thin-film model in the context of Continuum Mechanics.

Additive manufacturing (AM) of titanium (Ti) alloys has always fascinated researchers owing to its high strength to weight ratio, biocompatibility, and anticorrosive properties, making Ti alloy an ideal candidate for medical applications. The aim of this paper is to optimize the AM parameters, such as Laser Power (LP), Laser Scan Speed (LSS), and Hatch Space (HS), using Analysis of Variance (ANOVA) and Grey Relational analysis (GRA) for mechanical and surface characteristics like hardness, surface roughness, and contact angle, of Ti6Al4V ELI considering medical implant applications. The input parameters are optimized to have optimum hardness, surface roughness and hydrophilicity required for medical implants.

The effects of polishing pressure, polishing speed and pH value of the polishing slurry on the chemical activity of quartz glass, the material removal rate (MRR) and surface roughness (Ra) of the workpiece were studied. Using MRR and Ra as evaluation indexes, three factors and four levels of the orthogonal test were used to perform chemical mechanical polishing on quartz glass. By measuring the contact angle between the polishing slurry and workpiece, the influence of different polishing slurries on the chemical activity of quartz glass surface was studied. The processing mechanism of CMP quartz glass was analyzed. The order of important factors affecting MRR of quartz glass was: pressure $>$ rotation speed $>$ pH value; the order of significant factors affecting Ra of quartz glass was: pressure $>$ pH value $>$ rotation speed. The optimum polishing process parameter combination of the MRR was: pressure 27.58 kPa, rotation speed 85 rpm, pH value 12; the optimum polishing process parameter combination of the Ra was: pressure 13.79 kPa, rotation speed 85 rpm, pH value 12. The MRR and Ra of the workpiece are evaluated from the mechanical action of pressure and speed and the chemical action of polishing slurry on the workpiece. The results proved that the effect of the alkaline polishing solution on MRR and Ra of quartz glass is more significant than that of the acidic polishing slurry.

In this study, 8% fenpropathrin nanoemulsion was prepared by phase inversion temperature (PIT) method with 8% xylene and 4% solvent oil 150# as the solvent. The characteristics of this nanoemulsion were tested and compared with emulsifiable concentrate (EC). The size of 8% fenpropathrin nanoemulsion was 62.99nm, which was much smaller than that of 20% fenpropathrin EC (459.00nm). The mixed surfactants were added in fenpropathrin nanoemulsion with DBS-Ca:LAE at 1:2 to increase the stability, and the concentration of the mixed surfactants at 10wt.% showed the highest stability and much better synergism and surface activity. The absolute zeta potential of fenpropathrin nanoemulsion was much higher than that of EC, which can effectively prevent the cohesion between particles. Field control test also revealed that the 200mg/L, 100mg/L and 50mg/L fenpropathrin nanoemulsion had higher efficacy than 100mg/L fenpropathrin EC (contrast pesticide) in 4th, 7th, 15th days, respectively. In conclusion, nanoemulsion has a great application prospective in the future.

Spontaneous imbibition (SI) is a capillary-driven flow process, in which a wetting fluid moves into a porous medium displacing an existing non-wetting fluid. This process likely contributes to the loss of fracking fluids during hydraulic fracturing operations. It has also been proposed as a method for an enhanced recovery of hydrocarbons from fractured unconventional reservoirs. Numerous analytical and numerical approaches have been employed to model SI. Invariably, these idealize a fracture as the gap formed between parallel flat surfaces. In reality, rock fracture surfaces are rough over multiple scales, and this roughness will influence the contact angle and rate of fluid uptake. We derived an analytical model for the early-time SI behavior within a fracture bounded by parallel impermeable surfaces with fractal roughness assuming laminar flow. The model was tested by fitting it to experimental data for the SI of deionized water into air-filled rock fractures. Twenty cores from two rock types were investigated: a tight sandstone (Crossville) and a gas shale (Mancos). A simple Mode I longitudinal fracture was produced in each core by compressive loading between parallel flat plates using the Brazilian method. Half of the Mancos cores were fractured perpendicular to bedding, while the other half were fractured parallel to bedding. The two main parameters in the SI model are the mean separation distance between the fracture surfaces, $\bar{x}$, and the fracture surface fractal dimension $2\le D<3$. The $\bar{x}$ was estimated for each core by measuring the geometric mean fracture aperture width through image analysis of the top and bottom faces, while $D$ was estimated inversely by fitting the SI model to measurements of water uptake obtained using dynamic neutron radiography. The $\bar{x}$ values ranged from 45$\mu$m to 190$\mu$m, with a median of 93$\mu$m. The SI model fitted the height of uptake versus time data very well for all of the rock cores investigated; medians of the resulting root mean squared errors and coefficients of determination were 0.99mm and 0.963, respectively. Estimates of $D$ ranged from 2.04 to 2.45, with a median of 2.24. Statistically, all of the $D$ values were significantly greater than two, confirming the fractal nature of the fracture surfaces. Future research should focus on forward prediction through independent measurements of $D$ and extension of the existing SI model to late times (through the inclusion of gravity) and fractures with permeable surfaces.

