Polytetrafluoroethylene Particles Research Articles

Effect of Polytetrafluoroethylene Coating on Corrosion Wear Properties of AZ31 Magnesium Alloy by Electrophoretic Deposition

In this study, we aim to enhance the corrosion and wear resistance of AZ31 magnesium alloy using electrophoretic deposition (EPD) technology to apply a hydrophobic polytetrafluoroethylene (PTFE) coating. Polyethyleneimine (PEI) serves as a charged dispersant, facilitating uniform deposition of PTFE particles on the alloy surface. Results demonstrate a significant reduction in corrosion current density (from 67.5 μA/cm2 to 5.2 μA/cm2) and improved wear resistance (wear volume decreased from 0.24167 mm3 to 0.00167 mm3) in a 3.5 wt% NaCl solution compared to uncoated alloy. Moreover, the friction coefficient of the coated sample decreases. These findings underscore the potential of nano-PTFE coatings prepared via EPD in enhancing AZ31 magnesium alloy’s corrosion and wear resistance, providing a foundation for future protective coating design and optimization.

Contact-electro-catalysis for degradation of trace antibiotics in wastewater

Antibiotic contamination of water bodies is a major concern in environmental management. Despite their superior efficacy in antibiotic removal, advanced oxidation processes (AOPs) have yet to be widely adopted owing to their substantial cost associated with the large amounts of chemicals required. In this study, a novel contact-electro-catalysis (CEC) process with reusable polytetrafluoroethylene (PTFE) particles as a trigger catalyst was applied to replace traditional AOPs, and it was able to degrade three typical antibiotics (sulfamethoxazole [SMX], ciprofloxacin [CIP], and tetracycline [TET]) in the secondary effluent of a wastewater treatment plant for the first time. The PTFE particles at a concentration of 0.8 g/L were introduced into antibiotic solutions with an antibiotic concentration of 1 mg/L, and the removal rates of SMX, CIP, and TET after a 90-min operation time reached 50 %, 80 %, and 90 %, respectively. Our findings revealed that the CEC reaction generated ●OH and 1O2, contributing substantially to antibiotic degradation. Thus, new reactive oxygen species generation mechanisms during the CEC process were proposed. Furthermore, we fabricated polyvinylidene fluoride nanofiber membranes using electrospinning to recycle PTFE particles, where a nearly 100 % recovery rate through dead-end filtration was realized with a high water flux of 7.5 m3/(m2∙h). The results of this study provide a promising approach for antibiotic removal from wastewater.

Electrostatic Field in Contact‐Electro‐Catalysis Driven C−F Bond Cleavage of Perfluoroalkyl Substances

AbstractPerfluoroalkyl substances (PFASs) are persistent and toxic to human health. It is demanding for high‐efficient and green technologies to remove PFASs from water. In this study, a novel PFAS treatment technology was developed, utilizing polytetrafluoroethylene (PTFE) particles (1–5 μm) as the catalyst and a low frequency ultrasound (US, 40 kHz, 0.3 W/cm2) for activation. Remarkably, this system can induce near‐complete defluorination for different structured PFASs. The underlying mechanism relies on contact electrification between PTFE and water, which induces cumulative electrons on PTFE surface, and creates a high surface voltage (tens of volts). Such high surface voltage can generate abundant reactive oxygen species (ROS, i.e., O2⋅−, HO⋅, etc.) and a strong interfacial electrostatic field (IEF of 109~1010 V/m). Consequently, the strong IEF significantly activates PFAS molecules and reduces the energy barrier of O2⋅− nucleophilic reaction. Simultaneously, the co‐existence of surface electrons (PTFE*(e−)) and HO⋅ enables synergetic reduction and oxidation of PFAS and its intermediates, leading to enhanced and thorough defluorination. The US/PTFE method shows compelling advantages of low energy consumption, zero chemical input, and few harmful intermediates. It offers a new and promising solution for effectively treating the PFAS‐contaminated drinking water.

Electrostatic Field in Contact-Electro-Catalysis Driven C-F Bond Cleavage of Perfluoroalkyl Substances.

