Contact Angle Of Droplet Research Articles

Influence of the Porphyrin Structures on the Contact Angle of Water Wetting by Langmuir-Schaefer Films

Studying the contact angle of water droplets on the surfaces of thin films formed by organic compounds allows to establish hydrophilic/hydrophobic properties of the films. Knowledge of hydrophilicity/hydrophobicity makes it possible to optimize the composition and increase the adhesive properties of films, improving their functionality. In this study, the dependence of the contact angle of Langmuir-Schaefer films (LS-films) of three compounds: 5,10,15,20-tetraphenylporphyrin (I), 2-aza-21-carba-5,10,15,20-tetraphenyl-porphyrin (II), and 5,15-bis(2,6-bis(dodecycloxy)phenyl)porphyrin (III) was examined. Contact angle data were obtained for LS-films with different transfer numbers of floating layers of the studied porphyrins and different surface roughness. It was found that LS-films of compounds I and II are hydrophobic and their hydrophobicity increases with an increasing of transfer number. In addition, an increase in the surface roughness of the LS film of compound I compared to compound II reduces the value of the contact angle. Unlike porphyrins I and II, LS-films of compound III displayed hydrophilic properties. The obtained data can be used for the targeted design of compounds to create thin film materials of various purposes.

Electrowetting and Surface Tension of Chromonic Liquid Crystals

In this work, we report on measurements of the contact angle of sessile droplets of aqueous solutions of a chromonic liquid crystal at different temperatures and concentrations and on different hydrophobic surfaces, and we show that the wettability of this complex fluid can be easily controlled by an external electric field. Specifically, electrically induced variations of the contact angle up to 70° were obtained using external DC voltages. Complementary tensiometric measurements of the aqueous solutions confirmed that the observed variations in the contact angle were mainly related to variations in the surface tension, while they did not show an evident connection with the internal molecular order of the liquid crystal droplets. Our study is relevant in view of the use of chromonic liquid crystals in microfluidic devices, where the control of wettability is an important tool for handling fluid flow.

Optimization of Manufacturing Parameters for Fluorinated Ethylene Propylene (FEP)/Graphene Hydrophobic Coatings

The coating of surfaces carrying fluid with hydrophobic materials has shown effective results in reducing friction factors. In this study, the optimization of manufacturing parameters, including the additive ratio, curing temperature, and curing time was conducted to enhance the hydrophobic behavior of fluorinated ethylene propylene (FEP) material by incorporating nano graphene additives. Three different levels for the optimized parameters were determined based on the literature sources. These levels were set as 1% wt, 2% wt, and 3% wt for graphene additive ratios, 200 ˚C, 300 ˚C, and 400 ˚C for curing temperatures, and 30 min, 40 min, and 50 min for curing times. Following the L9 Taguchi design, the FEP/graphene mixture was applied to AISI 304 stainless steel surfaces, and the curing process was completed in an oven. The optimization process was performed based on the response of water droplet contact angles on the surfaces. The optimum graphene additive ratio was determined as 1%, the optimum curing temperature was 400 ˚C, and the optimum curing time was found to be 40 min. Variance analysis revealed that the curing temperature had the most significant effect on the contact angles with a contribution rate of 96.78%. Applying the optimal manufacturing parameters to the FEP coating material with added additives can contribute to energy savings in applications such as pumps, turbines, and pipelines.

Superhydrophobic coating composed of rosin acid and TiO2 with antimicrobial properties and excellent mechanical durability for oil/water separation

Developing multifunctional materials with green, lasting, and simple preparation processes is a hot topic and challenge in solving the problem of oil spill contamination. A multifunctionalized superhydrophobic coating was generated via cross-linking 3-(Trimethoxysilyl) propyl acrylate with Polyethyleneimine in a multifunctional covalent manner and modifying the cotton fabric surface with silylated modified rosin acid (RA-Si) as well as TiO2 nanoparticles. The coated samples had remarkable superhydrophobicity with self-cleaning as well as stain resistance. With bactericidal rates of 97.73 % and 98.36 %, respectively, the coated samples effectively inhibited the formation of biofilms and showed high antimicrobial performance for both Staphylococcus aureus and Escherichia coli. Meanwhile, the coated samples showed outstanding oil absorption and separation of the oil-water mixture. Both water-in-oil and oil-in-water stable emulsions would be effectively separated out of the coated samples after demulsifying. Additionally, the water droplet contact angle of the coated samples was maintained at approximately 150.0° after mechanical and chemical testing. It was noteworthy that the coated samples still exhibited satisfactory separation for stabilizing oil/water emulsions after mechanical wear and chemical corrosion treatment, indicating their excellent mechanical durability. The prepared multifunctional RA-TiO2 superhydrophobic coating has promising applications in oil-containing wastewater treatment and environmental remediation.

