Wettability Modification Research Articles

Wettability modification of polydimethylsiloxane surface by fabricating micropillar and microhole arrays

Fabrication of microscale surface structures is a promising method for controlling the surface wettability of materials. Herein, the micropillar and microhole arrays of polydimethylsiloxane (PDMS) were fabricated through a soft lithography process, and the modified wettability was investigated. Using PDMS samples with different degrees of crosslinking, a PDMS–PDMS pattern transfer was achieved, and the microhole and micropillar arrays were obtained from a single master substrate. The surface geometries of the prepared PDMS samples were characterized via scanning electron microscopy and laser scanning microscopy. It was demonstrated that the PDMS micropillar and microhole arrays were effective in changing the contact angles of liquids with different surface tensions (water, ethylene glycol, olive oil, and hexadecane). The measured contact angles of the liquids on a PDMS micropillar array were quantitatively interpreted in both the wetting and repellent regimes based on the Cassie-Baxter model.

Comparison of solidity and fractal dimension of plasma sprayed splat with different spreading morphologies

The paper deals with the quantitative characterization of spreading morphologies of plasma sprayed Fe-based alloy droplets deposited on mirror polished steels with different preheated temperature. The plasma torch was utilized as heat producer. The influence of substrate temperature on the solidification mechanism of molten droplets was investigated. The image analysis method (IMA) was employed to identify single splat from the field emission scanning electron microscope (FE-SEM) morphology. The result shows that the substrate preheated temperature has a significant effect on the flattening behavior of molten droplets. With the increment of substrate temperature, the solidification mode of splat changes from flower-like and splashed splat to disk-like splat due to the modification of wettability and cooling velocity between molten droplet and substrate. Compared with area and perimeter, both fractal dimension (FD) and solidity could separately detect the solidification mode of splat to a certain extent, while the FD seems to be more excellent in characterizing irregular morphology of splat in contrast with solidity. However, the combination of FD and solidity is more efficient in classifying solidification mode of splat.

Wettability Modification of Lignite by Adsorption of Dodecyl Based Surfactants for Inhibition of Moisture Re‐adsorption

AbstractIn order to restrain moisture re‐adsorption of dried lignite, a series of dodecyl based surfactants with various hydrophilic heads including dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfonate (SDS), dodecyl nonaethoxyl ether (C12EO9) and a gemini surfactant (G12‐2‐12) were used to adsorb on lignite surface for wettability modification. The adsorption isotherms and zeta potential were determined to study the adsorption process. Lagergren‐first‐order and pseudo‐second‐order kinetics models were used to simulate the adsorption kinetics. The modified lignite was characterized by FTIR spectroscopy, and the wettability of it was evaluated by the wetting heat and moisture re‐adsorption ratio. The results indicate that hydrophilic heads of surfactants play an important role in adsorption mechanisms and structures of their adsorption layers on lignite surface, which are responsible for wettability alteration. Four surfactants produce different effects on restraining moisture re‐adsorption of lignite: the effect of cationic surfactants is better and worse for anionic surfactant SDS, while the non‐ionic surfactant C12EO9 shows intermediate behavior. But with the formation of double‐layer adsorption, hydrophilic headgroups of surfactant face outward, which causes hydrophilicity of lignite to rise again. Combining adsorption situations and wettability modification effects, the relationship between molecular orientation of four surfactants on a lignite surface and wettability reversal of lignite are discussed.

Oil Configuration Under High-Salinity and Low-Salinity Conditions at Pore Scale: A Parametric Investigation by Use of a Single-Channel Micromodel