Perfluoroalkyl substances (PFASs) are persistent and toxic to human health. It is demanding for high-efficient and green technologies to remove PFASs from water. In this study, a novel PFAS treatment technology was developed, utilizing polytetrafluoroethylene (PTFE) particles (1-5 μm) as the catalyst and a low frequency ultrasound (US, 40 kHz, 0.3 W/cm2) for activation. Remarkably, this system can induce near-complete defluorination for different structured PFASs. The underlying mechanism relies on contact electrification between PTFE and water, which induces cumulative electrons on PTFE surface, and creates a high surface voltage (tens of volts). Such high surface voltage can generate abundant reactive oxygen species (ROS, i.e., O2⋅-, HO⋅, etc.) and a strong interfacial electrostatic field (IEF of 109~1010 V/m). Consequently, the strong IEF significantly activates PFAS molecules and reduces the energy barrier of O2⋅- nucleophilic reaction. Simultaneously, the co-existence of surface electrons (PTFE*(e-)) and HO⋅ enables synergetic reduction and oxidation of PFAS and its intermediates, leading to enhanced and thorough defluorination. The US/PTFE method shows compelling advantages of low energy consumption, zero chemical input, and few harmful intermediates. It offers a new and promising solution for effectively treating the PFAS-contaminated drinking water.

The design and performance research of PTFE/PVDF/PDMS superhydrophobic radiative cooling composite coating with high infrared emissivity

High infrared emissivity in the atmospheric transparent spectral band, high reflectivity in the solar radiation band, self-cleaning and no heat treatment process are crucial for the application of the radiative cooling materials. In this work, a superhydrophobic radiative cooling composite coating was facilely prepared by using two sizes of polytetrafluoroethylene (PTFE) particles as main fillers and silica (SiO2) nanoparticles as auxiliary fillers, and polydimethylsiloxane (PDMS) and polyvinylidene fluoride (PVDF) as binders. The coating can be scraped onto the substrate through a scraper without any heat treatment procedure. The water droplet contact angle (WCA) and rolling angle (SA) of the coating can reach a maximum of 158 ± 0.5° and a minimum of 3 ± 0.3°, respectively. The average reflectance of the coating in the visible spectral band was around 90.6%. The average infrared emissivity of the coating in 8 ∼ 13 µm spectral band was about 0.989. The test results show that the coating has excellent self-cleaning and cooling properties. Furthermore, the coating also exhibits good abrasion resistance, preferable adhesion performance, ultraviolet radiation resistance, high temperature stability, self-cleaning and anti-icing performance.

Continuous ammonia synthesis from water and nitrogen via contact electrification

We synthesized ammonia (NH3) by bubbling nitrogen (N2) gas into bulk liquid water (200 mL) containing 50 mg polytetrafluoroethylene (PTFE) particles (~5 µm in diameter) suspended with the help of a surfactant (Tween 20, ~0.05 vol.%) at room temperature (25 °C). Electron spin resonance spectroscopy and density functional theory calculations reveal that water acts as the proton donor for the reduction of N2. Moreover, isotopic labeling of the N2 gas shows that it is the source of nitrogen in the ammonia. We propose a mechanism for ammonia generation based on the activation of N2 caused by electron transfer and reduction processes driven by contact electrification. We optimized the pH of the PTFE suspension at 6.5 to 7.0 and employed ultrasonic mixing. We found an ammonia production rate of ~420 μmol L-1 h-1 per gram of PTFE particles for the conditions described above. This rate did not change more than 10% over an 8-h period of sustained reaction.

Boosting Oxygen Reduction through Microenvironment Modulation to Enhance Mass Transportation

Electroreduction of oxygen driven by renewable electricity holds significant promise for the sustainable production of value‐added hydrogen peroxide (H2O2). While water is a desirable source of protons and electrons for this reaction, its low gas solubility often limits the transportation of gas molecules and consequently leads to large concentration overpotential, resulting in unsatisfactory energy efficiencies. Herein, a facile and effective strategy to promote the 2e− oxygen reduction reaction (ORR) through microenvironment modulation is presented. In this work, it is specifically aimed to facilitate oxygen transportation at the reaction interface, particularly at high rates. To achieve this, hydrophobic polytetrafluoroethylene (PTFE) particles are introduced into a catalyst layer containing amino‐group‐functionalized carbon nanotube (CNT‐NH2) as the ORR catalyst for H2O2 production. As a result, the PTFE‐modified CNT‐NH2‐based gas‐diffusion electrode (GDE) substantially improves ORR activity. At 100 mA cm−2, the PTFE‐modified CNT‐NH2 achieves a high cathodic energy efficiency of 92%, 1.5 times higher than the pristine CNT‐NH2‐based GDE (63%). Detailed kinetic analysis reveals that this enhanced ORR performance is indeed due to the enhanced oxygen transportation induced by the persistent hydrophobic microenvironment created by the PTFE‐modified catalyst layer, reducing the concentration overpotential during ORR.

