Reduction Of Surface Energy Research Articles

Membrane distillation by novel Janus-enhanced membrane featuring hydrophobic-hydrophilic dual-surface for freshwater recovery

Membrane distillation (MD) is a promising membrane process with nearly 100% salt rejection, which can can realize freshwater recovery and reuse. However, wetting and low permeate flux are major concern for the hydrophobic microporous membrane during MD operation. To address this concern, a simple and effective method to fabricate anti-wetting and high permeate flux Janus-enhanced membranes with double-sided spraying was developed. The spraying materials on both sides of the polytetrafluoroethylene (PTFE) membrane were prepared by crosslinking reactions. Sulfosuccinic acid (SSA) crosslinked MXene was used in the permeate side to construct hydrophilic nanochannels, consequently improving the permeate flux. Methyltriethoxysilane (MTES) crosslinked polydimethylsiloxanes (PDMS) was used in the feed side to reduce surface energy and enhance the anti-wetting ability of the membrane. The optimal water contact angles for the feed and permeate side were 135° and 71.8°, respectively. During direct contact membrane distillation (DCMD) experiments of seawater desalination, Janus-enhanced membrane proved to be stable after 60 h with an average permeate flux as high as 33.5 kg/(m2·h). Therefore, this study provided a novel insight on preparing a MD membrane with simultaneous enhanced permeability and wetting resistance for freshwater recovery.

Achieving superhydrophobic surfaces with tunable roughness on building materials via nanosecond laser texturing of silane/siloxane coatings

In this work, we employ a versatile laser-based top-down approach that allows to create superhydrophobic and hydrophobic surfaces, with controlled roughness and wetting properties, on marble and potentially other building materials. The process involves two stages: (1) application of an organically modified silica coating to reduce surface energy. (2) Controlled texturing of the coating by ablation using a nanosecond-pulse laser. In general terms, at higher laser fluence (energy per unity of area), the contact angles increased from 110° of the non-textured surface to values around 155°, following a nearly linear correlation with the measured roughness values. Starting from fluence values of 154 J cm−2, the surfaces displayed water repellence (hysteresis ≤10°) and the micrographs showed the formation of sub-micrometric structures on top of the micro-roughness by melting and re-deposition of the coating material, suggesting the formation of a Cassie-Baxter wetting regime. Ablation at lower fluences created a random micro-roughness, leading to static contact angles of 135–145° but no water repellence, which is indicative of a Wenzel wetting regime. At the highest fluence values tested, the increasing trends respect roughness and hydrophobic/water repellent properties are inverted due to the damages suffered by the coating. In terms of durability, the coating demonstrated a good adhesion to the stone surface, maintaining its superhydrophobic properties after repeated cycles of an “adhesive tape test”. The sand falling test showed that water repellence is relatively sensitive to abrasion, although the hydrophobic character of the coating is maintained.

Failure analysis on weld joint of centrifugal pump diffuser for oil and gas pipeline transportation

The failure mechanism of weld joint in centrifugal pump diffuser was analyzed through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron back-scattering diffraction (EBSD). Meanwhile, the strength and toughness of weld joint, heat-affected zone (HAZ), and matrix are quantitatively compared by geometrically necessary dislocation density (ρGND). The result indicated that the strength and toughness of HAZ are the highest, followed by matrix, and weld joint is the lowest. Defects such as slag inclusion and residual austenite create initial conditions for the corrosion of weld joint. Severe chloride ion corrosion resulted in micro-cracks on the weld surface. Meanwhile, corrosion reduces the surface energy of the micro-cracks. Therefore, the concentrated driving force makes the micro-cracks with reduced surface energy spread rapidly, eventually causing the rapid failure of diffuser weld joint. This study may provide a reference for petroleum engineers and centrifugal pump manufacturers.

