Preparation of super-hydrophilic amorphous titanium dioxide thin film via PECVD process and its application to dehumidifying heat exchangers

The super-hydrophilic amorphous titanium dioxide (TiO₂) thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) process for an application to dehumidifying finned-tube heat exchangers. The chemical components and surface structure were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). The wettability and long-term durability were investigated by measuring the water contact angle and by performing wet/dry cycles. The samples were subjected to 1000 times of wet/dry cycles to establish long-term durability. The water contact angle of the amorphous TiO₂ thin film was about 8° at as-deposited film with O₂ plasma treatment and was about 15° after 1000 wet/dry cycles. The amorphous TiO₂ thin film had excellent wettability and long-term durability under full wetting conditions.     

Microstructure evolution of polycrystalline Ti2AlN MAX phase film during post-deposition annealing

Polycrystalline Ti₂AlN MAX phase films were fabricated by post-deposition annealing of Ti-Al-N film at annealing temperature in the range of 600?°C–800?°C in high vacuum. The temperature-dependent microstructure evolution from Ti-Al-N film to polycrystalline Ti₂AlN film has been investigated. It was found that after post-deposition annealing above 600?°C, the as-deposited amorphous Ti-Al-N film transformed to polycrystalline Ti₂AlN film. With the increase of annealing temperature from 600?°C to 700?°C, the crystallinity of polycrystalline Ti₂AlN film was improved. At 800?°C, the surface Ti₂AlN grains completely decomposed and transformed to TiN phase while inner grains was partial decomposed and surrounded by amorphous Al-rich phase. The polycrystalline Ti₂AlN film exhibited a highest hardness of 34.1?GPa while the hardness of amorphous Ti-Al-N film was only 24.2?GPa. The mechanism of texture changes and phase transformation as well as its effect on thermal stability was also discussed.     

Wetting and interfacial reactions in liquid Au-Ti alloys / ZrO2 system

This study investigates wetting of zirconia by Au-Ti alloys containing 0.6–4 wt% Ti in view of brazing zirconia to titanium with pure gold for biomedical applications. Experiments were carried out using sessile and dispensed drop methods under high vacuum at 1040–1250 °C. Bulk drops and Au-Ti / ZrO₂ interfaces were characterized by SEM and FEG-SEM with EDXS analysis. While Au does not wet zirconia, the contact angle θ being ∼ 120°, the addition of Ti in Au leads to a significant improvement of wetting due to the formation of a wettable oxide layer at Au-Ti / ZrO₂ interface. The nature of this oxide was determined by X-ray diffraction of the reaction layer after the detachment of the droplet from the substrate or after the dissolution of the droplet. The mechanism of formation and growth of the oxide layer and its growth kinetics were determined based on fine analysis of the Au-Ti / oxide layer / ZrO₂ interfacial system.     

Fabrication of superhydrophobic surfaces with tunable water droplet adhesion force by a two-step method

In this paper, we present a convenient approach to prepare hierarchical structured superhydrophobic coatings with tunable adhesion force, composed of micro-size glass beads, nano-size SiO₂ particles and epoxy resin. Surfaces of two types with different roughness were fabricated, one type is only with single-scale roughness demonstrating lotus effect with low sliding angle, the other type is hierarchically micro-nano-structured roughness exhibiting petal effect with high adhesion force. The surface roughness is pivotal for controlling the wetting behavior and regulating the contact angle including the contact angle hysteresis. Varying the density of micro-size glass beads could adjust the roughness of the surface, which means the adhesion force of the prepared surface could be easily controlled based on the proposed method. Through variation of glass beads’ amount, the surface could be designed to pin the water droplet with different adhesion force when the surface turned upside down. The surface wettability, surface morphology, adhesion force of the prepared samples are investigated and mechanism of the Cassie-to-Wenzel state transition are discussed in detail. Furthermore, the convenient method provides a possibility for controlling surface morphology, composition and corresponding surface adhesion which could be applied to various substrates such as tile, wood, steel and fabric.     

Investigating the wetting phenomena and fabrication of sticky,para-hydrophobic cerium oxide coating

We report fabrication of a novel sticky parahydrophobic cerium oxide (CeO₂) coating using a facile and industrially viable plasma spray technique, which has prospective applications in microfluidic chips, no loss microdroplet transportation and chemical microreactors. Our coating displays significantly high water contact angle (∼159.02˚) along with high contact angle hysteresis (CAH≥90˚), very much similar to a ‘Rose petal’. This is further strengthened by the fact that the coating displayed remarkable adhesion even with large inverted water droplets of 70 μL, which is significantly higher than the reported values of 18 μL for polymer and 20 μL for drop casted CeO₂ nanotubes. We also present systematic characterization results to clarify the ongoing confusion regarding the hydrophobicity of CeO₂ coatings often reported in literature. Meanwhile, our parahydrophobic coating also showed remarkable thermal and mechanical stability even at a significantly high temperature of 200 °C for 14 h and with 50 g abrasive paper.     

