Superhydrophilic Surface Research Articles

Regulation of fluorescence, morphology, surface wettability and function of naphthalimide-based self-assembly system by metal coordination

Three naphthalimide-based supramolecular gelators (N1, N2 and N3) that contained one, two, or three naphthalimide groups, respectively, were designed and synthesized, and the self-assembly processes of the three gelators were studied using different technique. Their self-assembly behavior could be regulated through the number of terminal branches. More importantly, their self-assembled structure, fluorescence behavior and surface wettability and function could be regulated through metal coordination, and helical nanofibers could be formed by gel N2 with Cd2+, Co2+, Eu3+, Tb3+, Mn2+, Ni2+ and Hg2+. The fluorescence emission intensities of these gels could change with different degrees under the addition of different metal ions, and a super-hydrophilic surface could be obtained from xerogel N3 in the presence of Co2+, Eu3+, Mn2+ and Tb3+. Specifically, gelator N3 could selectively and sensitively respond to Fe2+ in the solution and gel state with a response time of 0.5 s and a low limit of detection of 1.84 nM. This work provided a new regulation method for the supramolecular self-assembly process.

Super-hydrophilic nano-structured surface with antibacterial properties

Adhesion of bacteria to a surface followed by biofilm formation causes many problems in human health care and, in some cases, can even cause human death. Therefore, reducing bacterial attachment to surfaces and antibacterial surface fabrication are two of the most important issues in many applications, including healthcare, medical, food packaging, etc. Polycarbonate (PC) is one of the most widely used polymers in medicine. However, it does not have antibacterial properties. On the other hand, laser treatment is used as a standard method for surface modification of different materials. In this paper, excimer laser irradiation at a fluence below the ablation threshold was used for surface patterning and modification of the polycarbonate sample, aiming to improve its antibacterial properties. The results show that super-hydrophilic nanostructured polycarbonate surfaces have antibacterial properties compared to non-treated PC, which has no antibacterial properties.

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.

Novel and superhydrophilic bifunctional NiCuMn@TiN nanosheets supported on iron foam for high-performance supercapacitors and water oxidation

Synthesizing low-cost and highly efficient bifunctional electrocatalysts for hybrid supercapacitors and oxygen evolution reaction (OER) is critically essential for the progress of energy storage and conversion devices. Therefore, a novel, inexpensive and superhydrophilic bifunctional NiCuMn@TiN nanosheet supported on iron foam (NiCuMn@TiN/IF) is successfully designed and fabricated via spent cupronickel (SCN) as Ni and Cu precursor by a facile one-step electrosynthesis routine. With adding nano titanium nitride (TiN), the obtained NiCuMn@TiN/IF composite electrode not only possesses a large superhydrophilic surface that enhances ion/electron transfer efficiency and provides numerous activity sites for the electrochemical reaction but also achieves efficient recovery of metal resources using the secondary resource SCN as soluble anode further reduces the cost of electrode preparation. And since the synergistic effect of large specific surface area and superhydrophilicity, the NiCuMn@TiN/IF delivers a high specific capacity of 22.5 F cm−2 at 10 mA cm−2 in 3 M KOH and also illustrates superior OER activity with an extremely low overpotential (286 mV) and remarkable durability at a high current density of 100 mA cm−2 in 1 M KOH. This research provides a solid foundation for the large-scale preparation of low-cost and high-performance non-precious metal bifunctional electrocatalysts for the commercial development of electrochemical supercapacitors and electrochemical water-to-hydrogen conversion technology.