Potential tribological and antibacterial benefits of pulsed laser-deposited zirconia thin film on Ti6Al4V bio-alloy

Demand for artificial body implants has been on the rise over the years. However, wear and bacterial infection are identified as two major reasons that can lead to inflammation and implant failure. In this communication, the advantages of pulsed laser deposited zirconia thin film on Ti6Al4V bio-alloy at room temperature and at an elevated substrate temperature are discussed wherein a comparison of the change in surface roughness, wettability, surface free energy, tribological and antibacterial properties of uncoated and zirconia coated Ti6Al4V samples is presented. The results of tribological analysis carried out using a standard ball-on-disc tribometer at different loads (2N, 5N and 7N) exhibited advantageous effects of zirconia coating on Ti6Al4V. Prominently, the sample coated at 200 C substrate temperature maintained very low coefficient of friction up to hundreds of sliding cycles and showed a notable reduction in the wear rate by 49% at 5N load. The in vitro bacterial retention test showed a clear inhibition in growth of Staphylococcus aureus and Klebsiella pneumonia bacteria on the surface of the coated samples indicating the possibility of prevention of biofilm formation. More than 50% reduction in density of Staphylococcus aureus was observed on coated sample in comparison to pristine Ti6Al4V and this can be attributed to reduction in surface energy of the sample after coating. Additionally, the observation of a larger number of decimated bacteria on coated samples by fluorescence microscopy revealed superior antibacterial properties of zirconia coating. The novelty of this work is the use of pulsed laser deposition technique for zirconia coating which dearly improves tribological and antibacterial properties of Ti6Al4V simultaneously; this shows prospects of increasing durability of artificial implant in the human body.

Toward functionalization without functional agents: An X-ray photoelectron spectroscopy study

Changes to the surface composition of hydroxyapatite were measured after incubations in water, in ethanol or in a mixed aqueous-alcoholic medium. Ethanol decreased the surface presence of calcium ions in direct proportion to its amount in the medium. Because of its lower polarity than that of water, ethanol also increased the interfacial energy, in response to which the surface relaxed by rearranging into a more disordered state, as indicated by the increase in the heterogeneity of both calcium and oxygen electronic states. Accordingly, the binding energy of core-level oxygen electrons consistently increased with the concentration of ethanol and was compensated for by the decrease of the corresponding binding energies in calcium atoms, attesting to the weakened ionic bonds at the interface. The weakened ionic bonds increased the metallicity of the calcium ion, which prompted the offset of the valence band edge determined by the Ca4s electron energy state toward the Fermi level and the conduction band, thus shrinking the band gap and increasing the electrical conductivity of the surface. The surface energy reduction entailing the partial loss of the crystalline order at the surface predisposed the nanoparticles incubated in alcoholic media for diminished sorption of proteins, but also for an augmented osteogenic response. These results demonstrate that surface functionalization of materials for various physicochemical and biological effects could be achieved without the use of chemical ligands. Rather, more economical design techniques stemming from the repertoire of materials science and engineering could be employed with equally satisfactory outcomes.

Wettability control on imbibition behavior of oil and water in porous media

Wettability determines the spreading or adherence behavior of fluids at the solid surface and significantly influences the displacement and entrapment of multiphase fluids in porous media. The present study sets out to determine how wettability controls the imbibition physics of oil and water in a matrix–fracture medium. The displacement and distribution characteristics of fluids, the types of flow regimes, and the fluid morphology under various conditions were revealed in depth. The influences of wettability on oil recovery and energy conversion were analyzed. Finally, the application of the conventional scaling model to simulated imbibition data was also discussed. Results show that the imbibition front is complete and stable in a water-wet medium with the one-end open boundary condition. There are three flow regimes occurring in countercurrent imbibition, depending on the wettability and Ca (capillary number) situations. Increasing θ (contact angle, the affinity of wetting phase to the solid) or Ca can shift the flow pattern from the capillary regime to the capillary-viscous regime to the viscous regime. Additionally, the imbibition oil recovery is greatly affected by wettability, and a more water-wet state does not signify a larger oil recovery. There is a power-law relationship between the oil recovery and the fractal dimension of the nonwetting phase. On the other hand, we performed the energy conversion analysis in the strongly water-wet condition. The external work is positive for both the capillary-viscous and viscous regimes and declines with the decreased Ca. Oil recovery could be linked to the surface energy ratio to some degree, which is relevant to Ca. For the capillary regime, oil recovery is proportional to the final reduced surface energy and does not have an evident relationship with the dissipation energy ratio. Through scaling the recovery factor data vs time via the linear, the power-law, and the conventional models, we find that the conventional scaling model can be used to fit the data point, and the fitting performance is good when Ca is relatively high. However, the linear model is more appropriate when scaling the data in low Ca. Overall, our pore-scale simulation study could pave the way for a further step toward investigating other influencing factors on imbibition behaviors of fluids in more complex media like natural rock materials, which exhibit strong heterogeneity of wettability and pore structure.

