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  • 1.
    Anusuyadevi, Prasaanth
    et al.
    KTH Royal Institute of Technology, Sweden.
    Shanker, Ravi
    Linköping University, Sweden.
    Cui, Yuxiao
    KTH Royal Institute of Technology, Sweden.
    Riazanova, Anastasia
    KTH Royal Institute of Technology, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Jonsson, Magnus
    Linköping University, Sweden.
    Svagan, Anna
    KTH Royal Institute of Technology, Sweden.
    Photoresponsive and Polarization-Sensitive Structural Colors from Cellulose/Liquid Crystal Nanophotonic Structures2021Ingår i: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 33, nr 36, artikel-id 2101519Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cellulose nanocrystals (CNCs) possess the ability to form helical periodic structures that generate structural colors. Due to the helicity, such self-assembled cellulose structures preferentially reflect left-handed circularly polarized light of certain colors, while they remain transparent to right-handed circularly polarized light. This study shows that combination with a liquid crystal enables modulation of the optical response to obtain light reflection of both handedness but with reversed spectral profiles. As a result, the nanophotonic systems provide vibrant structural colors that are tunable via the incident light polarization. The results are attributed to the liquid crystal aligning on the CNC/glucose film, to form a birefringent layer that twists the incident light polarization before interaction with the chiral cellulose nanocomposite. Using a photoresponsive liquid crystal, this effect can further be turned off by exposure to UV light, which switches the nematic liquid crystal into a nonbirefringent isotropic phase. The study highlights the potential of hybrid cellulose systems to create self-assembled yet advanced photoresponsive and polarization-tunable nanophotonics. © 2021 The Authors.

  • 2.
    Eriksson, Mimmi
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign. KTH Royal Institute of Technology, Sweden; CR Colloidal Resource AB, Sweden.
    Claesson, Per M.
    KTH Royal Institute of Technology, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Wallqvist, Viveca
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Tuominen, Mikko
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Kappl, Michael
    Nordtreat Oy, Finland.
    Teisala, Hannu
    Max Planck Institute, Germany; Amcor Flexibles Valkeakoski Oy, Finland.
    Vollmer, Doris
    Max Planck Institute, Germany.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick A.C.
    University of Belgrade, Serbia; Aalto University, Finland.
    Mäkelä, Jyrki M.
    Tampere University, Finland.
    Swerin, Agne
    KTH Royal Institute of Technology, Sweden; Karlstad University, Sweden.
    Effects of Gas Layer Thickness on Capillary Interactions at Superhydrophobic Surfaces2024Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 40, nr 9, s. 4801-4810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Strongly attractive forces act between superhydrophobic surfaces across water due to the formation of a bridging gas capillary. Upon separation, the attraction can range up to tens of micrometers as the gas capillary grows, while gas molecules accumulate in the capillary. We argue that most of these molecules come from the pre-existing gaseous layer found at and within the superhydrophobic coating. In this study, we investigate how the capillary size and the resulting capillary forces are affected by the thickness of the gaseous layer. To this end, we prepared superhydrophobic coatings with different thicknesses by utilizing different numbers of coating cycles of a liquid flame spraying technique. Laser scanning confocal microscopy confirmed an increase in gas layer thickness with an increasing number of coating cycles. Force measurements between such coatings and a hydrophobic colloidal probe revealed attractive forces caused by bridging gas capillaries, and both the capillary size and the range of attraction increased with increasing thickness of the pre-existing gas layer. Hence, our data suggest that the amount of available gas at and in the superhydrophobic coating determines the force range and capillary growth. © 2024 The Authors.

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  • 3.
    Eriksson, Mimmi
    et al.
    RISE Research Institutes of Sweden. KTH Royal Institute of Technology, Sweden.
    Claesson, Per M
    KTH Royal Institute of Technology, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Wallqvist, Viveca
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Tuominen, Mikko
    RISE Research Institutes of Sweden.
    Kappl, Michael
    Max Planck Institute, Germany.
    Teisala, Hannu
    Max Planck Institute, Germany.
    Vollmer, Doris
    Max Planck Institute, Germany.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick
    Aalto University, Finland; University of Belgrade, Serbia.
    Mäkelä, Jyrki
    Tampere University, Finland.
    Swerin, Agne
    KTH Royal Institute of Technology, Sweden; Karlstad University, Sweden.
    Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces2023Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 13, nr 1, artikel-id 6794Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m−1), ethylene glycol (48 mN m−1) and hexadecane (27 mN m−1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient. © 2023, The Author(s).

