Water Wettability Research Articles

Electrical Impedance Tomography Monitoring of Salt Transportation in Cellulose Hydrogel for Solar‐Driven Evaporative Desalination via Laser Defined Wettability

AbstractThe scarcity of clean water has become a growing problem worldwide. Solar‐driven desalination based on evaporation has become a promising green technology for obtaining drinking water from saline water for the welfare of human society. However, the accumulation of salt precipitated from the saline at the evaporator surface remains a severe problem in improving evaporation efficiency. To overcome this problem, it is crucial to investigate the transportation mechanism of salt in the saline during the evaporation process. Herein, an in situ monitoring strategy with the electrical impedance tomography (EIT) method is proposed to characterize the salt transportation and accumulation process inside the nano‐crystal cellulose (NCC)‐MnO2 nanoparticle solar evaporator. The coating of laser‐induced graphene (LIG) with tunable water wettability shows that the hydrophobic structures can suppress salt accumulation during evaporation. The collected condensation water generated from the bacteria‐polluted saline proves to be clean. It is hoped that this work can further inspire research on the salt‐resistive evaporator design.

Optimizing oil-water separation using fractal surfaces.

Oil has become a prevalent global pollutant, stimulating the research to improve the techniques to separate oil from water. Materials with special wetting properties-primarily those that repel water while attracting oil-have been proposed as suitable candidates for this task. However, one limitation in developing efficient substrates is the limited available volume for oil absorption. In this study, we investigate the efficacy of disordered fractal materials in addressing this challenge, leveraging their unique wetting properties. Using a combination of a continuous model and Monte Carlo simulations, we characterize the hydrophobicity and oleophilicity of substrates created through ballistic deposition (BD). Our results demonstrate that these materials exhibit high contact angles for water, confirming their hydrophobic nature while allowing significant oil penetration, indicative of oleophilic behavior. The available free volume within the substrates varies from 60% to 90% of the total volume of the substrate depending on some parameters of the BD. By combining their water and oil wetting properties with a high availability of volume, the fractal substrates analyzed in this work achieve an efficiency in separating oil from water of nearly 98%, which is significantly higher compared to micro-pillared surfaces made from the same material but lacking a fractal design.

Janus Protein Nanoparticles Tailoring Bicontinuous Aerogels for Efficient Heavy Metal Ion Absorption.

Bicontinuous structures are exquisite interpenetrating constructs with an optimal balance between connectivity and surface area. Such unique geometry favors exceptional mechanical properties and efficient inward mass diffusion essential for an absorbent material. Although bicontinuous structures are found across many length scales in nature, synthesizing artificial analogs using biological building blocks remains largely unexplored. In this study, it is shown that manipulation of the surface chemistry of rapeseed cruciferin nanoparticles (≈50nm) leads to the formation of a highly amphiphilic stabilizer, ensuring equal wetting of water and oil phases in a demixed system, thereby enabling the formation of bicontinuous emulsions. By further eliminating both volatile liquid phases (water and toluene) through freeze-drying, bicontinuous emulsions are transformed into bicontinuous aerogels featuring highly interpenetrating networks with uniform domain size. These materials, characterized by high surface area (224 m2g-1) and mechanical robustness, can efficiently absorb various heavy metal ions multiple times displaying excellent absorption capacity (up to 200mgg-1) and efficiency (less than 30min). This study is at the forefront of constructing biomacromolecular bicontinuous structures, potentially expanding their applications in diverse fields such as food, cosmetics, and medicine.

Microscopic Effect of Mixed Wetting Capillary Characteristics on Spontaneous Imbibition Oil Recovery in Tight Reservoirs

