Initial Water Contact Angle Research Articles

Photo-induced time-dependent controllable wettability of dual-responsive multi-functional electrospun MXene/polymer fibers

Switchable wettability potential in smart fibers is of paramount importance in various applications. Light-induced controllable changes in surface wettability have a significant role in this area. Herein, smart waterborne homopolymer, functional copolymer with different polarity and flexibility, and multi-functional terpolymer particles containing a time-dependent dual-responsive acrylated spiropyran, as a polymerizable monomer, were successfully synthesized through eco-friendly single-step emulsifier-free emulsion polymerization. Presence of 10 wt% of butyl acrylate and dimethylaminoethyl methacrylate relative to methylmethacrylate as functional comonomers decreased the Tg of the samples almost 20 ℃ and increased their polarity. The optical properties of the particles were investigated, and the UV–vis and fluorescence spectroscopy results showed that not only polarity and flexibility of the polymer chains may have a positive effect on improving the optical properties, but also the simultaneous presence of functional groups has a synergistic effect. The smart polymer particles with flexibility and polarity features exhibited higher absorption and emission compared to other samples. Inspired by these findings, multi-functional smart polymer fibers were prepared using the electrospinning method. The smart multi-functional electrospun fibers containing few-layer Ti3C2 MXenes were synthesized to improve the fibers’ properties and change the surface wettability due to the hydrophilic functional groups of MXene. Field-emission scanning electron microscopy images displayed the successful preparation of few-layer MXenes. Smooth and bead-free fibers with bright red fluorescence emission under UV irradiation were shown using fluorescence microscopy. The study on the surface wettability of fibers revealed that UV and visible light irradiation induced reversible time-dependent changes in the wettability of the smart multi-functional MXene/polymer electrospun fibers from hydrophobic to hydrophilic, reaching a water contact angle of 10° from an initial water contact angle of 100° under UV light and also changing to superhydrophilic state with passing time. Upon visible light exposure, the fibers returned to their original state. Furthermore, the fibers demonstrated a high stability over five alternating cycles of UV and visible light irradiation. This study shows that the fabrication of time-dependent smart fibers, utilizing the flexibility and polarity in the presence of MXenes, significantly improves and controls surface wettability changes. The outstanding dynamically photo-switchable wettability of these fibers may offer exciting opportunities in various applications, especially in the separation of oil from water contaminants.

Preparation and Properties of Polyimide/Polysulfonamide/Polyethylene Glycol (PI/PSA/PEG) Hydrophobic Nanofibrous Membranes.

In this study, polyimide (PI) and polysulfonamide (PSA) were used as base materials, and polyethylene glycol (PEG) was added to successfully prepare PI/PSA/PEG nanofiber membranes through electrospinning technology. Subsequently, water etching was performed on the membranes, utilizing the water solubility of PEG to form the rough wrinkled structure, further enhancing the surface hydrophobicity. The experimental results showed that under the conditions of a spinning voltage of 10 kV, PI/PSA mass fraction of 15 wt.%, and PEG-to-PI/PSA mass ratio of 1/3, the obtained fiber membranes exhibit a uniform morphology (an average diameter of 0.73 µm) and excellent hydrophobicity (the initial water contact angle (WCA) reaching 130.4°). After PEG water etching, the surface of the PI/PSA/PEG hydrophobic membranes formed the rough wrinkled structure, which not only improved their mechanical properties but also further enhanced their hydrophobicity (the initial WCA increasing to 137.9°). Hence, fiber membranes are expected to have broad application prospects in fields such as waterproofing and moisture permeability.

