Durability enhancement of icephobic fluoropolymer film

An icephobic and superhydrophobic surface was made by the sputtering of fluoropolymer material (PTFE or Teflon^®) on anodized aluminum alloys. The study of this superhydrophobic coating under atmospheric icing conditions showed a 3.5 times reduction of its ice adhesion strength. To evaluate the longevity of such coated surfaces and to assess their potential outdoor applications, their durability was studied after several icing/de-icing cycles. However, these coatings showed weak stability after several icing/de-icing cycles. Plasma argon pretreatment of the anodized aluminum surface was used before sputtering to increase adhesion strength between the anodized aluminum surface and Teflon-like coating. Ice adhesion and contact angle measurements of the pretreated Teflon-like coating indicated clearly that the instability was associated with the low cohesion strength of the Teflon-like film. In order to improve the cohesive strength of the coating, the input power of the discharge was increased during the sputtering process. XPS, SEM, and contact angle analyses showed that an increase in input power renders the Teflon-like coating more stable. The results of ice adhesion measurement showed low variation in ice adhesion strength on such surfaces after 15 icing/de-icing cycles. This coating also showed an excellent stability under UV irradiation and condensation.     

The Relationship between Water Wetting and Ice Adhesion

Ice accretion on aircraft leads to difficulties in aircraft flight control due to weight increase and change in weight distribution. Conventionally these difficulties are overcome using anti-icing or de-icing products, such as freezing depressants and heating devices. A more cost effective way to solve these problems would be to use ice repellent surfaces (ice-phobic). As a first step in this direction the relationship between water wettability and ice adhesion was investigated. Using the appropriate chemistry and tailoring the surface roughness a variety of polycarbonate-coated surfaces were created: these included ultra-hydrophilic and ultra-hydrophobic surfaces and surfaces with surface properties in between the extreme ultra-surfaces. Ice adhesion tests and contact angle measurements indicated that the higher the contact angle the lower is the adhesion of ice. The best results were obtained in the case of ultra-hydrophobic surface treatment that led to an 18 fold decrease in ice adhesion compared to the untreated aluminum surface.     

Prevention of Ice Accretion on Aluminum Surfaces by Enhancing Their Hydrophobic Properties

The accretion of ice on the surfaces of power network systems, aircraft, communication networks, etc., is known to cause serious problems that often lead to costly safety issues. An ideal solution would be to prevent ice from accumulating in the first place, rather than waiting for ice to accrete and then to de-ice which is both time-consuming and expensive. This may be accomplished by depositing coating materials that are icephobic. A low dielectric constant surface is expected to reduce the adhesion of ice due to the screening of mirror charges, thereby eliminating one of the strongest interaction forces — the electrostatic force of attraction — at the ice–surface interface. Superhydrophobic surfaces, which demonstrate high water-repellency due to the negligible contact area of water with these surfaces, are also expected to minimize the contact area of ice. In the present research work, both concepts were studied by producing superhydrophobic nanorough low-ε (dielectric) surfaces on aluminum. Superhydrophobic properties were achieved on surfaces of aluminum by creating a certain nanoroughness using a chemical etch followed by 'passivation' of the surface by a low surface energy coating of rf-sputtered Teflon, providing a water contact angle greater than 160°. The same behavior is reported even when the nanorough substrates were coated with dielectric thin films of ZnO (lower ε) or TiO 2 (higher ε) prior to passivation. It is found that the superhydrophobic nanorough low energy surfaces are also icephobic and the presence of a low dielectric constant surface coating of Teflon (ε = 2) allows a considerable reduction of the ice adhesion strength. Ice adhesion strengths were determined using a centrifugal ice adhesion test apparatus.     

Ice adhesion on different microstructure superhydrophobic aluminum surfaces

The adhesion of ice to high -voltage overhead transmission lines should be small to ensure ease of ice shedding under small external forces. In this work, we studied the influence of the microstructure of superhydrophobic surfaces on the strength of ice adhesion at a working temperature of ?6?°C. Compared to a bare aluminum surface, the microstructure superhydrophobic aluminum surfaces did decrease ice adhesion strength. The superhydrophobic aluminum surfaces with a larger number of micro-holes produced the lowest strength of ice adhesion; its ice adhesion strength was ～163.8 times lower than that for the bare aluminum samples. Furthermore, such microstructure aluminum surfaces had water contact angles larger than 150° and water sliding angles of less than 8.2° even at a working temperature of ?6?°C. The low values of the ice adhesion strength of the above samples were mainly attributed to the superhydrophobic property, which was obtained by creating a structure of micro-nanoscale holes on the aluminum surface after treatment with a low- surface-energy fluoroalkylsilane (FAS).     