Theoretical and experimental study on plasma-induced atom-migration manufacturing (PAMM) of glass

Optical manufacturing plays an important role in various fields, such as optical lenses, telescopes, and laser optics. Generally, traditional optical manufacturing techniques are all subtractive processes based on the micro-shearing effect between the tool and surface protrusions. This paper reports a plasma-induced atom migration manufacturing (PAMM) process, which is a nonsubtractive finishing approach by which angstrom level surface roughness of fused silica has been successfully achieved. Inductively coupled plasma (ICP), which is characterized by high temperature and high radical density, is used as the tool of PAMM. After obtaining instantaneous plasma energy input on the fused silica surface, the peak site atoms migrate to the valley sites, thereby reducing the roughness. According to the energy minimization principle, this migration process continues until an ultra-smooth surface with reduced surface energy is formed. Atomic-scale molecular dynamics simulations were performed to clarify the microscopic mechanisms of PAMM, and experiments were conducted to verify its smoothing capability. The roughness of a ground silica surface was drastically reduced from Sa 391 nm to Sa 0.16 nm. This study demonstrates the feasibility of the PAMM as an alternative approach for atomic-level surface manufacturing.

Silane-modified wood fiber filled EPDM bio-composites with improved thermomechanical properties

Ethylene propylene diene monomer (EPDM) bio-composites filled with silane-modified wood fiber (Si-WF) were fabricated by melt batch mixing and compression molding. The effects of fiber loading, silane modification, and in situ cross-linking on the water absorption, thermal, and mechanical properties were investigated. Due to the reduced surface energy of the modified wood fibers, the EPDM bio-composites with Si-WF showed substantially lower water absorption and higher thermal stability than EPDM with unmodified wood fibers. With Si-WF and in situ cross-linking, the tensile strength and modulus of EPDM bio-composites exhibited up to 115.3 % and 258.9 % improvement over the pure EPDM, respectively. This was because of the enhanced dispersion of the Si-WF in the elastomer matrix, as noted from the fractography study.

Analysis of the Morphology of the Growth Interface as a Function of the Gas Phase Composition during the PVT Growth of Silicon Carbide

The growth conditions of 75 mm SiC crystals in the PVT process is varied by different methods while the temperature field is kept constant. The addition of graphite into the source material leads to the formation of an ordered step flow with step heights of 0.014 µm, while the addition of graphite into the source together with N2 doping changes the step kinetics on the main facet, leading to very large, bunched steps of 0.17 µm. When elemental Si was added into the source material large macro steps are formed on the whole crystal surface. While the doping induced step bunching is related to the incorporation kinetics, the large steps induced in Si-rich conditions are attributed the reduction of surface energy. With the variation of the inert gas pressure the morphology of the surface is altered, similarly. Under low pressure conditions (0.2 mbar) a fine step structure evolves, while at a high pressure (40mbar) large surface steps are formed on the whole growth interface. Large surface steps are strongly impeded in their lateral motion at defects permeating the growth interface. At these sites the formation of foreign polytypes is facilitated.

