Showing papers on "Sessile drop technique published in 2020"

Fabrication of Coatings with Structural Color on a Wood Surface

Abstract: A facile method for the fabrication of colloidal photonic crystal coatings with tunable structural color on a wood surface was presented. The photonic crystal coatings were formed from monodisperse latex spheres composed of poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)). The latex spheres with a hard PSt core and elastomeric P(MMA-AA) shell were prepared using the emulsion polymerization method. The sessile drop method, a rapid single-step self-assembly method through simple evaporation of emulsion, was used to form three-dimensional colloidal crystals. Coatings with brilliant colors and uniform Bragg’s diffraction covering the entire visible region were fabricated by controlling the sphere size. This simple method provided new insight into the development of wood color embellishment.

Temperature dependence of contact angles of water on a stainless steel surface at elevated temperatures and pressures: In situ characterization and thermodynamic analysis.

Abstract: Phase change heat transfer (e.g., boiling of water) on surfaces can be enhanced by tuning the surface wettability, which is often quantified by the contact angle and is expected to be influenced by temperature and pressure. However, the temperature (and pressure) dependence of contact angles of water on metallic surfaces remain unclear. In this study, an in situ characterization of the contact angles of water on 304 stainless steel surfaces at temperatures from room temperature to 250 °C and at pressures up to 15 MPa was performed using the sessile drop method. It was shown that three distinct regimes can be identified on the contact angle-temperature curves. A slightly-decreasing trend of the contact angles with temperature was observed below 120 °C, followed by a steeper linear decrease at higher temperatures. A further rise of the decreasing rate with temperature was observed above 210 °C. In contrast to temperature, the pressure was shown to have little effects on the contact angles. Based on the theory of surface thermodynamics, the effects of temperature (and pressure) on the contact angles were analyzed in terms of the interfacial tensions. An empirical correlation was developed to predict the contact angles as a function of temperature.

Dynamic Wettability on the Lubricant-Impregnated Surface: From Nucleation to Growth and Coalescence.

Abstract: The surface dynamic wettability during droplet nucleation and growth involved with phase change is different from the static wettability formed from a sessile drop. Revealing this dynamic wettabili...

LIPSS combined with ALD MoS2 nano-coatings for enhancing surface friction and hydrophobic performances

Abstract: To enhance the friction and hydrophobic performances of contact interfaces, the laser-induced periodic surface structures (LIPSS) by picosecond pulses and atomic layer deposition (ALD) MoS2 nano-coatings are fabricated on the cement carbide surface. The friction and wettability tests are carried out by the unidirectional sliding friction and sessile drop experiments. Results show that the friction and wetting properties can be regulated by the LIPSS and ALD MoS2 nano-coatings, and the anisotropic friction and hydrophobic properties are observed with respect to the groove orientations. A combination of ALD MoS2 nano-coatings with LIPSS in parallel orientation (MS-HT) exhibits the best potential for improving the friction and wear performance, and the ALD nano-MoS2 coated surface combined with LIPSS in perpendicular to the observation direction (MS-VT) is the most effective way for enhancing the hydrophobic property.

Lifting a sessile oil drop from a superamphiphobic surface with an impacting one

Abstract: Colliding drops are encountered in everyday technologies and natural processes, from combustion engines and commodity sprays to raindrops and cloud formation. The outcome of a collision depends on many factors, including the impact velocity and the degree of alignment, and intrinsic properties like surface tension. Yet, little is known on binary impact dynamics of low-surface-tension drops on a low-wetting surface. We investigate the dynamics of an oil drop impacting an identical sessile drop sitting on a superamphiphobic surface. We observe five rebound scenarios, four of which do not involve coalescence. We describe two previously unexplored cases for sessile drop liftoff, resulting from drop-on-drop impact. Numerical simulations quantitatively reproduce the rebound scenarios and enable quantification of velocity profiles, energy transfer, and viscous dissipation. Our results illustrate how varying the offset from head-on alignment and the impact velocity results in controllable rebound dynamics for oil drop collisions on superamphiphobic surfaces.