Direct-coating of cellulose hydrogel on PVDF membranes with superhydrophilic and antifouling properties for high-efficiency oil/water emulsion separation

As a well-known natural and innocuous plant constituent, cellulose consists of abundant hydroxyl groups and can tightly adsorb onto material surfaces hydrogen bonding, resulting in a superhydrophilic surface. In this work, the hydrophobic polyvinylidene fluoride (PVDF) membranes were modified by immersing them in cellulose hydrogel using a simple one-step process. The modified PVDF membrane exhibited excellent resistance to fouling and oil adhesion, making it highly effective in separating various oil-in-water emulsions. The cellulose-modified PVDF membranes achieved a high oil rejection rate (>99 %) and a maximum separation flux of 2675.2 L·m−2·h−1. Furthermore, even an oil-in-water emulsion containing bovine serum albumin maintained a steady permeation flux after four filtration cycles. Additionally, these cellulose-modified PVDF membranes demonstrated excellent underwater superoleophobicity across a wide range of pH levels and high saline conditions. Overall, these cellulose-modified superhydrophilic PVDF membranes are sustainable, environmentally friendly, easily scalable, and hold great promise for practical applications in oily wastewater treatment.

Structure and in-vitro bioactivity study of Nano-DCPD coatings on anodized TiO2 nanotubes deposited on Ti-alloy as scaffold applications

Ti and their alloys are commonly used metallic implants due to their good bio-activity. Post-surgery reflects inferior osseointegration that makes the material unhealthy in the long run after surgery. In this regard, surface characteristic remains one of the most trivial and incurable problems for hard tissue application. In the present study, Nano-Dicalcium Phosphate Dihydrate (DCPD) Coatings were deposited over anodized TiO2 Nanotubes and its structural, surface and in-vitro study has been done. Surface transitions from the contact angle analyser reveal hydrophilic to super-hydrophilic surfaces have been achieved over Ti6Al4V alloy. The highest absorbance value has been observed on TTOAD compared to TD in both 24 h and 48 h. FESEM Mapping and EDS unveil that the distribution of elements is not homogenous entirely. However, the AFM result reveals that the distribution of an ex-situ deposited layer is enriched in Calcium-Phosphorus elements and has distinct irregular topography. Besides more surface roughness value has been revealed in TTOAD surface. Optical density (O.D.) value at 570 nm with ∼ 1.09 O.D. at 24 h and ∼1.3 O.D. at 48 h was obtained on the TTOAD specimen reflecting the best cell proliferation of MG-63 compared to TD. In addition, superhydrophilicity with ∼8.5° contact angle was gained at TTOAD compared to TD and TTOCD specimens.

Collagen membrane functionalized with magnesium oxide via room-temperature atomic layer deposition promotes osteopromotive and antimicrobial properties.

Artificial bone grafting materials such as collagen are gaining interest due to the ease of production and implantation. However, collagen must be supplemented with additional coating materials for improved osteointegration. Here, we report room-temperature atomic layer deposition (ALD) of MgO, a novel method to coat collagen membranes with MgO. Characterization techniques such as X-ray photoelectron spectroscopy, Raman spectroscopy, and electron beam dispersion mapping confirm the chemical nature of the film. Scanning electron and atomic force microscopies show the surface topography and morphology of the collagen fibers were not altered during the ALD of MgO. Slow release of magnesium ions promotes bone growth, and we show the deposited MgO film leaches trace amounts of Mg when incubated in phosphate-buffered saline at 37°C. The coated collagen membrane had a superhydrophilic surface immediately after the deposition of MgO. The film was not toxic to human cells and demonstrated antibacterial properties against bacterial biofilms. Furthermore, in vivo studies performed on calvaria rats showed MgO-coated membranes (200 and 500 ALD) elicit a higher inflammatory response, leading to an increase in angiogenesis and a greater bone formation, mainly for Col-MgO500, compared to uncoated collagen. Based on the characterization of the MgO film and in vitro and in vivo data, the MgO-coated collagen membranes are excellent candidates for guided bone regeneration.

