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Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris
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Sirris Smart Coating workshop - Easy-to-clean and Self cleaning Coatings - 19 May 2011 - State of the art - Heidi Van Den Rul, Sirris

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The desire for self-cleaning or easy-to-clean surfaces has been identified in recent years as an important research topic to enhance the competitiveness of companies. The approaches to obtain such a …

The desire for self-cleaning or easy-to-clean surfaces has been identified in recent years as an important research topic to enhance the competitiveness of companies. The approaches to obtain such a surface are diverse, depending on the specific requirements of the industrial sectors involved. Two classical approaches for dirt repelling surfaces are (i) hydrophobic or superhydrophobic surfaces and (ii) superhydrophilic, photocatalytic surfaces. A brief summary of the principles of these kind of coatings will be given in this presentation, focusing on present state-of-the-art preparation and testing methods. Examples selected from the scientific literature, a patent study on superhydrophobic coatings and commercial products will be presented to identify advantages and problems of present self-cleaning coatings.

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  • 1. State of the art of easy-to-clean and self-cleaningcoatings<br />Dr. Heidi Van den Rul<br />Sirris Smart CoatingApplication Lab<br />
  • 2. Overview<br />Approachesforeasy-to-cleancoatings:<br />Hydrophobic<br />Superhydrophobic<br />Photocatalytic<br />Superhydrophobiccoatings:<br />What?<br />Scientific and patent preparationmethods<br />Testing of (commercial) coatings<br />Conclusions<br />Photocatalyticcoatings:<br />Principles and preparation<br />Testing of photocatalyticproperties<br />Conclusions<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />2<br />
  • 3. Liquid wettability of a flat surface<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />3<br />low wettability<br />high wettability<br />contact angle<br />Θ0°<br />0<Θ< 90°<br />90<Θ<180°<br />Θ180°<br />Tangent angle of the liquid-vapor interface measured at the threephase contact point<br />hydrophilic<br />hydrophobic<br />water<br />oil<br />oleophilic<br />oleophobic<br />Drop at equilibrium: contact anglecanbemeasuredbybalancing the interfacialforces: γSL + γLV cos θ = γSV<br />Young equation: cos θ = (γSV - γSL ) / γLV<br />Sourcefigures: Shirtcliffe et al., Adv. Coll. Interf. Sci (2009) - naturesraincoats.com<br />
  • 4. Hydrophobic, easy-to-clean coatings<br />Beading up of water, low dirtuptake<br />Examples:<br />Contact angleon flat hydrophobicsurface: max. 115-120°<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />4<br />silicone<br />PTFE<br />sol-gelwithhydrophobic building blocks<br />fluorine containing sol-gel coating with low surface free energy. <br />Source: inm-gmbh.de<br />
  • 5. Superhydrophobic, self-cleaning coatingsWhat?<br />Inspiredby lotus leave:<br />Water dropletsball up (contact angle 160°) and rolloff the surface (slippery) of manyplants<br />Rolling dropletsgather and transport dust: “self-cleaning”<br />Lotus leave has double scaleroughness<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />5<br />SEM picture showinghierarchicalroughness of Lotus leave: <br /><ul><li>microbumps (papillae)
  • 6. nanostructure (epicuticularwaxes)</li></ul>Nelumbonucifera “Lotus”<br />
  • 7. Superhydrophobic, self-cleaningcoatingsModels explainingbehavior of dropletsonrough surfaces<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />6<br />Dropletsmaintains contact withentireroughsurface<br />Droplets have no complete contact with the roughsurface at all points<br />roughness<br />roughness<br />Requirementsfor a superhydrophobiccoating:<br /><ul><li>Water contact angle > 150°
  • 8. Water contact anglehysteresis (or sliding angle) < 10° </li></ul>Sourcefigures: naturesraincoats.com<br />