Adhesive and Hydrophobic Bilayer Hydrogel Enabled On‐Skin Biosensors for High‐Fidelity Classification of Human Emotion

AbstractTraditional human emotion recognition is based on electroencephalogram (EEG) data collection technologies which rely on plenty of rigid electrodes and lack anti‐interference, wearing comfort, and portability. Moreover, a significant distribution difference in EEG data also results in low classification accuracy. Here, on‐skin biosensors with adhesive and hydrophobic bilayer hydrogel (AHBH) as interfaces for high accuracy emotion classification are proposed. The AHBH achieves remarkable adhesion (59.7 N m−1) by combining the adhesion mechanism of catechol groups and electrostatic attraction. Meanwhile, based on the synergistic effects of hydrophobic group rearrangements and surface energy reduction, the AHB‐hydrophobic layer exhibits 133.87° water contact angles through hydrophobic treatment of only 0.5 h. Hydrogen and electrostatic bonds are also introduced to form a seamless adhesive‐hydrophobic hydrogel interface and inhibit adhesion attenuation, respectively. With the AHBH as an ideal device/skin interface, the biosensor can reliably collect high‐quality electrophysiological signals even under vibration, sweating, and long‐lasting monitoring condition. Furthermore, the on‐skin electrodes, data processing, and wireless modules are integrated into a portable headband for EEG‐based emotion classification. A domain adaptive neural network based on the transfer learning technique is introduced to alleviate the effect of domain shift and achieve high classification accuracy.

Heat Treatment Influencing Porosity and Tensile Properties of Field Assisted Sintered AlSi7Mg0.6.

In this study, an attempt was made to improve the mechanical properties and in particular the strength of a precipitation-hardenable aluminum alloy while still maintaining high ductility. For this purpose, AlSi7Mg0.6 (A357) powder with an average particle diameter of d50 = 40 µm was consolidated using field assisted sintering technique (FAST), and two material conditions were compared: an as-sintered and an underaging heat treated condition (T61). Mechanical properties were determined using tensile tests and hardness measurements. In addition, the microstructure was investigated by optical microscopy. Further, porosity and density were analyzed after the different heat treatments. By the underaging heat treatment, the surface hardness was increased by 100% and the yield strength was increased by 80% compared to the as-sintered material. However, the elongation to failure dropped to one third of that of the as-sintered material. Presumably, this effect was a result of an increased porosity due to the heat treatment. It is assumed that the observed pores were generated by artefacts from the FAST process used to manufacture the samples. The internal gas pressure and equilibrium diffusion supported by heat treatment temperature, and the reduction in surface energy caused by coalescent micropores, led to the enlargement of previously undetectable inhomogeneities in the as-sintered material that resulted in pores in the heat-treated sintered alloy.

Atomic diffusion bonding in air using Ag films

Atomic diffusion bonding (ADB) of wafers at room temperature in air was studied using Ag films. Using an ultra-high vacuum magnetron sputtering system, Ag (20 nm) films with Ti (5 nm) underlayers were deposited. The propagation speed of crystal lattice rearrangement in the bonding process decreased with an increased exposure time of film surfaces to air (t exp). Propagation did not occur at t exp of 500 s. The cohesion of Ag film surfaces by film surface exposure to air and reduction of the Ag film surface energy by Ag oxide or sulfide formation probably cause ADB performance degradation.

New insights of the strength asymmetry in FCC single-crystalline nanopillars

Nanomaterials or structures usually exhibit characteristic performance under complex stress states. The tensile and compressive behaviors of [001]-oriented single-crystalline nanopillars were studied, by performing molecular dynamic simulations on several typical FCC metals. For all those metallic nanopillars, their yield strengths for nucleating the initial dislocation show strong loading direction dependence, i.e., the strength under tension is higher than that under compression, showing the typical T/C asymmetry. The origins of the T/C asymmetry were investigated from the new aspects of the surface energy difference under tension and compression, the large ultimate elastic deformation, and the non-Schmid stress, in detail. The results indicate that both the Schmid factor and the non-Schmid factors change considerably due to the large elastic deformation under tension or compression, which contribute negatively to the T/C asymmetry. The difference in surface energy reduction due to the large elastic deformation is one but not the only factor that results in the T/C asymmetry. Although the non-Schmid factor contributes negatively to the T/C asymmetry, the non-Schmid stress can increase the difference of unstable stacking fault energies under tension and compression, which has a significant positive influence on the T/C asymmetry by changing the ideal shear strength of the slip plane.