The wetting-to-nonwetting transition of CVD BN coatings deposited at different temperatures

Boron nitride (BN) coatings (thickness 20–40 μm) were prepared on graphite substrates by chemical vapor deposition, with precursors of BCl₃ and NH₃ (ratio of 1:4) and pressure of 500 ± 50 Pa. The influence of the deposition temperature (650°C–1250°C) on the wettability of BN coatings with deionized water was studied. The wetting angle rapidly increases at 1100°C–1250°C, and the wetting-to-nonwetting transition occurs. The crystal structure and surface morphology of the BN coatings were characterized by a stylus instrument, scanning electron microscopy, and transmission electron microscopy. Research shows that the contact angle or nonwettability increases with a higher degree of crystallinity and a lower surface roughness, which were both under the control of the deposition temperature since the pressure and gas flows were kept constant in this study. At a deposition temperature of 650°C–950°C, the increase in the degree of crystallinity dominates; at 950°C–1100°C, the increase in surface roughness takes over. At 1100°C–1250°C, the degree of crystallinity continues to increase, while the surface roughness decreases due to the advantage of nucleation and the breakage of large surface clusters into smaller clusters. This results in increases (650°C–950°C), then decreases (950°C–1100°C) and again fast increases (1100°C–1250°C) in the wetting angle between the BN coating and deionized water and finally in the wetting-to-nonwetting transition (1100°C–1250°C).     

Influence of treatment temperature on wettability of Norway spruce thermally modified in vacuum

Wettability of Norway spruce modified by a new vacuum thermal modification procedure was studied. The mass loss caused by this process ranged from almost 0% when treated at 140?°C to 4.3% at 210?°C. Apparent contact angles of water, formamide, and diiodomethane were measured by the Wilhelmy plate method on the specimens taken from the centers of the thermally modified wood samples. For the treatment at the highest temperature, the contact angle of water was significantly higher when compared to untreated spruce (96.6° vs. 83.6°); lower treatment temperatures, however, did not result in a clear correlation between treatment temperature and contact angle. Formamide yielded lower contact angles for treated spruce compared to the untreated one, but without clear influence of the treatment temperature and diiodomethane always gave perfect wetting. Surface energy calculations according to the Owens, Wendt, Rabel, and Kaelble method revealed that the thermal modification process in vacuum increased the surface free energy and lowered the polarity of wood significantly only at the highest applied temperature (210?°C); the treatment had only limited effect at lower temperatures of modification. These results indicate that adequate wetting and adhesion can be achieved on the surfaces of Norway spruce thermally modified in vacuum.     

Urine Advancing Contact Angle on Several Surfaces

Urine wetting properties may influence the design and performance of catheters, urinalysis instruments, and lab-on-a-chip technologies. In this study the advancing contact angle _adv of urine on several materials is characterized. Material type and surface tension have a significant effect on _adv, while pretreatment and aging do not. Mean urine _adv are between ≈78° and ≈89° on hydrophilic surfaces, and up to over ≈105° on hydrophobic surfaces. Expected urine contact angles will decrease from the DI water contact angles by on average 10°, and up to 20°, while urine surface tension will be lower than DI water by 12.12 mN/m and 18.53 mN/m. A unit change (mN/m) in surface tension results in a 0.75° change in _adv. These results indicate that systems attempting to exploit urine wetting must account for highly variable conditions.     

A simple method for the fabrication of silica-based superhydrophobic surfaces

The present article reports on a simple and convenient method for the fabrication of superhydrophobic surfaces based on silica particles by spraying the as-prepared silica suspension containing silica sol and silica microspheres on the substrate. The morphologies of the silica particulate coatings could be controlled by varying the silica microsphere concentration. The silica particulate coatings as prepared were exceptionally rough and superhydrophilic, with water contact angles less than 5°. The surface silanol groups of the hydrophilic coatings could be functionalized using 1H,1H,2H,2H-perfluorodecyltriethoxysilane to form hydrophobic groups. The resulting surface showed excellent superhydrophobic property with water contact angle up to 165.6 ± 0.9° and sliding angle of 3.5 ± 0.4°. In addition, the superhydrophobicity of the coating possessed a good stability after 3 months of exposure in air for a wide range of pH values.     