In-situ deposition modification of hydrophilic polytetrafluoroethylene (PTFE) membranes using surfactants as anchoring points for long-term stability

Polytetrafluoroethylene (PTFE) membranes are renowned for their excellent thermal stability, resistance to strong acids and alkalis, and superior mechanical stability. However, its inherent strong hydrophobicity significantly limits its use in water treatment. In this study, a SiO2 coating was successfully deposited in-situ on the surface of PTFE membranes using a hydrolyzed solution of tetraethyl orthosilicate (TEOS) compounded with the commercial fluorinated polyoxyethylene ether surfactant FS-31 (C6F13CH2CH2O(CH2CH2O)nH). The modification mechanism involves using the low surface energy nonionic fluorocarbon surfactant FS-31, which interacts hydrophobically with the PTFE substrate, serving as an “anchor” point around which the TEOS hydrolyzes and condenses around the fibers and nodes of the PTFE membrane, forming a complete and stable chemical network structure. The results show that the initial water contact angle of the modified membrane dropped to 36.5°, and the water flux reached 537.9 L m−2 h−1. After being continuously immersed in strong acid (5 wt% HCl), strong alkali (4 wt% NaOH), and oxidizing agent (5 wt% NaClO) for one week, the membrane maintained excellent hydrophilicity and stability. This study proposes a mild and efficient modification method to prepare durable hydrophilic PTFE membranes, portending great potential for applications in harsh environments.

Bio‐Based Foams to Function as Future Plastic Substitutes by Biomimicry: Inducing Hydrophobicity with Lignin

To replace common plastics, bio‐based alternatives are needed. Cellulose foams, as plant‐based materials, are the most attractive solution, being often biodegradable and inexpensive and having the potential for distributed production. Cellulose and its derivatives, as raw materials, present a fundamental challenge, as they are hydrophilic. Herein, this problem is solved by drawing inspiration from the hydrophobic barrier that lignin creates in wood and applying lignin to methylcellulose (MC) foams. The lignin (0.0–1.0 wt% being the range studied here) is applied directly to the suspension consisting of water and MC (1.8 wt%), which is then foamed and solidified to a dry 3D porous structure. By comparing different types of lignin and the resulting surface morphologies, it is shown that organosolv lignin (OL) most strongly self‐assembles to the air–foam interfaces, achieving area fractions up to 27%. Using different concentrations of OL, how hydrophobicity—described by the initial water contact angle and its time evolution—increases with increasing lignin concentration is then shown. Thus, significantly increased water resistance (up to 91 times higher compared to the pure MC foam), a crucial property for developing novel bio‐based materials that can compete with traditional plastics, is able to be achieved.

Enriched oil-in-water emulsions as bioactive agents for locust bean gum films: A comparative investigation

In this study, pracaxi oil (PO) and olive oil (OO) emulsions, enriched with turmeric powder (Cur) and stabilized by nanofribrillated cellulose (NFC), were developed and incorporated to glycerol-plasticized locust bean gum (LBG) dispersions. Films were obtained by solution casting, and their properties were compared, aiming to expand PO application as a potential constituent of active food packaging. The films were characterized for their morphological, structural, transparency, gas permeability, wettability, thermal, mechanical, and antioxidant properties. In relation with the plasticized LBG film, both emulsion films showed improved humidity content, surface wettability, oxygen barrier capacity, thermal stability, and mechanical properties. As for wettability, while the initial water contact angle for the LBG film was θ0 = 93.4°, values of θ0 = 105.5° and θ0 = 99.2° were determined for the LBG films incorporated with PO- and OO-based emulsions, respectively. In comparison with the LBG film, the incorporation of PO-based droplets led to an approximately 8.0% reduction in the water vapor transmission rate values. Also, in comparison with the LBG film, the LBG/NFC/PO-Cur and LBG/NFC/OO-Cur films were capable of reducing the peroxidation value of sunflower oil by 16% and 11%, respectively. Enhancements in tensile strength values of 44% and 49% were determined for the PO- and OO-based emulsion films. The emulsion films presented similar antioxidant properties and better preservation of strawberry model food than LBG and polyethylene films. The results of the comparative experiments suggested that the use of PO may be expanded as a component of active food packaging.