Effect of experimental primers on hydrolytic stability of resin zirconia bonding

This study assessed the effect of experimental silane primers and two adhesive resin cements on resin zirconia adhesion strength. The surfaces of cut Y-TZP zirconia blocks (Lava? Frame), 16 mm × 16 mm × 4.5 mm, were pretreated twice. First, they were grit-blasted with Korox? alumina powder (110 μm) followed by silica-coating with Rocatec? Soft. Next, the blocks were randomly assigned into eighteen sub-groups (n = 6, N = 108) according to three primers (control ESPE Sil?, 1.0 vol.-% 3-acryloxypropyltrimethoxysilane, and 1.0 vol.-% 3-acryloxypropyltrimethoxysilane + 0.5 vol.-% bis-12-(triethoxysilyl)ethane), two in dentistry used resin cement products (Multilink? Speed, and Multilink? N), and three storage conditions (24 h dry, 1 month immersed in distilled water, and 6 months immersed in distilled water at room temperature) used. Onto each pretreated zirconia block, four cylindrical resin composite cement stubs were prepared and light-cured. The surface roughness, contact angle, and adhesion (shear bond) strength (SBS) were measured, and statistically analyzed (ANOVA, the Tukey’s test, p < 0.05). No statistical differences were observed in surface roughness values of different primer-treated zirconia groups. After six months of water aging, the shear bond strength of the groups that employed 1.0 vol.-% 3-acryloxypropyltrimethoxysilane (9.0 MPa ± 0.8 MPa), and the blend of 1 vol.-% 3-acryloxypropyltrimethoxysilane + 0.5 vol.-% bis-12-(triethoxysilyl)ethane (8.9 MPa ± 2.0 MPa) with Multilink? Speed resin composite cement were statistically insignificantly higher compared to using ESPE Sil? (8.7 MPa ± 1.8 MPa). The experimental primers may have potential to be used for long-term resin zirconia adhesion.     

Improving the strength of adhesively bonded joints through the introduction of various surface treatments

The aim of this paper is to model an interface adhesion and failure mechanism of single lap joints, subjected to tensile loading, focusing on the effects of various surface treatments, including surface characterization parameters, such as surface roughness and contact angle of adherend surfaces. The applied surface treatments are sandblasting, etching, anodic oxidation and hybrid processes. The influence of surface treatment techniques and conditions on single lap joint strength and interfacial properties is investigated by performing a static tensile test. A numerical approach, which is a cohesive zone model, is implemented using ABAQUS? and introduced to create a correlation between maximum interface traction and surface processing parameters, such as surface roughness and work of adhesion. As a result of experiments, an etching plus sanding process was found to provide the best single lap joint performance (8726 N), having surface roughness of Ra = 2.93 μm and work of adhesion, W_a = 119.4 mJ/m². Based on numerical solutions, a correlation between maximum interface traction and type of surface treatment process has been established, taking certain assumptions into consideration.     

Ice adhesion to rubber materials

The aim of this study was to investigate the interfacial shear strength between ice and rubbers. Different rubber materials containing only a polymer and curing agent (peroxide) were tested with regard to surface wettability and interfacial shear strength. The effect of different grades and amounts of carbon black filler was also studied. The wettability was determined from contact angles, using water and diiodomethane as test liquids, measured on carefully cleaned and mirror smooth rubber sheets. The test showed that there is a correlation between ice adhesion and rubber substrate wettability. Below a water contact angle of 90°, the interfacial shear strength of ice decreases linearly with increasing contact angle. For contact angles above 90°, the interfacial shear strength of ice stays practically the same. The presence of high surface energy additives such as reinforcing carbon black (e.g. N220 ISAF) significantly increases the interfacial shear strength. The highly hydrophobic behaviour of different plant surface textures was also investigated regarding ice adhesion strength. The combination of a submicrometer textured surface and a hydrophobic surface characteristic showed an abrupt decrease in the adhesion force of a water droplet at measured macroscopic contact angles above approximately 150°. Despite this water repellency, the ice adhesion strength is not nil. However, it was among the lowest values experienced in the test.     

