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Experiment with superhidrophobic materials

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In this experiment you will analyse some innovative materials that are highly water repellent, stainless and require less cleaning thanks to their surface nano-engineering. Those materials have been …

In this experiment you will analyse some innovative materials that are highly water repellent, stainless and require less cleaning thanks to their surface nano-engineering. Those materials have been developed using nature as an inspiration, since some plant leaves have exceptional properties due to their surface composition.

The property you will analyse is the superhydrophobic effect found in some leaves, such as the lotus leaf. The effect is due to interplay of surface chemistry and surface topography at the micro- and nano-level.

To download the protocol and background information, as well as to watch some videos on the experiment, visit: www.nanoyou.eu

Translations to several languages are also availabe in the NANOYOU website.

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  • 1. Teachers Training Kit in Nanotechnologies Experiment Module A comprehensive training kit for teachers Experiment D Luisa Filipponi, iNANO, Aarhus University This document has been created in the context of the NANOYOU project. (WP4, Task 4.1) All information is provided “as is” and no guarantee or warranty is given that the information is fit for any particular purpose. The user thereof uses the information at its sole risk and liability. The document reflects solely the views of its authors. The European Commission is not liable for any use that may be made of the information contained therein.
  • 2. Before you use this presentation This Power Point Presentation is part of the Experiment Module of the NANOYOU Teachers Training Kit in Nanotechnologies. MATERIAL INCLUDED IN THIS EXPERIMENT D PACKAGE : For teacher: EXPERIMENT D-TEACHER DOCUMENT NANOYOU VIDEO 3 & 4- LOTUS EFFECT For students * : EXPERIMENT D-STUDENT BACKGROUND READING EXPERIMENT D-STUDENT LABORATORY WORKSHEET   LEVEL OF EXPERIMENT : Medium *These documents are available for the 11-13 and 14-18 age group in different languages DOCUMENTS CAN BE FOUND AT WWW.NANOYOU.EU This NANOYOU documents is distributed with Creative Commons Non-Commercial Share Alike Attribution, except where indicated differently. Please not that some images contained in this PPT are copyright protected, and to re-use them outside this document requires permission from original copyright holder. See slide 14 for details. DISCLAIMER : The experiments described in the following training kit use chemicals which need to be used according to MSDS specifications and according to specific school safety rules. Personal protection must be taken as indicated. As with all chemicals, use precautions. Solids should not be inhaled and contact with skin, eyes or clothing should be avoided. Wash hands thoroughly after handling. Dispose as indicated. All experiments must be conducted in the presence of an educator trained for science teaching. All experiments will be carried out at your own risk. Aarhus University (iNANO) and the entire NANOYOU consortium assume no liability for damage or consequential losses sustained as a result of the carrying out of the experiments described.
  • 3. EXPERIMENT D AGE LEVEL 11-13 YEARS & 14-18 YEARS
    • Superhydrophobic Materials
  • 4. Experiment D- Superhydrophobic Materials Applications of Nanotechnologies: Environment
    • Nano-structured surfaces can have peculiar wetting properties
    • Interplay of chemistry and nano-topography: superhydrophobic effect
    • Superhydrophobicity is found in Nature (Lotus Effect ® )
    • Scientists are engineering materials to be superhydrophobic and require less cleaning
    • Applications
    • Solar panels
    • Textiles
    • Coatings
  • 5. Experiment D- Superhydrophobic Materials Applications of Nanotechnologies: Environment
    • Surfaces can be classified depending on their contact angle as illustrated in the Table.
    • Contact angle is a measurement of the interaction energy between the surface and the liquid .
    • There are some natural materials that have superhydrophobic properties, such as the Lotus leaf, and the legs of the water strider
    • Another plant that has superhydrophobic leaves is Nasturtium
    Contact angle value Type of surface Example ~0 Super-hydrophilic UV irradiated TiO 2 > 30 Hydrophilic Glass 30-90 Intermediate* Aluminium 90-140 Hydrophobic Plastic 140+ Superhydrophobic Lotus leaf
  • 6. The Lotus effect