The surface modification mechanism of polyvinyl chloride (PVC) by ozonation was investigated to study the selective hydrophilization of PVC surface among other plastics. Infrared analysis confirmed the increase of hydrophilic groups. XPS analysis revealed that the increase was due to the structural change in chlorine group in PVC to hydroxylic acid, ketone, and carboxylic groups by ozonation. This chemical reaction by ozone could occur only for polymers with chlorides in its structure and resulted in the selective hydrophilization of PVC among various polymers.

Surface tension is one of the fundamental properties of the colloids, which can be altered by concentration and size of colloidal particles. In the current work, modeling of the surface tension of suspension as it would be analyzed by maximum bubble pressure method has been performed. A new modified equation to correlate the surface tension with the bubble pressure is derived by applying fundamental thermodynamic relation considering the presence of particles in suspension and curvature of the interface between the particles and bubbles inside liquid. Moreover, the change of particles concentration in air–water interface due to capillary force is also considered. The predicted surface tension using the developed model has been verified by numerous experimental data with deviation less than 5% in most of cases. It was found that the calculated surface tension is altered by contact angle and particle radius as well as particle concentration. The obtained model may have potential application to predict the surface tension of colloidal suspension.

A cold cathode plasma source is constructed for modifying PTFE surface characteristics. The source was easily built, had a consistent plasma discharge medium and acceleration system. A cylindrical Langmuir probe is also used to evaluate plasma parameters like density, temperature or even plasma potential. This probe is designed to be moveable so that it may approach any desired position in the plasma volume. The influences of nitrogen pressure and probe-cathode gap on plasma parameters were investigated. The electron temperature $T_e$ fluctuated from $7.73\times 10^4$ to $6.8\times 10^4$eV as the pressure rises from 0.2 to 0.4mbar. Further, by increasing the cathode-probe gap from 0.4 to 2cm, the electron densities increased from $0.46\times 10^{10}$cm${}^{-3}$ to $0.89\times 10^{10}$cm${}^{-3}$. Furthermore, the contact angles, work of adhesion and surface free-energy of pristine as well as irradiated PTFE films, were estimated. The results demonstrated that by extending the plasma exposure duration from 0 to 12min, the water contact angle is lowered from 82.2^∘ to 30.5^∘. At these conditions, the work of adhesion is raised from 81.9 to 134.1mJ/m², as the surface free energy is increased from 29.8 to 71.8mJ/m².

This paper focuses on effects of roughness on wettability. According to Wenzel's equation, the transition of theoretical wetting contact angles is 90°, whereas many experimental results have indicated that such a transition takes place at contact angles smaller than 90°. A new model of wetting on roughness surface is established in this paper. The model indicates that the influencing factors of wetting on roughness surface include not only equilibrium contact angle θ₀ and surface roughness, but also the system of liquids and solid substrates. There is a corresponding transition angle for every surface roughness, and the transition angle is lower than 90°. Surface roughness is propitious to improve the contact angle only when θ₀ is lower than the transition angle. The effect of surface roughness on the contact angle increases with the increase of r_E. To engineer the surface with different roughnesses, a Ti test sample is polished with sandpaper with abrasive number 350, 500, 1000 and 2000; the contact angles of water on Ti are measured by the sessile drop method. The results of the theoretical analysis agree with experimental ones.