  • 4.
    Eriksson, Mimmi
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Claesson, Per Martin
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Järn, Mikael
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Tuominen, Mikko
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Wallqvist, Viveca
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick A C
    Aalto University, Finland.
    Swerin, Agne
    KTH Royal Institute of Technology, Sweden.
    Wetting Transition on Liquid-Repellent Surfaces Probed by Surface Force Measurements and Confocal Imaging.2019Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, nr 41, s. 13275-13285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Superhydrophobic surfaces in the Cassie-Baxter wetting state retain an air layer at the surface which prevents liquid water from reaching into the porous surface structure. In this work we explore how addition of ethanol, which reduces the surface tension, influences the wetting properties of superhydrophobic and smooth hydrophobic surfaces. Wetting properties are measured by dynamic contact angles, and the air layer at the superhydrophobic surface is visualized by laser scanning confocal microscopy. Colloidal probe atomic force microscopy measurements between a hydrophobic microsphere and the macroscopic surfaces showed that the presence of ethanol strongly affects the interaction forces. When the macroscopic surface is superhydrophobic, attractive forces extending up to a few micrometers are observed on retraction in water and in 20 vol % ethanol, signifying the presence of a large and growing gas capillary. Submicrometer attractive forces are observed between the probe particle and a smooth hydrophobic surface, and in this case a smaller gas capillary is formed. Addition of ethanol results in markedly different effects between superhydrophobic and hydrophobic surfaces. In particular, we show that the receding contact angle on the superhydrophobic surface is of paramount importance for describing the interaction forces.

  • 5.
    Eriksson, Mimmi
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Tuominen, Mikko
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Järn, Mikael
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Claesson, Per Martin
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Wallqvist, Viveca
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Butt, Hans-Jürgen
    Max Planck Institute for Polymer Research, Germany.
    Vollmer, Doris
    Max Planck Institute for Polymer Research, Germany.
    Kappl, Michael
    Max Planck Institute for Polymer Research, Germany.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick A C
    Omya International AG, Switzerland.
    Teisala, Hannu
    Aalto University, Finland.
    Swerin, Agne
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Direct Observation of Gas Meniscus Formation on a Superhydrophobic Surface2019Ingår i: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 13, nr 2, s. 2246-2252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The formation of a bridging gas meniscus via cavitation or nanobubbles is considered the most likely origin of the submicrometer long-range attractive forces measured between hydrophobic surfaces in aqueous solution. However, the dynamics of the formation and evolution of the gas meniscus is still under debate, in particular, in the presence of a thin air layer on a superhydrophobic surface. On superhydrophobic surfaces the range can even exceed 10 μm. Here, we report microscopic images of the formation and growth of a gas meniscus during force measurements between a superhydrophobic surface and a hydrophobic microsphere immersed in water. This is achieved by combining laser scanning confocal microscopy and colloidal probe atomic force microscopy. The configuration allows determination of the volume and shape of the meniscus, together with direct calculation of the Young-Laplace capillary pressure. The long-range attractive interactions acting on separation are due to meniscus formation and volume growth as air is transported from the surface layer.

  • 6.
    Heydari, Golrokh
    et al.
    KTH Royal Institute of Technology, Sweden.
    Thormann, Espen
    KTH Royal Institute of Technology, Sweden; Technical University of Denmark, Denmark.
    Järn, Mikael
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Tyrode, Eric C.
    KTH Royal Institute of Technology, Sweden.
    Claesson, Per
    RISE., SP – Sveriges Tekniska Forskningsinstitut.
    Hydrophobic surfaces: Topography effects on wetting by supercooled water and freezing delay2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 42, s. 21752-21762Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hydrophobicity, and in particular superhydrophobicity, has been extensively considered to promote ice-phobicity. Dynamic contact angle measurements above 0 C have been widely used to evaluate the water repellency. However, it is the wetting properties of supercooled water at subzero temperatures and the derived work of adhesion that are important for applications dealing with icing. In this work we address this issue by determining the temperature-dependent dynamic contact angle of microliter-sized water droplets on a smooth hydrophobic and a superhydrophobic surface with similar surface chemistry. The data highlight how the work of adhesion of water in the temperature interval from about 25 C to below -10 C is affected by surface topography. A marked decrease in contact angle on the superhydrophobic surface is observed with decreasing temperature, and we attribute this to condensation below the dew point. In contrast, no significant wetting transition is observed on the smooth hydrophobic surface. The freezing temperature and the freezing delay time were determined for water droplets resting on a range of surfaces with similar chemistry but different topography, including smooth and rough surfaces in either the Wenzel or the Cassie-Baxter state as characterized by water contact angle measurements at room temperature. We find that the water freezing delay time is not significantly affected by the surface topography and discuss this finding within the classical theory of heterogeneous nucleation.