Preparation and characterization of wood coatings fabricated from 3D interpenetrating networks of hydroxylated rosin-CO2-polyurethane and benzoxazine

Rosin polyether polyol was synthesized through the hydroxylation of rosin and epoxy. This polyol was then used to modify CO2-polyols for the synthesis of rosin-CO2-polyurethane (RPU) as a wood coating. Simultaneously, a rosin-based benzoxazine (SBZ) was prepared using sesamol, paraformaldehyde, and dehydroabietylamine, and 3D interpenetrating network system, RPU/SBZ, was formed. The two coatings were further examined. Research has demonstrated that both RPU and the RPU/SBZ 3D interpenetrating network system exhibit excellent mechanical properties, with the latter outperforming the former. The hydrophobic angle of the RPU/SBZ coating measures 119° and remains unchanged over a short period, while the initial water contact angle of the RPU coating is 85° and decreases by 2° shortly after application. The RPU/SBZ composite system coating demonstrates superior chemical resistance, gloss, and adhesion to wood compared to the RPU coating. Additionally, RPU- and RPU/SBZ-based composite system coatings exhibit exceptional flame retardancy as wood coatings. These findings hold significant implications for the development of high-value products in the coating industry.

Enhanced hydrophilicity of low melting point polylactic acid by butenediol vinyl alcohol copolymer via melt blending

In order to solve the poor hydrophilicity of low melting point polylactic acid (LMPLA) limiting its application in absorbent sanitary products. LMPLA/butenediol vinyl alcohol copolymer (BVOH) blends with different ratios were manufactured by simple melt blending. The BVOH exhibited good compatibility and dispersity in LMPLA matrix without chemical reaction, and LMPLA/BVOH blends showed sea-island structure. The introduction of BVOH could promote the crystallization of LMPLA and improve the crystallinity, whereas the crystallization of BVOH were limited. Furthermore, the introduction of BVOH could also decrease the thermal stability of LMPLA without affecting its application, but the tensile stress of LMPLA could be significantly increased. The tensile stress of LMPLA/BVOH blends could reach 78.59 MPa (increased by 10.9%) when he BVOH content was 3 wt%. Most importantly, the introduction of BVOH could significantly improve the hydrophilicity of LMPLA. The initial water contact angle decreased from 68.5° to 51.4° with the increase of BVOH content, and the contact angle decreased from 63.7° to 44.6° at 60 s. Moreover, the contact angle change rate of LMPLA/BVOH blends increased with the increase of BVOH content at different contact time, which also indicated adding BVOH could sharply improve the hydrophilicity of LMPLA.

Recyclable oil resistant paper with enhanced water resistance based on alkyl ketene dimer modified sodium alginate

Abstract Sustainable coatings exhibit potential in enhancing oil resistance of packaging paper. Alkyl ketone dimer (AKD) was used to esterify sodium alginate (SA) to prepare water and oil resistant agent SAD. As SAD was coated on paper, it reduced the surface energy and blocked the fiber pores of paper, thus improving the barrier performance of paper. The oil resistance grade can reach grade 6 at coating amount of 2.13 ± 0.26 g/m2, which is qualified for food packaging. The coated paper also showed good barrier to hot castor oil. Resistance to organic solvent and water were also enhanced with initial water contact angle (WCA) increased to 69.2°. Compared with base paper, SAD coated paper had better mechanical properties and more importantly, coated paper can be effectively recycled to achieve green recycling.