The understanding of the mechanisms that govern water spontaneous imbibition in mixed wetting capillary channels plays a significant role in operating the oil extraction and energy replenishment for the tight oil reservoirs. In this work, the conservative form phase-field model together with the Navier–Stokes equation is employed to investigate the influence of the mixed wetting distribution and the wetting degree on the imbibition oil recovery effects and microscopic flow characteristics. Results indicate that there exist different oil detachment modes of spontaneous imbibition, and these modes are determined by the coupled effect of mixed wetting fraction and contact angle size. For the mixed wetting capillary with strong oil wetting, when fw is low, spontaneous imbibition can only partially detach the oil. Low fw slows down the fluid flow velocity and leads to the small imbibition oil recovery rate. After that, the influence of the surface contact angle size of the mixed wetting capillary is discussed. For the complete detachment mode, the capillary tube presents a form of water phase saturated filling, achieving the optimal imbibition oil recovery effect. For the mixed wetting capillary tube with the combination of weak water wetting and strong oil wetting (i.e., θw = 75° and θo = 165°), local spontaneous imbibition turbulence can only detach very little oil at the inlet of the water wetting area, ultimately achieving a recovery efficiency of less than 10%. This work illuminates the spontaneous imbibition oil recovery mechanisms and flow potentiality for the different mixed wetting capillary channels.

Pore-Scale Study of Fluid Displacement in Parallel-Layered Porous Media and Implications of Associated Distinct Flow Dynamics.

Fluid displacement within layered porous media is more complex than in nonlayered ones. Most of the previous studies placed a focus on the porous media with layerings perpendicular to the flow direction, and the effects of pore topology were often ignored. Therefore, this study aims to reveal the flow physics in porous media with layering parallel to the flow direction by accounting for the specific pore topology. Based on the phase-field method, a series of pore-scale numerical simulations were performed to investigate the dynamic displacement processes within layered porous media under various capillary numbers and wettability. The results showed that oil recovery was strongly affected by the heterogeneity of porous media in the capillary fingering regime compared to the viscous one. Besides, the alternative advancing phenomenon of the water fingers was suppressed in layered porous media. Compared with water wetting conditions, the viscous fingering regime of the invading water is more pronounced under oil wetting conditions. Last but not least, the center of mass of water flow paths can be used for fingering regime identification. These findings contribute to our better understanding of the flow dynamics of fluid displacement within layered porous media, which are of great significance to the industry related to oil recovery, underground storage of carbon dioxide and hydrogen gas, etc.

Study on wettability of water stemming for blasting dust adjusted by surfactants and inorganic salts.

Water stemming is an efficient method of removing blasting dust by wetting. There is still a lack of methods for rapid optimization of water stemming components with high wettability. Herein, blasting dust was collected from a tunnel in Chongqing (China) to investigate its removal performance by different water stemmings. The two most important components of blasting dust were SiO2 and CaCO3 by characterization analysis. Notably, hydrophilic blasting dust has significantly more SiO2 than hydrophobic blasting dust. The density functional theory calculation predicted the wettability of water stemming containing sucrose fatty acid ester (SE) higher than that of water stemming containing other surfactants. Moreover, the water contact angle and surface tension experiments determined the addition of inorganic salts to the water stemming containing SE could increase its wettability, with the addition of Al3+ giving the best performance. The sink test and water retention experiment further prove that our synthesized water stemming has a good wetting ability on both hydrophobic and hydrophilic blasting dust. The findings of this study advance the development of reliable methods for optimizing water stemming with high wettability for removing the blasting dust.

What determines the water wettability and permeability of Ti3C2Tx MXene thin films?

What determines the water wettability and permeability of Ti3C2Tx MXene thin films?

Dual-fluorescent starch biopolymer films containing 5-(4-nitrophenyl)-1,3,4-thiadiazol-2-amine powder as a functional nanofiller

Physical and photophysical properties of starch-based biopolymer films containing 5-(4-nitrophenyl)-1,3,4-thiadiazol-2-amine (NTA) powder as a nanofiller were examined using atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), stationary UV-Vis and fluorescence spectroscopy as well as resonance light scattering (RLS) and time-resolved measurements, and where possible, analyzed with reference to pristine NTA solutions. AFM studies revealed that the addition of NTA into the starch biopolymer did not significantly affect surface roughness, with all examined films displaying similar Sq values ranging from 70.7 nm to 79.7 nm. Similarly, Young’s modulus measurements showed no significant changes after incorporating the 1,3,4-thiadiazole. Adhesion force and water contact angle assessments demonstrated that the films maintained high hydrophilicity (water wetting) across all examined films. Color analysis corroborated the anticipated trend, showing that increasing additive content resulted in decreased lightness and increased yellowness. Interestingly, however, while in polar isopropanol solvent at low concentration, NTA shows a typical single-band emission, centered at 410 nm and a slight enhancement of the band on the long-wavelength side around 530 nm, its incorporation into the biopolymer matrices results in the appearance of dual fluorescence signal with maxima at 430 and 530 nm. Concentration-dependence emission experiments, demonstrating that with even a slight increase of the amount of NTA in solution, an additional, weak long-wavelength emission band emerged within the spectral range corresponding to the intensive band in the biopolymer film, along with results of the performed quantum-chemical studies, including both the monomeric and aggregated (dimer and trimer) models, conclusively unveil that the dual fluorescence observed in starch/NTA films is due to molecular aggregation effects resulting in aggregation-induced emission. This study underscores the potential of NTA as an additive in biobased polymer films, furnishing them with new photophysical features without substantially altering their surface properties and thus enabling their extended applications.

