Why can’t my pants do that?
Teacher Notes
Concepts: (1) Nanoscientists manipulate matter at the molecular level to make
improvements to products we use. [6.1.2.1.1] (2) Safety issues surround these
products. Because of their small size, nano particles pass through some of our
safety filters and body tissues. [6.1.2.1.2-4] (3) Students need the skills and
vocabulary to investigate products, their safety concerns and consequence of
using these products. [4.1.2.1.1, 4.1.2.2.1]
Questions to get students thinking before the activity or to use after:
•Where do ideas to make or improve products come from?
•What does hydrophobic mean? What does hydrophilic mean?
•What products could benefit from a hydrophobic or hydrophilic coating?
•What would it be like to have self cleaning windows?
•What would happen if you hold a head of broccoli on your lap and drip
several eyedroppers of water on it?
•What plants show the Lotus effect (or a hydrophobic)? Design an
experiment to find out. Share your results with your classmates. [5.1.1.2.1-3]
Materials per group:
Part 1
head of broccoli (each student needs one floweret)
water
eyedroppers
pepper
clean up materials
Part 2
a pair of water repelling pants (Dockers is one brand)
a regular pair of pants and a spray bottle of water (If you don’t have a pair of
pants like this, one of your students may be able to bring in a pair from home.)
(You can watch this video: https://www.youtube.com/watch?
v=a2ZDewL6seg&noredirect=1)
Procedure: There is nothing special about the procedure.
Observations/Results: Students will find it fascinating that the water beads up on the
broccoli instead of running through the floweret. The water will also pick up the
pepper and is in a way, self-cleaning. The same thing happens to the pants.
Water or any spill simply runs off the pants. They don’t stain.
Summing Up:
1.The word hydrophobic is based on the root word phobia and the prefix hydro-.
Look up the definitions of hydro- and phobia. Now combine the two definitions
to describe the term hydrophobic.
hydro- means water and phobia means fear of. Hydrophobic means fear of water.
2.Which pair of pants could be described as hydrophobic? Explain.
The one that sheds the water could be called hydrophobic or “afraid” of water.
3.Describe how what you observed with the broccoli was used to improve
clothing.
Both the broccoli and the pants shed water the same way.
4.Describe another use for a hydrophobic coating.
Answers will vary.
5.Do all leaves exhibit the property of hydrophobicity? Design and carry out an
experiment to answer the question. Describe your experiment and the results in
the space below.
Answers will vary but students should describe collecting and testing a variety of
leaves. Variables should be controlled and results should be described.
After doing this activity, have your students read the article What is biomimicry? Many
ideas for new products come from nature! This concept is called biomimicry. Your
students will enjoy investigating this topic. When reading the article students will need
some Magic Sand1 , water and a small piece of a disposable diaper.
Questions:
1.Frank Anthony2 makes swimwear using nanotechnology. They apply a
hydrophobic coating to the fabric. What problems would this solve?
Answers will vary but may include that you won’t feel cold when you get out of the
water, you can pack them in your bag right away and they won’t get sand stuck to
them when you sit on the beach.
2.Would you prefer a hydrophobic or hydrophilic coating on a cellphone?
Explain your choice.
Most will say a hydrophobic coating to shed rain water or help if accidentally
dropped in water.
3.List something you observe in nature that could be adapted to solve a
problem. Explain your idea.
Answers will vary with the background and creativity of your students.
4.Large particles of titanium dioxide (TiO2) block UV rays from the sun. They are
white in color and are not absorbed through the skin. Many sunscreens currently
use nano particles of TiO2. Nano TiO2 also blocks UV rays but they are invisible!
These sun screens rub easily into the skin without leaving a white residue. What
safety issue should be investigated?
Are nano particles of titanium dioxide absorbed by the skin? or If they are
absorbed, are they harmful to us?
Magic sand is available at http://www.stevespanglerscience.com/magic-sand.html and some craft
and gift stores. One use of this product is to clean up oil spills. It is also used to surround pipes in cold
climates. Why? Have your students do some research.
1
2
https://www.kickstarter.com
Why can’t my pants do that?
Purpose: The purpose of this activity is to learn where ideas may come from to improve
a product.
Materials: Part 1 - broccoli, cup of water, eyedropper, pepper, paper towels
Part 2 - sample pants, water in a spray bottle, dictionary
Procedure Part 1:
1.Look at the broccoli. What do you think will
happen if several drops of water are put on
top of the broccoli? Write your prediction
below.
2.Put several drops of water on the broccoli. Make careful observations.
Describe what happens to the drops. Draw a picture of what the drops look like.