  • 7.
    Järn, Mikael
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Kemi och material.
    Grund Bäck, Lina
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik.
    Andersson, Anne
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Mätteknik.
    Karlsson, Stefan
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik.
    Mesoporous sol-gel based SiO2 thin films with ordered pore orientation as antireflective coatings on glass2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Antireflective coatings on glass have increasing applications, on e.g. cover glass of PV modules, display glass, spectacle lenses or window glazing’s. Sol-gel derived mesoporous coatings can be tuned both in terms of porosity and thickness, thus allowing tuning of the refractive index. Additionally, the sol-gel approach is bottom-up, which facilitates easy upscaling. In the current work we present dip-coated mesoporous silica coatings of different pore orientation and film thickness prepared on microscope glass slides and silicon wafers. The silica coatings were derived from TEOS (tetraorthosilicates) mixed with ethanol and diluted HCl. Hexagonal and cubic pore ordering of the thin films with a pore size in the range of 5-10 nm were obtained. The thin films were characterized in terms of non-contact profilometry, stylus profilometry,  nanohardness, scratch resistance, UV-Vis-NIR transmittance and UV-Vis-NIR reflectance. The thicknesses of the studied films varied from 100 nm up to several hundreds of nm without jeopardizing the film homogeneity. All the mesoporous films exhibited higher transmittance than the uncoated glass substrate. The film with hexagonal pore orientation has a somewhat higher nanohardness than the cubic one, however,  no difference was found in the scratch resistance for the films with different pore orientations.

  • 8.
    Järn, Mikael
    et al.
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Swerin, Agne
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Claesson, Per
    RISE., SP – Sveriges Tekniska Forskningsinstitut.
    Superhydrophilic polyelectrolyte brush layers with imparted anti-icing properties: Effect of counter ions2014Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 6, nr 9, s. 6487-6496Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work demonstrates the feasibility of superhydrophilic polyelectrolyte brush coatings for anti-icing applications. Five different types of ionic and nonionic polymer brush coatings of 25-100 nm thickness were formed on glass substrates using silane chemistry for surface premodification followed by polymerization via the SI-ATRP route. The cationic [2-(methacryloyloxy)ethyl] trimethylammonium chloride] and the anionic [poly(3-sulfopropyl methacrylate), poly(sodium methacrylate)] polyelectrolyte brushes were further exchanged with H+, Li+, Na+, K+, Ag+, Ca2+, La3+, C16N+, F-, Cl-, BF4-, SO42-, and C12SO3- ions. By consecutive measurements of the strength of ice adhesion toward ion-incorporated polymer brushes on glass it was found that Li+ ions reduce ice adhesion by 40% at -18 °C and 70% at -10 °C. Ag+ ions reduce ice adhesion by 80% at -10 °C relative to unmodified glass. In general, superhydrophilic polyelectrolyte brushes exhibit better anti-icing property at -10 °C compared to partially hydrophobic brushes such as poly(methyl methacrylate) and surfactant exchanged polyelectrolyte brushes. The data are interpreted using the concept of a quasi liquid layer (QLL) that is enhanced in the presence of highly hydrated ions at the interface. It is suggested that the ability of ions to coordinate water is directly related to the efficiency of a given anti-icing coating based on the polyelectrolyte brush concept.

  • 9.
    Karlsson, Stefan
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Lindh, E Mattias
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Bioraffinaderi och energi.
    Nya ytbeläggningar ska minska snöförluster på solcellsanläggningar2023Ingår i: GLAS, nr 1, s. 34-37Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [sv]

    För att slippa vänta på plusgrader håller en samling forskare på RISE på attutveckla och testa nya ytbeläggningar för solceller som ska göra att snö och isinte fäster på dem. Snö och is kan leda till stopp i elproduktionen - en solcellsmodulsom är täckt av snö och is generar i praktiken ingen elektricitet eftersomsolljuset inte tränger igenom i tillräcklig omfattning. Dessutom kan rejälasnömängder leda till stora belastningar på underliggande konstruktioner.

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  • 10.
    Karlsson, Stefan
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik. RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Järn, Mikael
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Kemi och material.
    Welinder, Jan
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Elektronik.
    Andersson, Anne
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Mätteknik.
    Liinanki, Matilda
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik.
    Försth, Michael
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Safety.
    Transparent intelligens för en bättre värld - en sammanfattning av fyra år med TIME2017Ingår i: GLAS, nr 2, s. 58-59Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
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  • 11.
    Karlsson, Stefan
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Zäll, Erik
    Umeå University, Sweden.
    Antireflektiv beläggning i världsklass ger effektivare solfångare2023Ingår i: GLAS, nr 4, s. 36-37Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [sv]

    I ett nyligen avslutat forskningsprojekt har Absolicon Solar Collector tillsammans med RISE Research Institutes of Sweden och Umeå universitet utvecklat en ny toppmodern antireflektiv beläggning som kan göra Absolicons solfångare än mer effektiva. Nu siktar man på ett nytt projekt för att skala upp metoden.