Synthesis, Characterization and Wettability of Cu-Sn Alloy on the Si-Implanted 6H-SiC

Abstract: The wettability of the metal/SiC system is not always excellent, resulting in the limitation of the widespread use of SiC ceramic. In this paper, three implantation doses of Si ions (5 × 1015, 1 × 1016, 5 × 1016 ions/cm2) were implanted into the 6H-SiC substrate. The wetting of Cu-(2.5, 5, 7.5, 10) Sn alloys on the pristine and Si-SiC were studied by the sessile drop technique, and the interfacial chemical reaction of Cu-Sn/SiC wetting couples was investigated and discussed. The Si ion can markedly enhance the wetting of Cu-Sn on 6H-SiC substrate, and those of the corresponding contact angles (θ) are raised partly, with the Si ion dose increasing due to the weakening interfacial chemical reactions among four Cu-Sn alloys and 6H-SiC ceramics. Moreover, the θ of Cu-Sn on (Si-)SiC substrate is first decreased and then increased from ~62° to ~39°, and ~70° and ~140°, with the Sn concentration increasing from 2.5%, 5% and 7.5% to 10%, which is linked to the reactivity of Cu-Sn alloys and SiC ceramic and the variation of liquid-vapor surface energy. Particularly, only a continuous graphite layer is formed at the interface of the Cu-10Sn/Si-SiC system, resulting in a higher contact angle (>40°).

Understanding the Temperature Dependence of Contact Angles of Water on a Smooth Hydrophobic Surface under Pressurized Conditions: An Experimental Study.

Abstract: It is of both practical and scientific significance to understand the temperature dependence of contact angles of water on various surfaces. However, the variation trend of water wettability on a smooth hydrophobic surface with increasing temperature remains unclear. In this work, in situ characterization of the contact angle of water on Teflon (polytetrafluoroethylene) surfaces and the interfacial tension of water over a temperature spectrum from ∼25 to 160 °C under pressurized conditions (2, 3, and 5 MPa) in a nitrogen atmosphere was conducted by employing the sessile drop and pendant drop methods, respectively. A nearly invariant trend of the contact angle was observed over the entire temperature and pressure range. As expected, however, it was shown that the water-N2 interfacial tension almost linearly declines with increasing temperature and that pressure has a negative effect on the interfacial tension. Based on the theory of surface thermodynamics, the effects of temperature on the contact angles were analyzed in combination with the gas adsorption effect. Estimations on the solid-gas interfacial tension, surface entropy, and the heat of immersion were made to gain more insights into the temperature dependence of the water contact angle on a smooth hydrophobic surface.

Surface parameters of as-built additive manufactured metal for intraosseous dental implants.

Abstract: Statement of problem To improve osseointegration, current machined implants are submitted to different surface treatments such as airborne-particle abrasion and acid etching. Although additive manufacturing has allowed the fabrication of implants with custom design, porosity, and roughness, whether good osseointegration can be achieved without subsequent surface treatments is still unclear. Purpose The purpose of this in vitro study was to investigate the feasibility of using additive manufacturing technology for dental implants without the use of subsequent surface treatments. Material and methods The roughness, wettability, and surface energy of a flat test stainless-steel specimen produced from a 3D printer were evaluated. The roughness measurements were obtained by using a mechanical contact profilometer. The wettability was characterized by the sessile drop method by using deionized water and ethylene glycol. The surface energy values were calculated by using the Owens, Wendt, Rabel, and Kaeble (OWRK) computational method. Results The experimental data obtained were Ra=4.55 μm, Rq=5.64 μm, RSm=0.235 mm, Rsk=-0.071, Rku=3.740, Rdq=13 degrees; water contact angle=66 degrees; ethylene glycol contact angle=57 degrees; surface energy=38 mN/m. The measured values were compared with data reported in the literature for commercially available implants. The parameter Ra, which is the most used parameter to describe the surface of dental implants, was 50%, 270%, and 329% higher than that reported in the literature for commercial dental implants. The surface energy was 10% and 19% lower than the representative values in the literature for commercial dental implants. Conclusions The results indicate that specimens fabricated by additive manufacturing had higher roughness and lower surface energy than reported results in the literature. Therefore, additive manufacturing was found to produce suitable surface parameters for dental implants, and subsequent surface treatments could be removed from the manufacturing process.

Contact Angle Measurements Using Sessile Drop and Micro-CT Data from Six Sandstones

Abstract: Numerous sessile drop and micro-computed tomography (micro-CT) studies have been conducted to quantify geologic carbon storage formation wettability by measuring static contact angles (θ); however, the influence of pore geometry remains unknown. In this work, six sandstones (Bandera Brown, Berea, Bentheimer, Mt. Simon, Navajo, and Nugget) are used to measure θ using the two aforementioned experimental methods at identical testing conditions (45 °C and 12.41 MPa). The range of θ measured at in situ conditions (micro-CT) exceeds the range at ex situ (sessile drop method) conditions for all sandstones. However, when droplets with more representative in situ diameters are analyzed, θ averages show ex situ θ exceed those of in situ θ. Pore geometry does influence local θ, but the size of ex situ droplets relative to pore size appears to influence θ. This is important to consider for future sessile drop studies used for analysis of CO2 behavior in carbon storage reservoirs.