UV-Curable Fluorocarbon Polyurethane Coatings for Marble Kitchen Countertops

Marble kitchen countertops and other natural stone surfaces are often stained by various food ingredients and contaminants during daily use and require frequent cleaning, which is time-consuming and leads to the wasting of water. If the surface is coated with a hydrophobic and oleophobic coating, food ingredient contamination becomes easier to wipe clean. Therefore, a UV-curable monomer with fluorocarbon branched chains was synthesized and added to UV-curable coatings in different ratios. The preferred formulation that meets the basic performance requirements of UV-curable coatings, and has the best hydrophobic and oleophobic properties, was designed and selected. The formulation was upgraded by adding a hydrofluoric ether (HFE) solvent. These upgraded formulations were tested for hydrophobicity and oleophobicity under various conditions. The addition of an HFE solvent improves the initial water and cetane contact angles of the paint film, as well as the water and cetane contact angles under various conditions. Moreover, the upgraded formulations have better stain resistance. The degree of hydrophobicity and oleophobicity improvement is positively correlated with the addition of an HFE solvent. The UV-curable fluorocarbon polyurethane coating has good adhesion on a marble surface that has been polished and primed. Due to the presence of TEOH-6 instead of PFOA, the low content of fluorocarbon functional groups effectively located on the film surface makes the coating quite stable and safe.

Nanocomposites based on halloysite nanotubes and sulphated galactan from red seaweed Gloiopeltis: Properties and delivery capacity of sodium diclofenac

We developed novel composite films based on biocompatible components, such as halloysite clay nanotubes and sulphated galactan (Funori) from red seaweed Gloiopeltis. The filling of the nanotubes within the sulphated galactan matrix was carried out by a green protocol (aqueous casting method) assuring that Funori/halloysite nanocomposites can be totally considered as sustainable materials. The amount of halloysite in the composites was systematically changed to explore the effects of the nanofiller concentration on the mesoscopic properties of the films. We observed that the halloysite content significantly affects the initial water contact angle and the light attenuation coefficient of the Funori based films. These results were interpreted according to SEM images, which showed that the surface morphologies of the nanocomposites depend on the halloysite amounts filled within the polymeric matrix. The mechanical characterization of the nanocomposites was conducted by tensile experiments performed using a linear stress ramp. Moreover, tensile tests were conducted in oscillatory regime at variable temperature to investigate the viscoelastic properties of the nanocomposites.Finally, we filled the biopolymeric matrix with halloysite nanotubes containing sodium diclofenac. The drug release kinetics from the nanocomposites at variable halloysite contents were studied to evaluate their suitability as oral dissolving films for pharmaceutical applications.

Fabrication of sandwich structure membrane and its performance for photocatalytic reduction of Cr(VI)

The regenerated cellulose membrane (RC) was synthesized by dissolving cotton cellulose in NaOH/CO(NH2)2 system. The Polydopamine/Bismuth tungstate/RC composite membrane (RCPB) with photocatalytic activity was synthesized by loading polydopamine-modified bismuth tungstate (PDA/BWO) composite onto the RC by blending method. The RCPB/PAN/RCPB sandwich structure membrane was synthesized by combining the polyacrylonitrile (PAN) nanofiber membrane and RCPB by scraping method, which can reduce aqueous Cr(VI) under visible light effectively. Characterization shows that the tensile strength, elongation at break, roughness and initial water contact angle of RCPB/PAN/RCPB are 32.1 MPa, 5.34%, 0.658 μm and 69.0°, respectively. The photoreduction percent of Cr(VI) by RCPB/PAN/RCPB can reach 99.7% within 120 min with a rate constant of 0.0869 min−1, and the photoreduction percent remains above 84.6% after four cycles. The introduction of PAN nanofiber membrane further improves the mechanical properties and recycling ability of RCPB. Meanwhile, the capture experiments reveal that the main active substance for photocatalytic reduction of Cr(VI) by RCPB/PAN/RCPB is photogenerated e−. This work provides a new idea for the treatment of Cr(VI)-containing wastewater.

