Contact Angle Behavior Research Articles

3D electrohydrodynamic printing of highly aligned dual-core graphene composite matrices

The aim of this study was to develop an EHD printing method to fabricate graphene-loaded polycaprolactone (PCL)/polyethylene oxide (PEO) dual-core matrices. Graphene was incorporated in shell PCL components, while gelatin and dopamine hydrochloride (DAH) were encapsulated in two PEO cores to enhance biocompatibility of graphene-loaded matrices. Furthermore, the effect of PEO concentration on dual-core fiber formation was evaluated. The influence of process parameters (applied voltage, inner flow rate, outer flow rate and X-Y-Z collector stage speed) on dual-core fiber morphology was evaluated. Our findings show graphene-loaded structures to possess two inner cores and increasing graphene content yields matrices with smoother surfaces, causing a slight reduction in their contact angle behavior. Furthermore, the addition of graphene to matrices results in reduced elasticity. DAH release from matrices comprising various graphene concentrations showed no significant difference and drug release mechanism was diffusion based. In vitro biological tests indicate resulting graphene-loaded dual-core matrices exhibit good biocompatibility and also improve PC12 cell migration. The findings suggest matrices to have potential applications in nerve restoration and regeneration.

Studying the Wettability and Reactivity of Liquid Si-Ti Eutectic Alloy on Glassy Carbon

The contact heating sessile drop method was applied for a fundamental study concerning the wettability and reactivity of liquid Si-16.2 at.%Ti (eutectic composition) in contact with glassy carbon. The evolution of the contact angle behaviors and spreading kinetics were evaluated at three different temperatures. A strong temperature dependence was found by analyzing the spreading kinetics in determining the achievement of the equilibrium at the interface. Different spreading stages with different slopes depend on whether the diffusion of reacting phases (liquid Si and C) through the growing reaction layer (SiC) starts to be the rate-limiting factor. On the contrary, the final contact angle value seems not affected by the temperature. The solidified Si-Ti eutectics/GC samples were examined both at the top of the drop and at the cross section by SEM/EDS. The presence of C pockets of dissolution and a SiC layer at the interface confirmed the reactive nature of the interaction mechanisms. In addition, a thicker layer of SiC at the triple line was detected and most probably responsible for pinning the alloy drop at a measured final value of contact angle of 43° ± 2.

On the size-dependent behavior of drop contact angle in wettability alteration of reservoir rocks to preferentially gas wetting using nanofluid

Wettability alteration of rock surfaces toward gas wetting have been recognized as a practical approach for maximizing the production from the gas condensate reservoirs. Most of the reported work in this area applied the so called sessile drop contact angle measurement technique to examine the change in wetting state of a surface. However, the size-dependent wetting behavior of drop which could affect the exact determination of wettability and wettability changes was not well discussed in the previous studies. Therefore, in this work, the size dependency of contact angle for four different liquid-solid-gas systems; i.e., water-calcite-air, water-treated calcite-air (nanofluid treated calcite), oil-calcite-air, and oil-treated calcite-air, were investigated. To provide a better understanding of the displacement of reservoir gas and liquid following the wettability alteration process, a dynamic contact angle measurement approach was designed. The effect of drop size and surface roughness on the wetting state of calcite rock samples at the initial and altered condition of wettability was then investigated through experimental and modeling approaches. The surface roughness of calcite samples and drop contact angles were determined using Atomic Force Microscopy and Low bond axisymmetric drop shape analysis method, respectively. Analysis of results demonstrated that size dependency of contact angle imposed an error as high as 22.2° on the measurement of achieved wettability alteration in the case of water-calcite/treated calcite-air system. On the basis of calculated pseudo-line tension from the modeling schemes, it was also revealed that the surface roughness had a significant impact on wettability measurements. Both low and high pseudo-line tension values of order 10−9 and 10−6 N, respectively, could dictate some level of errors in contact angle measurements. However, high values were supposed to have a considerable degree of importance in gas condensate applications. The results of this study could provide a better understanding of the contact angle measurement experiments for petroleum engineers to evaluate the wettability alteration schemes.