High-Temperature Wettability Investigations on Laboratory-Developed CaO-CaF2-SiO2 -Al2O3 Flux System-Based Welding Electrode Coatings for Power Plant Applications

Abstract: This article is an attempt to examines high-temperature wettability properties of laboratory-developed electrode coatings for power plant applications. The properties include contact angle between the solid/liquid interfaces, spreading area, surface tension, and work of adhesion. Coatings were prepared using CaO-CaF2-SiO2 -Al2O3 basic flux system. The sessile drop method was used to estimate the contact angle at the liquid/solid interface while surface tension was calculated using Young’s and Boni’s equations based on the measured contact angle. The interaction effect of individual minerals and their binary mixtures (CaO.CaF2, CaO.SiO2, CaO.Al2O3, CaF2.SiO2, CaF2.Al2O3, and SiO2.Al2O3) on the wettability properties were studied using the regression analysis. Optimum flux compositions were estimated using Multi-response optimization. The contact angle decreases when basic oxides (CaO, CaF2) were added in a higher proportion than the acidic oxides. With the decrease in the contact angle spreading area increased and CaF2 comes out to be the significant constituent causes the increase in the spreading area. Binary mixtures CaO.CaF2, CaO.SiO2, and CaF2.SiO2 has an increasing effect on the work of adhesion.

Sessile volatile drop evaporation under microgravity.

Abstract: The evaporation of sessile drops of various volatile and non-volatile liquids, and their internal flow patterns with or without instabilities have been the subject of many investigations. The current experiment is a preparatory one for a space experiment planned to be installed in the European Drawer Rack 2 (EDR-2) of the International Space Station (ISS), to investigate drop evaporation in weightlessness. In this work, we concentrate on preliminary experimental results for the evaporation of hydrofluoroether (HFE-7100) sessile drops in a sounding rocket that has been performed in the frame of the MASER-14 Sounding Rocket Campaign, providing the science team with the opportunity to test the module and perform the experiment in microgravity for six consecutive minutes. The focus is on the evaporation rate, experimentally observed thermo-capillary instabilities, and the de-pinning process. The experimental results provide evidence for the relationship between thermo-capillary instabilities and the measured critical height of the sessile drop interface. There is also evidence of the effects of microgravity and Earth conditions on the sessile drop evaporation rate, and the shape of the sessile drop interface and its influence on the de-pinning process.

Liquid-liquid coffee-ring effect.

Abstract: The so-called coffee-ring effect (CRE) is extraordinarily common, problematic in industry and attractively puzzling for researchers, with the accepted rule that it requires two key-ingredients: solvent evaporation and contact line pinning. Here, we demonstrate that the CRE also occurs when the solvent of a pinned sessile drop transfers into another liquid, without involving any evaporation. We show that it shares all characteristic features of the evaporative CRE: solvent transfer-driven transport of solutes to the contact line, ring-shaped deposit, closely-packed particle organization at the contact line, and size-dependent particle sorting. We thus suggest expanding the definition of the coffee-ring effect to any pinned drop having its solvent transferring to an outer medium where the drop compounds cannot be dissolved.

Sessile drop response to a single wave electrokinetic excitation

Abstract: The response time for maximum drop deformation and its comparison with different time scales is established and verified with experiments. The applied fluctuation is achieved by applying a single wave perturbation of electrowetting with desired amplitude and frequency. To pinpoint the importance of the initial actuation conditions, the variance in the maximum drop deformation for a single wave perturbation is studied. The focus of this study was to analyze the maximum deformation of a drop for a wide range of actuation mechanism with a varied drop or surrounding medium viscosities. The drop response to this cyclic actuation is compared with the equivalent mass–spring–dampener system, and limitations of this approach are identified. Interestingly, the qualitative results were similar between the air and liquid medium cases, but the attainment of equilibrium configuration was dissimilar. As anticipated, the higher actuation magnitude and frequency deformed the drop significantly and thus altered the drop configuration. Higher viscosity of drops and the surrounding medium delayed the time to achieve the maximum deformation. Accurately predicting the time required for a drop to attain the maximum deformation is paramount for optimizing processes and based on microfluidics technology.