Digital Light Processing (DLP) 3D Printing Fabrication of Hydrophobic Meshes Incorporating Fluorinated and Silicone-Based Acrylates Combined with Surface Engineering: Comparison of Their Oil-Water Separation Efficiency.

Hydrophobic materials have been fabricated by DLP vat photopolymerization of isobornyl acrylate-based resins with chemical modification and/or surface geometry engineering. Fluorinated and polydimethylsiloxane (PDMS)-based acrylic monomers are used for chemical modification and are incorporated into the printed materials. The water wettability was significantly reduced and plateaued with as low as 5% (w/w) of the auxillary hydrophobic monomer. Regarding surface geometry, meshes with different pore sizes are 3D printed, and the surface hydrophobicity increased with the pore size. We compare the oil-water separation efficiency of the 3D-printed meshes hydrophobized by these three approaches. It was found that the isobornyl acrylate-based resin already demonstrated separation at the optimum pore size. Modification with PDMS showed a further improvement in separation efficiency, whereas no significant increase was observed by use of the fluorinated monomer. This highlights that careful design of surface geometry should be considered to avoid the use of environmentally unfriendly and potentially toxic chemicals when making hydrophobic materials.

Enhanced physicochemical and antifungal properties of starch bionanocomposites reinforced with nanocellulose and functionalized with AgNPs derived from cocoa bean shell.

This study explored the synergistic combination of silver nanoparticles (AgNPs), eucalyptus-derived nanofibrillated cellulose (NFC) and cassava starch to develop bionanocomposites with advanced properties suitable for sustainable and antifungal packaging applications. The influence of AgNPs synthesized through a green method using cocoa bean shell combined with varying concentrations of NFC were investigated. Morphological (scanning electron microscopy and atomic force microscopy), optical (L*, C*, °hue, and opacity), chemical (Fourier transform infrared spectroscopy), mechanical (puncture force, tensile strength, and Young's modulus), rheological (flow curve and frequency sweeps, strain, and stress), barrier, and hydrophilicity properties (water vapor permeability, solubility, wettability, and contact angle), as well as the antifungal effect against pathogens (Botrytis cinerea, Penicillium expansum, Colletotrichum musae, and Fusarium semitectum), were analyzed. The morphological analysis indicated excellent interaction between the bionanocomposites constituents. The maximum NFC addition increased the tensile strength of the bionanocomposites by approximately 283.93 % (14.85 MPa) while Young's modulus also showed a significant increase of 303.03 % (417.14 MPa), indicating increased stiffness. Water vapor permeability of the materials decreased by approximately 47.89 %. The materials exhibited hydrophilic properties while maintaining low wettability. Furthermore, the bionanocomposites demonstrated pseudoplastic (Ȳ = 0.59) behavior and an inhibitory effect against fungal pathogens. In conclusion, these innovative materials have the potential to transform packaging technology by serving as sustainable alternatives to petroleum-derived polymers while simultaneously adding value to agro-industrial waste.