Enhancing Hydrophobic/Hydrophilic Dual-Layer Membranes for Membrane Distillation: The Influence of Polytetrafluoroethylene (PTFE) Particle Size and Concentration

This study assesses the effects of different polytetrafluoroethylene (PTFE) particle sizes and concentrations on the performance of dual-layer membranes in direct contact membrane distillation (DCMD). Specifically, particle sizes of 0.5 μm, 1 μm, and 6 μm were systematically evaluated at concentrations of 0 wt%, 2 wt%, 4 wt%, and 6 wt%. Comprehensive analyses, including scanning electron microscopy (SEM), liquid entry pressure (LEP), contact angle, thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), atomic force microscopy (AFM), permeate flux, nitrogen gas permeation, and salt rejection, were employed to characterize the membranes. Under conditions of a feed temperature of 70 °C and a salt concentration of 8000 ppm for a 24 h duration, the results clearly indicated that a 0.5 μm PTFE particle size combined with a 6 wt% concentration exhibited the highest performance. This configuration achieved a permeate flux of 11 kg·m2/h and a salt rejection rate of 99.8%. The outcomes of this research have significant implications for the optimization of membranes used in DCMD applications, with potential benefits for sustainable water treatment and energy conservation.

Fabrication of hydrophobic PI nanofibrous membrane with controllable pore structures

Polyimide (PI) has garnered increasing attention in the field of membrane technology owing to its excellent comprehensive performance. In this work, PI nanofibrous membranes with a controllable pore structure were fabricated by the thermal imidization of electrospun polyamide acid (PAA) nanofibrous membranes. Polytetrafluoroethylene (PTFE) and poly(tetrafluoroethylene-hexafluoropropylene) (FEP) particles were introduced into the PAA nanofibrous membrane with the aim of enhancing the membrane's hydrophobicity and regulating its pore structure by electrospraying the PTFE/FEP mixed aqueous dispersion. During the thermal imidization process, melt casting of FEP particles occurred, leading to the adhesion of PI nanofibrous membranes and subsequent regulation of the membrane's pore structure. Meanwhile, due to the imidization temperature being lower than PTFE’s melting temperature, the unmelted PTFE particles would further enhance the membrane’s hydrophobicity. We have successfully provided a novel method for fabricating PI nanofibrous membranes with controllable pore structures and excellent hydrophobicity to expand their applications in membrane separation. Owing to the hydrophobicity and lipophilicity, the obtained PI nanofibrous membranes were applied to oil-water (kerosene/water) separation to characterize the separation performance. The results showed that, following the regulation of the pore structure, the PI nanofibrous membranes exhibited a high oil flux (203.83 L/m2·h) and separation efficiency (＞99.00%) without external pressure.