Preparation and anti‐icing property of a lotus‐leaf‐like superhydrophobic low‐density polyethylene coating with low sliding angle

A lotus‐leaf‐like superhydrophobic low‐density polyethylene (LDPE) coating with low sliding angle was prepared by a facile method. The water contact angle and sliding angle of the as‐prepared superhydrophobic LDPE coating were 156 ± 1.7° and 1°, respectively. The anti‐icing property of the as‐prepared LDPE coating with low sliding angle was investigated in a climatic chamber with a working temperature of ?5°C. The results showed that the superhydrophobic LDPE coating with low sliding angle can largely prevent ice formation on the surface, showing excellent anti‐icing property. The as‐prepared superhydrophobic LDPE coating with good anti‐icing property will be perfectly desirable for outdoor equipments to reduce ice formation on their surfaces in cold seasons. This work will provide a new way to fabricate anti‐icing coating and thus find applications in a variety of fields. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Controllable fabrication of superhydrophobic alloys surface on 304 stainless steel substrate for anti-icing performance

In this paper, 304 stainless steel-based ZnO (304SS-based ZnO) seed layer was prepared by using sol-gel method or electrochemical deposition. Superhydrophobic nano-ZnO (CSS–ZnO) surface were prepared on its surface by hydrothermal method. The results show that different structural morphologies of 304SS-based ZnO surface were prepared by varying different seed layer preparation methods. In the static icing test, compared with hydrophilic nano-ZnO (SS–ZnO) surface, hydrophobic nano-ZnO (QS-ZnO) surface and 304SS surface at −5 °C, −10 °C and −15 °C. The icing time of CSS-ZnO surface was prolonged by about 2.7 h at −5 °C, delayed by about 40 min at −10 °C and delayed by about 9 min at −15 °C. The CSS-ZnO surface is the most effective surface in static anti-icing. It is because that there has a residual air layer at the solid-liquid interface and the coating can still effectively retard ice formation in a partially wetted state. In the dynamic icing test, compared with QS-ZnO surface, SS-ZnO surface and 304SS surface at −16 °C, SS-ZnO surface and QS-ZnO surface have no anti-icing effect, and CSS-ZnO surface has a significant anti-icing effect. The mechanism for inhibiting condensation of water droplets by superhydrophobic surfaces was illustrated, which can be identified that the contact angle of the ice embryo will increase with the increase of the water contact angle. This work provides a practical application for promoting anti-icing ability of 304SS surfaces in industry.     

Long-term hydrophobicity and ice adhesion strength of latex paints containing silicone oil microcapsules

Waterborne anti-icing coatings were prepared by embedding silicone oil microcapsules in latex paints. The long-term hydrophobicity and ice adhesion strength of the coatings were examined with a QUV accelerated weathering tester and a pull-off adhesion tester. The effects of silicone oil content and pigment/binder (PB) ratio on the long-term hydrophobicity and the ice adhesion strength of the coatings were investigated. A higher silicone oil content and a PB ratio close to the critical pigment volume concentration favor long-term hydrophobicity of the coatings. An obvious decrease in ice adhesion strength was achieved for coatings with a PB ratio of 5.0 and a silicone oil content of 4.2%. For coatings with the same surface roughness, a higher water contact angle (WCA) led to lower ice adhesion strength. However, for coatings with different surface roughnesses, the ice adhesion strength was found to be dependent on surface roughness rather than on WCA.     