3.Tip the broccoli to the side. What happens to the water?
4.Blot the broccoli with a paper towel. Sprinkle the dry broccoli with pepper. Put
more drops of water on the “dirty” broccoli. Tip it to the side. Describe what
happens to the pepper. Explain how broccoli is “self cleaning.”
Procedure Part 2:
1.How would you like to have windows that self cleaned like the broccoli did?
What would happen to self cleaning windows every time it rained?
2.Would you like it if your dress pants could shed a spill instead of soaking in and
staining your pants?
3.There are two sample pairs of pants at the front of the room. Spray each of
them with water. Make careful observations. Describe what you observed.
Questions:
1.The word hydrophobic is based on the root word phobia and the prefix hydro-.
Look up the definitions of hydro- and phobia. Now combine the two definitions
to describe the term hydrophobic.
2.Which pair of pants could be described as hydrophobic? Explain.
3.Describe how what you observed with the broccoli was used to improve
clothing.
4.Describe another use for a hydrophobic coating.
5.Do all leaves exhibit the property of hydrophobicity? Design and carry out an
experiment to answer the question. Describe your experiment and the results in
the space below.
What is biomimicry?
Did you ever wonder where the idea for velcro came from? Have you
ever had to remove burrs from your clothes? Now you know where the
idea came from! George de Mestral invented the hook-and-loop fastener
in 1948. The idea came to him while removing burrs after a hike. The
invention of velcro is an example of biomimicry or the imitation of some
system in nature used to solve a human problem.
When water is put on broccoli, kale or even tulip leaves, it beads up and
runs off. The water even takes dirt with it. This is called the lotus effect.
Lotus leaves are very large leaves. The weight of accumulated rain water
would weigh down and break the stems of these plants. Dirt and bacteria
that might be left in the accumulated water could decay and cause the
leaves to rot. Because of the hydrophobic surface of the lotus leaves,
water and dirt simply run off leaving healthy plants. Hydrophobicity is an
advantage for lotus plants.
Hydrophobic coatings on clothing, windows, shoes or walls would make
them self cleaning! This is another example of biomimicry. Nanotechnologists used the idea of the lotus effect to develop coatings that
shed water and can even take dirt away at the same time. These
coatings contain molecules that are hydrophobic - they do not allow
water to stick to surfaces. Maybe that’s where the idea for the Impervius
spell in Harry Potter and the Prisoner of Azkaban came from!
The Rubbermaid® Company makes a plunger called The Clean & Dry™
plunger. This plunger immediately sheds bacteria laden water after use; it
comes up dry! No water or bacteria gets dripped around your bathroom.
Put some water drops on Magic Sand or better yet, put some Magic Sand
in a glass of water! What happens? Magic Sand is engineered with a
hydrophobic coating.
Other materials can be manipulated at the molecular level to have
different properties. Put several drops of water on a small piece of a
disposable diaper. Add some more drops. How many drops of water can
be taken in by the small piece? How much water could be taken in by a
whole diaper? Would you call the material in a diaper hydrophobic?
The stenocara beetle takes advantage of both hydrophobic and
hydrophilic materials. “The insect’s back and wings have hydrophilic
bumps that encourage condensation from fog; these are surrounded by
hydrophobic troughs, which collect the resulting droplets and funnel them
toward the beetle’s mouth-allowing it to survive in one of Earth’s driest
places.”3
Nanoscientists have engineered nano-sized ceramic particles that are
used to coat everything from pans to curling irons. These very small nano
particles make very smooth, nonstick surfaces. Would you eat food
cooked in a nano ceramic coated pan? That’s a really good question.
Scientists have not settled the debate on the safety of nano materials. For
one thing, there have not been many toxicology studies about nano
particles. Secondly, because the particles are so small (30 to 70 nm)
scientists think they can become imbedded in human tissue and even
enter cells. The issue of safety and nano particles will not be settled soon.
Questions:
1.Frank Anthony 4 makes swimwear using nanotechnology. They
apply a hydrophobic coating to the fabric. What problems would
this solve?
2.Would you prefer a hydrophobic or hydrophilic coating on a
cellphone? Explain your choice.
3.List something you observe in nature that could be adapted to
solve a problem. Explain your idea.
4.Large particles of titanium dioxide (TiO2) block UV rays from the
sun. They are white in color and are not absorbed through the skin.
Many sunscreens currently use nano particles of TiO2. Nano TiO2 also
blocks UV rays but they are invisible! These sun screens rub easily into
the skin without leaving a white residue. What safety issue should be
investigated?
3
http://newsoffice.mit.edu
4
https://www.kickstarter.com