ONE-STAGE ELECTROCHEMICAL SYNTHESIS OF A POLYMETHYLOLACRYLAMIDE/ULTRAFINE POLYTETRAFLUOROETHYLENE COMPOSITE

A method for one-stage electrochemical synthesis of a composite consisting of two non-conductive polymers has been developed. Using the example of electropolymerization of acrylamide in the presence of particles of ultrafine polytetrafluoroethylene (UPTFE), it is shown that the electrochemical approach makes it possible to simplify the traditional multistage technologies for the formation of composite polymer materials by combining in one process the electropolymerization of acrylamide and the formation of a polymethylolacrylamide (PMAA) film on the cathode, the capture of UPTFE particles by a growing polymer matrix, and formation of a PMAA/UPTFE composite. This technology makes it possible to reduce the total time for creating a polymer/polymer composite to 5-10 minutes. A procedure for the preparation of stable aqueous dispersions of UPTFE has been developed. It has been established that the most effective stabilizers of UPTFE aqueous dispersion are sodium lauryl sulfate (LS) and siloxane-acrylate emulsion SE 13-36. The formation of the PMAA/UPTFE composite was confirmed by XRD, SEM, SAXS, and spectrophotometry. It was found that the composite includes both large (~1 μm) and nanosized (1–10) nm UPTFE particles. The color of the PMAA/UPTFE composite films changes from colorless and transparent, characteristic of PMAA, to milky white (color of UPTFE and SE 13-36). This reduces the light transmission of composite films, reaching the minimum value for PMAA/UPTFE/SE 13-36. The mass of the PMAA/UPTFE composite increases with increasing electropolymerization time, and the residual current, which characterizes the degree of electrode insulation, decreases in comparison with the PMAA coating. Modification of the film with ultrafine polytetrafluoroethylene leads to a decrease in the swelling of composite coatings by a factor of 1.26–2.60, depending on the nature and concentration of the additive. The maximum insulating effect and reduced swelling is achieved for the PMAA/UPTFE(LS) composite, which indicates the preferred use of UPTFE(LS) for the modification of PMAA. The thermal stability of the PMAA/UPTFE(LS) composite and matrix PMAA is almost identical.

Electrodeposition of Zn-Ni/PTFE composite coating on 20 steel and its corrosion behavior in simulated sewage

Zn-Ni alloy coating was electrodeposited on 20 steel, which was commonly used in the manufacture of pipes and connectors. Polytetrafluoroethylene (PTFE) is a kind of polymer chemical material. Although many researchers have prepared metal composite coatings with decent corrosion resistance by adding PTFE particles to the plating solution, a large number of PTFE particles are easy to agglomerate in aqueous solutions, which affects the compactness and properties of composite coatings. In this paper, by adding PTFE emulsion to Zn-Ni plating solution, the agglomeration phenomenon of PTFE particles can be effectively reduced to improve the content of PTFE particles in Zn-Ni/PTFE composite coating and enhance corrosion resistance, which has certain innovation and significance. The surface morphology, chemical composition and phase structure of Zn-Ni alloy coating and Zn-Ni/PTFE composite coatings were characterized and analyzed by scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. Moreover, the bonding strength and thickness of Zn-Ni alloy coating and Zn-Ni/PTFE composite coatings were tested by grid testing and step profiler. The results show that PTFE particles incorporate into the coating and play a role in increasing the corrosion resistance of the composite coating in simulated sewage. However, the incorporated PTFE particles have no obvious effect on the phase structure of the composite coating. When the addition amount of PTFE emulsion is 30 mL/L, the electrodeposited Zn-Ni/PTFE composite coating has the highest content of PTFE particles (4.24 %), and the corrosion current density is only 0.90 μA/cm2, which is nearly two orders of magnitude lower than that of 20 steel. The Zn-Ni/PTFE composite coating electrodeposited from the plating solution containing 30 mL/L PTFE emulsion has the lightest corrosion degree in simulated sewage and shows excellent corrosion resistance, which can effectively delay the corrosion of 20 steel.

Particle size effect of PTFE on friction and wear properties of glass fiber reinforced epoxy resin composites

Self-lubricating spherical plain joint bearings play a crucial role in aerospace equipment, with their performance primarily depending on the self-lubricating materials positioned between the inner and outer rings. As a typical polymer-based self-lubricating material, glass fiber reinforced epoxy resin composites receive high expectations. Polytetrafluoroethylene (PTFE) as an additive can significantly improve the friction and wear performance of glass fiber reinforced epoxy resin composites. The primary objective of the present study is to reveal the effect law of PTFE particle size on friction and wear properties of glass fiber reinforced epoxy resin composites under dry sliding conditions. Hence, the four particle sizes (P1, average < 1 μm; P2, average 12 μm; P3, average 25 μm; P4, 75–180 μm) of PTFE-filled epoxy composites were prepared. The hardness, compressive strength, and compressive modulus of the epoxy resin composites filled with four particle sizes of PTFE were measured. The coefficient of friction (COF) was evaluated using a reciprocating ball-on-disk tribometer, with a GCr15 ball as the stationary part and the composite disc as the reciprocating component. The wear rate was determined using a Mahr profilometer. The results show that the friction coefficients of four PTFE-filled epoxy resin composites have little difference. However, the wear rate of epoxy composite filled with PTFE particles of the large size (RE/P4) is an order of magnitude lower than that of epoxy composites filled with PTFE particles of the other size. The wear morphology of the composites was analyzed by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The higher wear resistance of RE/P4 can be attributed to it exhibiting a stronger role in anchoring glass fibers (GF), compared to other particle-sized PTFE-filled epoxy resin composite materials.

