MOLECULES
Molecules are small particles that make up matter. They are made up of even tinier particles called atoms. Some molecules have as few as two atoms while some have millions of atoms. Each molecule has its own special shape that allows it to interact with other molecules. These interactions allow living things to do the things which are characteristic of being alive, such as moving and reproducing.
POLYMERS
The word polymer means "many parts". A polymer is a large molecule made up of many smaller molecules linked together like a long chain. Polymers have many distinct properties which allow them to be used for lots of different things including car parts, food storage, adhesives, packaging and protective coverings.
There are polymers almost everywhere in nature. Proteins that make up hair, feathers, cartilage, and other body parts are polymers. So are the starches in our food, and cellulose in wood, leaves, and other plant parts. Bone, horn, cotton, silk, rubber, paper, and leather are all polymers. Even DNA is a polymer!
There are many manmade polymers as well. Fabrics such as rayon and polyester, polystyrene (used in Styrofoam coffee cups), and PVC (used in pipes) are common examples of manmade polymers.
Flexible Molecules
Materials:
Ziplock bag
sharpened pencil
water
wooden skewer
balloon
vegetable oil
What To Do:
Fill the plastic bag almost full of water. Seal the bag. Hold the bag over a sink or bucket or over the ground outside. While you hold the bag, your partner should slowly push the point of the pencil through the side of the plastic bag and into the water. Did any water spill? Don't take the pencil out. Why do you think very little or no water spills? Look closely at the plastic bag surrounding the pencil. How would you describe the way the plastic bag fits around the pencil? Do you think the pencil can go all the way through the water and out the other side of the bag with no water spilling? Ask your partner to slowly push the pencil all the way through the other side of the bag. What happened?
Try to poke a wooden skewer through a balloon without popping it. This takes some practice! Rub a little vegetable oil along the length of the skewer. Carefully poke it through the thick, unexpanded material near the knot of the balloon. Then twist the skewer as you move it through the balloon. Poke the skewer out through the thickest part at the other end of the balloon. Is there anything about long thin polymer strands that might help explain why the pencil can do this?
How it works:
The plastic bag and the balloon are very flexible because of the long, stretchy molecules called polymers from which they are made. When a sharp pencil or skewer is poked through, some of the long thin polymer strands shift over and then flex enough to squeeze back around the pencil or skewer. This flexibility creates somewhat of a seal so that the water or air does not spill out much. Rubber tires on cars also work this way. A gummy layer on the inside of the tire seals around any nails or sharp objects that poke directly into the tire.
Skim Milk Glue
Materials:
skim milk (whole milk won't work because the fat molecules separate with the casein and interfere with the glues structure, making it too weak)
vinegar
glass jar
cheesecloth
baking soda
What To Do:
Place 1/2 cup skim milk in a glass or jar. Add 1/8 cup vinegar and stir for a few minutes. Small lumps, which are curds, will form. Let them settle for a few minutes, then pour off as much liquid (the "whey") as possible. Filter the remainder through a cheesecloth until the curds are dry, and return them to the glass. Add about 1/2 teaspoon baking soda (for neutralization) to the curds, and mix. You should see some slight foaming. Keep mixing until the curd becomes smoother and more liquid. The curd has now become glue. If the mixture is too thick, add a few drops of water. If it is too lumpy, add another pinch of baking soda, and stir. You should see some foaming. Don't be afraid to experiment by adding more water or baking soda to improve the consistency of your glue. The finished product can vary from a thick liquid to a thick paste. This depends on how much curd there is, and how much water and baking soda are used. Use your new glue to paste together pieces of paper. It may take 15-30 minutes to dry depending on how much you use, but it should work as well as a traditional white school paste. Cover your cup of glue with plastic wrap and let it sit for a few hours, or even overnight. The consistency should become smoother and clearer. Dispose of the wet glue in the trash within 24-48 hours or it will start to spoil and smell like spoiled milk.
How it works:
When you added the vinegar to the milk, it caused the milk's protein, the polymer casein, to separate from the liquid part of the milk and clump together to form solids. The baking soda neutralizes the acid in the vinegar. When the curd no longer has acid in it, it returns to a more liquid form. The liquefied casein protein is a natural glue. The foaming you see when the baking soda is added to the curd is carbon dioxide gas, which is made when the baking soda reacts with the acid in the vinegar. Casein has a lot of industrial uses. It is used in food products such as non-dairy creamers and as a raw material in adhesives, paints, and even plastics.
BONDS
Molecules are held together by bonds. Some bonds are stronger than others. Two types of bonds are covalent bonds (formed by the sharing of electrons) and ionic bonds (formed by the attraction of oppositely charged ions).
ELASTOMERS AND PLASTICS
Two important polymeric materials are elastomers and plastics. Elastomers and plastics are groups of polymer chain molecules held together by secondary bonds. If the molecules aren't stuck to each other too much, they will form an elastomer. Elastomers allow movement of individual polymer molecules. They can be stretched and will return to their original shape. But if the molecules are well-attached to each other, you get a plastic. Plastics are a large group of man made polymers containing many polymer molecules locked into place.
We can use cooked spaghetti to help us understand elastomers and plastics better. When a pile of spaghetti is taken out of the pan, the strands flow like a liquid. The long "molecules" are slippery and slide past each other easily, almost like a liquid. After a while, the water drains off the pasta, the strands start to stick together in a few places, and the spaghetti takes on a rubbery texture. Then the substance behaves like an elastomer. Wait a little while longer and the pile of spaghetti turns into a solid mass. The "molecules" become stuck together, just like a plastic.