Summary Low-salinity waterflooding (LSF) is receiving increased interest as a promising method to improve oil-recovery efficiency. Most of the literature agrees that, on the Darcy scale, LSF can be regarded as a wettability-modification process, leading to a more-water-wet state, although no consensus on the microscopic mechanisms has been reached. To establish a link between the pore-scale and the Darcy-scale description, the flow dynamic at an intermediate scale—i.e., networks of multiple pores—should be investigated. One of the main challenges in addressing phenomena on this scale is to design a model system representative of natural rock. The model system should allow for a systematic investigation of influencing parameters with pore-scale resolution while simultaneously being large enough to capture larger-length-scale effects such as saturation changes and the mobilization and connection of oil ganglia. In this paper, we use micromodels functionalized with active clay minerals as a model system to study the low-salinity effect (LSE) on the pore scale. A new method was devised to deposit clays in the micromodel. Clay suspensions were made by mixing natural clays (montmorillonite) with isopropyl alcohol (IPA) and were injected into optically transparent 2D glass micromodels. After drying the models, the clay particles were deposited and stick naturally to the glass surfaces. The micromodel was then used to investigate the dependence of the LSE on the type of oil (crude oil vs. n-decane), the presence of clay particles, and aging. Our results show that the system is responsive to low-salinity brine as the effective contact angle of crude oil shifts toward a more-water-wetting state when brine salinity is reduced. When using n-decane as a reference case of inert oil, no change in contact angle occurred after a reduction in brine salinity. This responsiveness in terms of contact angle does not necessarily mean that more oil is recovered. Only in the cases where the contact-angle change (because of low-salinity exposure) led to release of oil and reconnection with oil of adjacent pore bodies did the oil become mobile and the oil saturation effectively reduce. This makes contact-angle changes a necessary but not sufficient requirement for incremental recovery by LSF. Interestingly, the wettability modification was observed in the absence of clay. Osmosis and interfacial tension (IFT) change were found not to be the primary driving mechanisms of the low-salinity response.

Analysis of Liquid–Liquid Droplets Fission and Encapsulation in Single/Two Layer Microfluidic Devices Fabricated by Xurographic Method

This paper demonstrates a low cost fabrication approach for microscale droplet fission and encapsulation. Using a modified xurography method, rapid yet reliable microfluidic devices with flexible designs (single layer and double layer) are developed to enable spatial control of droplet manipulation. In this paper, two different designs are demonstrated, i.e., droplet fission (single layer) and droplet encapsulation (double layer). In addition, the current fabrication approach reduces the overall production interval with the introduction of a custom-made polydimethylsiloxane (PDMS) aligner. Apart from that, the fabricated device is able to generate daughter droplets with the coefficient of variance (CV) below 5% and double emulsions with CV maintained within 10% without involvement of complex surface wettability modification.

Enhanced Wettability Modification and CO2 Solubility Effect by Carbonated Low Salinity Water Injection in Carbonate Reservoirs

Carbonated water injection (CWI) induces oil swelling and viscosity reduction. Another advantage of this technique is that CO2 can be stored via solubility trapping. The CO2 solubility of brine is a key factor that determines the extent of these effects. The solubility is sensitive to pressure, temperature, and salinity. The salting-out phenomenon makes low saline brine a favorable condition for solubilizing CO2 into brine, thus enabling the brine to deliver more CO2 into reservoirs. In addition, low saline water injection (LSWI) can modify wettability and enhance oil recovery in carbonate reservoirs. The high CO2 solubility potential and wettability modification effect motivate the deployment of hybrid carbonated low salinity water injection (CLSWI). Reliable evaluation should consider geochemical reactions, which determine CO2 solubility and wettability modification, in brine/oil/rock systems. In this study, CLSWI was modeled with geochemical reactions, and oil production and CO2 storage were evaluated. In core and pilot systems, CLSWI increased oil recovery by up to 9% and 15%, respectively, and CO2 storage until oil recovery by up to 24% and 45%, respectively, compared to CWI. The CLSWI also improved injectivity by up to 31% in a pilot system. This study demonstrates that CLSWI is a promising water-based hybrid EOR (enhanced oil recovery).

Laser Modification of Wettability of Glass Surface and its Application for Surface Flow Channel

Laser Modification of Wettability of Glass Surface and its Application for Surface Flow Channel

Laser surface texturing of granite

Presence of contaminants on surfaces becomes a significant problem both in industry and at home. Small particles or bacteria adhered to surfaces of domestic kitchens are not easily removed by regular cleaning procedures. The effect of substratum wettability upon contaminants adhesion has been known for a long time. The phenomenon of surface cleaning is closely related to morphology, and chemistry of surfaces. These characteristics can be modified by subjecting materials to surface treatments. One of the most promising techniques aiming to modify surface features is the laser texturing. In such a way, it is possible to achieve the surface properties leading to the desired wettability in an accurate manner, and with minor contamination. In this work, the wetting features of Zimbabwe black granite, a middle-to-fine-grained natural stone commonly employed as countertops in kitchens and bathrooms, are modified by laser surface texturing. The main aim is to increase its hydrophobic degree so as to reduce the attachment of contaminants on the surface. For such purpose, two laser sources (λ = 1064 and 532 nm) were employed. The influence of different laser processing parameters on surface characteristics (wettability, roughness, and chemistry) of granite was statistically assessed. The morphology resulted from the laser surface texturing was found to be the principal phenomenon governing the wettability modifications, as the chemical composition remained virtually unaltered after treatment.