The Tendency of Nature towards Hexagon Shape Formation due to Minimizing Surface Energy

Nature, for instance, bubble and honeycomb, tend to form a hexagon shape naturally. The array of bubbles and honeycomb is formed by merging and sharing the common wall with the adjacent unit. Even though each of the unit shapes size may vary, the noticeable elements that built up the array are hexagons. There are many regular and irregular shapes available in nature, but the shape formation still leads to hexagon at the end of the shape evolving due to surface tension. Based on the phenomenon, this study was carried out to investigate the effect of surface tension, energy, and geometry features, which affect the tendency of hexagon formation. The study was carried out by comparing hexagon with triangle, trapezium, and square. From the result, it is found that the reduction of surface energy ranged from 10-23 percent from the initial shape. As expected, the hexagon shape is packed with the lowest surface parameter and very stable in single unit or array form by showing the lowest energy reduction. The energy content is a reflection to structure equilibrium and its stability for nature tendency.

Molten Salt Assisted Synthesis of Boron Carbon Nitride Nanosheets for Enhanced Photocatalytic Activity of Silver Phosphate

Thin 2D boron carbon nitride nanosheets (BCNNS) possess high thermal and chemical stability as well as tunable electronic properties, but the lack of effective synthesis methods hinders their practical application. Herein, a facile and efficient approach for the synthesis of large-area boron carbon nitride nanosheets in molten KCl–NaCl salt media has been proposed. A Single precursor compound, ethylenediamine bisborane, was first heated to 1000 °C in KCl–NaCl salt melts and then held for only two minutes to produce BCNNS. Benefiting from the effective solvation of precursors and reduced surface energy in liquid salt melt, the lateral size of resultant BCNNS can reach up to 12 microns. The as-prepared products are subsequently used as a co-catalyst with silver phosphate (Ag3PO4) for degradation methyl orange under simulated sunlight. Due to the improved electronic property and interfacial effect of BCNNS, the photocatalytic performance of Ag3PO4 was significantly improved. The photodegradation rate increased from 0.369 min−1 of Ag3PO4 to 1.006 min−1 of BCN/Ag3PO4 composite with only 0.6 wt% BCNNS loading, a 2.73-fold higher value than that of pure Ag3PO4.

Surface tension as the destabiliser of a vortical interface

We study the dynamics of an initially flat interface between two immiscible fluids, with a vortex situated on it. We show how surface tension causes vorticity generation at a general curved interface. This creates a velocity jump across the interface which increases quadratically in time, and causes the Kelvin–Helmholtz instability. Surface tension thus acts as a destabiliser by vorticity creation, winning over its own tendency to stabilise by smoothing out interfacial perturbations to reduce surface energy. We further show that this instability is manifested within the vortex core at times larger than ${\sim}(k We)^{1/4}$ for a Weber number $We$ and perturbation wavenumber $k$ , destroying the flow structure. The vorticity peels off into small-scale structures away from the interface. Using energy balance we provide the growth of total interface length in time. A density difference between the fluids produces additional instabilities outside the vortex core due to centrifugal effects. We demonstrate the importance of this mechanism in two-dimensional turbulence simulations with a prescribed initial interface.