Experimental study on frosting and defrosting characteristics for inclined cold plates with surface wettability considered

Frost formation is a ubiquitous phase-change phenomenon, which is a nonlinear and complex physical process involving heat and mass transfer. Most of previous studies focused on frosting and defrosting characteristics of cold surfaces at horizontal or vertical angles, indicating that the inclination angle has a significant effect on the dynamic of frosting and defrosting. However, what happens to the frosting and defrosting process at other different inclination angles have not been clarified. In this study, to explore the effects of inclination angles, surface wettability on frosting and defrosting characteristics, three surfaces with different wettability properties including superhydrophobic, superhydrophilic and hydrophilic surfaces were prepared, and a frosting and defrosting experimental platform with adjustable inclination angle from 0° to 180° was built. Experiment results show that the inclination angle was found to impact both frost quality and thickness. For different wettability surfaces, both frost quality and thickness exhibited a rising trend within the 0°∼90° range, followed by a decrease within the 90°∼180° range. Moreover, the inclination angle has a significant effect on the frost melting process on superhydrophobic and superhydrophilic surfaces. With the increase of the inclination angle, the amount of retained water decreases gradually, and in the interval of 30°∼90°, it does not change much, and the quality is the smallest at 180°.

Janus membrane with asymmetric wettability for efficient oil/water separation

The rapid development of society and industry as well as the frequent occurrence of oil spills cause the shortage of fresh water resources, which not only affects human safety and life, but also impedes the world-wide sustainable development. To address these challenges, novel membrane materials with unique wettability properties have gained significant attention, particularly in the field of oil/water separation. In this research, we modified the hydrophobic PET fabric to achieve superhydrophilic characteristics using impregnation method. Subsequently, we electrospun hydrophobic PVDF fibers onto the superhydrophilic fabric surface, and PVDF/Ca10(PO4)6(OH)2@PET Janus membrane with asymmetric wettability was obtained. The membrane has an excellent unidirectional liquid transport capacity, and can effectively separate heavy oil or light oil, the separation efficiency is more than 90 %. The results also show that the Janus membrane can be used under alkaline conditions and has satisfactory tensile resistance and re-use performance. This work provides a new idea for Janus membrane design and effectively improves the application potential of the Janus membrane in the field of oil/water separation.

Reinforced water hyacinth based biodegradable cutlery: Green alternative to single-use plastics

Water hyacinth (WH) is an invading water plant that severely threatens biodiversity. The aim of this study was to utilize fibres from this underutilized plant to develop binderless biodegradable plates, in combination with different proportions (10%, 20% and 30%) of waste paper (WP), sugarcane leaf (SC), and banana stem fibre (BF), added as reinforcing agents. The properties of these products are compared with WH plates with starch as a binder (ST). The use of an epoxidized castor oil-based coating to enhance hydrophobicity was also studied. Analytical tests including functional group analysis, mechanical property, wettability, surface morphology, thermal stability and biodegradability studies were performed. It was observed that BF samples had the best mechanical properties, followed by SC, WP and ST, with BF-20 showing the maximum tensile strength (6.23 MPa) and elongation (10.09%). The thermogravimetric analysis showed the reinforced samples to be suitable for high-temperature applications, with SC-30 having a T5 value of 269.75 °C. The contact angles indicated that WH could be considered a suitable raw material for manufacturing biodegradable products with low wettability, and the addition of cellulose-rich reinforcing agents can further enhance its water resistance. SC-30 showed the highest hydrophobicity with a contact angle of 124.3°. Coating using an epoxidized castor oil-based solution can reduce the wettability of even super hydrophilic surfaces. All the samples showed good biodegradability, with most samples degrading completely within 20 days. Hence, water hyacinth reinforced with cellulose-rich reinforcing agents can be regarded as a superior raw material for manufacturing biodegradable cutlery.

Hierarchically Multiscale Vertically Oriented NiFeCo Nanoflakes for Efficient Electrochemical Oxygen Evolution at High Current Densities