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  • 12.
    Karlsson, Stefan
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik.
    Österlund, Lars
    Uppsala university, Sweden.
    Niklasson, Gunnar
    Uppsala university, Sweden.
    Granqvist, Claes-Göran
    Uppsala university, Sweden.
    Järn, Mikael
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Yta, process och formulering.
    Eriksson, Jerry
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik.
    Welinder, Jan
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Elektronik.
    Försth, Michael
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Safety. Luleå tekniska universitet, Sweden.
    Ludvigsson, Mikael
    RISE - Research Institutes of Sweden (2017-2019), Samhällsbyggnad, Byggteknik.
    “Transparent Intelligence” for Sustainable Development2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Transparent materials are essential in everyone’s life. They enable daylight to reach the interior of buildings, thereby contributing to both our physical and mental well-being; they are the primary component for communication via optical fibers and a key component in electronic devices such as protective cover and/or dielectric material; and they enable clean energy production through solar panels or algae reactors by acting as protective and light transmitting barriers. Adding functions to transparent materials in an intelligent way creates further opportunities to use and enhance the beneficial impacts of transparency. The concept Transparent Intelligence covers transparent materials and products with integral intelligent functions – passive, active or interactive. By using Transparent Intelligence it is possible to embrace many of the societal challenges that we are facing today. The concept can be divided into five broad industrial sectors: Built Environment, Information and Communication Technologies (ICT), Solar Energy, Mobility, and Materials. A perspective on how Transparent Intelligence can improve the sustainable development of our world will be presented, using examples of electrochromic windows for energy-efficient buildings, photocatalytic coatings for improved indoor air quality, transparent conductive coatings for antennas, bandpass filters for mobile phone indoor coverage, UV down-converting components for efficient solar energy, hygienic surfaces for infection mitigation on electronic devices, printed electronics for sustainable glass packaging, and IR-reflecting coatings for fire safety.

  • 13.
    Nilsson, Fritjof
    et al.
    KTH Royal Institute of Technology, Sweden.
    Moyassari, Ali
    KTH Royal Institute of Technology, Sweden.
    Bautista, Angela
    E2F Electroficación y Estudios Ferroviarios, Spain.
    Castro, Abraham
    E2F Electroficación y Estudios Ferroviarios, Spain.
    Arbeloa, Ignacio
    Amayuelas SL, Spain.
    Järn, Mikael
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Kemi och material.
    Lundgren, Urban
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Elektronik.
    Welinder, Jan
    RISE - Research Institutes of Sweden (2017-2019), Säkerhet och transport, Elektronik.
    Johansson, Kenth
    RISE - Research Institutes of Sweden (2017-2019), Biovetenskap och material, Kemi och material.
    Modelling anti-icing of railway overhead catenary wires by resistive heating2019Ingår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 143, artikel-id 118505Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aggregation of ice on electrical cables and apparatus can cause severe equipment malfunction and is thus considered as a serious problem, especially in arctic climate zones. In particular, cable damage caused by ice accumulation on railway catenary wires is in wintertime a common origin for delayed trains in the northern parts of Europe. This study examines how resistive heating can be used for preventing formation of ice on metallic, non-insulated electrical cables. The heat equation and the Navier Stokes equations were solved simultaneously with FEM in 3D in order to predict the cable temperature as function of external temperature, applied voltage, wind speed, wind direction, and heating time. An analytical expression for the heat transfer coefficient was derived from the FEM simulations and it was concluded that the influence of wind direction can typically be neglected. Experimental validation measurements were performed on Kanthal cables in a climate chamber, giving temperature increase results in good agreement with the simulation predictions. The resistive heating efficiency, i.e. the ratio between applied electrical energy and resulting thermal energy, was found to be approximately 68% in this particular study.

  • 14.
    Nordenström, Malin
    et al.
    KTH Royal Institute of Technology, Sweden; WWSC Wallenberg Wood Science Center, Sweden.
    Riazanova, Anastasia V
    KTH Royal Institute of Technology, Sweden; WWSC Wallenberg Wood Science Center, Sweden.
    Järn, Mikael
    RISE - Research Institutes of Sweden, Biovetenskap och material, Yta, process och formulering.
    Paulraj, Thomas
    KTH Royal Institute of Technology, Sweden; WWSC Wallenberg Wood Science Center, Sweden.
    Turner, Charlotta
    Lund University, Sweden.
    Ström, Valter
    KTH Royal Institute of Technology, Sweden.
    Olsson, Richard T
    KTH Royal Institute of Technology, Sweden; WWSC Wallenberg Wood Science Center, Sweden.
    Svagan, Anna J
    KTH Royal Institute of Technology, Sweden; WWSC Wallenberg Wood Science Center, Sweden.
    Superamphiphobic coatings based on liquid-core microcapsules with engineered capsule walls and functionality2018Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 8, nr 1, artikel-id 3647Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microcapsules with specific functional properties, related to the capsule wall and core, are highly desired in a number of applications. In this study, hybrid cellulose microcapsules (1.2 ± 0.4 µm in diameter) were prepared by nanoengineering the outer walls of precursor capsules. Depending on the preparation route, capsules with different surface roughness (raspberry or broccoli-like), and thereby different wetting properties, could be obtained. The tunable surface roughness was achieved as a result of the chemical and structural properties of the outer wall of a precursor capsule, which combined with a new processing route allowed in-situ formation of silica nanoparticles (30-40 nm or 70 nm in diameter). By coating glass slides with "broccoli-like" microcapsules (30-40 nm silica nanoparticles), static contact angles above 150° and roll-off angles below 6° were obtained for both water and low surface-tension oil (hexadecane), rendering the substrate superamphiphobic. As a comparison, coatings from raspberry-like capsules were only strongly oleophobic and hydrophobic. The liquid-core of the capsules opens great opportunities to incorporate different functionalities and here hydrophobic superparamagnetic nanoparticles (SPIONs) were encapsulated. As a result, magnetic broccoli-like microcapsules formed an excellent superamphiphobic coating-layer on a curved geometry by simply applying an external magnetic field.