Hydrophobic modification of castor oil-based polyurethane coated fertilizer to improve the controlled release of nutrient with polysiloxane and halloysite

Castor oil has been developed rapidly as a bio-based coating material for controlled-release fertilizers. However, the release characteristics of coated fertilizers are limited because the coating materials are hydrophilic with many micropores. To improve the surface hydrophobicity of coating materials, superhydrophobic halloysite nanotubes (SHTs) were fabricated by hydrolytic condensation of siloxane on the surface of halloysite nanotubes (HNTs). SHTs were used to modify the castor oil-based polyurethane (SHPU) to enhance the surface nanoscale roughness and reduce surface energy. Compared with a PU-coated fertilizer (PUC), the nitrogen-release properties of the hydrophobic PU-coated fertilizer (SHPUC) were improved significantly. This improvement was because the nanoscale surface roughness and hydrophobicity of SHPU increased the water contact angle, and the micropores on the surface were blocked by nanotubes and hindered water entrance into the coating. This method of hydrophobic modified coating materials could provide a new idea for development of high efficiency and environmentally friendly bio-based coated controlled-release fertilizer and sustainable development of agriculture.

Enhanced oil–water separation via superhydrophobic electrospun carbon fiber membrane decorated with Ni nanoclusters

Traditional polymer-based membranes used for oil–water separation are limited in practical application because of their poor chemical stability, easy scaling, and low efficiency. In this study, a durable superhydrophobic electrospun carbon fiber (CF/Ni/F) membrane was successfully prepared by combining electroless plating of Ni nanoclusters and fluorination treatment, and used for highly-efficient oil–water separation in harsh environment. The increased roughness and reduced surface energy endowed the superhydrophobicity of membrane. The water contact angle (WCA) and oil flux of CF/Ni/F membrane reached 164.2° and 3669 L/(m2·h). For non-emulsified and/or emulsified oil–water mixtures, the separation efficiency of CF/Ni/F membrane remained above 99% under gravity drive after only several cycles. In addition, the as-prepared CF/Ni/F demonstrated good chemical stability in the harsh environment.

Multiphase media superwettability regulated by coexisting prewetting phase

Understanding the wetting behaviors of a given superwetting surface in multiphase media is important for elaborately tailoring superwettability. Here the surface chemistry of two types of superhydrophobic surfaces was programmed to reveal crucial effect of a coexisting prewetting phase rather than the prewetting process on their wetting states in water and oil–water separation application. After prewetting with ethanol to remove the air layer, underwater contact angles of superhydrophobic surfaces for oil droplet and bubble gradually decreased from over 150° along with the reduced surface energy. When the superhydrophobic surfaces were directly immersed in water or prewetted with oil, a stable air layer or infused oil as the prewetting phase enabled oil droplet and bubble to rapidly spread out. Moreover, air-prewetting superhydrophobic/underwater superoleophobic fabric can selectively adsorb oils from water, whereas it showed an excellent antifouling property without the air layer. For the separation of oil-in-water emulsions using superhydrophobic/underwater superoleophilic sponge, the stable air layer obstructed emulsions into three-dimensional porous structures. After removing the air layer, emulsion separation can be efficiently realized. This discovery provides a feasible approach for the regulation and development of unusual superwettability in multiphase media.

Vaterite production and particle size and shape control using seawater as an indirect carbonation solvent

Vaterite, a type of calcium carbonate, has recently raised the potential for use as a drug delivery material and a filler for bone defects due to its high specific surface area and solubility, low specific gravity, and high porosity. However, existing methods of producing fine-particle vaterite exhibit limitations that annexed processes such as adding excessive additives or irradiating ultrasound are necessary, and mass production is impossible. We developed a simple, chemical additive-free, low-cost technology with mass production capability that can overcome problems faced in conventional vaterite production. We found that seawater is favorable for vaterite production and enables the reduction of its particle size because of its supersaturation in CaCO3, absence of magnesium, and high viscosity, and the reduced surface energy of vaterite. Using seawater as a solvent for indirect carbonation, we succeeded in producing a vaterite content of 100% containing fine particles without additives or additional processing. Spherical or elliptical vaterite was separately formed by adjusting the ionic strength of seawater. In addition, the ionic strength of seawater controlled the surface area and pore size of vaterite.