Surfactant-catalyzed SiO2 thin films preparation and characterization

SiO₂ thin films are in high demand for wide range of applications including microelectronics, optoelectronics, solar energy conversion, photocatalysis, and self-cleaning coatings. The performance of thin film is strongly influenced by surface properties like surface roughness, thickness, morphology, wetting behavior, and thermal stability. In these applications, the SiO₂ sols were prepared using tetraethylorthosilicate as a source of SiO₂ and deposited on 100?×?40?×?2?mm³ glass slide using dip-coating method for 2?min and calcined at 250?°C for 30?min. The SiO₂ thin films were obtained using DTAB, SDS, and Tween 20 (Tw 20) surfactants with the thickness of 36.92, 47.15, and 52.39?nm, respectively. Surface morphology was studied with AFM and surface roughness was depicted with 0.9528, 3.6534, and 0.9294?nm. Contact angle measurements have been performed with goniometer to evaluate the wetting behavior of the film. The contact angle of 58.01°, 48.40°, and 37.88° was observed with SDS, DTAB, and Tw 20 film, respectively. The SiO₂ thin films with SDS showed more surface roughness and water repelling ability when compared to DTAB and least with Tw 20.     

Electrospun polylactic acid non-woven mats incorporating silver nanoparticles

This research is focused on the influence of silver nanoparticles (AgNPs) on the spinnability, morphology and wetting properties of electrospun polylactic acid (PLA) non-woven mats. PLA was electrospun from a chloroform solution (4.7 % g/g) and a filament and beads morphology was obtained, the filaments having an average diameter of 1.25 μm. Interestingly, water contact angle measurements showed a contact angle of θ = 81°, an improvement relative to as-cast film which exhibited a contact angle of θ = 54°. When AgNP, of ca. 12 nm size, were incorporated at 1 % g/g relative to PLA weight, to the 4.7 % PLA-chloroform solution, and electrospun, the filaments diameter was greatly reduced to an average of 0.65 μm, and the density of polymer beads was also reduced. It is believed that the electric conductivity of silver enhanced the spinnability of the polymer solution. Strikingly, water contact angle measurements showed that the PLA/AgNP mats exhibited an angle as high θ = 134°. Increasing the solution concentration to 6.7 % g/g still produced a beads-and-filament morphology, but with larger filament diameters, probably due to an increase in solution viscosity. When AgNP were added (again at 1 % g/g relative to PLA weight), the occurrence of beads diminished and the average filament diameter decreased confirming the enhancement in spinnability by the AgNPs. Moreover, contact angles remained above 110° suggesting that the overall morphology is key to PLA’s mats hydrophobic behavior and not only filament diameter. Finally, the non-woven mats were rather amorphous, as revealed by differential scanning calorimetry and X-ray scattering, due presumably to the quenching process associated with the electrospinning process.     

Porous water repellent silica coatings on glass by sol–gel method

Development of the solid surfaces with water-repellent and self-cleaning ability has attracted much research interest in recent years. In the present research work, we have prepared water repellent silica coatings on glass at room temperature (~27 °C) by sol gel process and surface silylation technique. Coating sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS), methanol (MeOH) and water (H₂O) constant at 1:12.36:4.25, respectively, with 0.01 M NH₄F. The dip coated silica films were surface silylated using two different silylating agents namely hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDZ). The HMDSO and HMDZ in hexane solvent were varied from 0 to 1 vol.% and silylation period was varied from 1 to 3 h. The HMDSO and HMDZ modified films showed dense and porous surface morphology, respectively. The HMDSO modified silica films showed static water contact angle of 122° whereas HMDZ modified films showed 165°. The HMDZ modified films displayed the extreme water repellency comparing with that of lotus leaves. The silica films were characterized by surface profilometer, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared microscopy, thermal and chemical aging tests, optical transmission and static water contact angle measurements.     