Cooperative evaporation in two-dimensional droplet arrays

Abstract: The evaporation of a sessile drop in a gaseous environment may be critical to many practical applications. Evaporation dynamics of interacting sessile droplets is strongly influenced by the proximity of adjacent droplets. We study the effects of droplet-droplet vapor-mediated interactions on the evaporation lifetime of two-dimensional arrays of sessile water droplets. We observe that the presence of neighboring droplets acts as a mode of vapor accumulation which slows down the evaporation process. By considering an arbitrarily configured two-dimensional array of droplets, here we provide a simple generalized theoretical limit to their lifetime in an evaporating state. Using a scaling analysis, we put forward that the sessile droplet lifetime in a two-dimensional array is a linear function of the extent of confinement for various surface wettability and droplet geometric parameters (contact angle and contact radius). Notwithstanding the geometrical and physical complexity of the effective confinement generated due to their cooperative interactions, we show that the consequent evaporation characteristics may be remarkably insensitive to the topographical details of the overall droplet organization for a wide range of droplet-substrate combinations. With subsequent deployment of particle-laden droplets, however, our results lead to the discovery of a unique pathway towards tailoring the internal flows within the collective system by harnessing an exclusive topologically driven symmetry-breaking phenomenon, yielding a strategy of patterning particulate matters around the droplet array.

Surface tensiometry of phase separated protein and polymer droplets by the sessile drop method

Abstract: Phase separated macromolecules play essential roles in many biological and synthetic systems. Physical characterization of these systems can be challenging because of limited sample volumes, particularly for phase-separated proteins. Here, we demonstrate that a classic method for measuring the surface tension of liquid droplets, based on the analysis of the shape of a sessile droplet, can be effectively scaled down for this application. The connection between droplet shape and surface tension relies on the density difference between the droplet and its surroundings. This can be determined with small sample volumes in the same setup by measuring the droplet sedimentation velocity. An interactive MATLAB script for extracting the capillary length from a droplet image is included in the ESI.

Thermal degradation behavior of self-assembled monolayer surfactant on silicon substrate

Abstract: In nanoimprint lithography, a release agent on the mold surface is usually necessary for easy demolding between the mold and the imprinted (thermal) resist. In this work, the thermal stability of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) monolayers is studied using x-ray photoelectron spectroscopy. The FDTS monolayers are deposited on Si (100) substrates via vapor phase reactions. Significant fluorine desorption of the monolayers is observed for samples annealed at 250 and 300 °C in air. The fluorine coverage decreases as a function of annealing time at a given annealing temperature. The desorption is proposed to be dependent on the monolayer packing details and may be influenced by the intermolecular heat transfer. Removal of the CF3 groups is found to be faster than that of the CF2 group as evidenced by the CF2/CF3 peak area ratios that increase with the annealing time. Sessile drop water contact angle and fluorine coverage evolution results show that the estimated useful coating lifetime is 180 min when the samples are annealed at 300 °C and ∼560 min when annealed at 250 °C. The peak position of the binding energy of the F 1s spectral line is related to the monolayer fluorine coverage and it may be a result of the interactions between the molecular chain and the negatively charged silicon substrate. Furthermore, nearly no chain desorption is detected for samples annealed in an inert environment, which may be attributed to the elimination of reactive oxygen and moisture molecules. The thermal degradation behaviors in ambient and inert atmosphere provide useful information for designing a nanoimprint process for the commercial manufacturing of polymeric microstructure and nanostructure.

Synthesis and Characterization of Polystyrene/CuO-Fe2O3 Nanocomposites from Natural Materials as Hydrophobic Photocatalytic Coatings

Abstract: This study reports on the synthesis, characterization of polystyrene(PS)/CuO-Fe2O3 nanocomposites, and their application as hydrophobic coatings. CuO and Fe2O3 materials were synthesized from natural materials by the milling method. Meanwhile, the PS/CuO-Fe2O3 nanocomposites were synthesized by the sol-gel method. Furthermore, the hydrophobic coating on the glass substrate was made by the spin-coating. To obtain highest value of contact angle, the composition of both CuO and Fe2O3 in nanocomposite as well as calcination temperatures were varied. Sample characterization was conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible (Uv-Vis) spectrophotometry analysis. The Sessile drop method was used to determine the contact angle of the layer. The results showed that PS/CuO-Fe2O3 nanocomposite was successfully obtained with a crystal size between 40–52 nm and grain size of 92 nm. In addition to the basic material of composites, hematite and tenorite, the presence of copper ferrite phase was also identified. The CuO-Fe2O3 composition and its large calcination temperature also plays an effective role in the magnitude of the contact angle. The highest value of contact angle obtained was 125.46° at 3:1 composition and calcination temperature of 200 °C. We found that the PS/CuO-Fe2O3 composite was hydrophobic, but the photocatalyst activity was very small at 0.24%.

