by Kathleen Carrado Gregar, PhD, Argonne National Labs |
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Kids, do your parents or other adult friends enjoy coffee? Here
is something to try with their bag of vacuum-packed coffee
grounds. Before opening a new bag, notice that it is rather
solid. Cut off a corner of the bag and what happens? The
coffee grounds will become instantly fluid-like. Wikipedia
tells us that this phenomenon is called “jamming”, which is the
physical process by which some materials, such as granular materials,
glasses, foams, and other complex fluids, become rigid with increasing
density.
The so-called “jamming transition” happens when density is increased1.
The crowding of particles makes the aggregate material behave like a
solid. The density at which systems jam is determined by many factors
including shape, deformability, friction, and dispersity. Cutting
the corner off the coffee bag instantly decreases the density by
allowing air to flow inside.
Granular materials that readily change between fluid and solid states are the basis for a new universal "gripper" technology recently invented by chemists at the University of Chicago. Most robots are designed with grippers that resemble the human hand and are extremely complex. Such robots need hinges and motors to control movement as well as image-processing systems so the gripper knows when to grab an object and sensors so the gripper knows not to crush it.
The new idea is to design a bag-like gripper that, like the bag of coffee grounds, can readily change between fluid and rigid states. This allows the gripper to conform to the shape of the object to be lifted and then to be made rigid in order to lift and hold that object. The inventors wanted a low-cost, adaptable solution, something that would enable the gripper material, itself, to make decisions.
What the inventors found most satisfying about this project was starting from a basic physics idea (the jamming transition), extending it in a new direction that has real-world applications, and finally translating it into a working prototype. Their next goal is to see the universal gripper technology adopted as an alternative or supplement to the hand-based model for robotic grippers.
** The jamming transition has been proposed as a new type of phase transition, with similarities to a glass transition but very different from the formation of crystalline solids.
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References:
1. http://en.wikipedia.org/wiki/Jamming_%28physics%29
2. Prof. Heinrich Jaeger, the William J. Friedman and Alicia
Townsend Professor of Physics at the University of Chicago: http://tech.uchicago.edu/features/20100816_jaeger/
Kids, would you like to see DNA extracted from your very own mouth? Deoxyribonucleic acid, or DNA, is present in all living things from bacteria to plants to animals. In animals, it is found in almost all cell types: muscles, reproductive cells, hair roots, and skin cells -- anything that has a nucleus. The basic procedure for extracting DNA in a laboratory is:
· Collect cells.
· Split cells open and release contents (proteins, fats and carbohydrates).
· Destroy enzymes which break apart DNA.
· Separate DNA from other cell components (proteins, fats and carbohydrates).
· Precipitate DNA.
· Resuspend DNA in solution so it can be studied.
Many of these steps can be accomplished in a simple experiment at home. You will need a bottle of clear Gatorade™, Dixie™ cups, dishwashing liquid, rubbing alcohol and a clear vial with a screwcap (20 ml is a good size).
First, chill the bottle of rubbing alcohol on ice. Pour a small squirt of dishwashing liquid into the vial and add water (1 part detergent to 3 parts water). Put 15-20 ml of Gatorade™ in your mouth and swish it around for 30 seconds, gently grinding the inside of your cheeks against your teeth. Spit this into a clean Dixie™ cup. Pour this into the vial of detergent until nearly full. Gently rock the vial back and forth for a few minutes. Do not agitate – you don’t want to make foam or bubbles. Now add a teaspoon of the chilled rubbing alcohol to the vial and let sit for a few minutes. You should see the DNA separate out as white strands.
What’s happening? The salt solution keeps the cells from lysing, or splitting open, too soon. The detergent releases DNA from the nucleus by breaking open the fatty molecules the make up the cell membranes and helps remove proteins associated with DNA. DNA doesn’t dissolve in rubbing alcohol, so it precipitates out as white strands. If you took all of the DNA from a single cell and laid it end to end, it would be almost 2 meters long!