Catalytic synthesis of SiC coated graphite and its application in carbon containing castables

SiC coated graphites were prepared via a catalytic conversion method, employing graphite flakes and silicon powder as the starting materials, and Fe, Co and Ni as catalysts, respectively. The effects of firing temperature and various kinds of catalyst on the growth and morphologies of SiC coating on graphite surface were evaluated. Density functional theory (DFT) calculations revealed that the catalytic role of catalysts on the formation of SiC could be attributed to the occurrence of chemisorption between CO (g) molecule and catalysts owing to charge transfer effects. The graphites.coated with SiC displayed better oxidation resistance and water wettability than uncoated graphites. Also, mechanical strength, thermal shock resistance, slag resistance and oxidation resistance of a model of Al2O3-C castables containing coated graphites were better than its uncoated counterparts.

TiO2 nanoparticle coated carbon nanotube sponge with high sunlight absorption and good hydrophilicity for efficient interfacial solar-powered vapor generation

Solar-powered interfacial vapor generation is considered a promising sustainable energy technology. We use porous TiO2 nanoparticle coated carbon nanotube sponges (CNTS@TiO2) as sunlight absorbers to study solar-powered interfacial vapor generation due to the extremely strong sunlight absorption of CNTs and TiO2. The highly porous structures have great benefits to water transport in the sunlight absorbers. The formation of TiO2 on the sidewalls of CNTs improves the hydrophilicity of the light absorber and wettability of water on the sidewalls of CNTs. The water can rapidly infiltrate the porous CNTS@TiO2 composites. Additionally, the multiple internal reflections in “TiO2 forest” greatly reduce the diffused reflection and thus enhance sunlight absorption. The CNTS@TiO2 composites exhibit high sunlight absorption (96.7 %). The efficient water transport and strong light absorption in the porous light absorbers significantly improved the evaporation performance. The CNTS@TiO2 composite with the rhombic TiO2 shows high water evaporation rate of 3.15 ± 0.14 kg m-2 h-1 and energy transfer efficiency of 89.5 ± 3.9 % under 1-sun radiation.

Friction reduction and anti-wear mechanisms of surface-textured graphite under water lubrication

In this study, tribological behaviors of surface-textured graphite samples under water lubrication are analyzed by experiments and molecular dynamics simulations to reveal the underlying friction and anti-wear mechanism. Circular dimple-type textures are chosen for investigations. Ball-on-disc frictional tests are performed to investigate the influence of texture spacing on friction coefficient and wear degree. The sample with a texture spacing of 200 μm possesses the lowest friction coefficients and the smallest cross-sectional area of the wear mark. The roles of support strength of solid part among textures, water wettability and water film in determining the water-lubricated tribological behaviors are analyzed in detail. The water molecules trapped by the dimple-type textures can produce additional hydrostatic pressure, which is the most crucial factor. The results of this study can guide the design of water-lubricated graphite components with surface textures, such as mechanical seals and graphite bearings in nuclear main pumps and ships.

Development of Innovative Thermoplastic Foam Materials Using Two Additive Manufacturing Technologies for Application in Evaporative Cooling Systems.

Evaporative cooling systems have emerged as low-energy consumption alternatives to traditional vapor compression systems for building air conditioning. This study explored the feasibility of utilizing polymeric foamed materials produced through additive manufacturing as wetting materials in evaporative cooling systems. Specifically, two different commercial polylactic acid filaments, each containing a percentage of a chemical blowing agent, were studied. Experiments were designed to evaluate the influence of critical process parameters (line width, flow rate, speed, and layer height) on the performance of the resulting foamed materials in terms of evaporative cooling by conducting water absorption, capillarity, porosity, and wettability tests. Considering that high water absorption, capillarity, and porosity, coupled with an intermediate contact angle, are advantageous for evaporative cooling effectiveness, a low flow rate was found to be the most important parameter to improve these properties' values. The results showed that the appropriate combination of polymer and process parameters allowed the production of foamed polymer-based materials processed by additive manufacturing technology with optimal performance.

Analysis of Spontaneous and Dynamic Imbibition Characteristics of Silica-Based Nanofluid in Microscopic Pore Structure of Tight Oil Reservoirs.