Plasma Processing with Fluorine Chemistry for Modification of Surfaces Wettability.

Using plasma in conjunction with fluorinated compounds is widely encountered in material processing. We discuss several plasma techniques for surface fluorination: deposition of fluorocarbon thin films either by magnetron sputtering of polytetrafluoroethylene targets, or by plasma-assisted chemical vapor deposition using tetrafluoroethane as a precursor, and modification of carbon nanowalls by plasma treatment in a sulphur hexafluoride environment. We showed that conformal fluorinated thin films can be obtained and, according to the initial surface properties, superhydrophobic surfaces can be achieved.

Influence of Superhydrophobic Properties on Deicing

Nowadays the creation of anti-icing, or deicing, surfaces is one of the most important problems, as such surfaces are widely used in aeronautics, wind turbines, and telecommunication antennas. In this paper, we focus mainly on reducing the ice adhesion forces and easy ice removal, once ice has formed. Removal of a liquid from a surface can be provided by modification of the surface wettability by means of applying superhydrophobic coatings. Such coatings are water-resistant, i.e., are characterized by low water adhesion forces. To study the impact of superhydrophobic coatings, tests were performed on the surface of a wing in a wind tunnel. By spraying Teflon and polyphenylene sulfide (PPS) on the wing, we obtained a superhydrophobic film. This film has a structure that provides superhydrophobic properties, so that the wetting angle is above 140°. A comparison of the resulting surface with a clean Teflon one shows that adhesion of the Teflon + PPS mixture to an aluminum surface is five times higher. We also investigate the degree of ice formation on the surfaces of simple and superhydrophobic aircraft wings at a temperature of –18°C. It was shown that ice was formed on a simple wing within 40 s and on a superhydrophobic wing within 25 s. When the simple wing with a mass of 23 g was inserted into the wind tunnel, its mass reached 50 g, and for a superhydrophobic wing with a mass of 26 g the latter reached 42 g. The sample of the airfoil wing we prepared has a low adhesion, which helps in easy ice removal.

Femtosecond laser-induced surface wettability modification of polystyrene surface

In this paper, we demonstrated a simple method to create either a hydrophilic or hydrophobic surface. With femtosecond laser irradiation at different laser parameters, the water contact angle (WCA) on polystyrene’s surface can be modified to either 12.7° or 156.2° from its original WCA of 88.2°. With properly spaced micro-pits created, the surface became hydrophilic probably due to the spread of the water droplets into the micro-pits. While with properly spaced micro-grooves created, the surface became rough and more hydrophobic. We investigated the effect of laser parameters on WCAs and analyzed the laser-treated surface roughness, profiles and chemical bonds by surface profilometer, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). For the laser-treated surface with low roughness, the polar (such as C—O, C=O, and O—C=O bonds) and non-polar (such as C—C or C—H bonds) groups were found to be responsible for the wettability changes. While for a rough surface, the surface roughness or the surface topography structure played a more significant role in the changes of the surface WCA. The mechanisms involved in the laser surface wettability modification process were discussed.

Influence of the Oxygen Plasma Treatments on Surface Wettability of Glass Micro Fibers Used as Reinforcement in any Mortars

Presented work deals with the surface treatments and its effect on micro fibers using as randomly dispersed reinforcement in many types of composite materials. Cool oxygen plasma was used to surface wettability modification of chopped glass fibers having diameter equal to 14 μm. Plasma treatments were carried out at three different times of exposition equal to 4 min, 8 min and 16 min. The influence of executed treatments was observed by the horizontal direct optical method enabling static contact angle measurements on micro fibers which were submerged in a distilled water. The identified differences between the contact angles size of original fibers and the treated fibers were equal to several tens of percent.