TIPS: A 0.9% saline solution will also work (9 gm NaCl in 1 liter distilled water) but Gatorade™ tastes better; clear is best but if you can’t find it then the yellow lemon-lime should work. Powerade™ doesn’t have enough salt to work.
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References:
Elizabeth Neis and also the California Science Center at:
http://www.californiasciencecenter.org
The exact reference:
http://www.californiasciencecenter.org/Education/GroupPrograms/HomeSchool/docs/DNA.pdf
Kids, imagine rocks getting hot enough to actually melt and flow like molasses! Let’s find out how viscosity affects the way lava flows and volcanoes grow. When lava is very hot it’s thin and runny, but as it cools down it gets thicker and stickier. Temperature, along with the specific minerals contained in the melted rock, affects the way that volcanoes grow.
All you’ll need to see viscosity-in-action are two cans of molasses, 2 plates, a heatproof bowl and boiling water. First, put one unopened can of molasses in a refrigerator overnight. Open the can the next day and pour the contents onto a plate. Notice how thick the molasses is, and how it piles up to form a heap. When a liquid is thick like this it’s called “viscous”.
Next, have an adult partner boil water and pour it into the bowl. Put the other unopened can of molasses into the bowl and allow it to warm up for 30 minutes. Now open this can and pour the contents onto the other plate. Notice that the molasses is much runnier and spread quickly into a wide, flat puddle.
What does this mean for volcano shapes? Conical volcanoes grow from thick, viscous lava, together with ash and rubble, because the lava cools before running far away. Shield volcanoes have long gently sloping sides because they grow from runny lava that can travel a long way before cooling. Dome volcanoes are created from lava so viscous and cooling so quickly that it barely flows at all.
Here is some chemistry to explain the viscosity. Thick, highly viscous lava has a large amount of silicate (silicon dioxide type, SiO2) minerals. Runny lava has less silicate minerals. Instead, there are more iron and magnesium minerals; the more "ferromagnesian" the content, the less viscous the lava.
Which type of volcano do you think is responsible for the Hawaiian Islands? (Answer: shield volcanoes).
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References:
“Rock and Fossil Hunter”, a Smithsonian series book by Ben Morgan; DK Publishing, Inc. NY;
2005; page 18, “On the Lava Trail”.
Also Wikipedia at http://en.wikipedia.org/wiki/Lava
Kids, what do you think makes the vivid color of paints stay bright for years and years? Unlike paints made from plants or other sources, paints made from minerals hold their color well over time. But they can be hard to make when the minerals are rock-hard. Soft minerals, like chalk (also known as gypsum, calcium sulfate, CaSO4), are the easiest to make into paints because they’re easy to crush.
Here is how you can make your own mineral paint. Wearing a common dust mask, grind a mineral to a fine powder using a mortar and pestle. The mineral can be chalk, clay, red ochre (an iron oxide pigment found in art supply stores), or charcoal. The finer the powder is ground, the smoother the paint will be. Pour the powder into a shallow bowl and add a few drops of water; stir with the pestle until it becomes a smooth paste. A binding agent is needed to stop the paste from drying out to dust. You can use white craft glue for this, or a very clean egg yolk (separate the yolk from the white and gently roll it in a kitchen towel to clean it). Add the binding agent in about a 1:3 ratio of binder:paste, and stir with a mixing stick.
Imagine you are in prehistoric times as a cave painter using your handmade mineral paints. Use clay or red ochre for the red paint, chalk to make white paint for highlights, and charcoal to make black outlines and shadows. The paints used in the finest cave paintings 17,000 years ago were made from these materials. Look up cave paintings in books or on-line to find an original you want to copy.
Pigments and dyes create intense colors. Dyes dissolve in water and soak into fabrics, coloring them throughout. Pigments don’t dissolve, so they are ground into powder and made into paint. Azurite was once an important source of blue paint; it is a soft, deep blue copper carbonate mineral: Cu3(CO3)2(OH)2.