Esterification process of incorporation CS2 activation and its effect on the properties of hydrophobic modified cotton filter fabric via ARGET-ATRP

Hydrophobic modification of cellulose via activation synergistic activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) method has been proved to effectively improve the long-term hydrophobic stability of cotton filter fabric. However, the extra activation process will inevitably increase the complexity of the reaction process. In this work, carbon disulfide (CS2) was incorporated into the ARGET-ATRP reaction system to avoid adding redundant reaction links. Specifically, the activation and acyl bromination processes were combined, and then the graft modification reaction between the acyl bromide cotton filter fabric and 1-octadecene (1-Oct) was realized by the ARGET-ATRP. The effect of the combined process on the hydrophobic modification reaction and performance of cotton filter fabric was investigated. The results showed that, under the optimum dosages of activator CS2, acyl bromide reagent BiB and monomer 1-Oct, the activator CS2 was directly incorporated into the acyl bromination process. And after ARGET-ATRP Hydrophobic modification, the initial water contact angle (CA) of the obtained hydrophobically modified cotton filter fabric reached 145.0°, the residual contact angle (RCA) after the water droplet retention time of 210 min could still arrive at 125.4°, showing a corresponding attenuation rate (Dr) of 13.5%, which suggested excellent hydrophobicity and durability. Notably, the hydrophobically modified cotton filter fabric also exhibited excellent resistance to chemical corrosion, abrasion resistance and ultrasonic stripping resistance. Furthermore, this hydrophobically modified filter fabric can efficiently separate different types of oil–water mixtures. Even after 12 cycles of oil–water separation process, the separation efficiency still exceeded 95%, and the CA of the modified filter fabric before and after separation was basically unchanged.

Electrostatic Spinning based on Aqueous Polyurethane Block‐Modified Polycaprolactone and Its Hydrophilicity Study

AbstractIn this study, waterborne polyurethane hydrophilic block copolymer PCL‐b‐WPU is obtained through step‐growth addition polymerization reaction to improve the hydrophilicity of polycaprolactone (PCL). Then, films are prepared via solution casting method and electrospinning. PCL‐b‐WPU nanofibrous membranes have a higher initial water contact angle of 106°, but they can be completely wetted from the surface to the back within 120 s, with good wet absorption and quick‐drying performance. Hollow fibers are fabricated via coaxial electrospinning by controlling the process parameters. PCL‐b‐WPU is used as shell material and polyoxyethylene as the core. Low‐field nuclear magnetic resonance technology is used to analyze the moisture distribution and the state of water within solid, porous, and porous hollow fibers. Their bound water is 14.5%, 27.5%, and 31.1%, respectively. These results suggest that the introduction of the WPU chain and the construction of a rough surface significantly improve the hydrophilicity of PCL. PCL‐b‐WPU membranes are expected to be further developed and utilized for moisture‐absorbing and quick‐drying textiles, wound dressings, and biological scaffolds.

Facile Fabrication of Multi-Hydrogen Bond Self-Assembly Poly(MAAc-co-MAAm) Hydrogel Modified PVDF Ultrafiltration Membrane to Enhance Anti-Fouling Property.

In this work, a facile preparation method was proposed to reduce natural organics fouling of hydrophobic membrane via UV grafting polymerization with methacrylic acid (MAAc) and methyl acrylamide (MAAm) as hydrophilic monomers, followed by multihydrogen bond self-assembly. The resulting poly(vinylidene fluoride)-membranes were characterized with respect to monomer ratio, chemical structure and morphology, surface potential, and water contact angle, as well as water flux and organic foulants ultrafiltration property. The results indicated that the optimal membrane modified with a poly(MAAc-co-MAAm) polymer gel layer derived from a 1:1 monomer ratio exhibited superior hydrophilicity and excellent gel layer stability, even after ultrasonic treatment or soaking in acid or alkaline aqueous solution. The initial water contact angle of modified membranes was only 36.6° ± 2.9, and dropped to 0° within 13 s. Moreover, flux recovery rates (FRR) of modified membranes tested by bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA) solution, respectively, were all above 90% after one-cycle filtration (2 h), significantly higher than that of the pure membrane (70–76%). The total fouling rates (Rt) of the pure membrane for three foulants were as high as 47.8–56.2%, while the Rt values for modified membranes were less than 30.8%. Where Rt of BSA dynamic filtration was merely 10.7%. The membrane designed through grafting a thin-layer hydrophilic hydrogel possessed a robust antifouling property and stability, which offers new insights for applications in pure water treatment or protein purification.