Surface modification of low‐density polyethylene (LDPE) film and improvement of adhesion between evaporated copper metal film and LDPE

To improve the interfacial adhesion between evaporated copper film and low‐density polyethylene (LDPE) film, the surface of LDPE films was modified by treating with chromic acid [K₂Cr₂O₇/H₂O/H₂SO₄ (4.4/7.1/88.5)]/oxygen plasma. Chromic‐acid‐etched LDPE was exposed to oxygen plasma to achieve a higher content of polar groups on the LDPE surface. We investigated the effect of the treatment time of chromic acid in the range of 1–60 min at 70°C and oxygen plasma in the range of 30–90 sec on the extent of polar groups created on the LDPE. We also investigated the surface topography of and water contact angle on the LDPE film surface, mechanical properties of the LDPE film, and adhesion strength of the evaporated copper metal film to the LDPE film surface. IR and electron spectroscopy for chemical analysis revealed the introduction of polar groups on the modified LDPE film surface, which exhibited an improved contact angle and copper/LDPE adhesion. The number of polar groups and the surface roughness increased with increasing treatment time of chromic acid/plasma. Water contact angle significantly decreased with increasing treatment time of chromic acid/plasma. Combination treatment of oxygen plasma with chromic acid drastically decreased the contact angle. When the treatment times of chromic acid and oxygen plasma were greater than 10 min and 30 sec, respectively, the contact angle was below 20°. With an increasing treatment time of chromic acid, the tensile strength of the LDPE film decreased, and the film color changed after about 10 min and then became blackened after 30 min. With the scratch test, the adhesion between copper and LDPE was found to increase with an increasing treatment time of chromic acid/oxygen plasma. From these results, we found that the optimum treatment times with chromic acid and oxygen plasma were near 30 min and 30 sec, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1677–1690, 2001     

Fabrication of self‐cleaning poly(vinylidene fluoride) membrane with micro/nanoscaled two‐tier roughness

Based on the “lotus effect” principle, smooth microreliefs of polyvinylidene fluoride (PVDF) membrane were prepared via thermally induced phase separation process. Hydroxyl groups were introduced into PVDF membrane by pretreatment with KOH/alcohol solution. Subsequently, these hydroxyl groups grafted with (CH₃)₂SiCl₂/CH₃SiCl₃ to form nano‐clusters, which were decorated on the microreliefs of PVDF membrane. Scanning Electronic Microscopy (SEM) and Atomic Force Microscope (AFM) analysis showed the micro‐ and nano‐scale structures, similar to lotus leaf, were successfully fabricated on the PVDF membrane surface. The water contact angle and sliding angle on the fabricated lotus‐leaf‐like PVDF membrane surface were 154 and 4°, respectively. Self‐cleaning test indicated that the lotus‐leaf‐like surface of PVDF membrane has excellent superhydrophobic and self‐cleaning properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Tailoring intrinsic hydrophobicity and surface energy on rough surface via low-T Cassie–Wenzel wetting transition method

Wettability is an important parameter of micro/nanostructured composites. The measurement of apparent contact angle is strongly affected by surface roughness, which induces some challenges to study the intrinsic hydrophobicity correlating to the nature of chemistry. Carbon-Nafion composites exhibited about 30° decrease in apparent contact angle from 30 to 10°C due to the condensation of water vapor into cavities, suggesting a significant Cassie–Wenzel wetting transition phenomenon. The focus of this work has been on the first-time use of a low-T Cassie–Wenzel wetting transition method to evaluate Young's (ideal) contact angle and surface free energy. A maximum Young's contact angle (113°) and minimum total surface energy (12 mJ/m²) were determined at Nafion content of 70 wt%, indicating the orientation effect that sulfonate groups in Nafion preferentially pointed toward polar carbon. This approach provided the reasonable prediction of intrinsic hydrophobicity, especially when a rough solid surface is not easily wetted by liquids.     

Investigating the effect of water-mixing nitrogen atmospheric pressure plasma jet on polyether-ether-ketone and time stability under different conditions

Possessing excellent properties including good biocompatibility, high strength, and stiffness, polyether-ether-ketone (PEEK) has significant application values in medical and industrial fields. However, the relatively poor wettability and low adhesion limit its further applications. Atmospheric pressure plasma jet (APPJ) has been utilized for adjusting PEEK properties, but better hydrophilization effect and time stability after treatment are still urgently needed. In this paper, we employ a water-mixing nitrogen (N₂ H₂O) APPJ to process PEEK, and surface wettability can be effectively improved (contact angle ~18° within 2 min, distance between sample and nozzle outlet: 10 mm) without inducing obvious microstructure damages. Additionally, after storing for 40 days, the sample treated by N₂ H₂O APPJ also possessed better wettability (~54°) compared with that treated by N₂ APPJ (~65°). On the basis of this low-damage and high-efficient modification method, we perform aging experiments under different conditions (different temperatures 25, −10°C; and low vacuum condition: 50 kPa) to determine a relatively optimum storing condition for this method. The experiment results indicate that low temperature and vacuum are conducive to retaining the plasma-induced wettability (~34°). The treatment method and storing conditions for PEEK presented here may facilitate the application of PEEK in various fields.     

