Lubrikantti-impregnoitujen huokoisten pintojen kastuvuus- ja jäätymättömyysominaisuudet

Nature has provided intriguing possibilities to tackle wetting and to some extent even icing. By capturing the unique and inventive structures, novel surfaces with low wettability and low adhesion to ice are being under research. After deliberate material selection, these surfaces would provide easement to many industries suffering from ice accretion. In the Arctic region, buildings, wind turbines, maritime vessels, aviation and other transportation operators could benefit surfaces with anti-ice or ice-repellent properties. The aim of this master’s thesis was to study slippery liquid infused porous surfaces, SLIPS, by selecting proper porous solid and water immiscible lubricant combinations. The focus was in finding a surface which would have low ice adhesion and good anti-wetting properties with low lubricant evaporation. Different lubricants and oils with altered viscosities, were used in the tests as they naturally repel water. As a porous solid material, polytetrafluoroethylene (PTFE) –membrane was used to impregnate the lubricant into. The membranes had altering pore sizes and were manufactured by two different companies. Since PTFE is also water-repellent, that is hydrophobic, the produced SLIPS surfaces functioned in wettability tests as expected. From the fabricated SLIPS, the evaporation was examined as to its effects on wettability of the surface. The wettability was observed as a function of time as static contact angle, contact angle hysteresis and sliding angle tests were performed to the SLIPS. From the evaporation and wettability tests, the most promising and interesting SLIPS –samples were selected to the cyclic ice adhesion test. The cyclic ice adhesion test encompassed ice accretion in icing wind tunnel, ice adhesion measurement with centrifugal machinery and wettability tests afore next cycle. It was noticed that different pore sizes in the membranes had effects on wettability, but more significantly on ice adhesion strength. Moreover, when the results of the work are reviewed, submicrometer pore sizes were superior to micrometer pore sizes, as the ice detached from them more easily. It was detected that different lubricants had altering evaporation rates but also differenced in wettability experiments. Altogether, more cyclic ice adhesion testing is needed to perform in order to gain better comprehension towards SLIPS lifespan in icing and de-icing cycles. In addition, more lubricant and porous solid pairs are needed to tests to yield good performance SLIPS with exceptionally low ice adhesion strength

The effect of mechanical and thermal stresses on the performance of lubricated icephobic coatings during cyclic icing/deicing tests

Evaluating the performance of icephobic coatings interests various industries, such as aviation, maritime, energy, and transportation. Recent developments on icephobic coatings have consistently highlighted the need for durable icephobic surfaces in cold conditions. This study investigates the icing performance and durability of lubricated polymer coatings under cyclic icing/deicing tests. Coatings were made of polyethylene and a solid lubricant and manufactured using flame spray technology. Icing was performed by accreting ice in an icing wind tunnel. Deicing was conducted by removing ice with a centrifugal ice adhesion tester. Surface properties, such as surface morphology, roughness, wettability and chemical composition, were measured before and after the cyclic tests. The results showed stable icephobic behaviour for some coatings, while the performance of others decreased over the cycles. The cyclic tests caused mechanical damage to the surfaces, producing erosion, scratches and, for some coatings, surface cracks. These defects resulted in increased surface roughness and reduced hydrophobicity. However, no chemical changes were revealed for any of the surfaces. Moreover, the causes of cracks were attributed to the difference in thermal expansion behaviour of substrate and coating materials. This result highlights the importance of materials and process parameters selection in flame sprayed coatings designed for cold applications.publishedVersionPeer reviewe

Lubrikantti-impregnoitujen huokoisten pintojen kastuvuus- ja jäätymättömyysominaisuudet

Nature has provided intriguing possibilities to tackle wetting and to some extent even icing. By capturing the unique and inventive structures, novel surfaces with low wettability and low adhesion to ice are being under research. After deliberate material selection, these surfaces would provide easement to many industries suffering from ice accretion. In the Arctic region, buildings, wind turbines, maritime vessels, aviation and other transportation operators could benefit surfaces with anti-ice or ice-repellent properties. The aim of this master’s thesis was to study slippery liquid infused porous surfaces, SLIPS, by selecting proper porous solid and water immiscible lubricant combinations. The focus was in finding a surface which would have low ice adhesion and good anti-wetting properties with low lubricant evaporation. Different lubricants and oils with altered viscosities, were used in the tests as they naturally repel water. As a porous solid material, polytetrafluoroethylene (PTFE) –membrane was used to impregnate the lubricant into. The membranes had altering pore sizes and were manufactured by two different companies. Since PTFE is also water-repellent, that is hydrophobic, the produced SLIPS surfaces functioned in wettability tests as expected. From the fabricated SLIPS, the evaporation was examined as to its effects on wettability of the surface. The wettability was observed as a function of time as static contact angle, contact angle hysteresis and sliding angle tests were performed to the SLIPS. From the evaporation and wettability tests, the most promising and interesting SLIPS –samples were selected to the cyclic ice adhesion test. The cyclic ice adhesion test encompassed ice accretion in icing wind tunnel, ice adhesion measurement with centrifugal machinery and wettability tests afore next cycle. It was noticed that different pore sizes in the membranes had effects on wettability, but more significantly on ice adhesion strength. Moreover, when the results of the work are reviewed, submicrometer pore sizes were superior to micrometer pore sizes, as the ice detached from them more easily. It was detected that different lubricants had altering evaporation rates but also differenced in wettability experiments. Altogether, more cyclic ice adhesion testing is needed to perform in order to gain better comprehension towards SLIPS lifespan in icing and de-icing cycles. In addition, more lubricant and porous solid pairs are needed to tests to yield good performance SLIPS with exceptionally low ice adhesion strength