Constructing a Novel Xylan-Based Film with Flexibility, Transparency, and High Strength.

Xylan-based films have great potential to replace petroleum-based polymers used for packaging and coatings due to their excellent biocompatibility, biodegradability, and good gas barrier properties. However, fabricating a xylan-based film with flexible, transparent, water-proof, and excellent mechanical properties is an enormous challenge. Herein, we manufactured a series of degradable films with adjustable properties via solution-casting using a water-soluble xylan derivative. This is the first report of a pure xylan-based film with high performance, requiring no additives. The tensile strength of the xylan-based film could be controlled by adjusting the aldehyde content, which varied from 105.0 to 132.6 MPa. The smallest initial water contact angle of the xylan-based films is 93.26°, indicating that these films are hydrophobic. This work shows a simple and viable route toward manufacturing xylan-based films with high tensile strength, flexibility, and transparency, which can be used for packaging materials and coatings.

Modification of PET surfaces with gum Arabic towards its bacterial anti-adhesiveness using an experimental factorial design approach

Bacterial adhesion onto hospital material surfaces still represents a big healthcare issue, being preventive measures required to mitigate this problem, such as increasing material surface hydrophilicity. In the present study, gum Arabic, a hydrophilic polysaccharide, was used to modify the surface of polyethylene terephthalate (PET). Initial water contact angle (WCA) and WCA after several washing cycles were studied as response variables by a 24 full factorial design. Several reaction parameters, such as contact time between gum Arabic and PET, gum Arabic concentration, curing temperature and curing time for PET modification were investigated. The most significant parameters were found to be the curing temperature and curing time. The optimized parameters led to a WCA reduction from 70° to 27°. The modified PET samples were characterized using several techniques including AFM, colorimetric, ATR-FTIR and contact angle which further confirmed a successful surface modification. Furthermore, bacterial adhesion assays have clearly shown that the treated PET material was highly effective in preventing the bacterial adhesion of Escherichia coli expressing YadA, an adhesive protein from Yersinia so-called Yersinia adhesin. The use of design of experiments techniques allowed for successfully attaining a PET material with a high bacterial anti-adhesiveness, using a simple grafting approach.

Electrowetting-on-dielectric behavior of micro-nano hierarchical SiO2 layers decorated with noble metals

The performances of electrowetting-on-dielectric (EWOD) devices were investigated using micro-nano hierarchical structures of pristine and noble metal-decorated SiO2 layers, with the entropy wetting model. The SiO2 layers were prepared by an electrospray technique, and noble metals were decorated by UV irradiation. In addition, a thin Teflon coating was applied to enhance their initial hydrophobicity. The initial water contact angle (WCA) value of the Pd-decorated SiO2 (Pd–SiO2) and Ag-decorated SiO2 (Ag–SiO2) layers was 165°, while that of the Au-decorated SiO2 (Au–SiO2) and pristine SiO2 layers was 154°. Different external voltages (up to 200 V) were used to investigate the EWOD behavior of the fabricated layers. In all cases, the WCA decreased with increasing applied voltage. Under 200 V (maximum applied voltage), WCA values of 129, 120, 115, and 102° were measured for pristine SiO2, Pd–SiO2, Ag–SiO2, and Au–SiO2 layers, respectively. Moreover, the EWOD properties of the noble metal-decorated layers were studied in the presence of dodecane oil. At 200 V, the WCAs of the Pd–SiO2, Ag–SiO2, Au–SiO2, and layers were 134, 97 and 100°, respectively. Finally, we applied the entropy wetting model to further understand the results of the EWOD experiments.