Superhydrophobic electrospun FPI/PTFE nanofiber membranes for robust vacuum membrane distillation

In this study, we firstly proposed a fluorinated polyimide (FPI) /polytetrafluoroethylene (PTFE) nanofiber membrane for vacuum membrane distillation (VMD) by electrospinning FPI and double eletcrospraying PTFE particles. The resultant FPI /PTFE nanofiber membrane possessed desirable superhydrophobicity (water contact angle (WCA) of 155.3°), anti-wettability and durability due to the rough micro/nano structure of the membrane surface. The surface morphology and chemical composition of obtained FPI nanofiber membranes were characterized by SEM, FTIR, XRD and XPS, and the effects of PTFE content on the VMD performance were investigated. Results showed that the liquid entry pressure (LEP) of FPI/PTFE nanofiber membranes increased significantly after PTFE particles were introduced (LEP of 158 kPa). In the VMD process, the FPI/PTFE nanofiber membrane showed stable MD flux (33.49 L·m2·h−1) and excellent salt rejection (99.96%). Furthermore, the FPI/PTFE nanofiber membrane maintained its favorable performance, resulting in stable MD flux (30.21 L·m2·h−1) and salt rejection (99.96%) after the 120 h continuous long-term operation. It shows a promising future for VMD of FPI/PTFE nanofiber membranes.

Impact of PTFE particle size in designing BaTiO3 dielectric composites under the cold sintering process

The Cold Sintering Process (CSP) can provide opportunities to fabricate high-performance BaTiO3 dielectric composites with polymer materials that are typically difficult to impossible to co-process under a conventional sintering process. Therefore, we investigated the preparation process of BaTiO3 sintered body by CSP and integrated a well-dispersed intergranular polymer phase. In this study, we focused on preparing BaTiO3 and Polytetrafluoroethylene (PTFE) composites. We considered the importance of the particle size of the PTFE phase, and correlated the impact on the composite dielectric properties. Through fitting a general-mixing-law to the dielectric properties as a function of volume fraction, we could deduce more homogeneous composites obtained in using the 200 nm PTFE powders. In addition, the temperature dependent dielectric properties and field dependent conductivity of the composites was investigated. It was found that with the good dispersion of the PTFE can suppress the leakage current density in the dielectric composites.

Study on mechanical and tribological properties of electroformed nickel composite mould co-deposited with nano-sized PTFE particles

To improve the lubrication and wear resistance of nickel composite moulds, nano-sized polytetrafluoroethylene (PTFE) particles were co-deposited with nickel. This work reports the effect of using micro-sized and nano-sized PTFE particles on the surface, mechanical and tribological properties of Ni composite moulds. The experimental results indicate that using nano-sized PTFE particles is significantly more effective than micro-sized PTFE particles in improving the lubrication, mechanical and tribological properties of the composite moulds. The microhardness of the composite mould increases by 2.5 times to 483 Hv for a Ni-PTFE nanocomposite mould, along with the COF against polymethyl methacrylate (PMMA) decreasing by 52.2% to 0.22. Using micro-sized PTFE particles serves to roughen the mould surface, which results in faster adhesive wear. In comparison, the Ni-PTFE nanocomposite mould has a low surface roughness and enhanced wear resistance against PMMA, while the tool lifetime increases by 11.5 times. Finally, a Ni/PTFE nanocomposite mould was successfully fabricated via UV-LIGA, and its lubricating properties were validated by producing high-quality PMMA replicas via micro hot embossing.

Water-repelling, vapor-resisting, self-cleaning, oil–water-separating, water-purifying, antibacterial Hanji cellulose papers coated with Teflon and ZnO particles via supersonic spraying

Cellulose-based Korean mulberry paper, called Hanji, has been used as a functional material in heaters, supercapacitors, sensors, and light-emitting diodes because of its low weight, high mechanical strength, antibacterial activity, and eco-friendliness. Imparting water resistance property to these functional papers is critical to protect them against potential moisture-associated damage and to ensure their longevity. This study applied supersonic spraying technique to deposit superhydrophobic Teflon and antibacterial ZnO particles on Hanji. The results show that functionalized Hanji deposited with Teflon/ZnO exhibited water-repelling, anti-fogging, and antibacterial properties. Furthermore, the photoinduced water purification and self-cleaning features of functionalized Hanji has been demonstrated. Hanji enabled the passage of purple-colored hexane; however, blue-colored water could not permeate the Hanji filter, demonstrating the oil–water separation capability of Hanji.