AbstractCrucial advancements in versatile catalyst systems capable of achieving high current densities under industrial conditions, bridging the gap between fundamental understanding and practical applications, are pivotal to propel the hydrogen economy forward. In this study, vertically oriented hierarchically multiscale nanoflakes of NiFeCo electrocatalysts are presented, developed by surface modification of a porous substrate with nano‐structured nickel. The resulting electrodes achieve remarkably low overpotentials of 139 mV at 10 mAcm−2 and 248 mV at 500 mAcm−2. Further, scaled‐up electrodes are implemented in a water‐splitting electrolyser device exhibiting a stable voltage of 1.82 V to deliver a constant current density of 500 mA cm−2 for over 17 days. Moreover, the role of the unique structures on electrochemical activity is systematically investigated by fractal analysis, involving computation of structure factors such as Minkowski connectivity, fractal dimension, and porosity using scanning electron microscope images. It is found that such structures offer higher surface area than typical layered double hydroxide structures due to morphological coherence that results in a superhydrophilic surface, while the base Ni layer boosts the charge transfer. This study demonstrates a Ni/NiFeCo(OH)x heterostructure with highly porous morphology, a key to unlocking extremely efficient oxygen evolution reaction activity with exceptional stability. Moreover, fractal analysis is presented as a valuable tool to evaluate the electrochemical performance of catalysts for their structured morphology.

Construction of Janus structures on thin silk fabrics via misting for wet–thermal comfort and antimicrobial activity

Owing to their small fiber diameter (10–15 μm), silk fabrics are always thin (32–90 g m−2). Therefore, construction of the Janus surfaces of silk fabrics that possess excellent multifunctionality remains a formidable challenge. Herein, first, silk fabrics were grafted using glycidyltrimethylammonium chloride to form a superhydrophilic surface (G-side). Then, a unilateral hydrophobic surface (O-side) was readily fabricated by mist coating octadecyltrichlorosilane-functionalized SiO2 nanoparticles (NPs) to produce hierarchical surface textures. To prevent NP penetration from the G-side to the O-side, a “fireproof isolation” method was employed. Consequently, Janus silk fabrics (JanSFs) bearing asymmetric wettability were prepared, and their wetting gradient could be conveniently regulated. With the mist time ranging from 4 to 7 min, the unidirectional transport index and efficiency of the unidirectional water transport increased and decreased by 13.2 and 10.4 times, respectively. Sweat could be effectively drained away from human skin to ensure that the skin was dry and comfortable. Compared with the surface temperature of the raw fabric, the raw fabric of JanSFs increased by 2.7 °C. Furthermore, the breathability of JanSF was negligibly affected, and the outer O-side of the JanSF showed substantial antibacterial activity. This study is important for designing JanSFs that exhibit unidirectional water transport.

A biomimetic superwetting Bi2MoO6-dotted PAA/CS@CuC2O4 membrane with self-cleaning and self-healing ability to aggregate oil droplets for enhanced demulsification of O/W emulsion

Separation of thermodynamically-stable emulsions is of great significance, yet challenging due to the low efficiency and membrane fouling associated with existing methods. Inspired by the water-collection functionality of the hierarchically-structured back of desert beetles, we fabricated a novel inversely beetle-back-like copper mesh membrane, featuring superhydrophobic bumps on a superhydrophilic surface to facilitate the capture-aggregation of tiny oil droplets in oil-in-water (O/W) emulsions. Such membrane was composed of superhydrophobic (SH) Bi2MoO6 microparticles-dotted superhydrophilic polyacrylic acid/chitosan-coated CuC2O4 nanosheet arrays on copper mesh membranes. A cross-flow asymmetric filtration (CAF) device was constructed using the as-prepared membrane to continuously and efficiently separate O/W emulsions. The dispersed oil droplets were captured and coalesced by SH Bi2MoO6 on the superhydrophilic nanoarrays, then detached from the mesh membrane. Simultaneously, the continuous water phase could permeate freely through the mesh pores. The combination of the SH Bi2MoO6-dotted superhydrophilic membrane and CAF device ensured an excellent separation efficiency with an average water permeation flux of 2.7 kL m−2 h−1 for different surfactant-stabilized O/W emulsions and oil residual contents in the filtrate being less than 40 mg L−1. Moreover, the cross-flow of the feed solution in the CAF system strengthened the separation of the coalesced oil phase on the membrane surface, thus preventing the formation of a filter cake caused by the aggregation of emulsified oil droplets.