Evaluation of oxy-acetylene flame angle effect on the erosion resistance of SiC/ZrB2–SiC/ZrB2 multilayer coatings fabricated by the shielding shrouded plasma spray technique

In the present study, the effect of oxy-acetylene flame angle on the erosion resistance of SiC/ZrB₂–SiC/ZrB₂ multilayer coatings with the gradient structure was investigated. To this aim, first, the SiC inner layer was applied by the reactive melt infiltration (RMI) technique; then ZrB₂ and ZrB₂–SiC layers with 10, 20 and 30%wt. SiC were applied on graphite by the plasma spraying technique. To prevent the oxidation of ZrB₂ and SiC particles, the plasma spraying process was performed by a solid protective shield. To evaluate the performance of the coatings in erosive environments, the samples were exposed to oxy-acetylene flame at the angles of 30°, 60° and 90° for 360 s; the destruction mechanism of SiC/ZrB₂–SiC/ZrB₂ multilayer coatings appeared to be controlled mechanically and chemically. The results of the erosion test showed that at the low flame angles of about 30°, due to the shear forces of oxy-acetylene flame, mechanical erosion overcame the chemical one. With increasing the flame angle, due to raising the surface temperature, chemical erosion overcame the mechanical one; so, most chemical destruction occurred at the flame angle of 90°. Also, the results of the erosion test showed that the total chemical and mechanical destruction at the angle of 60° was greater than that in other angles. Also, among the coatings tested, SiC/ZrB₂- 20% wt. SiC/ZrB₂ coatings had the best erosion resistance; so, the weight changes under the oxy-acetylene flame at the angles of 30° and 60°, respectively, were about ?0.038%. and ?0.355%; meanwhile, at the angle of 90°, it was about +4.3%.     

Robust superhydrophilic coatings by electropolymerization of sulfonated pyrrole

Superhydrophilic coatings were prepared by electropolymerization of sufonated pyrrole from aqueous solutions. The monomer was prepared in one step from commercially available reagents. Electropolymerized polymer films exhibited significant surface roughness and porosity as evidenced by scanning electron microscopy analysis. Advancing water contact angles of the pristine coatings were as low as 12°, while receding angles were 0° for almost all samples. Soaking the films in hot water resulted in decrease in the advanced contact angles to as low as 0°. The produced coatings retained their extreme wetting characteristics even when treated in harsh environments, such as dry heat for a week. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012     

Surface biomedical effects of plasma on polyetherurethane

Surface biomedical effects of plasma treatment and plasma polymerization on medical-grade polyetherurethane were studied. N₂ and Ar plasma treatments and hexamethyldisiloxane (HMDS) plasma polymerization were performed at a power of 100 W with exposure times ranging from 1 to 15 min. The results showed that the contact angle of water was decreased from 79° to 62° by N₂ and Ar plasma treatments, and N₂ plasma treatment caused a slight enhancement in anti-coagulability and anti-calcific behavior. HMDS polymerization resulted in a decrease from 79° to 43° in the contact angle and an increase from 30.5 to 37.4 s in the recalcification time. At the same time, the anti-coagulability of polymerized samples for the exposure time of 2-5 min was 2.5 times that of the untreated sample. Results of XPS and ESR analyses showed that HMDS deposited onto the polyetherurethane surface and formed new Si-N bonds, and increased the number of radicals in the sample. XPS analysis also showed that N₂ and Ar plasma treatments broke some of the C-O and C=O bonds at the surface and resulted in oxidation of the surface.     

A new reutilization strategy of waste printed circuit board nonmetal powders for constructing superhydrophobic coatings

Reutilization of waste printed circuit board nonmetal powders (WPCBP) has been one of the major bottlenecks in the comprehensive utilization of electronic wastes. Herein, a new reutilization strategy of WPCBP was innovatively proposed to develop a superhydrophobic coating. Typically, WPCBP@SiO₂ hybrid filler was successfully prepared by the in-situ growth of silica on WPCBP surface, and the structures and compositions of WPCBP@SiO₂ were systematically investigated by SEM, FTIR, and TGA. Then the obtained WPCBP@SiO₂ was combined with polydimethylsiloxane (PDMS) to prepare a superhydrophobic coating. The as-prepared PDMS/WPCBP@SiO₂ coatings exhibited excellent superhydrophobicity and self-cleaning ability, whose static water contact angle (WCA) is more than 150° while the sliding angle (SA) is <10°. In summary, this study provides a green and efficient reutilization strategy of WPCBP in superhydrophobic coatings, which may open up a new opportunity for the high-valued utilization of WPCBP.