A low-temperature ionic liquid demulsifier derived from recycled PET waste plastics

The petroleum industry produces a large volume of water-in-oil (W/O) emulsion annually, which has detrimental consequences for both the industry and the environment. Therefore, effective demulsification of these emulsions is crucial. In current work, a low-temperature demulsifier (EBTA) for W/O emulsions was synthesized using PET waste plastic as starting materials through a simple method. Chemical structure of EBTA was characterized by FT-IR and 1H NMR. The demulsification performance was assessed using bottle-test method, and a comprehensive examination was conducted on the influence of EBTA concentration, settling time, temperature, pH value, and salinity on the demulsifying efficiency (DE). At a low temperature of 40 ℃ and a concentration of 250 mg/L, EBTA achieved a DE of 95.36% in an Emul30 emulsion, while a DE of 100% could be obtained in an Emul70 emulsion. Furthermore, EBTA demonstrated excellent tolerance for salts, acids and alkalis. In addition, the demulsification mechanism of EBTA was investigated using various techniques, such as interfacial tension (IFT), zeta potential, three-phase contact angle and coalescence time of droplets. The results revealed that EBTA had a lower IFT and was easily adsorbed on the oil–water interface. This led to the damage of the interface film and facilitated the oil–water separation. Due to the simple and safe synthesis process and remarkable demulsification performance, EBTA is a promising demulsifier for separating W/O emulsions.

Anti-frosting characteristics of superhydrophobic-hydrophilic wettability switchable surfaces

Combining hydrophobicity with hydrophilicity on hybrid surfaces generates unique phenomena in anti-frosting. However, limited attention has been paid to investigate the anti-frosting effects of wettability switchable surfaces in response to temperature changes. Herein, frosting and defrosting characteristics of thermo-responsive, wettability switchable surfaces are investigated. Specifically, the wettability switchable surfaces are successfully fabricated by coating a poly(ε-caprolactone) (PCL) layer onto the microstructured aluminum substrates, resulting in the wettability transition from superhydrophobicity with an apparent contact angle of water droplet as 152° in the surface temperatures under 60 °C to hydrophilicity with an apparent contact angle of water droplet as 63° in the surface temperatures over 60 °C. The wettability transition capabilities of the surfaces not only enable excellent frost retardation comparable to superhydrophobic surfaces in frosting process, but also realize fast full drying capabilities slightly shorter than superhydrophilic surfaces in defrosting process. The unique feature of wettability switchable surfaces represents an effort to combine the distinct advantages of superhydrophobic and superhydrophilic surfaces to realize anti-frosting functionalities.

Preparation and Performance Evaluation of Amphiphilic Polymers for Enhanced Heavy Oil Recovery.