Facile preparation and strong adhesive strength of honeycomb polyurethane films with small pore diameter

With the continuous development of bionics, such as, geckos and virginia creeper with both superhydrophobic and super-adhesive, the surface wetting and super-adhesive properties of various porous materials have attracted extensive attention of the scientific and medical communities. Here, the honeycomb polyurethane (PU) porous films with strong adhesion were successfully prepared by microphase separation method and the effects of growth parameters on their microstructure and adhesive strength to ice were investigated. It was found that a high relative humidity (e.g., 100%) and a low solution concentration (e.g., 2%) facilitated the formation of ordered honeycomb PU porous films, and as-prepared PU pores with average pore diameter as small as 5 μm are better ordered and more uniform than these in related documents. Although the contact angle of water droplets on the surface of PU porous films increased from the premodification value of 85–130° to more than 160° after surface modification with polydopamine (PDA), the corresponding rolling angle remained approximately constant (180°), indicating that the surface of PU porous films has strong adhesion similar to geckos and virginia creeper. Furthermore, at lower temperature, the PU porous films exhibited the high adhesive strength of 142.13 kPa on ice, which was strongly dependent on the porous microstructures and surface compositions. The improved adhesive behavior to ice of honeycomb PU porous films modified with PDA provides new strategies for surface modification of materials and potential applications in medical domain.     

Analysis of structural,morphological alterations,wettability characteristics and adhesion to enamel after various surface conditioning methods

Minimal invasive dental reconstructions and orthodontic appliances are bonded to enamel without removing the enamel with rotating instruments but the top layer of enamel may be partially aprismatic and impair adhesion. The objectives of this study were to investigate the effect of mechanical surface conditioning methods for removing enamel on its structural, morphological alterations, wettability characteristics, and adhesion of resin-based cement to the conditioned surfaces. Maxillary human incisors (N = 40, n_quadrant = 160) were obtained and coronal sections were embedded in acrylic with their labial surfaces exposed. The teeth were randomly divided into four groups and the enamel surface of each tooth was divided into four quadrants. The surfaces were conditioned in a clockwise manner by one of the following methods: (1) Non-conditioned enamel acted as the control group (C); (2) Silicone-coated disk (Sof-Lex disc, Black, 3 M ESPE) (SD); (3) Diamond bur at slow speed (DB) and (4) Airborne particle abrasion (50 μm Al₂O₃, 2 bar, 5 s) (AA). Surface roughness was measured at each quadrant using a non-contact digital profilometer and contact angle measurements were performed using a goniometer. Enamel surfaces were then etched with 37% H₃PO₄ for 60 s and roughness and wettability measurements were repeated. The enamel surfaces in each quadrant received resin composite luting cement (Variolink II, Ivoclar Vivadent) incrementally in a polyethylene mold (diameter: 1 mm²; height: 4 mm) and photopolymerized. The specimens were stored in distilled water for 24 h at 37 °C until the testing procedures and then shear force was applied to the adhesive interface until failure occurred in a Universal Testing Machine (0.5 mm/min). Microshear bond (μSBS) was calculated by dividing the maximum load (N) by the bonding surface area of the resin cement. Representative enamel surfaces were analyzed under the scanning electron microscope (SEM) (x5000) to assess the surface morphology. Failure types were analyzed using optical microscope and SEM. Data (MPa) were analyzed using one-way ANOVA and Tukey`s test for each parameter and Linear model for group comparisons (α = 0.05). Surface conditioning method significantly affected the adhesion results (p < 0.001), surface roughness (p = 0.017), and contact angle (p < 0.001). Interaction terms were significant (p > 0.05). AA (338 ± 182) created significantly higher surface roughness compared to SD (308 ± 180) and DB (242 ± 197) (p < 0.05). After etching with 37% H₃PO₄, DB (307 ± 223) resulted in significantly lower roughness than those of SD (385 ± 173) and AA (414 ± 193) (p < 0.05). AA (40 ± 11) delivered significantly lower contact angle compared to those of SD (61 ± 9) and DB (59 ± 10). After etching with 37% H₃PO₄, AA (42 ± 10) and DB (50 ± 10) presented the lowest contact angle (p < 0.05). Mean μSBS results (MPa) showed significant difference between the experimental groups (p = 0.011) and were in descending order as follows: DB (20 ± 8)^a?a b < C (12 ± 5)^b. Failure types were predominantly mixed failure type between the enamel and the resin cement with more than half of the resin remained on the enamel surface (32 to 33 out of 40) in all groups. Cohesive failure in the enamel was not observed in any of the groups. SEM analysis showed that AA group leaves abundant particles on the enamel surface and after DB and AA, etching could not remove the particles completely and expose the enamel prisms.     