Wettability and Infiltration of Liquid Silicon on Graphite Substrates

The energy crisis has stimulated a rapid growth of developments in the photovoltaic industry in recent years. To reduce the high cost and the toxicity of classical metallurgical routes, new methods, such as vacuum refining of silicon, have been developed. Moreover, at the industry level, parameters such as the porosity in crucibles and dies are not controlled, so wettability, infiltration, and reaction between silicon and graphite are the key factors in the purification process. In this work, the behavior of several refractory substrates against melted silicon was studied by the classic sessile drop method. The most important phenomena, i.e., wettability and infiltration, were compared with the properties of the substrates. According to the results, for the carbonaceous materials, the reaction of triple line silicon-graphite manages these phenomena, whereas for alumina, a passive layer is formed due to the presence of oxygen, which is subsequently eliminated by the chemical reactions, delaying the process. Regarding the contact angle and infiltration behavior, alumina showed the best results, but due to its reactivity, it contaminates Si, so that this material is not recommended for solar silicon application. However, composite 2 is compatible with the application, as it shows good results in comparison with the other materials.

Deposition of Stainless Steel Thin Films: An Electron Beam Physical Vapour Deposition Approach.

This study demonstrates an electron beam physical vapour deposition approach as an alternative stainless steel thin films fabrication method with controlled layer thickness and uniform particles distribution capability. The films were fabricated at a range of starting electron beam power percentages of 3–10%, and thickness of 50–150 nm. Surface topography and wettability analysis of the samples were investigated to observe the changes in surface microstructure and the contact angle behaviour of 20 °C to 60 °C deionised waters, of pH 4, pH 7, and pH 9, with the as-prepared surfaces. The results indicated that films fabricated at low controlled deposition rates provided uniform particles distribution and had the closest elemental percentages to stainless steel 316L and that increasing the deposition thickness caused the surface roughness to reduce by 38%. Surface wettability behaviour, in general, showed that the surface hydrophobic nature tends to weaken with the increase in temperature of the three examined fluids.

Thin film composite membranes: Preparation, characterization, and application towards copper ion removal

A novel thin film composite (TFC) membrane was fabricated from a thin layer of hybrid membrane formulated from a blend of polyvinyl alcohol (PVA)/chitosan and cross linked with tetraethylorthosilicate (TEOS), which was layered on the polysulfone (PSF) membrane. Besides producing membrane from polymer blend of PVA/chitosan only, concentrations of TEOS as cross linker was varied at 1 wt%, 3 wt% and 5 wt% with fixed concentration of PVA solution (10 wt.%) and chitosan (2 wt.%) respectively during the formulation of hybrid membranes. The thermal properties, mechanical strength, water contact angle, swelling measurement and anti-fouling behaviour of these membranes were investigated. The performance of the thin film composite was evaluated through filtration of the pure copper ion solution and the industrial wastewater containing copper respectively. The fabricated TFC with 3 wt.% TEOS was found to possess better tensile strength and strain, and thermal stability as compared with other concentration of TEOS. The membrane also exhibit good rejection of copper ion (> 90%) from pure copper solution especially at pH 7 of feed solution. A further treatment conducted on the wastewater reveals that TFC with 3 wt.% TEOS could remove the copper ion, where the filtered water could be directly discharged to the river. Furthermore, the TFC portrayed good anti fouling behaviour, where it have 3% of relative flux decay and 76% of relative flux recovery even with the presence of humic acid as NOM (natural organic matter).

Contact Angle and Condensation of a CO2 Droplet on a Solid Surface

Anthropogenic release of carbon dioxide (CO2) is a major contribution to manmade increase in global warming. Carbon capture and storage (CCS) is a necessary technology for lowering CO2 emissions to an acceptable level that limits global warming to below 2 °C. Liquefaction of CO2 is a key process both in capture technologies and in conditioning before ship transport. The efficiency of this process can be remarkably enhanced by promoting dropwise CO2 condensation on cooling surfaces, yet this remains largely unexplored. Here, using molecular dynamics (MD) simulations, we report for the first time the contact angle and condensation behavior of CO2 droplets on a smooth solid surface. The contact angle of the condensed CO2 droplet is greatly dependent on the CO2–solid characteristic interaction energy, but this does not hold true for the sum of condensed molecules. In contrast, the sum of condensed molecules for the filmwise condensation regime increases monotonically at first, but then remains constant as the...