The continuous growth in global energy and chemical raw material demand has drawn significant attention to the development of heavy oil resources. A primary challenge in heavy oil extraction lies in reducing crude oil viscosity. Alkali-surfactant-polymer (ASP) flooding technology has emerged as an effective method for enhancing heavy oil recovery. However, the chromatographic separation of chemical agents presents a formidable obstacle in heavy oil extraction. To address this challenge, we utilized a free radical polymerization method, employing acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, lauryl acrylate, and benzyl acrylate as raw materials. This approach led to the synthesis of a multifunctional amphiphilic polymer known as PAALB, which we applied to the extraction of heavy oil. The structure of PAALB was meticulously characterized using techniques such as infrared spectroscopy and Nuclear Magnetic Resonance Spectroscopy. To assess the effectiveness of PAALB in reducing heavy oil viscosity and enhancing oil recovery, we conducted a series of tests, including contact angle measurements, interfacial tension assessments, self-emulsification experiments, critical association concentration tests, and sand-packed tube flooding experiments. The research findings indicate that PAALB can reduce oil-water displacement, reduce heavy oil viscosity, and improve swept volume upon injection into the formation. A solution of 5000 mg/L PAALB reduced the contact angle of water droplets on the core surface from 106.55° to 34.95°, shifting the core surface from oil-wet to water-wet, thereby enabling oil-water displacement. Moreover, A solution of 10,000 mg/L PAALB reduced the oil-water interfacial tension to 3.32 × 10-4 mN/m, reaching an ultra-low interfacial tension level, thereby inducing spontaneous emulsification of heavy oil within the formation. Under the condition of an oil-water ratio of 7:3, a solution of 10,000 mg/L PAALB can reduce the viscosity of heavy oil from 14,315 mPa·s to 201 mPa·s via the glass bottle inversion method, with a viscosity reduction rate of 98.60%. In sand-packed tube flooding experiments, under the injection volume of 1.5 PV, PAALB increased the recovery rate by 25.63% compared to traditional hydrolyzed polyacrylamide (HPAM) polymer. The insights derived from this research on amphiphilic polymers hold significant reference value for the development and optimization of chemical flooding strategies aimed at enhancing heavy oil recovery.

Preparation of carbon-based active nanofluids with temperature and salt resistance for enhanced oil recovery

The abundant hydrophilic surface groups endow carbon-based nanoparticles (CDs) with intrinsic great dispersibility, however, the strong hydrophilicity limits the oil–water interface activity, restraining the performance in enhanced oil recovery. Developing CDs with simultaneously ultra-small sizes, high temperature and salt tolerance, as well as superior interfacial activity is of great significance. In this work, CDs with the size of 3.3 nm and excellent temperature and salt resistance were prepared by hydrothermal reaction, using citric acid (CA) and ethylenediamine (EDA) as precursors. Carboxyl ether carboxylate-6Na (APEC-6Na) was selected as the compound agent to construct carbon-based active nanofluids (CANs) with excellent oil–water and oil-solid interfacial activities. CANs can reduce the oil–water interfacial tension to 8.9 × 10-4 mN m−1, withstand a temperature up to 90°C and a salinity up to 6.3 × 104 mg·L-1. Even at the highest tolerant salinity, the underwater oil contact angle of 155° can be achieved, demonstrating excellent wettability control capability, which could be attributed to the synergistic effect of the compound CANs system. The increase of the contact angle of underwater oil droplets facilitates the coalescence of oil film on the lipophilic surface to form oil droplets. The electrostatic repulsion generated by the adsorption of CDs and APEC-6Na at the oil–water interface and rock surface makes the coalesced oil droplets more easily detached from the rock surface, and the oil film reduction rate exceeds 97.7 % within 24 h. The excellent oil–water and oil-solid interface properties and the structural separation pressure endows CANs with remarkable performance in core displacement experiments. Compared with simulated formation water, CANs can improve the recovery rate by 26.3 %, exhibiting important application value for improving the recovery rate of ultra-low permeability reservoirs.

CO2-philicity to CO2-phobicity Transition on Smooth and Stochastic Rough Cu-like Substrate Surfaces.

CO2 on metal substrates is essential to CO2 liquefaction and transportation of CO2, yet the manipulation of the wettability of the CO2 and the elucidation of its underlying mechanism have not been fully achieved. Here, using molecular dynamics simulations, we report CO2 wetting characteristics on both smooth and stochastic rough Cu-like substrate surfaces. The results indicate that the apparent contact angle (CA) of the CO2 droplet on the smooth surface decreases from 180° to 0° as the CO2-solid characteristic interaction energy increases from 0.002 to 0.016 eV. In addition, the CAs become greater with increasing the density of surface asperities, regardless of the intrinsic surface wettability. This is attributed to the capillary drying-out of liquid CO2 molecules in gaps between surface asperities at the three-phase contact line of the droplet, which is usually overlooked in previous theoretical studies. Notably, the intrinsically CO2-philic surface transforms to the CO2-phobic due to an increase in the density of surface rugosity. Moreover, we verify the range of applicability of the CA prediction models concerning the nanoscale asperities. This work is beneficial for fully understanding the influence of nanoscale surface topography on CO2 wettability and shedding light on the design of functionalized and patterned surfaces to manipulate CO2 wettability.