  • 9. Superhydrophobic, self-cleaningcoatingsContact anglehysteresis and sliding angle<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />7<br />Measures of howgood a droplet can move on a surface:<br />Contact anglehysteresis = advancing – receding contact angle<br />the lower the hysteresis, the easier the droplet slides<br />Wenzel state: high hysteresis<br />Cassie-Baxter state: low hysteresis<br />Sliding angle = smallestsurfacetiltingangle at which the dropletsrollsoff<br />Dependsonsize of droplets<br />Dependsonhysteresis<br />Sensitive to vibration<br />A droplet of liquid on a tilted surface has an advancing contact angle at the front and a receding contact angle at the rear edge<br />
  • 10. Superhydrophobic, self-cleaningcoatings<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />8<br />Requirementsfor a superhydrophobiccoating:<br /><ul><li>Water contact angle > 150°
  • 11. Water contact anglehysteresis (or sliding angle) < 10° </li></li></ul><li>Superhydrophobic, self-cleaningcoatingsPreparationstrategies<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />9<br />low surfaceenergy + high surfaceroughness<br />
  • 12. Superhydrophobic, self-cleaningcoatingsPreparationmethods<br />Lithography<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />10<br />Oner et al., Langmuir 16 (2000) 7777<br />C.H. Choi, UCLA<br />
  • 13. Superhydrophobic, self-cleaningcoatingsPreparationmethods<br />Etching<br />Wet chemicaletching of metals<br />Plasma etching of polymers<br />Laser etching of inorganicmaterials<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />11<br />Etched steel<br />Etchedcopperalloy<br />Etched Cu (0.5 wt% oxalic acid 5-7 days)<br />Etched Cu in aq. Solution 2M NaOH + 0.1M K2S2O8 60’<br />All etched surfaces are treatedwith a hydrophobic agent afterwards<br />Guo et al., J. Coll. Interf. Sci. 353 (2011) 335<br />
  • 14. Superhydrophobic, self-cleaningcoatingsPreparationmethods<br />Crystal growth, e.g. hydrothermal<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />12<br />Nanolamellatestructures of CaTiO3on Ti<br />ZnOcrystals<br />ZnOnanowire film<br />Spiral Co3O4 nanorodarraysonglass<br />All hydrothermallygrownstructures are treatedwith a hydrophobic agent afterwards<br />Wu et al., Mat. Lett. 65 (2011) 477<br />Wu et al., Mat. Lett. 64 (2010) 1251<br />Guo et al., J. Coll. Interf. Sci. 353 (2011) 335<br />
  • 15. Superhydrophobic, self-cleaningcoatingsPreparationmethods<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />13<br />Polyelectrolyemultilayercoating made bylayer-by-layermethod<br />Porous Cu film byelectrochemicaldeposition<br />Porouspolymermembraneobtainedbyphaseseparationof a multicomponent mixture<br />SuperhydrophobicPECVD-formedcoatingfrom C6F6<br />Coatingformedbytemplating<br />Guo et al., J. Coll. Interf. Sci. 353 (2011) 335 – Xue et al., Sci. Techn. Adv. Mater. 11 (2010) 033002 – Crick et al., Chem. Eur. J. 16 (2010) 3568 - Shirtcliffe et al., Adv. Coll. Interf. Sci (2009)<br />
  • 16. Superhydrophobic, self-cleaningcoatingsPreparationmethods<br />Depositionfrom “particles”<br />(hydrophobized) silica, (mixed with) other metal oxides, (carbon nanotubes)<br />Micron ornanoparticlesor micron + nanoparticles or nanoparticles bond to micronparticles<br />With/without binder<br />Particlesformed in situbysol-gelmethod<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />14<br />Sol-gel route to roughsurface<br />Dualsize “raspberry” silicaparticles<br />Coatingformedfromsol-gel precursor + silicananoparticles<br />
  • 17. Superhydrophobic, self-cleaningcoatingsPreparationmethods<br />Afterrougheningoften a low energycoatingneeds to bedeposited to obtain a superhydrophobiccoating:<br />Fluoroalkylsilanes<br />Alkyl molecules, e.g. stearic acid<br />Non-fluorinatedpolymers<br />Alkylsilanes<br />
  • 18. Superhydrophobic, self-cleaningcoatingsPreparationmethods: whichone is relevant?<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />16<br />
  • 19. Superhydrophobic, self-cleaningcoatingsPreparationmethods: results of a patent study<br />20-5-2011<br />17<br />