Wettability modification and restraint of moisture re-adsorption of lignite using cationic gemini surfactant

Adsorption of surfactants onto lignite surface may result in wettability changes and slow the re-adsorption of moisture onto dried lignite. In this work, a cationic gemini surfactant, ethanediyl-1,2-bis(dimethyl dodecyl ammonium bromide) (12-2-12), was chosen, and its adsorption characteristics and the influence on the surface wettability of lignite were investigated. The results suggest that a strong attraction takes place between the negatively charged lignite surface and a gemini surfactant with positively charged head groups to form a monolayer adsorption in low surfactant concentration. Electrostatic forces play a dominant role in the adsorption of a cationic gemini surfactant on the lignite surface while hydrogen bonding does not. The adsorption density of a gemini surfactant on coal surfaces increased with an enhancement in the amount of polar oxygen containing functional groups and the addition of KCl. A decrease in wetting heat indicated that the lignite treated with the gemini surfactant led to a significant decrease in the hydrophilicity of lignite. The high concentration of oxygen-containing functional groups increased the negative charge of the coal surface, which is beneficial for adsorption of the cationic gemini surfactant adsorption onto the coal surface that decreased the hydrophilicity of lignite effectively. The lignite wettability surface modification results were compared with the traditional cationic surfactant cetyltrimethyl ammonium bromide (CTAB); these results suggested that the unique chemical structure of the gemini surfactant with two hydrophilic and two hydrophobic groups had a more prominent impact on lignite surface hydrophilicity. The gemini surfactant adsorbed on lignite surface also had a significant improvement in resisting moisture re-adsorption and could create pathways toward utilizing lignite industrially.

Water based EOR from clastic oil reservoirs by wettability alteration: A review of chemical aspects

Water flooding of oil reservoirs has been, and still is, the most important technique to increase oil recovery from both carbonate and clastic oil reservoirs. Significant improvements in the general understanding of the wetting properties of oil reservoirs have been the fundament for a lot of research during the last 15–20 years with the objective to optimize the oil recovery by wettability modification. The ion composition of the injected water can modify the wetting properties of the porous rock during the production time, and improve the displacement of oil. Such an EOR technique is environmentally friendly, because no external chemicals are added, and significant extra oil amounting to 5–20%OOIP have been reported, both in the laboratory and in field pilots. Therefore, water based EOR by wettability modification has received great interest among oil companies and researchers. A large number of different mechanisms have been suggested for this EOR process. This paper is a chemical review of the EOR technique called Smart Water flooding, which also include aspects of low salinity flooding in clastic reservoirs. The review is divided into four main parts; (1) The most important wetting parameters for the different phases, oil, brine and rock, are presented, (2) The symbiotic interaction between the different wetting parameters on the initial wetting properties is discussed, (3) The chemical mechanism for observing “Smart Water” EOR effects at different initial wetting conditions is presented, and (4) The suggested chemical mechanism is verified by lab and field data.

Wettability modification, interfacial tension and adsorption characteristics of a new surfactant: Implications for enhanced oil recovery

This paper concerns with the interfacial tension (IFT), wettability modification and adsorption behavior of a new plant-based surface active agent, Zizyphus Spina Christi, onto sandstone minerals which has been rarely attended in the available literature. Both kinetics and equilibrium adsorption data were obtained from batch mode tests. It was revealed that Freundlich isotherms matched better fit to the equilibrium data which implied that multilayer coverage of Zizyphus Spina Christi onto the sandstone particle surfaces was more likely to occur. Analysis of experimental kinetic data based on intraparticle diffusion model disclosed that the intraparticle diffusion mechanism is not the only rate limiting step and the boundary layer diffusion or surface adsorption also contributes to the rate-controlling step. The reservoir rock wettability modification was evaluated on sandstone-oil phase−water system by change of surfactant concentration, time and solution salinity. The results of this work help toward a clearer understanding the impact of various influencing parameters on the efficiency of a surfactant flooding project.

Aluminum surface wettability changes by pool boiling of nanofluids

Boiling of colloidal suspensions has been found to modify surface properties, which can lead to enhancements in heat transfer processes. In this paper, a systematic study of the surface modification after nanofluid boiling is reported. Aluminium substrates of different initial roughness were used to study the roughness effect on the wettability after boiling in various nanofluid concentrations, boiling durations and heat fluxes. Experimental results show that these parameters are significant to surface wettability changes. Extending boiling duration and increasing nanofluid concentration exhibits positive impact on the surface wettability enhancement, while roughness has a more complex influence. The mechanism of the wettability modification is revealed by microscopy and goniometry. It was found that the enhanced wettability on aluminium surfaces after boiling in Al2O3 nanoparticle aqueous suspensions is due to the growth of hydroxides and the deposition of particles during the boiling process, so both chemical and topographical modifications were caused by nanofluid boiling on aluminium surface. Scanning electron microscope (SEM) images demonstrate that, micro and nano multi-scale structures were introduced to the surface after the treatment, which contributes to the enhancement of wettability, and improves longevity. The good agreement of roughness factor obtained by atomic force microscopy (AFM) and water contact angle experiment indicates Wenzel wetting state on the surface.