    • The Lotus plant ( Nelumbo Nucifera ) is a native Asian plant which has the distinct property of having its leaves particularly clean even if its natural habitat is muddy.
    • The leaves of the Lotus plant have the outstanding characteristic of totally repelling water because they are superhydrophobic.
    • Droplets of water on the lotus leaf appear spherical like beads .
    • When you splash the Lotus leaf with water, water rolls off the leaf, and in doing so drags dirt away.
    • The result is that the Lotus leaf is dry and clean .
    • The surface of the Lotus leaf self-cleans . This is called the Lotus Effect ® .
    • The same effect is seen in Nasturtium .
    • Watch Video 3_ Lotus Effect ® (Part 1)
  • 7. How is this “nano”?
    • Detailed SEM analysis of leaves that display the Lotus-effect has revealed the presence of wax nanocrystals on the leaf surface.
    • These crystals provide a water-repellent layer, which is enhanced by the roughness of the surface, making it a superhydrophobic surface, with a contact angle of about 150.
    • Water droplets interfacing with the leaf are in contact with a large fraction of air . This forces the water to bead and roll off . The image below shows the progressive magnification of a Nasturium leaf.
    nanocrystals few tens of nanometres Figure 1. Micro and nanostructure of a nasturtium leaf (Image credits: see slide 16) A B C D
  • 8. Self-cleaning: how does it work?
    • The consequence is that water droplets roll off the leaf surface and in doing so it drag dirt away from it . This effect, called “self-cleaning” renders the Lotus leaf clean and resistant to dirt.
    •   Contaminants on the surface rest on the tips of the rough surface. When a water droplet rolls over the contaminant, the droplet removes the particle from the surface of the leaf.
    Figure 2. (Top) Diagram summarising the connection between roughening and self-cleaning: in the top image a droplet of water removes dirt from a surface thanks to the Lotus effect (bottom): Graphical representation of contaminants and water droplets on a lotus leaf (Image credits: see slide 16)
  • 9. Lotus-inspired innovative materials
    • The Lotus effect has been an inspiration for several superhydrophobic innovative materials , such as paints, coatings, and textiles.
    • Some applications are:
      • Environmentally friendly coatings and textiles that are dirt repellent and require less cleaning (façade paints, textiles, sanitary coatings etc.).
      • Improving the performance of solar cells (energy application) . One of the problems with this technology is that they are kept outdoors and therefore prone to become very dirt. This layer of dirt “masks” the catalytic areas of the solar cells and therefore reduces its efficiency and life-time. Coating the solar panel with a superhydrophobic coating keeps the panel considerably cleaner. Because of the nano-surface roughness, the coating is transparent to UV light, a necessity for these types of devices. The superhydrophobic coating is also durable, which further improves the solar panel life-time.
  • 10. Lotus-inspired innovative materials
    • In this experiment students learn the properties of two materials that are engineered to mimic the Lotus Effect®
    • Nano-Tex ®
    • Porous silicon
  • 11. Experiment D- Superhydrophobic Materials Materials expored in this experiment Nano-Tex ® : this is a textile that is engineered to mimic the Lotus leaf. In the experiment students compare Nano-Tex to a real lotus leaf. Stain e spill resistance is tested. How does it work ? The fibres of the textile contain a large number of very small “pins”, or “whiskers” on their surface. Therefore the fabric does not contain a surface coating (which could be removed by washing, or sweating), but rather the fibres are nano-engineered. Figure 3. Nano-Tex ® Resist Spills fabric (Image credits: see slide 16) NANO-TEX LOTUS 1
  • 12. Experiment D- Superhydrophobic Materials Materials expored in this experiment Porous silicon (iNANO/Lund University research) : this is a modified version of silicon, which is naturally hydrophilic. Students cannot see a real piece of porous silicon; therefore they should watch the NANOYOU Video 4- Lotus Effect ® -Part 2) How does it work ? Porous silicon contains many “pins”. The porosity and spacing of this fine structure determines the wetting properties of the material . The material shown in the video has a contact angle of 167. The superhydrophobic effect results from the peculiar micro/nanotexture of this surface. Figure 4. Contact angle of different porous silicon surfaces (Image credits: see slide 16) 2 Sample Contact Angle (°) A 64 B 110 C 155 D 167
  • 13. Experiment D - Protocol