The influence of pre-bond surface treatment over the reliability of steel epoxy/glass composites bonded joints

A main objective of present research is to consider adhesive bonding as a novel maintenance and repairing damaged section trend for fluid transporting tubes. Nowadays, applying glass fiber reinforced epoxy composite patches (GFRECPs) is considered as an alternative rapid and affordable repair system instead of traditional techniques such as removing strained sections. The main problem with repairing metal pipes using GFRECPs is low strength of adhesion between GFRECPs and a steel substrate. To make adhesion strong enough, it is necessary to excite the intrinsic adhesion forces such as dipoles across the interface which consequently increases a bonding strength due to Van der Waals forces; but secondary forces activation depends on surface regulation levels. In fact, providing a surface with a suitable roughness and increased pureness without any polluters is a key parameter achieving a highly resistant GFRECPs-steel adhesion. To do so, samples were prepared using the SiC paper up to 100, 220, 500 and polished to investigate the effect of different roughness levels in the range of 90.77±1.81 to 2.97±0.05 nm. The surfaces, interface features and bonding strength were characterized applying the atomic force microscope (AFM), water contact angle measurements, FE-SEM, single lap shear (SLS) and T-peel (90°) tests. The results revealed that the highest adhesion strength could be achieved at the polished substrate.     

Plant leaves icephobicity

Ice adhesion and accumulation are well known to cause serious problems for different structures such as wind turbines, power transmission and distribution systems, and aircraft. Development of coatings that can resist icing can solve many challenges in various areas of industry. This work was inspired by nature and ice resistivity and superhydrophobicity of plants leaves. Kale is a winter plant with superhydrophobic behaviors, which is normally known as an advantage for cleaning the leaves; however, this article reveals that kale leaves have special surface microstructures delaying the ice formation initiation making them good candidates for designing ice-repellent coatings. In-depth experimental analyses, IR thermography, contact angle measurements, and scanning electron microscopy of the leaves were performed to discover how different plants can prevent icing and further find an optimal design for an artificial ice-repellent coating.     

The effects of surface roughness on varnish adhesion strength of wood materials

In this study, the effects of surface roughness of wood material on the adhesion strength of varnish layers have been tested. For this purpose, test samples of beech (Fagus orientalis L.), Scots pine (Pinus sylvestris L.), and cherry (Prunus cerasus) wood species were prepared and sanded with 80, 120, and 180 grit abrasives. The surface roughness values of specimens were determined using a stylus-type profilometer TIME TR 200 according to the ISO 4287 standards. Then, water-based, polyurethane, and acrylic varnish were applied to the surfaces of the samples in accordance with ASTM-D 3023. Layer adhesion strength was determined to the TS EN ISO 4624 standards. As a result, the highest adhesion strength value (2.52 N/mm²) was found in cherry, while the Scots pine had the lowest value (2.32 N/mm²). For the varnish types, polyurethane varnish types gave the highest value (3.15 N/mm²), while the lowest value was obtained from the water-based varnish. Looking at interactions between adhesion strength and surface roughness, the water-based varnish had the strongest correlation with adhesion strength (69%) and acrylic varnish also had a similar result (67%), while polyurethane varnish had the weakest result (33%) in this interaction.     

Surface Roughness on Adhesion of Silver Colloids to a Polyimide Substrate

The adhesion of silver colloids to a polyimide (PI) substrate was investigated in this study. This issue would be of concern when one tried to print electronic circuits on a flexible PI substrate. To enhance the adhesion between them, the PI surface was first roughened by using the sandblasting technique, and varying degrees of roughness were achieved using various sizes of alumina particles and various air pressures for sandblasting. The adhesion strength of silver colloids to the PI substrate after sintering was then measured according to both ASTM D4541 and ASTM 3359 standards. The results indicated that adhesion strength increased proportionally with surface roughness; however, this enhancement effect was lessened when the roughness was above 880 nm. Sintering temperature was also beneficial in increasing adhesion to the substrate; however, the electrical resistance of the silver colloids after sintering also increased with the degree of roughness. This implied that the packing of silver colloids was also affected by surface roughness. Consequently, values of surface roughness were optimal when adhesion strength and electrical resistivity were balanced.     