Tips: Dip your paintbrush in water if your paint starts to dry out. Wear a dust mask in case some mineral powders are an inhalation risk; adults should crush very hard minerals for you. Don’t ever use yellow or orange minerals because some are toxic.
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References:
“Rock and Fossil Hunter”, a Smithsonian series book by Ben Morgan; DK Publishing,
Inc. NY; 2005; page 32.
Kids, which will dissolve more quickly, a Tic-Tac™ mint or a mouthful of cotton candy? The answer may seem easy but why does it happen? Exploring this can also help you to understand why, in the world of nanoscience, nanoparticles are so unique. A nanometer is a billionth of a meter, or 60,000 times smaller than a human hair. To help you realize how and why properties change dramatically at the nanometer scale, we’ll look at how an increase in surface area increases the reactivity of particles.
In March 2007, the ChemShorts article on Alka-Seltzer™ tablets (http://chicagoacs.net/ChmShort/CS07.html#3) established that if a tablet is divided into smaller pieces the surface area increases. In this experiment you will dissolve a sugar tablet (or cube or mint) and an equal mass of sugar crystals (or cotton candy) to see if there is a difference in how fast they dissolve. Cotton candy can represent carbon nanotubes and the tic-tac can represent a chunk of graphite for this experiment.
You need small snack-size (1 oz, 28 gm) bags of fluffy cotton candy and a small package of Tic-Tac™ mints for this demonstration. There is roughly the same amount of sugar in one tic-tac mint (about 0.5 gm) as in about 1 tablespoon of cotton candy. Devise a controlled way to measure the rate of dissolution for these two forms of sugar. As a quick test you can try it out in your mouth, but think of better ways to control the variables (how to dissolve the sugar, weigh the sugar, what liquid to use, how to measure the time, etc.).
For large materials that you can see with your eyes (larger than micrometers), the percentage of atoms at the surface is tiny compared to the total number of atoms in the material. If the pieces are continually cut, the surface area will increase but the total volume does not change.
This is significant in nanoscience where nanoparticles acquire new chemical or physical properties different from bulk materials. Some properties of nanoparticles are due to the surface area of the particle. Small nanoparticles have a larger percentage of atoms on the surface. Small particles have a high surface to volume ratio.
Finer sugar grains have a vastly larger surface area than larger chunks. The larger the exposed surface, the faster the dissolution (or reaction rate) because the liquid has greater access to the sugar.
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References:
University of Houston College of Education, http://atlantis.coe.uh.edu/texasipc/units/solution/sugar.pdf and http://www.materialsworldmodules.org/modules/intro_to_nanoscale.shtml
Kids, can you test for little bits of space in your own backyards? Every day, 500 tons of dust and rock from space collide with Earth. Much of this burns up in the atmosphere as ‘shooting stars’. However, particles smaller than a millimeter sometimes slip through the air without burning. These are micrometeorites. They can float through the sky as dust and fall to the ground in rain. With a powerful magnet and some luck you just might be able to find one of your own.
You’ll need a paper cup with two holes poked through the paper at the top near the lip of the cup, across from each other. Through these holes tie a loop of string about one foot long so that you have a basket. Into the cup place a very strong U-shaped or bar magnet. This is your micrometeorite collector. Bring it outside on a dry day and gently tap it over areas of ground that are dry (but that do get wet after rain) and not disturbed by people or vehicles. Good places to try might be near downspouts, areas of lawn not often used, or areas next to hiking trails.
When black specks become stuck to the bottom of the cup, take it inside and place the cup on clean white paper. Remove the magnet and tap the cup to shake off the specks. Use a magnifying glass and tweezers to pick out the roundest particles less than half a millimeter wide. These have the greatest chance of being micrometeorites made of iron or nickel, which are magnetic. Particles that aren’t round are flecks of iron from other sources.
If you have a microscope, put the best particles on a glass slide for examination. Micrometeorites often are smooth because the surface melts in the heat of entering the atmosphere.