Corrosion protection and enhanced biocompatibility of biomedical Mg-Y-RE alloy coated with tin dioxide

Oxide films composed of mainly tin dioxide and a small amount of stannous oxide are sputter-deposited onto the biomedical Mg-Y-RE (WE) alloy to enhance the anticorrosion properties and biocompatibility. The film composition, thickness, water contact angle, corrosion resistance, protein adsorption, and initial cell behavior are evaluated. Compared to the control, the corrosion current density and charge transfer resistance of the coated WE alloy in simulated body fluids show a 345-fold decrease and increase of more than 3 orders of magnitude, respectively, thus indicating excellent protection rendered by the surface layer. Furthermore, the modified WE alloy shows enhanced attachment and spreading of MC3T3-E1 pre-osteoblasts resulting from more protein adsorption.

Nano-sized amorphous carbon covered surface formed by selective laser melting of ink-printed (SLM-IP) copper (Cu) nanoparticles (NPs)

In this paper, a nano-sized amorphous carbon covered surface was fabricated by an additive manufacturing process of selective laser melting of ink-printed (SLM-IP) copper (Cu) nanoparticles (NPs) in ambient condition. This technique synthesizes pure Cu by chemical reduction route using an organic solvent during laser melting. Additionally, the polymer in the solvent was decomposed by the thermal energy, which resulted in the formation of nano-sized amorphous carbon. Consequently, two layers of copper and carbon were fabricated on the substrate of stainless steel which was illustrated by the cross-section SEM. The upper layer of carbon possesses super-hydrophobic and high-light absorptance properties. The reaction products were characterized by the analyze of XRD, XPS and EDS. The contact angle and dynamic behavior of water droplet on the fabricated surface were carried out to demonstrate the super-hydrophobicity. The study provides an easy and flexible method for the fabrication of the functional surface by laser sintering in air ambient.

The physics of water droplets on surfaces: exploring the effects of roughness and surface chemistry

This paper explores the fluid property commonly called surface tension, its effect on droplet shape and contact angle, and the major influences of contact angle behaviour (i.e. surface roughness and surface chemistry). Images of water droplets placed on treated copper surfaces are used to measure the contact angles between the droplets and the surface. The surface wettability is manipulated either by growing a self-assembled monolayer on the surface to make it hydrophobic or by changing the surface roughness. The main activities in this experiment, then, are (1) preparing and studying surfaces with different surface wettability and roughness; (2) determining the shape and contact angles of water droplets on these surfaces; and (3) demonstrating the spontaneous motion of water droplets using surface tension gradients.

Aqueous Dispersion of Carbon Fibers and Expanded Graphite Stabilized from the Addition of Cellulose Nanocrystals to Produce Highly Conductive Cellulose Composites

Conductive cellulose composites have received much attention as emerging materials due to their unique properties, such as biodegradability and flexibility. However, the achievable levels of conductivity of these cellulose composites are generally low due to the intrinsically nonconductive properties of cellulose. In this study, cellulose nanocrystals (CNC) were applied for preparation of a carbon fibers/expanded graphite (CF/EG) dispersion which was coated on cellulose paper to prepare highly conductive cellulose composites. Such composite materials were characterized based on transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) observation, FT-IR, XPS, and XRD and by determining the zeta potential, particle size, contact angle, and rheological behavior. It was found that the addition of CNC resulted in a significant improvement in the stability of the CF/EG dispersion. These results were explained by the following facts: (1) CNC improved the surface charge of t...