  • 15.
    Wojas, Natalia
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign. KTH Royal Institute of Technology, Sweden.
    Dobryden, Illia
    KTH Royal Institute of Technology, Sweden; Luleå University of Technology, Sweden.
    Wallqvist, Viveca
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Swerin, Agne
    Karlstad University, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick A C
    Aalto University, Finland.
    Claesson, Per M
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign. KTH Royal Institute of Technology, Sweden.
    Nanoscale Wear and Mechanical Properties of Calcite: Effects of Stearic Acid Modification and Water Vapor2021Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 37, nr 32, s. 9826-9837Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the wear of mineral fillers is crucial for controlling industrial processes, and in the present work, we examine the wear resistance and nanomech. properties of bare calcite and stearic acid-modified calcite surfaces under dry and humid conditions at the nanoscale. Measurements under different loads allow us to probe the situation in the absence and presence of abrasive wear. The sliding motion is in general characterized by irregular stick-slip events that at higher loads lead to abrasion of the brittle calcite surface. Bare calcite is hydrophilic, and under humid conditions, a thin water layer is present on the surface. This water layer does not affect the friction force. However, it slightly decreases the wear depth and strongly influences the distribution of wear particles. In contrast, stearic acid-modified surfaces are hydrophobic. Nevertheless, humidity affects the wear characteristics by decreasing the binding strength of stearic acid at higher humidity. A complete monolayer coverage of calcite by stearic acid results in a significant reduction in wear but only a moderate reduction in friction forces at low humidity and no reduction at 75% relative humidity (RH). Thus, our data suggest that the wear reduction does not result from a lowering of the friction force but rather from an increased ductility of the surface region as offered by the stearic acid layer. An incomplete monolayer of stearic acid on the calcite surface provides no reduction in wear regardless of the RH investigated. Clearly, the wear properties of modified calcite surfaces depend crucially on the packing d. of the surface modifier and also on the air humidity.

  • 16.
    Wojas, Natalia
    et al.
    RISE - Research Institutes of Sweden, Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Swerin, Agne
    RISE - Research Institutes of Sweden, Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Wallqvist, Viveca
    RISE - Research Institutes of Sweden, Biovetenskap och material, Yta, process och formulering.
    Järn, Mikael
    RISE - Research Institutes of Sweden, Biovetenskap och material, Yta, process och formulering. Omya International AG, Switzerland.
    Schoelkopf, Joachim
    Omya International AG, Switzerland; Aalto University, Finland.
    Gane, Patrick
    Claesson, Per M.
    RISE - Research Institutes of Sweden, Biovetenskap och material, Yta, process och formulering. KTH Royal Institute of Technology, Sweden.
    Iceland spar calcite: Humidity and time effects on surface properties and their reversibility2019Ingår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 541, s. 42-55Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the complex and dynamic nature of calcite surfaces under ambient conditions is important for optimizing industrial applications. It is essential to identify processes, their reversibility, and the relevant properties of CaCO3 solid-liquid and solid-gas interfaces under different environmental conditions, such as at increased relative humidity (RH). This work elucidates changes in surface properties on freshly cleaved calcite (topography, wettability and surface forces) as a function of time (≤28 h) at controlled humidity (≤3–95 %RH) and temperature (25.5 °C), evaluated with atomic force microscopy (AFM) and contact angle techniques. In the presence of humidity, the wettability decreased, liquid water capillary forces dominated over van der Waals forces, and surface domains, such as hillocks, height about 7.0 Å, and trenches, depth about −3.5 Å, appeared and grew primarily in lateral dimensions. Hillocks demonstrated lower adhesion and higher deformation in AFM experiments. We propose that the growing surface domains were formed by ion dissolution and diffusion followed by formation of hydrated salt of CaCO3. Upon drying, the height of the hillocks decreased by about 50% suggesting their alteration into dehydrated or less hydrated CaCO3. However, the process was not entirely reversible and crystallization of new domains continued at a reduced rate.