Imbibition behavior plays a crucial role in tight oil reservoir development, to increase tight oil production, a novel sodium lauryl ether sulfate (SLES) nanofluid was developed. Spontaneous and dynamic imbibition performance of nanofluid and the relative influencing factors were systematically investigated using the online low-field nuclear magnetic resonance (LF-NMR) technique. The microscopic mobilization characteristics and mechanism of nanofluid-enhanced matrix crude oil recovery in tight oil reservoirs were further explored. The experimental results showed that the proposed SLES nanofluid achieved the highest imbibition efficiency, and appropriate concentrations of nanoparticle and surfactant were helpful in enhancing the imbibition recovery. Excessive concentrations of chemical agents may block the tiny pores. A reasonable injection rate and shut-in time should be determined to fully leverage capillary forces for water phase imbibition and oil phase displacement as well as the displacement effect of the viscous force and increased water wetness of the rock surface provided by the nanofluid. In addition, NMR T2 cutoff was applied to distinguish the imbibition and displacement regions during dynamic imbibition process. The pore sizes corresponding to the T2 cutoff values after nanofluid and deionized (DI) water flooding were 0.6 and 5 μm, indicating that nanofluid considerably increased the movable crude oil in pores of tight oil reservoirs compared with DI water. Furthermore, imbibition behavior was dominant in micropores (<0.1 μm) and mesopores (0.1-1 μm), and displacement principally occurred in microfractures and macropores. Finally, the underlying mechanisms responsible for nanofluid enhanced oil recovery were related to wettability alteration, capillary pressure, and viscous force. This work provides further understanding of spontaneous and dynamic imbibition when employing nanofluid in tight oil reservoirs.

Sub-ambient water wettability of hydrophilic and hydrophobic SiO2 surfaces.

The wettability of SiO2 surfaces, crucial for understanding the phase transition processes of water, remains a topic of significant controversy in the literature due to uncertainties in experiments. Molecular dynamics (MD) simulations offer a promising avenue for elucidating these complexities, yet studies specifically addressing water contact angles on hydrophilic and hydrophobic SiO2 surfaces at sub-ambient temperatures are notably absent. In this study, we experimentally measured water contact angles of hydrophilic and hydrophobic SiO2 surfaces at ambient temperature and employed MD to investigate water contact angles on Q3, Q3/Q4, and Q4 SiO2 surfaces across temperatures ranging from 220 to 300K. We investigated the effects of the distribution of hydroxyl groups, droplet size, and hydroxyl density and found that the hydroxyl density had the largest impact on contact angle. Moreover, hydrogen bond analysis uncovered enhanced water affinities of Q3 and Q3/Q4 SiO2 surfaces at lower temperatures, and the spreading rate of precursor films reduced with decreasing temperature. This comprehensive study sheds light on the intricate interaction between surface properties and water behavior, promoting our understanding of the wettability of SiO2 surfaces.

Transparent and Mechanically Robust Janus Nanofiber Membranes for Open Wound Healing and Monitoring.

The electrospun nanofiber membrane has demonstrated great potential for wound management due to its porous structure, large surface area, mechanical strength, and barrier properties. However, there is a need to develop transparent bioactive nanofibers with strong mechanical properties to facilitate the monitoring of the healing process. In this study, we present an electrospinning-based method for creating transparent (∼80-90%), strong (∼11-13 MPa), and Janus nanofiber membranes. The innovative square pattern architecture of the membrane includes a thin hydrophobic polycaprolactone layer on top of a layer of hydrophilic ethylene-vinyl alcohol nanofiber, which enables the absorption of excess biofluid from the wound and exhibits Janus wettability for water. Furthermore, incorporating 5% chitosan into the composition of the nanofibers accelerates the healing process through its antioxidant properties and antimicrobial activity against various bacteria, including drug-resistant strains. The developed membrane also demonstrates skin-repairing function, quick blood clotting (around 145 ± 12 s), and biocompatibility with keratinocyte (≥90%), as well as in vitro quick cell migration (∼24 h). With a tensile strength of 11-13 MPa, the membrane effectively adheres to the knee joint even after running 4 km. These optimal properties of the electrospun nanofiber membrane make it suitable for effective wound management and inspection of the healing process, without the need for frequent dressing changes.