Numerical Investigations on Enhancement of Pool Boiling Heat Transfer on a Mixed Wettability Surface Employing Lattice Boltzmann Method

Abstract In this paper, a systematic numerical study of pool boiling heat transfer on a mixed wettability heated surface is done using the lattice Boltzmann method (LBM) with a multiple relaxation time (MRT)-based collision operator. The effect of the design parameters, viz, size of the hydrophobic patch (D), spacing between hydrophobic patches (L), number of hydrophobic patches (N), and uneven-sized patches, on pool boiling was studied and results are explained through detailed analysis of bubble nucleation, growth, coalescence, and departure from the heated surface. The results show that mixed wettability surfaces with strategically sized and positioned hydrophobic patches on a hydrophilic surface can result in high heat flux for pool boiling across the entire range of surface superheat or Jacob number (Ja) by combining the advantages of hydrophobic surface in nucleate boiling and hydrophilic surface in transition and film boiling. Further, the mixed wettability surface can delay the onset of film boiling compared to a pure or superhydrophilic surface thereby resulting in higher critical heat flux (CHF). A hydrophobic to total surface area ratio of 30–40% was found to be optimal for all ranges of surface superheat or Jacob number (Ja), which agrees well with the experimental result of 38.46% reported by Motezakker et al. (2019, “Optimum Ratio of Hydrophobic to Hydrophilic Areas of Biphilic Surfaces in Thermal Fluid Systems Involving Boiling,” Int. J. Heat Mass Transfer, 135, pp. 164–174).

Pumping and sliding of droplets steered by a hydrogel pattern for atmospheric water harvesting.

Atmospheric water harvesting is an emerging strategy for decentralized and potable water supplies. However, water nucleation and microdroplet coalescence on condensing surfaces often result in surface flooding owing to the lack of a sufficient directional driving force for shedding. Herein, inspired by the fascinating properties of lizards and catfish, we present a condensing surface with engineered hydrogel patterns that enable rapid and sustainable water harvesting through the directional pumping and drag-reduced sliding of water droplets. The movement of microscale condensed droplets is synergistically driven by the surface energy gradient and difference in Laplace pressure induced by the arch hydrogel patterns. Meanwhile, the superhydrophilic hydrogel surface can strongly bond inner-layer water molecules to form a lubricant film that reduces drag and facilitates the sliding of droplets off the condensing surface. Thus, this strategy is promising for various water purification techniques based on liquid-vapor phase-change processes.

Enhancing wettability of sapphire (Al2O3) substrate through laser surface texturing

Sapphire (Al2O3) has emerged as an incredibly versatile ceramic material, attracting significant interest across various fields due to its superior properties. The potential to control its wettability offers opportunities for enhancing the functionalities of sapphire-based devices. This study focuses on achieving superhydrophilic surfaces on sapphire substrates using a 355 nm nanosecond laser. The effects of the Laser Surface Texturing (LST) parameters on the morphology and wettability of the samples were examined through a Taguchi L16 experimental design. The results showed that the repetition rate and scanning speed influenced the Contact Angle (CA) and Surface Roughness (Ra) of the laser-textured sapphire. Lower repetition rates and higher scanning speeds resulted in rougher surfaces and smaller contact angles. The minimum CA of 4.5° was obtained at a repetition rate of 50 kHz and a scanning speed of 1100 mm/s. The study highlights the importance of controlling processing parameters to achieve desired wetting properties for superhydrophilic surfaces. The findings of this research provide insights into the application of LST for achieving superhydrophilic surfaces on sapphire substrates.

Effect of superhydrophilic surface on the cavitation behaviors of rotating blades

We experimentally confirmed the idea of mitigating (or delaying) the cavitation on the turbomachinery (rotating blades) by transforming the blade surface to be superhydrophilic, thereby the population of the cavitation nuclei is reduced near the surface. We focused on the changes in the cavitation incidence rate, amount of cavitation bubble, and bubble distribution on the superhydrophilic blade through the high-speed camera imaging, compared to the case with a regular (i.e., smooth) surface. With superhydrophilic blades, the cavitation incidence rate decreased significantly, indicating that fewer nuclei evolved into the actual cavitation bubbles. This is also associated with 8.6% delay of the critical rotational speed at which the cavitation process is almost completely established (incidence rate exceeds 80%), and the reduction in the total amount of cavitation bubbles was achieved as much as 18% (maximum 38% in the tested range of rotational Reynolds number). Additionally, the distribution of cavitation bubbles was generally pushed upstream, with fewer bubbles extending downstream, i.e., pushed away from the blade trailing edge. We believe the present results are promising enough to spur the follow-up investigation for the in-depth analysis and practical application toward the robust cavitation control without the substantial modulation of the geometry.