  • 20. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />18<br />Superhydrophobic, self-cleaningcoatingsA commercial coating<br /><ul><li>Superhydrophobiccoating “lotusleafcoatings” (USA)</li></ul>“Basedonamorphoussilica and a customengineeredpolymer”<br />“Abrasion resistance testing show only a reduction in contact angle by 10 to 20% in worst cases” <br /><ul><li>Test samples onglass</li></ul>Testedby Sirris, Smart CoatingApplication Lab <br />within CO project – multifunctionalcoatingswithnano and hybridmaterials<br />
  • 21. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be <br />19<br />Superhydrophobic, self-cleaningcoatingsA commercial coating: testing<br />Water contact angle<br />Water sliding angle<br />Water contact angle and sliding angleafterabrasionwithcrocktest<br />Taber linear abrasion with crock adapter kit, cotton cloth<br />Dataphysics contact angle measuring instrument with tilting table<br />Tested by Sirris, Smart Coating Application Lab <br />within CO project – multifunctional coatings with nano and hybrid materials<br />
  • 22. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />20<br />Superhydrophobic, self-cleaningcoatingsA commercial coating: test<br /><ul><li>Contact angle (beforeabrasion) > 150°
  • 23. Sliding angle (beforeabrasion) with 5 µl droplet: 30°
  • 24. Best coating of 5 tested
  • 25. But: strong decrease of contact angle and increase of sliding angle after abrasion: the surface is very abrasion sensitive
  • 26. Applicableonly in “abrasionlimited” environment</li></ul>Abrasion with taber linear abraser with crock adapter kit, weight 350 g, cotton cloth<br />1 cycle = 2 movementson sample <br />Testedby Sirris, Smart CoatingApplication Lab <br />within CO project – multifunctionalcoatingswithnano and hybridmaterials<br />
  • 27. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />21<br />Superhydrophobic, self-cleaning coatingsresearch @ Smart Coating Application Lab Sirris<br />Solvent<br />Adhesive sol<br />Nanoparticles SiO2<br />Micron particles SiO2<br />Nanoparticles Al2O3<br />Research doneby Sirris, Smart CoatingApplication Lab <br />within CO project – multifunctionalcoatingswithnano and hybridmaterials<br />
  • 28. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />22<br />Superhydrophobic, self-cleaning coatingsresearch @ Smart Coating Application Lab Sirris<br />Coatingfromnanoparticles in solvent<br />silica<br />Abrasionresistancebetteronmicrostructuredglass<br />Research done by Sirris, Smart Coating Application Lab <br />within CO project – multifunctional coatings with nano and hybrid materials<br />
  • 29. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />23<br />Superhydrophobic, self-cleaning coatingsresearch @ Smart Coating Application Lab Sirris<br />Coatingfromnanoparticles + adhesive sol<br />onsandblastedglass<br />Silica + alumina<br />nanoparticles<br />Superhydrophobicsurface<br />Abrasionresistancebetterwithadhesive sol and/ormicrostructuredglass<br />Research done by Sirris, Smart Coating Application Lab <br />within CO project – multifunctional coatings with nano and hybrid materials<br />
  • 30. Superhydrophobic, self-cleaning coatingsConclusions<br />Superhydrophobiccoatings: veryappealingwithmuchpromiseforself-cleaning and otherapplications (e.g.anti-icing)<br />Manypreparationmethods are reported in literature<br />Relatively few industrialapplications have resultedfrom the Lotus effect up to now<br />Reason: abrasionproblems<br />Solutions are available at R&D stage <br />Other issues:<br />Transparency of a roughsurface<br />A superhydrophobicsurface is generallynot (super)oleophobic<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />24<br />
  • 31. Photocatalytic, self-cleaningcoatings<br />Photocatalytic: <br />Organic, oxidizable and microbialcontaminants are degradedbylighton a suitablecatalyst<br />Superhydrophilic: <br />water droplets have a very low contact angle – nodropletsbut a water film is formedon a superhydrophilicsurface<br />Self-cleaning: <br />water wets the surfacecompletely and water film takesalong the degradeddirt<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />25<br />