Numerical investigation of oil droplet detachment from wall surface by a microbubble using ternary phase‐field model

AbstractIn this study, we investigated the detachment of an oil droplet from a wall surface by microbubbles (MBs) using the numerical simulation of a gas–liquid–liquid three‐phase flow based on a phase‐field model. A single MB was collided with an oil droplet adhered to a wall surface to determine whether the droplet would detach from the wall. It was confirmed that the oil droplet detached from the wall when the interfacial tension between the water and oil or between the bubble and oil was low. To clarify the mechanism, we theoretically calculated the balance of interfacial tension at the three‐fluid contact line. The lower the interfacial tension between the water and oil and between the bubble and oil, the smaller the contact angle of the oil droplet on the bubble. This increased wettability was the driving force that caused the oil droplet to detach from the wall surface.

Machine-Learning Approach in Prediction of the Wettability of a Surface Textured with Microscale Pillars.

Tuning the wettability of a flat surface by introducing an array of microscale pillars finds wide applications, especially in engineering a superhydrophobic surface. The wettability of such a pillared surface is quantified by the contact angle (CA) of a water droplet. It is desired to know the CA prior to construction of pillars, in order to obviate the trial-and-errors in experimenting with many different topographies. Given an accurate theoretical prediction of CA has been elusive, we propose a convolutional neural network (CNN) model of CA for a surface patterned with rectangular or cylindrical pillars. By employing a three-dimensional descriptor of the surface topography, the present CNN model can predict experimental CAs within errors comparable to the uncertainties in measuring CAs.

A study on the model of solar radiation transfer in multi-layer glass facade with attached droplets

To obtain the optical properties of the spray cooling double skin façade (SC-DSF), a solar radiation transfer model of the multi-layer glass system with attached droplets is proposed in this study. The solar radiation is segmented into direct and diffuse radiation, and the monte carlo ray tracing method and angle discretization method are used to obtain the optical properties of the single layer glass with attached droplets. And then, the energy balance equation of the multilayer glass system is established based on the net-radiation method, and the transmittance, reflectance and absorptance of the multilayer glass system are calculated. The effectiveness of the proposed method is verified by the experimental results, which shows the numerical results are in good agreement with the experimental data. In addition, some important influence factors are analyzed and discussed, including the solar incidence angle, the droplet contact angle, the droplet coverage rate, and the average droplet diameter. It is found that there is little influence on the system transmittance when the incidence angle is smaller than 40°. However, the transmittance decreases with the increase of the incidence angle when the solar incidence angle is greater than 40°. When the droplet contact angle is small (less than 40°) or large (larger than 140°), its influence on the transmittance of the system is negligible. Subsequently, with the increase in the droplet contact angle within 40–140°, the transmittance firstly decreases and then increases. Adjusting the droplet coverage rate and droplet size is an effective measure to decrease transmittance and solar heat gain.

Enhanced lipophilicity and wear resistance of 20CrMnTi induced by laser surface texturing

Gear transmission is crucial in mechanical engineering, extensively used in automobiles, ships, machine tools, and airplanes. However, as gear systems advance towards higher speeds, heavier loads, and smaller sizes, the tooth surface becomes more prone to pitting, wear, and other failures. The use of laser surface texturing technology has shown great promise in enhancing the hydrophobic and lipophilic properties of material surfaces. Thus, this paper presents a novel approach for machining equally spaced parallel and perpendicular microgrooves on the surface of gear steels (20CrMnTi) to facilitate lubricant storage and enhance the material’s surface lipophilicity. Laser power and scanning speed are optimized as parameters for laser processing to investigate the lipophilic properties, including the contact angle, diffusion velocity, and contact behavior of oil droplets. Comparative analysis of the processed and unprocessed specimens revealed that both static and dynamic contact behaviors are significantly changed. Compared with the unprocessed specimens, the static contact angle of the processed specimens decreases from 47° to 0° and is super lipophilic at different temperatures; the oil droplet diffusion distance increases by a maximum of 1.27 times; the vertical diffusion height increases by a maximum of 2.8 mm; and the wetting hysteresis coefficient increases by a maximum of 2.55 times. Additionally, the friction coefficient decreases during the stable wear phase, and the wear depth is reduced by 33.53 %. The research has demonstrated that the oil-attracting properties of 20CrMnTi can be greatly enhanced using laser micro-nano texture technology. This improves lubrication conditions and wear resistance, providing a novel approach to mitigating failure risks such as pitting and wear in various gear mechanisms. Furthermore, this method effectively extends the service life of gears, making it a valuable tool for gear engineering applications.