The necessity for innovative biomaterials has been growing recently due to the rising cost of materials for intricate biomedical equipment. An important tactic to improve critical attributes like hemocompatibility, osseointegration potential, corrosion resistance, and antibacterial capabilities is surface modification. In this paper, an investigation has been made in the field of laser surface modification and the complex interactions between laser parameters and output performance metrics, such as contact angle and surface roughness. Surface modification by laser has been successful and, in this research, the laser parameters such as laser energy (Watts), standoff distance(mm), and frequency (kHz) along with dimple distance on the surface ($\mu$m) were considered on the output performance namely surface roughness in “$\mu$m” and contact angle in “degree”. The experiment has been carried out using the L16 orthogonal array to interpret the complex correlations between these factors and the resulting surface features. Non-dominated sorting genetic algorithm II (NSGA-II) has successfully navigated the complex parameter space and found the optimal combinations that yield the intended outcomes. The results show how important dimple distance and laser frequency are in creating hydrophobic surfaces, as well as how much of an impact they have on surface properties. It has been discovered that higher frequencies and longer standoff distances specifically reduce surface roughness, which is a crucial component in ensuring enhanced biomaterial performance. The result shows that the dimple distance and frequency of the laser have a significant effect on the development of hydrophobic surfaces. Moreover, high frequency and more standoff distance reduce the surface roughness. The predicted combination of laser parameters as per the NSGA-II is 102.91$\mu$m, 33.35W, 223.12mm, 50.01kHz, and gives a surface roughness of 0.86$\mu$m and contact angle of 158.83^∘. In essence, this study not only sheds light on the intricate dynamics governing laser-based surface modification but also paves the way for the design and development of advanced biomaterials with tailored surface properties, poised to revolutionize biomedical applications.

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.

Polytetrafluoroethylene (PTFE) has been increasingly used in many industries due to its low frictional coefficient and excellent chemical inertness. The surface properties of PTFE are of importance in various applications. The surface properties of PTFE can be modified by different techniques. In this study, PTFE film was treated in oxygen plasma for improving surface wettability. The effects of plasma treatment on dynamic wetting behavior were characterized using Scanning Probe Microscopy (SPM), Fourier transform infrared spectroscopy (FTIR), and dynamic contact angle (DCA) measurements. SPM observations revealed the etching effect of the plasma treatment on the film. The introduction of hydrophilic groups by plasma treatment was detected by FTIR. The roughened and functionalized surface resulted in the change in both advancing and receding contact angles. Advancing and receding contact angles were significantly reduced, but the contact angle hysteresis was obviously increased after plasma treatment.

In this report, the general validity of the Einstein viscosity relation, ${\eta }_r=1+2.5\phi$, $\phi <0.02({\eta }_r={\eta }_s∕{\eta }_0$, ratio of solution to solvent viscosity), is examined in nanofluids where monodisperse spherical nanoparticles (polystyrene latex spheres) of size 50–400nm were dispersed in water at room temperature, 25${}^{\circ }$C. In addition to viscosity, we also measured contact angle, $\theta$, and surface free-energy, $U$, as function of particle concentration and observed that the universal relation $X_r=1+X\phi$, $\phi <0.02$, remained valid, where $X_r$ may be relative viscosity, contact angle or surface free-energy and $X$ is a shape-dependent constant and is 2.5 in the Einstein limit. Thus, the Einstein relation has a wider validity than is generally thought encompassing both bulk and surface properties of nanofluids. Furthermore, we extend the study to establish an empirical relation between intrinsic viscosity [$\eta$] and Huggins interaction parameter $k_H$, with particle size $D$, which obeyed: $[\eta ]$ or $k_H=a+\frac{b}{D}+\frac{c}{D^2}$, where $D$ is in nm, [$\eta$] is in cc/g, $k_H$ is in (g/cc)² and $a$, $b$ and $c$ are constants of particle size. Identical expressions could be established for contact angle and surface free energy. These remarkable observations have not been reported hitherto.