Contact angle and adhesion of CaO-SiO2- and CaO-Al2O3-based mold slags on solid steel of various compositions

Abstract: To evaluate the lubrication capacity and flaking behavior of mold slag during continuous casting, the contact angle and spreading of CaO-SiO2 and CaO-Al2O3-based mold slags on solid substrates of three steel grades were investigated systematically by the sessile drop technique. The optical basicity and viscosity were combined to clarify the relationship between melt structure and contact angle, and the Mills’ model was used to determine the work of adhesion of mold slags on steel substrates. The primary results indicated that an increasing content of Al and Mn in steel was favorable for decreasing the contact angles. The wettability of the mold slags was related to the network structure, where a more complex network structure, correlated with a larger contact angle on the solid steel surface. The separation of the low-reactive or non-reactive mold slags from the solidified shell was more difficult than that of the CaO-SiO2-based mold slags. Considering the contact angles and works of adhesion, the developed low-reactive or non-reactive mold slags could present both satisfactory lubricating capacity and flaking behavior from the strand surface.

Role of Trapped Air in the Attachment of Staphylococcus aureus on Superhydrophobic Silicone Elastomer Surfaces Textured by a Femtosecond Laser.

Abstract: Surface texturing is an easy way to control wettability as well as bacterial adhesion. Air trapped in the surface texture of an immersed sample was often proposed as the origin of the low adhesion of bacteria to surfaces showing superhydrophobic properties. In this work, we identified two sets of femtosecond laser processing parameters that led to extreme superhydrophobic textures on a silicone elastomer but showed opposite behavior against Staphylococcus aureus (S. aureus, ATCC 25923) over a short incubation times (6 h). The main difference from most of the previous studies was that the air trapping was not evaluated from the extrapolation of the results of the classical sessile drop technique but from the drop rebound and Wilhelmy plate method. Additionally, all wetting tests were performed with bacteria culture medium and at 37 °C in the case of the Wilhelmy plate method. Following this approach, we were able to study the formation of the liquid/silicone interface and the associated air trapping for immersed samples that is, by far, most representative of the cell culture conditions than those associated with the sessile drop technique. Finally, the conversion of these superhydrophobic coatings into superhydrophilic ones revealed that air trapping is not a necessary condition to avoid Staphylococcus aureus retention on one of these two textured surfaces at short incubation times.

Effects of Various Polishing Techniques on the Surface Characteristics of the Ti-6Al-4V Alloy and on Bacterial Adhesion

Abstract: Ti-6Al-4V, although widely used in dental materials, causes peri-implant inflammation due to the long-term accumulation of bacteria around the implant, resulting in bone loss and eventual failure of the implant. This study aims to overcome the problem of dental implant infection by analyzing the influence of Ti-6Al-4V surface characteristics on the quantity of accumulated bacteria. Ti-6Al-4V specimens, each with different surface roughness are produced by mechanical, chemical, and electrolytic polishing. The surface roughness, surface contact angle, surface oxygen content, and surface structure were measured via atomic force microscopy (AFM), laser scanning confocal microscopy (LSCM), drop shape analysis (using sessile drop), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The micro and macro surface roughness are 10.33–120.05 nm and 0.68–2.34 μm, respectively. The surface X direction and Y direction contact angle are 21.38°–96.44° and 18.37°–92.72°, respectively. The surface oxygen content is 47.36–59.89 at.%. The number of colonies and the optical density (OD) are 7.87 × 106–17.73 × 106 CFU/mL and 0.189–0.245, respectively. The bacterial inhibition were the most effective under the electrolytic polishing of Ti-6Al-4V. The electrolytic polishing of Ti-6Al-4V exhibited the best surface characteristics: the surface roughness of 10 nm, surface contact angle of 92°, and surface oxygen content of 54 at.%, respectively. This provides the best surface treatment of Ti-6Al-4V in dental implants.