    • Understanding surface properties: hydrophilic and hydrophobic . Student get different materials (plastic, aluminium sheet, glass etc), and test their surface properties. Images of contact angles provided.
    • Analysis of natural nanomaterials: the Lotus leaf (or Nasturtium) . Collect different plant leaves and test their wetting properties. Lotus or nasturtium should be tested (NB. Nasturtium can be grown easily from seeds). NANOYOU Video 3
    • Innovative materials engineered to mimic the Lotus effect . Show NANOYOU Video 4
  • 14. Experiment D - Protocol
    • Analysis of Nano-Tex ® . Students should analyse and test this innovative fabric:
      • Compare it with Lotus or Nasturtium leaf
      • Compare it with cotton fabric and semi-synthetic fabrics and test it
        • For spill resistance against coke, vinegar, oil, coffee…you name it!
        • Test it for stain resistance against ketchup, mayonnaise, mustard, permanent marker
        • Test it against organic soil
        • Test the fabric resistance using sand paper
  • 15. Running the experiment D in class
    • 1. Start with a general discussion on surface properties :
    • - What property can be used to compare different surfaces?
    • How does water interact with different surfaces?
    • 2. Introduce the concept hydrophobicity and hydrophilicity
    • - Give definition and some examples
    • - How can one make a hydrophilic surface (such as glass), hydrophobic? Students/teacher should discuss about coatings and their effect on surfaces
    • Define the contact angle as a surface characterization method (depending on the level of the class, this can be less or more advanced; for an advanced class, refer to Appendix 1 )
    • 3. Test different surfaces . Different materials should be tested for their wetting behaviour. The details are given in the next session. Materials that can be tested (from more hydrophilic to more hydrophobic) are: glass, coated wood, aluminium, plastic, paraffilm.
    • - Ask the students to make a scale of hydrophobicity based on what they can see. Use the images provided in this kit (at the end of the Student Laboratory Worksheet for Experiment D).
  • 16. Running the experiment D in class
    • 4. Test of a superhydrophobic surface: the Lotus leaf . If available a Lotus leaf should be collected at a botanical garden . If not available, use Nasturtium. Watch the NANOYOU Video 3
    • - Discuss the Lotus effect and how this is inspirational for new materials.
    • - Watch the NANOYOU Video 4 showing the Lotus effect on a real Lotus plant and the same effect on an artificially made surface (porous silicon, iNANO research labs)
    • Let the students observe the effect on a real leaf and compare with other leaves
    • 5. Test a superhydrophobic textile
    • - Test the Nano-Tex® textile for spills of liquids, solids, dirt etc.
    •  
    • 6. Discuss applications and implications
    • The Nano-Tex® is an example of a practical application of nanotechnologies. Ask the students to think of other application where the super-hydrophobic effect might be useful.
    • Highlight that Nano-Tex ® is not magic (e.g., it cannot resist permanent marker stains).
  • 17. Images credits Figure 1 : Close-up views at progressive magnification of a nasturtium leaf revealing the presence of surface nanocrystals (image on the far right). (Image credit (A): A. Snyder, Exploratorium; (B, C): A. Marshall, Stanford University, (D): A. Otten and S. Herminghaus, Göttingen, Germany, all images are material of the NISE Network, www.nisenet.org, reprinted under NISE network terms and conditions.) Figure 2 : (Top) Diagram summarising the connection between roughening and self-cleaning: in the top image a droplet of water removes dirt from a surface thanks to the Lotus effect (bottom): Graphical representation of contaminants and water droplets on a lotus leaf (Image credit: by William Thielike, Wiki commons, Creative Commons ShareAlike 3.0.) Figure 3 : (Left) Liquid staining on a Nano-Tex ® fabric. (Image credit: image courtesy of Nano-Tex, Inc., Copyright Nano-Tex. Inc.); (right) High resolution images of the Nano-Tex® fabric (Images courtesy of Nano-Tex, Inc., Copyright Nano-Tex. Inc). (Right): contact angle images of water droplets on Nano-Tex fabric and Lotus leaf (Images: iNANO; Aarhus University, Creative Commons Attribution ShareAlike 3.0) . Figure 4: SEM Images of four different samples showing a change in contact angle from hydrophilic (A) to hydrophobic and superhydrophobic. Samples B-D are made of porous silicon, sample D is the one with the higher contact angle (Image reprinted with permission from: A. Ressine, “Development of protein microarray chip technology”, PhD thesis 2005)