Lesson: Exploring the Lotus Effect

Quick Look

Grade Level: 12 (10-12)

Time Required: 30 minutes

Lesson Dependency:

Subject Areas: Biology, Chemistry, Life Science, Physical Science, Physics

Two photos show bead-shaped water droplets, one on a lotus leaf (left) and one on a piece of blue cloth (right).
The superhydrophobic properties of the lotus leaf have been synthetically reproduced as a fabric treatment used for water- and stain-repellent clothing and other applications. A water droplet on these surfaces "floats" on a cushion of air and easily rolls off the material.
copyright
Copyright © (left) Michael Gasperl, Wikimedia Commons and (right) 2010 Jean Stave http://commons.wikimedia.org/wiki/File:Tropaeolum-majus%28Lotus-oben%29.jpg

Summary

Students test and observe the "self-cleaning" lotus effect using a lotus leaf and cloth treated with a synthetic lotus-like superhydrophobic coating. They also observe the Wenzel and Cassie Baxter wetting states by creating and manipulating condensation droplets on the leaf surface. They consider the real-life engineering applications for these amazing water-repellent and self-cleaning properties.
This engineering curriculum aligns to Next Generation Science Standards (NGSS).

Engineering Connection

Inspired by the lotus leaf, a revolution in self-cleaning surfaces is underway. Many researchers and engineers are developing synthetic superhydrophobic materials and products that mimic the lotus leaf's extremely water-repellent and self-cleaning properties. These materials and textiles would enable skyscraper windows and walls to never need human cleaning, not to mention an unlimited number of other objects: tents and awnings, painted houses, vehicle undercarriages, etc. Already in everyday use is clothing fabric that repels ketchup, mustard, red wine and coffee. Extreme water-shedding materials have the potential for applications in energy and medicine. Some technologists are developing self-deodorizing and disinfectant surfaces for bathrooms and hospitals, as well as similar technologies for keeping surfaces from fogging. Some technologies use the "lotus effect," whereas others employ the opposite property — superhydrophilicity. Future products may combine the two properties or use substances that can be switched back and forth to control the flow of liquids through microfluidic components.

Learning Objectives

After this activity, students should be able to:

  • Describe the behavior of water on superhydrophobic surfaces.
  • Define "lotus effect" and describe its water-repellent and self-cleaning properties.
  • Explore how damage to Nano-TexTM cloth affects its "lotus effect" properties.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS Performance Expectation

HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. (Grades 9 - 12)

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This lesson focuses on the following Three Dimensional Learning aspects of NGSS:
Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts
Communicate scientific and technical information (e.g. about the process of development and the design and performance of a proposed process or system) in multiple formats (including orally, graphically, textually, and mathematically).

Alignment agreement:

Attraction and repulsion between electric charges at the atomic scale explain the structure, properties, and transformations of matter, as well as the contact forces between material objects.

Alignment agreement:

Investigating or designing new systems or structures requires a detailed examination of the properties of different materials, the structures of different components, and connections of components to reveal its function and/or solve a problem.

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  • Knowledge gained from other fields of study has a direct effect on the development of technological products and systems. (Grades 6 - 8) More Details

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  • Chemical technologies provide a means for humans to alter or modify materials and to produce chemical products. (Grades 9 - 12) More Details

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  • Humans devise technologies to reduce the negative consequences of other technologies. (Grades 9 - 12) More Details

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  • Compare physical and chemical properties of various types of matter. (Grades 9 - 12) More Details

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Worksheets and Attachments

Visit [www.teachengineering.org/lessons/view/duk_surfacetensionunit_act4] to print or download.

More Curriculum Like This

Superhydrophobicity — The Lotus Effect

Students are introduced to superhydrophobic surfaces and the "lotus effect." Students learn how plants create and use superhydrophobic surfaces in nature and how engineers have created human-made products that mimic the properties of these natural surfaces.