  • 32. Photocatalytic, self-cleaningcoatingsPhotocatalysis<br /> Titanium dioxide:<br />Amorphous, anatase, rutile, brookite<br />Anatase and rutile are photocatalyticallyactive (rutileloweractivity)<br />Band gap 3.2 ev = 380 nm (UV)<br />Anatase most commonlyusedphotocatalyst<br />cheap, non-toxic, easy to produce, chemically and biologically inert<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />26<br />Withphotonenergy > bandgap<br />semiconductor<br />
  • 33. Photocatalytic, self-cleaning coatings<br />Variousways to manufacturetitaniaphotocatalyticcoatings:<br />CVD, sol-gel, precipitation, hydro/solvothermalsynthesis<br />“paintlike” layers: stabledispersions of titania in binders<br />Stabledispersions of titania are requiredwithadditivessuitable to incorporate in paint<br />Binder must beresistant to photoactiveattackby the reactiveradicals<br />The particleson the paintsurface must bereadilyaccessible<br />TiO2photocatalytic surfaces are commerciallyavailable and have been used in variousapplications (Japan, Europe)<br />water and air purification<br />self-cleaningglass, concrete products, coatings<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />27<br />
  • 34. Decoloration of dye<br />Methylene blue (standard), Methyl orange, Rhodamine …<br />In solution<br />As stain<br />Photo-oxidation of organic film<br />Stearic acid (standardforthin films), Palmitic acid<br />Degradation of gas<br />Ethanol, Propanol<br />Measurement of rate of hydroxyl radical generation<br />by using specific fluorescent probes<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />28<br />Photocatalytic, self-cleaning coatingsestablised methods to evaluate photocatalytic effect<br />
  • 35. Photocatalytic, self-cleaning coatingsdegradation of methylene blue test<br />ISO standard test 10678:2010<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />29<br /><ul><li>2 identicalcoatingshaving the sameactivesurface
  • 36. In methylene blue solution 10-5M
  • 37. One is stored in the dark – one is exposed to a defineddose of UV light
  • 38. The concentration of methylene blue is measured at specificintervalsduringirradiation
  • 39. Sample 1 shows a decrease in MB concentrationdue to adsorption
  • 40. Sample 2 shows a decrease in MB concentrationdue to adsorption and photocatalyticdegradation
  • 41. Difference = measurefor the photocatalyticactivity of the coating</li></li></ul><li>20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />30<br />Photocatalytic, self-cleaning coatingsdegradation of methylene blue test<br />commercial coating<br />0 2 4 6 h<br />Decrease of absorbance/concentration of methylene blue afterUV-irradiation in presence of coating<br />
  • 42. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />31<br />Photocatalytic, self-cleaning coatingsdegradation of methylene blue test<br />P25 coating<br />MB 10-5M 2 h 4 h 6h <br />Decrease of absorbance/concentration of methylene blue afterUV-irradiation in presence of coating<br />
  • 43. Photocatalyticcoatings = mature product field <br />Titania is UV activated<br />Inside room use?<br />Doping of TiO2 to have a photocatalytic effect in VIS<br />Maintaining of the photocatalytic effect?<br />Theoretically TiO2maintainsitsactivity<br />But: deactivation of photocatalystbyenvironmental factors <br />e.g. volatilesilicon-containingcompounds (fromsealants, cleaningagents, shampoos, printinginksadditives, …) can cover the activesurface<br />Inorganiccontaminantscannotberemovedphotocatalytically<br />Onorganicsubstrates the reactiveradicalscanalsoattack the substrate and anintermediatelayer is required<br />20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />32<br />Photocatalytic, self-cleaningcoatingsConclusions<br />
  • 44. 20-5-2011<br />© Sirris | www.sirris.be | info@sirris.be |<br />33<br />State of the art of easy-to-clean and self-cleaningcoatings<br />Thanks to <br /> IWT forfinancial support<br /> Joey Bosmans for the experimentalwork<br />youforyourattention<br />Questions ?<br />heidi.vandenrul@sirris.be<br />

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