Effect of CO2 laser treatment on the leather surface morphology and wettability

The aim of this research was to determine the influence of pulsed CO2 laser treatment on crust leather surface morphology and wettability. The obtained results revealed that pulsed CO2 laser engraving can be used as an effective tool for crust leather surface treatment. Pulsed CO2 laser treatment only negligible affects the macrostructure of leather, while the morphology and wetting of the leather surface after treatment were changed. It was found that an increase of laser pulses number increases the initial water contact angle value and intensifies the water droplet relaxation process. After laser treatment, the water droplet contact angle relaxation rate increases twofold compare to those for untreated leather. SEM micrographs showed increased defectiveness with rough surface patterns, thermally affected areas, and change of microstructure. The EDX analysis revealed that the engraved leather surface contains a significantly higher amount of carbon but smaller quantities of oxygen compared to those of untreated samples. It was found that only after laser treatment chromium and sulfur in the EDX spectra appear while for untreated samples these elements on the surface were not observed. The results indicate that for investigated samples laser engraving does not affect the concentration of hexavalent chromium and are in accordance with EU requirements.

Ag3PO4 composite nanofiltration membrane and its visible-light photocatalytic properties

Ag3PO4 and AgBr–Ag3PO4 were deposited on the surface of nanofiltration membrane (FT) with tannic acid (TA) and toluene-2,4 diisocyanate (TDI) as functional layers by alternate impregnation method to obtain composite NF membranes (FTA and FTAB) with visible catalytic activity. Under optimal conditions, the catalyst loads on the surfaces of FTA and FTAB were uniform, the initial water contact angle was lower than 28°, the zeta potential was close to −17 mV, the fluxes with FTA and FTAB were respectively 16 and 17.5 L m−2 h−1 (0.4 MPa), and the rejection of Na2SO4 and sulfamethoxazole (SMZ) were more than 75% and 90%, respectively. FTA and FTAB had good photochemical properties, strong absorption of visible light, low electrochemical impedance and sensitive transient photocurrent response. FTA and FTAB with an effective area of 16 cm2 had a static degradation rate of over 90% for 100 mL of 10 mg L−1 SMZ and ciprofloxacin and can achieve dynamic degradation in NF within 300 min under visible light. FTAB effectively alleviated the photo-corrosion behaviour of FTA, maintained the degradation rate of Congo red above 85% after four cycles and had good stability and anti-pollution self-cleaning performances.

Improving the wettability of structural steels by employing ionic liquids

Surface wetting behavior is tied to different surface phenomena such as lubrication and corrosion resistance of steel surfaces. In this study, the surface wetting behavior of room-temperature ionic liquids (RTILs) treated steel surfaces is investigated. To this end, polished steel surfaces are individually surface-treated using seven imidazolium-based RTILs with varying alkyl chain lengths ([CnMIM], n = 2, 4, 6) and anion groups ([PF6], [NTf2], [Br], [BF4], [AlCl4]) for two different exposure durations (0.5 h and 4 h). The wetting behavior of RTIL-treated steel surfaces is quantified in terms of contact angles and surface energies corresponding to polar (water) and non-polar (diiodomethane) probing liquids. The RTIL surface treatment is observed to improve the surface wetting behavior of steel surfaces for both polar and non-polar probing liquids. The average initial water contact angle of steel surfaces decreased by 24−87% after RTIL surface treatment. Similarly, the average initial non-polar liquid contact angles of RTIL-treated steel surfaces decreased by 25−66% when compared to the untreated steel surface. The water contact angle decreased with an increase in the time elapsed after droplet impingement on the surface, whereas, for the non-polar liquid, the contact angle remained relatively unchanged during the elapsed duration adopted herein. The average surface free energy of RTIL-treated steel specimens increased by 49%−100%, which rendered the RTIL-treated steel surfaces more wettable. The increase in the RTIL treatment time only nominally improved the wetting of steel surfaces for both polar and non-polar probing liquids. The results reported herein can be used to prepare the surfaces of inaccessible structural steel components and bridge bearings for efficient water cleaning and lubrication.