Surface Tension

Through hands-on activities, students learn how the combination of adhesive forces and cohesive forces cause capillary motion. They study different effects of capillary motion and use capillary motion to measure surface tension. Students explore the phenomena of wetting and hydrophobic and hydrophil...

preview of 'Surface Tension' Unit
High School Unit
Wetting and Contact Angle

Students are presented with the concepts of wetting and contact angle. They are also introduced to the distinction between hydrophobic and hydrophilic surfaces. Students observe how different surfaces are used to maintain visibility under different conditions.

preview of 'Wetting and Contact Angle' Lesson
High School Lesson

Introduction/Motivation

(Begin with the associated lesson, and its Introduction/Motivation talk, to set the stage for conducting this activity with students. The lesson provides photos, short videos and background information on superhydrophobic surfaces, including condensation and the Wenzel and Cassie Baxter wetting states, and real-life engineering applications.)

How many of you have ever spilled something on yourself at lunch? If you do that at school, you just have to make do with a stain on your shirt until you get home. (Students probably have a few good stories to share about this.) What if you could make your clothes out of something that could not stain? ...So whatever you spilled on yourself would just run right off and leave you clean and dry? Well today we are going to do just that.

Lotus plants (as well as some other plants) have a special surface on their leaves that allows water to flow right off of it without sticking, and take any dirt on the leaf off with it. This is an example of biomimicry — which is when we study a process or object in nature and figure out how to "mimic" its effect or properties with a synthetic product. Right now, scientists and engineers are learning how to copy the superhydrophobicity of lotus leaves and apply it to everything from clothing to outdoor paints.

(At this point, conduct the pre-lab questions activity as described in the Assessment section.)

In this lab, you will observe the superhydrophobicity phenomenon on a natural item and a synthetic material designed to mimic nature.

Assessment

Pre-Activity Assessment

Pre-Lab Questions: After the introductory talk, but before conducting the lab, have students write on note cards their answers to the following questions.

  1. How are hydrophobic and hydrophilic different?
  2. What is the lotus effect?
  3. How is the lotus flower's importance in Asian religions related to this effect?

Activity Embedded Assessment

Worksheet Observations: Circulate throughout the classroom, checking each student's observations, as recorded on the The Lotus Effect Worksheet table. Ask questions about student answers to gauge their comprehension, and help them gain clearer pictures of the concepts in the lab and their extensions to real-world engineering problems and products (such as self-cleaning, stain-repellent garments).

Post-Activity Assessment

Concluding Questions: Assign students to write answers (on separate sheets of paper), to the concluding questions of the lab.

  • The Nano-Tex™ cloth is an example of biomimicry. The self-cleaning properties of the lotus plant were studied and a synthetic version of its surface was developed. When this treatment is added to fabric, the garments repel dirt and stains just like the lotus plant. What other products could benefit from a self-cleaning surface? Include at least three examples and explain how the self-cleaning ability would be especially useful for each application.
  • Water droplets formed from dew or other condensation may act differently on supherhydrophobic surfaces than water poured or dropped on these surfaces. Does this limit the applications for self-cleaning surfaces? How could some products be modified to help self-cleaning products work even for water condensation? Write at least one paragraph to answer each question.

Lesson Extension Activities

Use plants and fabrics that are not superhydrophobic to show how water behaves differently on them.

References

de Gennes, Pierre-Gilles, et al. Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves. New York, NY: Springer, 2004.

Forbes, Peter. "Self-Cleaning Materials: Lotus Leaf-Inspired Nanotechnology." Published July 30, 2008. Scientific American. Accessed July 2010. http://www.scientificamerican.com/article/self-cleaning-materials/

Zenner, Greta M., et al. "Lotus Leaf Effect." University of Wisconsin-Madison Materials Research, Science and Engineering Center (MRSEC) Interdisciplinary Education Group, Nanoscale Informal Science Education Network. Accessed July 2010. http://mrsec.wisc.edu/Edetc/EExpo/surfaces/NanoSurfaces_ProgramGuide.pdf

Copyright

© 2013 by Regents of the University of Colorado; original © 2011 Duke University

Contributors

Jean Stave, Durham Public Schools, NC; Chuan-Hua Chen, Mechanical Engineering and Material Science, Pratt School of Engineering

Supporting Program

NSF CAREER Award and RET Program, Mechanical Engineering and Material Science, Pratt School of Engineering, Duke University

Acknowledgements

This digital library content was developed under an NSF CAREER Award (CBET- 08-46705) and an RET supplement (CBET-10-09869). However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: February 13, 2020

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