What is a meteorite? These space rocks are fragments of broken asteroids. Meteorites made of iron are from the cores of asteroids.
Trivia: The dust on cars after a rain comes from high in the sky, too, and may contain desert sand and volcanic ash in addition to micrometeorites.
TIP: Don’t touch your dust with the magnet or it will stick and be very difficult to remove. This is why the paper cup shield is used.
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References:
“Rock and Fossil Hunter”, a Smithsonian series book by Ben Morgan; DK Publishing, Inc. NY; 2005; page 36, “Rocks from space”.
Kids, The International Year of Chemistry (IYC 2011) is already half over! It’s been a great year so far and there’s more to come. This recognition for chemistry was made official by the United Nations in December 2008.
IYC is a worldwide celebration of the achievements of chemistry and its contributions to the well-being of humankind. Under the theme “Chemistry—our life, our future”, it offers interactive, entertaining, and educational activities for all ages. The goals are to increase the public appreciation of chemistry in meeting world needs, to encourage interest in chemistry among young people, and to generate enthusiasm for the creative future of chemistry.
IYC 2011 events emphasize that chemistry is a creative science essential for sustainability and improvements to our way of life. Activities such as lectures, exhibits, and hands-on experiments, explore how chemical research is critical for solving our most vexing global problems involving food, water, health, energy, transportation, and more. The IYC holds a full list of events on its website and include: - conferences, congresses, symposia, fairs, exhibitions, expositions, grand openings, lectures, meetings, open discussions, workshops, celebrations, shows, art exhibitions, and quizzes.
Examples of the American Chemical Society IYC activities (go to www.acs.org) include the monthly IYC Virtual Journal. Each issue features free access to 15 to 20 articles from ACS’s 39 journals and C&EN that illustrate the many ways in which chemistry improves life for people around the world. And “365: Chemistry for Life” features a chemistry highlight for each day of the year. Day 178, for example, features an essay on the origins of the oil industry.
Other organizations are also celebrating chemistry during IYC. The National Science Foundation has teamed up with NBC Learn and the National Science Teachers Association to create “Chemistry Now” a weekly online video series that explains the chemistry of everyday molecules like water and chemical principles such as chirality in a clever and easy-to-understand fashion.
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References:
Official website: http://www.chemistry2011.org/
Chemical & Engineering News Cover Story, 6/26/11:
http://pubs.acs.org/cen/coverstory/89/8926cover.html
Kids, Halloween is the perfect time of year to try out spooky mad scientist projects. With some laundry detergent you can make a glow-in-the dark skull that you can put on your sidewalk or window that will be invisible during the day but will glow at night.
Materials
Make the Decoration
How It Works
Laundry detergents contain brightening agents that glow when exposed to light, especially ultraviolet light like in sunlight or under fluorescent lights. When you shine a black light on detergent you get a very bright glow. The glow is bright enough that you don't need total darkness to get a nice effect. One of the most common classes of molecules with this property is the stilbenes (see below for more information) which absorb energy in the UV portion of the spectrum and re-emit it in the blue portion of the visible spectrum.
Stilbene: diarylethene, a hydrocarbon consisting of a cis-ethane double bond with a phenyl group on both carbon atoms; derived from the Greek word stilbos which means shining.
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References: http://chemistry.about.com/od/halloweenchemistry/a/glowingskull.htm (a link to the stencil can be found here, too)
http://en.wikipedia.org/wiki/Optical_brightener
For more Halloween Science projects check out:
http://chemistry.about.com/od/halloweenchemistry/a/halloweensci.htm
Kids, what is it about slime that captivates everyone? There are so many slime varieties available now that I challenge you to create your very own. Here are some examples to get your creative juices flowing.