Improvement of anti‐icing properties of low surface energy coatings by introducing phase‐change microcapsules

Polymers with low surface energy such as silicone and fluoropolymers are widely applied in preparing anti‐icing coatings, but they may have some limitations. To improve the anti‐icing properties of the coatings, composite coatings were developed by introducing phase‐change microcapsules (PCMs). Room temperature vulcanized silicone rubber and a fluorosilicone methacrylate copolymer were examined. Tests involving infrared thermal imaging, icing delay time, and ice shear strength were performed to determine the anti‐icing properties of the coatings. It was found that during cooling the composite coatings containing PCMs could release the latent heat of phase change to delay the icing process of water droplets on its surface. The introduction of PCMs increased the surface roughness, and the ice shear strengths of the composite coatings could remain at a low level and ice on the coatings could be easily removed, indicating that PCMs could be practicably applied in anti‐icing coatings. POLYM. ENG. SCI., 58:973–979, 2018. © 2017 Society of Plastics Engineers     

Gradient and weather resistant hybrid super‐hydrophobic coating based on fluorinated epoxy resin

A weather resistant super‐hydrophobic coating that can offer good substrate adhesion and yet to be easily processed at large scale can be of practical use in emerging fields of self‐cleaning and anti‐icing paint, combing all these properties together remains challenging task. Here we describe a composite coating composed of a fluorinated epoxy resin emulsion with embedded in situ surface‐modified dual‐scale nano‐silica, which displayed durable super‐hydrophobicity and excellent adhesive strength. The as‐prepared coating possesses water contact angle of 158.6 ± 1°, sliding angle around 3.8 ± 0.2° which remain stable even under acidic/alkaline, heat/cool, and accelerated aging treatment. The results demonstrate that surface roughness had a micron‐ and nanometer scale distribution with increased particle loading beyond 40 wt %. Through quantitative comparison of surface Attenuated Total Reflection (ATR) with bulk FT‐IR transmission spectra, a gradient coating with surface enrichment of hydrophobic groups was determined. The air‐side fluorinated polysiloxane‐rich layer endows coating with weather‐resistance and ultra‐hydrophobicity while bottom epoxy resin layer enhances substrate adhesion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40955.     

Adhesion of Wax Droplets to Porous Polymer Surfaces

An experimental study was done to measure the force of adhesion of molten wax droplets, 3.1 mm in diameter, dropped from heights ranging from 20 to 50 mm onto porous polyethylene and Teflon surfaces. The Teflon surface had 0.25-mm holes drilled in it and the three polyethylene surfaces had random pores with mean diameters of 35, 70, and 125 μm, respectively. The force required to remove the solidified ink from the surface was measured using a pull test. Wax splats were attached to the substrate by both adhesive and cohesive forces. The cohesive force was calculated by multiplying the ultimate tensile strength of the wax (2.2 MPa) by the cross-sectional area of the wax penetrating into surface pores. The adhesive force was obtained by multiplying the contact area between the wax and substrate by the adhesion strength per unit area, estimated to be 0.2 MPa for polyethylene and 0.1 MPa for Teflon surfaces. The contact area between splats and the substrate was typically about 60–70% of the splat area. The edges of splats lifted up, preventing complete contact.     

Fluorine-free,highly transparent,chemically durable and low ice adhesion icephobic coatings from biobased epoxy and polydimethylsiloxane

Passive icephobic surfaces have been extensively studied by researchers due to their advantages of delaying icing time and reducing ice adhesion strength. However, icephobic materials with petroleum-based resources and toxic fluorine-containing chemicals, as one of the excellent icephobic materials, are very unfavorable for resource conservation and environmental protection. In this study, we report fluorine-free, highly transparent, chemically durable and low ice adhesion icephobic coatings prepared by glycerol triglycidyl ether (GTE) derived from natural glycerin and bis(3-aminopropyl) terminated polydimethylsiloxane (PDMS) via one-pot method. On the one hand, PDMS with multiple methyl groups and two amine groups acts as a hydrophobic modifier to modulate the surface energy of the coatings, and also acts as a structure modifier to modulate the mechanical properties of the coatings, which allow us to design and synthesis the coating with excellent deicing performance (ice adhesion strength can reach about 16 kPa). On the other hand, GTE with multiple epoxy groups works as cross-linker to endow the coatings with good cross-linked networks, so that the coatings showed good durability after being subjected to different temperature treatment and different solution treatments. In additional, the transmittance of the coating is above 91.4%, which is expected to be applied to windows and sensors.