Effect of high directional convex structure on droplet morphology and contact angle

The morphology of a surface has certain influences on its wettability as reflected by the shape of a sessile droplet thereon. The topological structure of superhydrophobic silicone rubber (MVQ) prepared by template method has the characteristics of simple shape and regular arrangement, but such a structure will lead to unstable contact angle (CA) of superhydrophobic surface. Through this study, it is found that the CA value of the original flat MVQ surface is the same in any direction. However, from 0° to 90°, it is observed that the CA on the MVQ surface, the contact radius between water droplets and MVQ and the projected area of water droplets are different. In different directions, the maximum error of CA is 13.75°, the maximum error of contact radius between water droplets-MVQ is 209.5 μm, and the maximum error of projected area of water droplets is 0.284 mm2. In addition, it is found that the contact radius between water droplets and the surface of silicone rubber decreases with the increase of the projected area of water droplets in the direction of larger CA. In order to explain the error of CA and droplet shape due to directionality, this phenomenon is explained by micro-morphology and three-dimensional morphology combined with contact line density theory. This discovery is beneficial to design super-hydrophobic surface with high directionality and realize the application of micro-channel control technology.

Visible light induced self‐cleaning performance of iron‐doped TiO2 nanoparticles for surface applications

AbstractThis study aimed to enhance the visible light photosensitivity of TiO2 nanoparticles for self‐cleaning applications by doping with Fe3+. Nanocrystalline undoped and Fe‐doped TiO2 (Ti1 − xFexO2, x = .01–.04) were synthesized via sol–gel method. The results demonstrated that Fe‐doped TiO2 nanoparticles exhibited visible light sensitivity and self‐cleaning properties. An increased Fe concentration resulted in a red shift in the absorption band edge. Fe0.03‐doped TiO2 with an average particle size of ∼21 nm, a crystallite size of ∼12 nm, and a band gap of ∼2.86 eV showed the highest photocatalytic activity (60% methylene blue degradation) and super‐hydrophilicity (water droplet contact angle 9°) under visible light radiation. These findings highlight the potential of Fe‐doped TiO2 nanoparticles as a promising material for self‐cleaning applications.

Integrated design of a robust superhydrophobic cement mortar layer via sizing sand grains

This work reported a facile route for fabricating super-hydrophobic concrete via sizing sand grains. It was found that mixing the sands with a size ranging from 150–180 μm into cement enabled the formation of a lotus-like surface with a papillary structure at micro-scale. SEM showed that the size of bumper was about 3 μm. When spraying a fluorocarbon solution onto this surface, the porous nature of the cement matrix showed the advantage of taking the fluorocarbon into the internal structure of the concrete via capillary force. As a result, the sub surface up to a depth of ∼1.5 mm were transformed into a thick superhydrophobic layer directly. The contact angle (CA) of water droplets could reach 157° on this surface, and which could remain more than 150° after abrasion 100 cycles under a weight of 300 g at 360 grit sandpaper. This thick hydrophobic layer significantly reduced the corrosion rate of the steel the concrete at the Cl- environment by 620 times. The measurement of British pendulum number and compression strength revealed that this superhydrophobic layer was beneficial for maintaining the friction coefficient of the concrete surface in wet condition without altering the mechanical integrity of the concrete.