Multi-compartment centrifugal electrospinning based composite fibers

Multi-faceted technological advances in fiber science have proven to be invaluable in several emerging biomaterial and biomedical engineering applications. In the last decade, notable fiber engineering advances have been demonstrated ranging from co-axial flows (for micron and nano-scaled layering), non-concentric flows (for Janus composites) and even 3D printing (for controlled alignment). The ES process is however limited, both for commercial impact (low production rates) and also in its facile capability to deliver reliable mimicry of numerous biological tissues which comprise blended and aligned fibers (e.g. tendons and ligaments). In the technological advance demonstrated here, a combinatorial multi-compartment centrifugal electrospinning (CMCCE) system is developed and demonstrated. A proof-of-concept enabling multiple formulation solution hosting (including combinatorial grading) in a single centrifugal electrospinning system (CES) comprising one spinneret is shown. Using this process, controlled blending and tuning of resulting fibrous membrane properties (contact angle and active release behavior) via aligned and phased fiber mat composition is demonstrated. In addition, the CMCCE process is capable of replicating production rates of recently developed centrifugal electrospinning systems (∼120g/h), while potentially permitting better mimicry of naturally occurring fibrous tissue blends. It is envisaged the advance in technology will be ideally suited to engineer synthetic fibrous biomaterials with greater host surface replication and will fulfil production rate requirements for the industrial sector.

Effects of particle size on flotation parameters in the separation of diaspore and kaolinite

An attempt has been made in this paper to examine the effect of particle size on flotation parameters in the separation of diaspore and kaolinite. First of all, the basic properties such as zeta potential and contact angle and flotation behaviors of diaspore and kaolinite in sodium oleate (NaOL) and dodecylamine (DDA) solution were investigated. And then direct and reverse flotation experiments of mixed binary minerals at different size fractions were carried out. The classical first order flotation kinetics were used to fit the flotation data and first-order rate constant (k), ultimate recovery (R∞), modified rate constant (Km), selectivity index (SI) and separation efficiency (SE) were calculated and used as the flotation parameters to evaluate the separation effect of the two minerals. The results show that in the separation of diaspore and kaolinite, the particle size has a significant influence on the flotation parameters. The favorable particle size fractions for direct flotation were −38+20μm and −54+38μm and the adverse particle size fractions were −10μm and −20+10μm. While for reverse flotation, the favorable particle size fractions were −74+54μm and −10μm and the adverse particle size fractions were −38+20μm and −54+38μm. The optimal flotation times for the favorable size fractions were shorter than that for unfavorable size fractions. For the same size fractions, longer flotation times were required to reach the maximum separation efficiency in reverse flotation than those in direct flotation. Under the optimized condition (direct flotation, pH=10, NaOL dosage was 2×10−4mol/L, ore particle size was −38+20μm), concentrate products with diaspore recovery of 83.79% and A/S value of 7.96 can be obtained.

Effect of Nanoparticles on Spontaneous Imbibition of Water into Ultraconfined Reservoir Capillary by Molecular Dynamics Simulation

Imbibition is one of the key phenomena underlying processes such as oil recovery and others. In this paper, the influence of nanoparticles on spontaneous water imbibition into ultraconfined channels is investigated by molecular dynamics simulation. By combining the dynamic process of imbibition, the water contact angle in the capillary and the relationship of displacement (l) and time (t), a competitive mechanism of nanoparticle effects on spontaneous imbibition is proposed. The results indicate that the addition of nanoparticles decreases the displacement of fluids into the capillary dramatically, and the relationship between displacement and time can be described by l(t) ~ t1/2. Based on the analysis of the dynamic contact angle and motion behavior of nanoparticles, for water containing hydrophobic nanoparticles, the displacement decreases with the decrease of hydrophobicity, and the properties of fluids, such as viscosity and surface tension, play a major role. While for hydrophilic nanoparticles, the displacement of fluids increases slightly with the increase of hydrophilicity in the water-wet capillary and simulation time, which can be ascribed to disjoining pressure induced by “sticking nanoparticles”. This study provides new insights into the complex interactions between nanoparticles and other components in nanofluids in the spontaneous imbibition, which is crucially important to enhanced oil recovery.

Low salinity water–Surfactant–CO 2 EOR

Coreflood, interfacial tension (IFT), contact angle, and phase behavior measurements were performed to investigate the viability of a hybrid of low-salinity water, surfactant, and CO2 flood enhanced oil recovery (EOR) process. Low-permeability carbonate reservoir cores were aged for eight weeks at reservoir temperature and pressure. Coreflood and contact angle between oil droplets and core surface measurements were performed. Additional contact angle measurements on sandstone and shale cores were also performed. The coreflood sequences were seawater flood, followed by low-salinity water flood, followed by surfactant floods until residual oil saturations to each flooding sequences and finally CO2 injection. Coreflood in low-permeability carbonate cores show that the hybrid EOR process produces incremental oil up to twenty-five percent beyond seawater flooding. Contact angle measurements on carbonate, sandstone and shale cores indicate that wettability alteration and IFT decrease are the main oil-mobilizing mechanisms in the hybrid EOR process. The hybrid EOR process mobilizes part of the residual oil because: (i) low-salinity brine improves wettability towards hydrophilic condition favorable for surfactant flooding; (ii) surfactant in low-salinity water solubilizes some of the remaining oil as Winsor type II− microemulsion and lowers IFT between oil and water; and (iii) CO2 will follow surfactant to mobilize more of the remaining oil in the wettability-improved condition.