Thermally sprayed coatings - Novel surface engineering strategy towards icephobic solutions

Surface engineering promotes possibilities to develop sustainable solutions to icing challenges. Durable icephobic solutions are under high interest because the functionality of many surfaces can be limited both over time and in icing conditions. To solve this, one potential approach is to use thermally sprayed polymer or composite coatings with multifunctional properties as a novel surface design method. In thermal spraying, coating materials and structures can be tailored in order to achieve different surface properties, e.g., wetting performance, roughness and protection against several weathering and wearing conditions. These, in turn, are beneficial for excellent icephobic performance and surface durability. The icephobicity of several different surfaces are tested in our icing wind tunnel (IWiT). Here, mixed-glaze ice is accreted from supercooled water droplets and the ice adhesion is measured using a centrifugal adhesion tester (CAT). The present study focuses on the icephobicity of thermally sprayed coatings. In addition, surface-related properties are evaluated in order to illustrate the correlation between the icephobic performance and the surface properties of differently tailored thermally sprayed coatings as well as compared those to other coatings and surfaces.publishedVersionPeer reviewe

Achieving a slippery, liquid-infused porous surface with anti-icing properties by direct deposition of flame synthesized aerosol nanoparticles on a thermally fragile substrate

Slippery, liquid-infused porous surfaces offer a promising route for producing omniphobic and anti-icing surfaces. Typically, these surfaces are made as a coating with expensive and time consuming assembly methods or with fluorinated films and oils. We report on a route for producing liquid-infused surfaces, which utilizes a liquid precursor fed oxygen-hydrogen flame to produce titania nanoparticles deposited directly on a low-density polyethylene film. This porous nanocoating, with thickness of several hundreds of nanometers, is then filled with silicone oil. The produced surfaces are shown to exhibit excellent anti-icing properties, with an ice adhesion strength of ∼12 kPa, which is an order of magnitude improvement when compared to the plain polyethylene film. The surface was also capable of maintaining this property even after cyclic icing testing. Slippery, liquid-infused porous surfaces (SLIPSs) are nature inspired surfaces that are designed to repel liquid and solid materials. These surfaces have been shown to pose anti-icing properties, which broadens the available end-uses from the chemical industry to arctic transportation and energy production. The method behind repellency of SLIPSs relies on preventing outside liquids from penetrating the surface structure to the Wenzel state. Instead, the slippery liquid within the porous solid supports the Cassie-Baxter state (instead of air, here the porous structure is filled with lubricant), where the reduced area of the porous solid surface is available to interact with the liquid or ice to be repelled. The difference between Wenzel and Cassie-Baxter states is illustrated in Figure 1. This phenomenon is exploited in many superhydrophobic surfaces where an air cushion is entrapped within the porous solid surface. As a result, spherical water drops easily roll off the surface (and have static contact angles larger than 150°).publishedVersionPeer reviewe

Characteristics of nFOG, an aerosol-based wet thin film coating technique

An atmospheric pressure aerosol-based wet thin film coating technique called the nFOG is characterized and applied in polymer film coatings. In the nFOG, a fog of droplets is formed by two air-assist atomizers oriented toward each other inside a deposition chamber. The droplets settle gravitationally and deposit on a substrate, forming a wet film. In this study, the continuous deposition mode of the nFOG is explored. We determined the size distribution of water droplets inside the chamber in a wide side range of 0.1–100 µm and on the substrate using aerosol measurement instruments and optical microscopy, respectively. The droplet size distribution was found to be bimodal with droplets of approximately 30–50 µm contributing the most to the mass of the formed wet film. The complementary measurement methods allow us to estimate the role of different droplet deposition mechanisms. The obtained results suggest that the deposition velocity of the droplets is lower than the calculated terminal settling velocity, likely due to the flow fields inside the chamber. Furthermore, the mass flux of the droplets onto the substrate is determined to be in the order of 1 g/m3s, corresponding to a wet film growth rate of 1 µm/s. Finally, the nFOG technique is demonstrated by preparing polymer films with thicknesses in the range of approximately 0.1–20 µm