Effect of hydroxyl position in reagent molecule on coal dust dedusting

Using the high-speed motion acquisition system, we studied the adhesion ability and wetting ability of coal dust under the effect of four octanol solutions. The adhesion ability followed the order: 2-Octanol > 4-Octanol > 1-Octanol > 3-Octanol. The wrap angle of coal dust on the octanol surface exhibited an increasing trend with the rise in coal proportion of dust. The observed behavior was substantiated by the interaction force, ascertained through molecular dynamic simulations. The interaction force between coal dust and 3-Octanol was the smallest leading to the weakest adhesion ability by the 3-Octanol solution. The contact angle of octanol solution droplet at the coal dust surface under the same octanol concentration was investigated to follow the order: 2-Octanol > 4-Octanol > 1-Octanol > 3-Octanol. The wetting velocity decreased as the coal proportion of dust increased. The wetting ability followed the order: 2-Octanol < 4-Octanol < 1-Octanol < 3-Octanol. The surface energy of dust increased as the coal proportion decreased. The dedusting efficient under the effect of octanols depended on the difference in surface energy between the coal dust and the octanol solution. The greater the Δγ (difference between the surface energy of the dust and solution), the weaker the adhesion ability, and the stronger the wetting ability. The findings of our study can offer valuable insights for the development of dedusting reagent design.

Effect of different Cu:Co film concentrations on photocatalytic reactions of ethanol, MB, AMX, and Cr(VI): A study of film properties & effects of photooxidation

Wastewater treatment is an urgent challenge of the 21st century, and photocatalysis represents a promising approach. However, much of the research has focused on powdered photocatalysts and complex, costly methods, leading to limitations in practical applications. This study introduces an innovative approach to produce Cu:Co thin films with different weight ratios (70:30, 50:50, and 30:70) by the low-cost dip-coating technique. The photocatalytic activity of Cu:Co films was investigated through the photooxidation of alcohol (EtOH), degradation of dye (MB), antibiotic (AMX), and photoreduction of heavy material ions (Cr(VI)) under sunlight irradiation. The results clearly show that higher Cu concentration ratios (70:30%) resulted in smoother surfaces (49.7 nm), higher droplet contact angle (72.43°), smaller particles (67 nm), lower film thickness (365 nm), narrower band gap (1.68 eV), higher transmittance (26.7%), and improved degradation of MB (78% for 4 h) and amoxicillin (43% for 45 min). Conversely, higher Co ratios may yield contrasting effects in most cases. The photoreduction of Cr(VI) showed similar results for Cu:Co films with 70:30 and 50:50 ratios, reaching 42.81% and 43.82% for 30 min, respectively. The effect of the ethanol photooxidation process significantly reduced the roughness, film thickness, and band gap in all Cu:Co films while enhancing transmittance, except for the 50:50 Cu:Co ratio. Cu:Co films are ideal for practical applications such as photoreaction processes due to their efficiency, sustainability, and stability.

Micromachining on Stainless Steel 304 for Improved Water Condensation Properties

Microstructure fabrication and chemical surface functionalization with low-surface-energy materials are the key steps to achieve hydrophobic surfaces with high water droplet contact angles (CA). In this work we employed wire Electric Discharge Machining (EDM) as a way to induce microstructure topography on stainless steel 304 coupons. The resulting topography was rendered hydrophobic using trichloro-1H,1H,2H,2H-perfluorooctyl silane (PFOTS) via gas phase deposition. The channels created by machining and PFOTS functionalization facilitate water condensation by increasing nucleation sites and enhancing droplet coalescence. The resulting surface is hydrophobic (CA~140o) in contrast to the bare stainless steel 304, which is hydrophilic (CA~76o).

A molecular dynamics investigation on CO2–H2O–CH4 surface tension and CO2–CH4–H2O–graphite sheet contact angles

Introduction: We perform molecular dynamics (MD) simulations of nanoscopic liquid water drops on a graphite substrate mimicking the carbon-rich pore surface in the presence of CH4/CO2 mixtures at temperatures in the range 300 K–473 K.Methods: The surface tension in MD simulation is calculated via virial expression, and the water droplet contact angle is obtained through a cylindric binning procedure.Results: Our results for the interfacial tension between water and methane as a function of pressure and for the interfacial tension between water and CH4/CO2 mixtures as a function of their composition agree well with the experimental and computational literature.Discussion: The modified Young’s equation has been proven to bridge the macroscopic contact angle and microscopic contact with the experimental literature. The water droplet on both the artificially textured surface and randomly generated surface exhibits a transition between the Wenzel and Cassie–Baxter states with increased roughness height, indicating that surface roughness enhances the hydrophobicity of the solid surface.