Sessile Nanodroplets on Elliptical Patches of Enhanced Lyophilicity.

We theoretically investigate the shape of a nanodroplet on a lyophilic elliptical patch in lyophobic surroundings on a flat substrate. To compute the droplet equilibrium shape, we minimize its interfacial free energy using both Surface Evolver and Monte Carlo calculations, finding good agreement between the two methods. We observe different droplet shapes, which are controlled by the droplet volume and the aspect ratio of the ellipse. In particular, we study the behavior of the nanodroplet contact angle along the three-phase contact line, explaining the different droplet shapes. Although the nanodroplet contact angle is constant and fixed by Young’s law inside and outside the elliptical patch, its value varies along the rim of the elliptical patch. We find that because of the pinning of the nanodroplet contact line at the rim of the elliptical patch, which has a nonconstant curvature, there is a regime of aspect ratios of the elliptical patch in which the nanodroplet starts expanding to the lyophobic part of the substrate, although there is still a finite area of the lyophilic patch free to be wetted.

Recent Progress in Fabricating Superaerophobic and Superaerophilic Surfaces

In spite of large amount of research in fabricating surfaces of varying wettability by biomimicking the naturally occurring surfaces, the work on fundamentally and industrially important air bubble adhesion on solid surfaces and its applications are still in the burgeoning stage. The present progress report provides a discussion and a critical evaluation of the recent literature available on the fabrication of superaerophilic/superaerophobic surfaces via synergic modification of surface topography and surface chemistry. An abridge on the physics behind bubble wetting on a solid in a liquid medium is deciphered here, considering the interfacial surface tension balance at the three‐phase contact line, Laplace pressure, hydrostatic pressure, and surface forces, respectively. Emphasis is made on the advancement in micro/nanofabrication technologies to fabricate surfaces that break the conventional wisdom of complementary behavior of water and air bubble contact angles. The progress report presented here also shines light on the mechanism of air bubble dynamics on solid surfaces and the latest developments in achieving surfaces of varied air bubble adhesion and its applications. Finally, the prospects of the superaerophobic and superaerophilic surfaces in the near future together with the challenges faced in accomplishing them are also insinuated.

Synthesis and characterization of sputtered nanostructured ZnO films: Effect of deposition time and pressure on contact angle behavior of ethylene glycol and water

Synthesis and characterization of sputtered nanostructured ZnO films: Effect of deposition time and pressure on contact angle behavior of ethylene glycol and water

Investigation of behavior of the dynamic contact angle in a problem of convective flows

Investigation of behavior of the dynamic contact angle in a problem of convective flows

Numerical Investigation of a Dependence of the Dynamic Contact Angle on the Contact Point Velocity in a Problem of the Convective Fluid Flow

Received 07.12.2015, received in revised form 09.02.2016, accepted 20.06.2016 A two-dimensional problem of the fluid flows with a dynamic contact angle is studied in the case of an uniformly moving contact point. Mathematical modeling of the flows is carried out with the help of the Oberbeck-Boussinesq approximation of the Navier-Stokes equations. On the thermocapillary free boundary the kinematic, dynamic conditions and the heat exchange condition of third order are fulfilled. The slip conditions (conditions of proportionality of the tangential stresses to the difference of the tangential velocities of liquid and wall) are prescribed on the solid boundaries of the channel supporting by constant temperature. The dependence of the dynamic contact angle on the contact point velocity is investigated numerically. The results demonstrate the contact angle behavior and the different flow characteristics with respect to the various values of the contact point velocity, friction coefficients, gravity acceleration and an intensity of the thermal boundary regimes.