  • 17.
    Wojas, Natalia
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign. KTH Royal Institute of Technology, Sweden.
    Swerin, Agne
    Karlstad University, Sweden.
    Wallqvist, Viveca
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Schoelkopf, Joachim
    Omya International Ag, Switzerland.
    Gane, Patrick
    Aalto University, Finland.
    Claesson, Per M
    KTH Royal Institute of Technology, Sweden.
    Surface-Modified and Unmodified Calcite: Effects of Water and Saturated Aqueous Octanoic Acid Droplets on Stability and Saturated Fatty Acid Layer Organization2021Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 37, nr 48, s. 14135-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A profound understanding of the properties of unmodified and saturated fatty acid-modified calcite surfaces is essential for elucidating their resistance and stability in the presence of water droplets. Additional insights can be obtained by also studying the effects of carboxylic acid-saturated aqueous solutions. We elucidate surface wettability, structure, and nanomechanical properties beneath and at the edge of a deposited droplet after its evaporation. When calcite was coated by a highly packed monolayer of stearic acid, a hydrophilic region was found at the three-phase contact line. In atomic force microscopy mapping, this region is characterized by low adhesion and a topographical hillock. The surface that previously was covered by the droplet demonstrated a patchy structure of about 6 nm height, implying stearic acid reorganization into a patchy bilayer-like structure. Our data suggest that during droplet reverse dispensing and droplet evaporation, pinning of the three-phase contact line leads to the transport of dissolved fatty carboxylic acid and possibly calcium bicarbonate Ca(HCO3)2 molecules to the contact line boundary. Compared to the surface of intrinsically hydrophobic materials, such as polystyrene, the changes in contact angle and base diameter during droplet evaporation on stearic acid-modified calcite are strikingly different. This difference is due to stearic acid reorganization on the surface and transport to the water-air interface of the droplet. An effect of the evaporating droplet is also observed on unmodified calcite due to dissolution and recrystallization of the calcite surface in the presence of water. In the case where a water droplet saturated with octanoic acid is used instead of water, the stearic acid-coated calcite remains considerably more stable. Our findings are discussed in terms of the coffee-ring effect. © 2021 The Authors. 

  • 18.
    Wojas, Natalia
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign. KTH Royal Institute of Technology, Sweden.
    Tyrode, Eric
    KTH Royal Institute of Technology, Sweden.
    Corkery, Robert
    KTH Royal Institute of Technology, Sweden; Australian National University Department of Applied Mathematics, Australia.
    Ernstsson, Marie
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Wallqvist, Viveca
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Swerin, Agne
    Karlstad University, Sweden.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick A C
    Aalto University, Finland; University of Belgrade, Serbia.
    Claesson, Per M.
    KTH Royal Institute of Technology, Sweden.
    Calcite Surfaces Modified with Carboxylic Acids (C2 to C18): Layer Organization, Wettability, Stability, and Molecular Structural Properties2023Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 39, nr 42, s. 14840-14852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fundamental understanding of the interactions between mineral surfaces and amphiphilic surface modification agents is needed for better control over the production and uses of mineral fillers. Here, we controlled the carboxylic acid layer formation conditions on calcite surfaces with high precision via vapor deposition. The properties of the resulting carboxylic acid layers were analyzed using surface-sensitive techniques, such as atomic force microscopy (AFM), contact angle measurements, angle resolved X-ray photoelectron spectroscopy (XPS), and vibrational sum-frequency spectroscopy. A low wettability was achieved with long hydrocarbon chain carboxylic acids such as stearic acid. The stearic acid layer formed by vapor deposition is initially patchy, but with increasing vapor exposure time, the patches grow and condense into a homogeneous layer with a thickness close to that expected for a monolayer as evaluated by AFM and XPS. The build-up process of the layer occurs more rapidly at higher temperatures due to the higher vapor pressure. The stability of the deposited fatty acid layer in the presence of a water droplet increases with the chain length and packing density in the adsorbed layer. Vibrational sum frequency spectroscopy data demonstrate that the stearic acid monolayers on calcite have their alkyl chains in an all-trans conformation and are anisotropically distributed on the plane of the surface, forming epitaxial monolayers. Vibrational spectra also show that the stearic acid molecules interact with the calcite surface through the carboxylic acid headgroup in both its protonated and deprotonated forms. The results presented provide new molecular insights into the properties of adsorbed carboxylic acid layers on calcite.