Wettability modification of graphene oxide thin film through the photocatalytic reduction

In this paper, the effect of photocatalytic reduction on hydrophilicity of graphene oxide nanosheets is presented. The graphene oxide nanosheets were prepared by oxidation and exfoliation of natural graphite. The prepared samples were exposed to UV irradiation in presence of TiO2 nanoparticles. Raman spectroscopy and atomic force microscopy show that roughness of the surface is increased due to increasing irradiation. Also, the hydrophilicity of samples by measuring the contact angle of micro-liter droplets of deionized water, showed that by increasing exposure time up to 8 hours the contact angle of samples in crease from about 27 degrees to about 89 degrees.

Tailoring the surface wettability of polyimide by UV laser direct texturing in different gas atmospheres

Surface wettability modification of polyimide film was studied by UV laser direct texturing (UVLDT). The influences of laser fluence on surface microstructure, chemical composition and wettability were explored in air, O2, and N2 atmospheres, respectively. Scanning electron microscopy (SEM), surface probe profilometry, X-ray photoelectron spectroscopy (XPS), and water contact angle measurement were utilized for the characterization of laser-textured surfaces. It was found that in the same modification atmosphere, surface microstructure and roughness played a major role in changing the wetting behavior of polyimide film with varied laser fluence. However, in the three different atmospheres, when polyimide film was textured with the same laser fluence, no significant difference of surface microstructure and roughness was observed. Here, XPS analysis showed that O2 atmosphere was the most favorable environment for increasing surface oxygen-containing groups and realizing superhydrophilicity. Whereas, in N2 atmosphere, the least oxygen-containing groups were produced and the superhydrophilic surface could not be obtained. It could be inferred that the effect of different modification atmospheres on wettability was due to the change of surface chemistry. Understanding of wetting mechanism and fabricating superhydrophilic polyimide film would benefit the development of surface engineering for flexible electronics, microfluidics and adhesion applications.

Modification of wettability property of titanium by laser texturing

Three different microstructures with line pattern, grid pattern, and spot pattern were fabricated on titanium surfaces by nanosecond laser. Scanning electron microscopy (SEM), contact angle measurement, surface roughness gage, and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize and measure the surface morphology, contact angle, surface roughness, and chemical composition of titanium after laser processing. The results indicate that the contact angle of titanium surface is 77.8° immediately after laser processing, which shows hydrophilicity, and the contact angle presents a rising tendency with time in general. At steady state, the maximum contact angles for line pattern, grid pattern, and spot pattern increased to 157.2°, 153°, and 132.5°, respectively. It can be found that the surface wettability has changed from hydrophilicity to hydrophobicity and even to superhydrophobicity. The influence of surface morphology on the surface wettability effects immediately after laser treatment and does not change with time, while the effect of surface chemical composition on the surface wettability will continue from the beginning of laser processing to the stabilization of surface chemical composition. Finally, it can be deduced that the accumulation of carbon on the surface is probably the critical factor to improve the surface hydrophobicity. Therefore, it is concluded that laser-induced modification of surface wettability correlates with surface morphology and surface chemical composition.

Controlled wettability based on reversible micro-cracking on a shape memory polymer surface.

Wettability modification on a polymer surface is of immense importance for flexible electronics and biomedical applications. Herein, controlled wettability of a styrene-based shape memory polymer has been realized by introducing micro-cracks on the polymer surface for the first time. The cracks were purposely prepared by thin metal film constrained deformation on the polymer. After the removal of the metallic film, wettability was dramatically enhanced by showing a remarkable reduction in the contact angle with water droplets from 85° to 25°. Subsequent systematic characterization techniques like XPS and SEM revealed that such observation could be attributed to the increased density of hydrophilic groups and the roughened surface. In addition, by controlling the temperature for annealing the treated polymer, the surface could be switched reversely to water-repellent. Therefore, this paper offers a smart tactic to manipulate the surface wettability of a shape memory polymer freely. The features of the controlled wettability surface such as high tenability, high stability and easy fabrication are promising for microfluidic switching and molecule/cell capture-release.