Contact-electro-catalysis for Direct Synthesis of H2 O2 under Ambient Conditions.

Hydrogen peroxide (H2 O2 ) is an indispensable basic reagent in various industries, such as textile bleach, chemical synthesis, and environmental protection. However, it is challenging to prepare H2 O2 in a green, safe, simple and efficient way under ambient conditions. Here, we found that H2 O2 could be synthesized using a catalytic pathway only by contact charging a two-phase interface at room temperature and normal pressure. Particularly, under the action of mechanical force, electron transfer occurs during physical contact between polytetrafluoroethylene particles and deionized water/O2 interfaces, inducing the generation of reactive free radicals (⋅OH and ⋅O2 - ), and the free radicals could react to form H2 O2 , yielding as high as 313 μmol L-1 h-1 . In addition, the new reaction device could show long-term stable H2 O2 production. This work provides a novel method for the efficient preparation of H2 O2 , which may also stimulate further explorations on contact-electrification-induced chemistry process.

Contact‐electro‐catalysis for Direct Synthesis of H2O2 under Ambient Conditions

AbstractHydrogen peroxide (H2O2) is an indispensable basic reagent in various industries, such as textile bleach, chemical synthesis, and environmental protection. However, it is challenging to prepare H2O2 in a green, safe, simple and efficient way under ambient conditions. Here, we found that H2O2 could be synthesized using a catalytic pathway only by contact charging a two‐phase interface at room temperature and normal pressure. Particularly, under the action of mechanical force, electron transfer occurs during physical contact between polytetrafluoroethylene particles and deionized water/O2 interfaces, inducing the generation of reactive free radicals (⋅OH and ⋅O2− ), and the free radicals could react to form H2O2, yielding as high as 313 μmol L−1 h−1. In addition, the new reaction device could show long‐term stable H2O2 production. This work provides a novel method for the efficient preparation of H2O2, which may also stimulate further explorations on contact‐electrification‐induced chemistry process.

Sustainable charged composites with amphiphobic surfaces for harsh environment–tolerant non-contact mode triboelectric nanogenerators

In this work, the sustainable charged composites with amphiphobic surfaces are reported regarding harsh environment tolerance and robust contactless mode triboelectric nanogenerators (TENGs). SiO2 and polytetrafluoroethylene (PTFE) particles are well dispersed in thermoplastic polyurethane (TPU) and polydimethylsiloxane (PDMS), respectively. Both surfaces become very rough after a chemical etching method and the surface of PTFE-PDMS is fluorinated using a fluorinated alkylsilane, resulted in the formation of amphiphobic surfaces. This significantly enhances the environment tolerance of the contactless mode TENGs as well as the charge retention characteristics of the composites. As a practical non-contact mode application, a speed sensor fabricated using two composites can stably detect a low vehicle speed less than 3.75 km/h when exposed to high humidity (∼ 99%) and various chemical oils. Over 50% of initial output voltage are still generated after 2 weeks with no more decrease after 5 days, showing a 1.4 times slower charge decay rate, compared with the reference Ni-PTFE based TENG.

Direct observation of the wetting state of Cassie and Wenzel

In order to directly observe the solid–liquid-gas three-phase interface, we prepared the superhydrophobic coatings and high adhesion coatings respectively. The surface structure of the two coatings were observed by scanning electron microscopy. The superhydrophobic coating has good micro-nano structure, while the high adhesion coating has only micrometer structure due to the lack of nanometer Polytetrafluoroethylene particles. The wetting state of water droplets on the surface of the two coatings was observed by polarizing microscope and goniometer respectively. The results show that the water droplets in the superhydrophobic coating are in Cassie wetting state, while the water droplets in the high adhesion coating are in Wenzel wetting state. The experimental results provide direct observational evidence for the wetting state of Cassie and Wenzel.