  • 19.
    Xu, Qian
    et al.
    Åbo Akademi University, Finland.
    Järn, Mikael
    RISE., SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. Åbo Akademi University, Finland.
    Linden, Mika
    Åbo Akademi University, Finland; University of Ulm, Germany.
    Smått, Jan Henrik
    Åbo Akademi University, Finland.
    Nanopatterned zinc titanate thin films prepared by the evaporation-induced self-assembly process2013Ingår i: Thin Solid Films, ISSN 0040-609, Vol. 531, s. 222-227Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanopatterned thin films prepared by the evaporation-induced self-assembly process have up to now been limited to a few transition metal oxides (i.e. Al2O3, TiO2 and ZrO2). Here we describe the formation of zinc titanate nanoperforated thin films with different Zn/Ti ratios using the dipcoating process. Atomic force microscopy and scanning electron microscopy reveal that the structure consists of well-ordered pseudohexagonal nanoperforations in the range of 30 nm in diameter separated by 25 nm wide metal oxide ridges, while the film thickness is close to 2 nm. For films with a zinc precursor content up to 50 mol%, the well-organized structure of the thin film can be maintained, while at higher Zn contents the nanostructure is gradually becoming more disordered, which we have shown is consistent with the partial charge model. Grazing incidence X-ray diffraction measurements on the films calcined at 700 C indicate that the anatase phase of the pure TiO2 films is gradually consumed at the expense of a newly formed Zn2Ti3O8 phase upon increasing the Zn/Ti ratio in the starting precursor solution. The unique combination of the nanostructure with the zinc titanate composition grants these nanopatterned thin films significant application prospects in for instance optics and catalysis. 

  • 20.
    Yin, Haiyan
    et al.
    RISE Research Institutes of Sweden, Bioekonomi och hälsa. KTH Royal Institute of Technology, Sweden.
    Sedighi Moghaddam, Maziar
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Tuominen, Mikko
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Eriksson, Mimmi
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign. KTH Royal Institute of Technology, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Dėdinaitė, Andra
    RISE Research Institutes of Sweden. KTH Royal Institute of Technology, Sweden.
    Wålinder, Magnus
    KTH Royal Institute of Technology, Sweden.
    Swerin, Agne
    KTH Royal Institute of Technology, Sweden.
    Superamphiphobic plastrons on wood and their effects on liquid repellence2020Ingår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 195, artikel-id 108974Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The increasing utilization of wood-based products raises new demands for improved durability, for example an enhanced liquid repellence. Superhydrophobic or superamphiphobic surfaces have been widely fabricated. Less attention has been paid to such modifications on wood and the changes of its hygroscopic or solvoscopic properties. In this work, wood veneers were surface modified by hydrophobized silicone nanofilaments. Results revealed that the surface-modified wood showed a superamphiphobic behavior, i.e. it repelled water, ethylene glycol and hexadecane with contact angles greater than 150° and roll-off angles of less than 10°. Most importantly, a plastron effect was observed when the surface-modified wood was submerged in water, ethylene glycol or hexadecane, which reduced the liquid sorption rate and extent to various degrees. By comparing the measured permeabilities and the estimated diffusive mass flux and supported by Hansen solubility parameters and the degrees of swelling, it is concluded that diffusion is the major cause for the liquid uptake in the surface-modified wood. Moreover, the interaction between the liquid and the modified layer (the solubility of the liquid in the modified layer) also needs to be considered, especially in hexadecane. © 2020 The Authors

  • 21.
    Zäll, Erik
    et al.
    Absolicon Solar Collector, Sweden; Umeå University, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Karlsson, Stefan
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Tryggeson, Henrik
    RISE Research Institutes of Sweden, Samhällsbyggnad, Bygg och fastighet.
    Tuominen, Mikko
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Sundin, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Wågberg, Thomas
    Umeå University, Sweden.
    Aerosol-based deposition of broadband antireflective silica coating with closed mesoporous structure2023Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 250, s. 112078-112078, artikel-id 112078Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Solar energy will be a crucial part of the sustainable, fossil free energy production of the future. A majority of this will be produced by solar collectors and photovoltaics. Important for the efficient utilization of the incident solar energy for both technologies are a cover glass with antireflective coatings giving it a high solar transmittance. In the current paper we describe the development of antireflective mesoporous silica coatings on low-iron float glass using the aerosol-based nFOG™ deposition technique. The coatings exhibit a hexagonal and closed pore structure, high smoothness, superhydrophilic properties (contact angle <5°) and consistent thicknesses of approximately 110 nm. This is in line with optimal thickness determined from simulations of the antireflective behavior. Low-iron float glass coated on both sides show a highly reproducible solar weighted transmittance of 95% in the wavelength range 300–2500 nm and an antireflective effect increasing with incident angle. The smoothness, closed pores and low contact angle indicate a high cleanability, which in combination with the high transmittance render a competitive broadband antireflective coating well adapted for solar glass applications.