A robust floating oxygen-doped graphitic carbon nitride sheet for efficient photocatalytic CO2 conversion

Photocatalytic CO2 reduction offers a promising approach for converting CO2 into valuable chemicals. However, typical conversion systems suffer from inefficient CO2 mass transfer and complex recycling processes. In this study, we developed a floating sheet as a robust photocatalytic CO2 conversion system by integrating graphitic carbon nitride (CN) nanosheets onto polytetrafluoroethylene (PTFE) fiber membrane, followed by oxygen (O) doping into the CN (CN-O) via oxygen-plasma treatment. The floatable CN-O/PTFE sheet exhibits slight wettability in water under 0.25 MPa of CO2 pressure in our reactor system, facilitating the delivery of dissolved CO2 to the CN-O photocatalyst surface. O-doping enhances the visible light absorption and improves the separation and transport efficiency of photogenerated electrons and holes due to O-doping-induced states in CN. Consequently, the floating CN-O/PTFE system achieves an exceptional photocatalytic CO2 conversion rate of 102.3 μmol g-1h-1, approximately 4.8 times higher than a conventional CN-powder dispersion system in water. Moreover, the sheet demonstrates excellent cycling durability, with no significant exfoliation of the catalytic layer or reduction in CO2 photoreduction activity after 20 consecutive cycles. This study presents a novel approach to designing photocatalytic systems for efficient CO2 conversion.

Citicoline eluting hydrogels for therapeutic contact lenses intended to treat neurodegenerative diabetic ocular diseases

Ophthalmic neurodegenerative diseases related to diabetes, such as glaucoma and retinopathy, are among the major causes of blindness in the world. Citicoline (CIT) in the form of eye drops is currently used for the treatment/prevention of these diseases, which affect the posterior segment of the eye. To ensure the drug penetration into the back of the eye, frequent instillations of highly concentrated drug solutions are required with potential side effects. Drug-loaded soft contact lenses (SCLs) may be an effective alternative to the conventional eye drop treatment, since they may enable a sustained drug release during daily wear, ensuring a higher drug bioavailability, and avoiding drug waste. In this work, one 2-hydroxyethyl methacrylate (HEMA) based hydrogel was functionalised with N-(3-aminopropyl) methacrylamide hydrochloride (APMA), molecularly imprinted with CIT and loaded with the same drug. The material was extensively characterised, in terms of morphology, optical, mechanical, and physical–chemical properties, namely, equilibrium water content, wettability, oxygen and ionic permeability, Young’s modulus, shear deformation, transmittance and refractive index, before and after steam sterilisation. Additionally, the tendency of the material to adsorb proteins of the lachrymal fluid was evaluated and its biocompatibility was assessed by irritation and cytotoxicity assays. Comparison with the non-functionalised and non-imprinted hydrogel showed that the modified hydrogel led to a sustained in vitro release of a much higher amount of CIT than the original one, while keeping typical values for physical–chemical properties of SCLs. The drug-loaded material resisted steam sterilisation and proved to be biocompatible, demonstrating adequate properties to be used in therapeutic SCLs for the prophylaxis/treatment of neurodegenerative diabetic ocular diseases. The neuroprotective effect of the released drug was confirmed with tests using porcine retinal explants.

Water Droplet Equilibration on Silicone Elastomer Substrates Containing Mobile Silicones.

Understanding interfacial behavior at the water/silicone elastomer interface is vital in many applications, including microfluidics, antibiofouling, and self-cleaning surfaces. Silicone elastomers are not always static systems, however. Unreacted silicone molecules within a substrate may change the water-wetting behavior compared to fully reacted substrates. To investigate the impact of free silicone species at the interface, we systematically studied water wettability as a function of contact time with various silicone elastomer substrates. One set of Sylgard 184 substrates was prepared from curing at optimal stoichiometry and included doses of silicone molecules of varying molecular weights. Another set of substrates was made by mixing Sylgard 184 in imbalanced ratios to provide incomplete cross-linking. In the absence of added silicone oils, we observe a linear decrease in contact angle with time due to the evaporation of water. However, within certain molecular weight and loading levels of additional inert oils, nonlinear wetting behavior occurs as oils migrate to the interface and the system stabilizes. Similar nonlinear wetting behavior occurs without including silicone oils by mixing pure Sylgard 184 in very imbalanced mixing ratios, resulting in incomplete cross-linking. Such substrates contain unbound mobile silicone species that diffuse to the water-substrate interface. We show how the water contact angle technique can elucidate the presence of unbound silicone oils in the substrate.