Chocolate slime
This is the ultimate edible slime! You need a 14-ounce can of sweetened condensed milk, 2 tablespoons chocolate syrup, and 1-1/2 tablespoons cornstarch. In a saucepan over low heat, stir the milk, syrup and cornstarch. Stir and heat until the mixture thickens. Remove from heat and let the slime cool. When you are finished playing with the chocolate slime, it can be stored in a sealed plastic bag in the refrigerator for a day or two. Chocolate will stain some surfaces, so keep this slime away from clothing or furniture.
You need 1 teaspoon soluble fiber (such as Metamucil psyllium), 1 cup water, food coloring and/or glow paint. Pour the water and fiber into a large microwave-safe bowl. Microwave on high for 3 minutes, stir, and microwave for another 3 minutes. Stir. If you want drier ectoplasm, microwave for 1-2 minutes. Add a drop of food coloring and/or glow paint. Interesting effects happen if you incompletely mix them, such as multicolored ectoplasm or ectoplasm slime with glowing streaks. Stored in a sealed baggie this will last for up to a week.
This interesting slime reacts to electrical charge (like a charged balloon, plastic comb, or piece of styrofoam) as if it has a life of its own. You’ll need 3/4 c (175 ml) cornstarch, 2 c (475 ml) vegetable oil, a glass, and 1x6x6 inch styrofoam. Mix the cornstarch and vegetable oil in the glass. Refrigerate until chilled. Stir (separation is normal). Let it warm enough to flow. Charge a block of styrofoam by rubbing it on hair, carpet, or wool. Tip the container of slime. Place the charged styrofoam about an inch from the flowing slime. It should stop flowing and seem to gel! If you wiggle the styrofoam the slime may follow or pieces of it may break off. When the styrofoam is removed the slime will continue to flow. After use, refrigerate slime in a sealed container.
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Reference:
These recipes, with photos, and others (such as Fruity Kool-Aid Slime, Edible Goo Slime, and tasty edible slime) can be found at: Anne Marie Helmenstine’s
http://chemistry.about.com/od/slimerecipes/tp/edible-slime-recipes.htm?nl=1
See the ChemShorts columns from April 1993, May & December 1994, February 2005, and January 2008 for similar ooey-gooey materials. They go into more detail about the chemistry behind the magic.
Kids, what makes a microfiber cloth so good at picking up dust and water? Believe it or not, it’s chemistry behind the magic. Here are some tests to determine the quality of a microfiber towel or cloth. All you need are some different brands of microfiber cleaning cloths, a paper towel, and a rag made from a cotton t-shirt.
The first test is touch. How does the microfiber cloth feel? Soft? Does the material “grab” the imperfections on your skin when you run it over the palm of your hand? When this happens it means the cloth is made from ‘split microfiber’. The tip of a split microfiber looks like an asterisk under a microscope. The open spaces in the split microfiber allow it to pick up and hold dirt and liquid. If you don’t feel a “grab” from the towel it may not be split, and if it’s not split it won’t be any more effective as a cleaning towel than a cotton rag.
Another test is absorbency. Pour a little water on a flat, smooth surface, take a folded microfiber cloth and slowly slide the towel towards the puddle. Observe as the cloth contacts the water. Does it suck the water up like a vacuum? Does it push the water away? Is it somewhere in between? Does the water quickly wick through? You want a cloth that sucks the water up like a vacuum and wicks throughout the cloth. Compare the behavior to the paper towel and the piece of cotton cloth.
Synthetic microfibers are exceptionally strong yet have very thin fibers (three times thinner than cotton fibers). Microfibers are specialized polymers – long chain-like molecules made of repeating units strung like beads on a thread. They wick moisture away by absorbing up to seven times their weight in moisture. Cotton soaks water by absorbing it, but microfibers pull water away to a drier part of the fabric.
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Reference: http://www.microfiberwholesale.com/Determining-the-quality-of-a-microfiber-towel.html
and
Roberta Baxter, ChemMatters, American Chemical Society, October 2011, page 4, “Polymers: The amazing properties of microfibers”.
Updated 10/24/11 by ML