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  • 22.
    Zäll, Erik
    et al.
    Absolicon Solar Collector. Sweden; Umeå University, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Karlsson, Stefan
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Tryggeson, Henrik
    RISE Research Institutes of Sweden, Samhällsbyggnad, Bygg och fastighet.
    Tuominen, Mikko
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Sundin, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Wågberg, Thomas
    Umeå University, Sweden.
    Aerosol-based deposition of broadband antireflective silica coating withclosed mesoporous structure2023Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 250, s. 112078-, artikel-id 112078Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Solar energy will be a crucial part of the sustainable, fossil free energy production of the future. Amajority of this will be produced by solar collectors and photovoltaics. Important for the efficientutilization of the incident solar energy for both technologies are a cover glass with antireflectivecoatings giving it a high solar transmittance. In the current paper we describe the development ofantireflective mesoporous silica coatings on low-iron float glass using the aerosol-based nFOGTMdeposition technique. The coatings exhibit a hexagonal and closed pore structure, a high smoothness,and consistent thicknesses of approximately 110 nm. This is in line with optimal thicknessesdetermined from simulations of the antireflective behavior. Low-iron float glass coated on both sidesshow a highly reproducible solar weighted transmittance of 95 % in the wavelength range 300-2500nm and an antireflective effect increasing with incident angle. The smoothness and closed poresassociated with high cleanability, as well as high transmittance makes it a competitive broadbandantireflective coating well adapted for solar glass applications.

    Ladda ner fulltext (pdf)
    fulltext
  • 23.
    Zäll, Erik
    et al.
    Absolicon Solar Collector AB, Sweden; Umeå University, Sweden.
    Karlsson, Stefan
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Segervald, Jonas
    Umeå University, Sweden.
    Lundberg, Petter
    Umeå University, Sweden.
    Wågberg, Thomas
    Umeå University, Sweden; SLU Swedish University of Agricultural Sciences, Sweden.
    Durability of antireflective SiO2 coatings with closed pore structure2023Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 261, artikel-id 112521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of antireflective coatings to increase the transmittance of the cover glass is a central aspect of achieving high efficiencies for solar collectors and photovoltaics alike. Considering an expected lifetime of 20–30 years for solar energy installations, the durability of the antireflective surfaces is essential. Here, a novel antireflective SiO2 coating with a hexagonally ordered closed pore structure, produced with an aerosol-based sol-gel method is benchmarked against two commercial coatings; produced with acid etching and sol-gel roll coating. The optical and mechanical properties together with contact angle characteristics were evaluated before and after various durability tests, including climate chamber tests, outdoor exposure, and abrasion. Compared to the commercial antireflective coatings with open pore structures, the novel coating performed in parity, or better, in all tests. Based on the results of humidity freeze and industrial climate chamber tests, it appears that the coating with closed pore structure has a better ability to prevent water adsorption. Additionally, the closed pore structure of the coating seems to minimize the accumulation of dirt and deposits. The abrasion and cleanability test further confirm the advantages of a closed pore structure, showcasing the coating's mechanical durability. While the coatings exhibit similar hardness and reduced elastic modulus, the closed pore coating proves to be even harder after undergoing the industrial climate chamber test, but also slightly more brittle, as indicated by the probability of crack initiation. In summary the closed pore structure is well suited for tempered and arid climates, making it a truly competitive alternative to existing antireflective coatings.

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    Supporting information
  • 24.
    Zäll, Erik
    et al.
    Umeå University, Sweden; Absolicon Solar Collector AB, Sweden.
    Nordenström, Andreas
    Umeå University, Sweden.
    Järn, Mikael
    RISE Research Institutes of Sweden, Bioekonomi och hälsa, Material- och ytdesign.
    Mossegård, Jonatan
    Absolicon Solar Collector AB, Sweden.
    Wågberg, Thomas
    Umeå University, Sweden.
    Environmentally sustainable electroplating of selective cobalt-chromium coating on stainless steel for efficient solar collectors2022Ingår i: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 245, artikel-id 111821Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Half of today's global energy consumption is in the form of heating and cooling. Solar collectors are the most promising sustainable alternative to fossil fuels in this sector. The most important component in a solar collector is the receiver, which by use of a selective surface absorbs and converts solar irradiance to thermal energy. Herein, a novel selective surface for low-to mid-temperature solar collectors is developed, studied and presented. The surface is produced by electroplating a cobalt-chromium coating on a stainless steel substrate using an electrolyte based on a deep eutectic solvent. Our method makes use of trivalent instead of traditionally used hexavalent chromium, which significantly reduces health-related issues and makes it more environmentally benign. We obtain a coating of chromium doped cobalt where the surface exhibits an absorptance and emittance of 0.96 and 0.14, respectively, giving it a solar-to-thermal efficiency of 0.95. An observed loss in optical efficiency, is shown to correlate to an oxidation of the metallic cobalt to Co3O4 at elevated temperatures. We further show that this oxidation can be mitigated by dip-coating a protective silica top coating, which concurrently improves the optical selectivity of the surface. The present selective surface is efficient, cheap, scalable, and easy to produce sustainably, making it competitive to industry standards. We foresee that our method will have impact on the advancement of improved low-to mid-temperature solar collectors, assisting a faster transition towards a sustainable society.

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