Pre-oxidized ultramicroporous carbon cloth with ultrahigh volumetric capacity and ultralong lifespan for capacitive desalination

Capacitive deionization is a promising desalination technique to tackle with freshwater scarcity, due to its facile, energy-efficient and eco-friendly operation. Carbon materials are primary electrode materials in capacitive deionization devices; however, their practical applications are limited by the low salt adsorption capacity and poor cycling stability. Here, we report a pre-oxidized strategy to significantly improve the salt adsorption capacity and cycling lifespan of carbon clothes. By the simple pre-oxidation treatment, it creates abundant ultramicropores and a superhydrophilic surface, which lead to a high salt adsorption capacity (31.5 mg g−1 and 13 mg cm−3) in 0.01 M NaCl aqueous solution. Moreover, the surface of each carbon fiber is oxidized, combined with a high mechanical strength, resulting in a stable surface during the cycling process. The retention rate is 74% even after 5000 adsorption/desorption cycles in diluted seawater. This work provides a new avenue to the design of high-performance, low-cost, and durable electrodes for capacitive deionization applications.

Statically Very Hydrophilic but Dynamically Hydrophobic Surfaces Showing Surprising Water Sliding Performance

AbstractIt is generally believed that water droplets on (super)hydrophilic surfaces is spread and strongly pin to the surface. The surface chemistry that achieves the paradoxical surface properties of being statically very hydrophilic, but exhibiting outstanding water sliding properties, has not yet established. Here, a facile approach to prepare such unusual surfaces based on a combination of a sol–gel process using an organosilane containing polyethylene glycol units and tetraethoxysilane, and subsequent alkali‐treatment is reported. The resulting sol–gel thin films are smooth, transparent, hydrophilic (static contact angle (CA) (θS) of ≈37°) and show a liquid‐like nature with both low CA hysteresis (≈4°) and sliding angle (α) for 10 µL water droplets (≈10°). Surprisingly, after alkali‐treatment for sufficient time, the surface becomes very hydrophilic (θS of ≈14°) while improving its dynamic wetting behaviors (CA hysteresis of ≈3° and α for 10 µL water droplet of ≈4°), such that even a mere 0.5 µL water drop can slide down smoothly without pinning and/or tailing.

Effect of wall free energy formulation on the wetting phenomenon: Conservative Allen-Cahn model.

Cahn introduced the concept of wall energy to describe the interaction between two immiscible fluids and a solid wall [J. W. Cahn, J. Chem. Phys. 66, 3667-3672 (1977)]. This quintessential concept has been successfully applied to describe various wetting phenomena of a droplet in contact with a solid surface. The usually formulated wall free energy results in the so-called surface composition that is not equal to the bulk composition. This composition difference leads to a limited range of contact angles which can be achieved by the linear/high-order polynomial wall free energy. To address this issue and to improve the adaptability of the model, we symmetrically discuss the formulation of the wall free energy on the Young's contact angle via Allen-Cahn model. In our model, we modify the calculation of the fluid-solid interfacial tensions according to the Cahn's theory by considering the excess free energy contributed by the distorted composition profile induced by the surface effect. Additionally, we propose a semi-obstacle wall free energy which enforces the surface composition to be the bulk composition within the framework of bulk obstacle potential. By this way, the accuracy of the contact angle close to 0° and 180° is significantly improved in the phase-field simulations. We further reveal that the volume preservation term in the conservative Allen-Cahn model has a more significant impact on the wetting behavior on superhydrophobic surfaces than on hydrophilic surfaces, which is attributed to the curvature effect. Our findings provide alternative insights into wetting behavior on superhydrophilic and superhydrophobic surfaces.