Stretching Bonds
Materials:
one sheet each of newspaper, typing paper, construction paper, writing paper, and cardboard
gummy candy
candy containing chewy caramel
marshmallow
standard (metric) ruler
What To Do:
Hold the sheet of newspaper so that it looks as if you are holding a rectangle. With your hands, pull (in opposite directions) both ends of the paper. Notice what happens. Rip the sheet of newspaper in half. Notice how easily it rips and the shape formed on each piece of paper after it is ripped. Repeat steps 1 and 2 with each type of paper. Carefully and slowly stretch a marshmallow to the point where it is ready to separate into two pieces. Using the standard (metric) ruler, measure to the nearest inch (centimeter) the farthest distance that the bonds in the marshmallows stretched. Repeat steps 4 and 5 with a piece of gummy candy and with a piece of candy containing chewy caramel.
Slime
Materials:
school glue
Borax brand powdered soap
Ziplock bag (quart size)
Empty plastic soda bottle with cap
Water
What To Do:
Add 1 tablespoon of Borax powder to 1 cup of water. Remember that one cup of Borax water will make many batches of Slime. Measure 2 tablespoons of glue into a plastic cup. Add 1 tablespoon of plain water to the cup and mix. The additional water makes the glue very runny. Add 1 tablespoon of the Borax water to the bag of watered down glue. Mix completely. What is happening to the runny glue? What changes are taking place? Is it a solid? Is it a liquid? What is this slimy stuff?
How it works:
When you poured the Borax into the glue solution, your blob of glue did not act like regular glue anymore. It became stretchier and was not as sticky. This change happened because of a change with the polymer in the glue. The polymer in Elmer's glue is a liquid polymer called polyvinyl acetate. The molecule strands are not joined so they slide past each other as the glue flows. A chemical in the Borax solution connects the polyvinyl acetate molecules to make a large network - rather like a flexible scaffolding-so they can't slide as much. This is called cross-linking. This turns the liquid polymer into an elastomer which is soft or stiff depending on the amounts of glue, water, and Borax you use. The molecules aren't fixed in place so they can still be stretched, unlike a hard plastic.
Putty
Materials:
glue (wood glue works well but white glue will work too)
Epsom salts
water
measuring spoons
plastic spoon
2 small cups
waxed paper
What To Do:
In one cup, put 1/2 tsp Epsom salt and 1/2 tsp water, stir to dissolve salt. (NOTE: It may not all dissolve.) In the other cup, put 1 tablespoon glue. Add the Epsom salt water to the glue and stir. Watch as your new material starts to form. Pull out the putty and put it on the waxed paper. You can experiment with it to find out more about its properties. You can store the new putty in a plastic bag.
How it works:
The glue with Epsom salts polymer is similar to the Borax polymer. The way that these strands are connected by the other chemical gives each polymer its unique characteristics.
NON-NEWTONIAN FLUIDS
Back in the 1700s, a scientist named Isaac Newton studied fluids and wrote down what he learned about their behavior. He observed that the viscosity of an ideal liquid could only be changed by changing the liquid's temperature. Viscosity is a big word which means "resistance to flow." If a liquid is heated, it tends to become less viscous (it flows better); and if cooled, it tends to be more viscous (it flows more slowly). Liquids that pour and behave like the liquids Newton wrote about are called Newtonian fluids. But some liquids don't follow Newton's model of viscosity. Their viscosity can be affected by things other than temperature. These are called Non-Newtonian fluids.
Ooblech
Materials:
One box of corn starch (16 oz.)
Large mixing bowl
Cookie sheet, square cake pan, or something similar
Pitcher of water
Spoon
What To Do:
Pour approximately 1/4 of the box of cornstarch into the mixing bowl and slowly add about 1/2 cup of water. Stir. Sometimes it is easier to mix the cornstarch and water with your bare hands. Continue adding cornstarch and water in small amounts until you get a mixture that has the consistency of honey. Notice that the mixture gets thicker or more viscous as you add more cornstarch. Pour the mixture onto the cookie sheet or cake pan. Run your fingers through it slowly and quickly. Notice the different ways it reacts. Slap your hand on the surface, or pick some up and let it run through your fingers.
WARNING:
Over time, the grains of cornstarch will separate from the water and form a solid clump at the bottom of the plastic storage bag. It is for this reason that you must not pour this mixture down the drain. It will clog the pipes and stop up the drain. Pour the mixture into a zipper-lock bag and dispose of it in the garbage.
How it works:
Your Oobleck is a non-Newtonian liquid that becomes more viscous when force is applied to it. It acts this way because it is made up of tiny, solid particles of cornstarch suspended in water. Chemists call this type of mixture a colloid. Colloids or colloidal suspensions are mixtures of solids and liquids in which the solid particles remain suspended but do not dissolve. When you squeeze the colloid or stir it quickly, the particles don't have time to move out of each other's way. This causes them to pile up on each other and makes the liquid act as if it were a solid.
GELS
Gels are polymers made of long, thin molecules that are cross-linked to form a random network. This network has microscopic gaps that trap and hold liquids. When the gaps in the network are empty, the gel is shrunken and stiff. But when liquid creeps in, the gel expands and becomes softer and wobblier.
Diaper Dissection
Materials:
diaper (large, disposable and super-absorbent)
Ziplock bag (1 gallon size)
water
small cup
clear plastic cup
paper towel
food coloring
dropper
measuring spoons
WARNING:
The powder found in the diaper (sodium polyacrylate) will irritate the nasal membranes if inhaled. Avoid eye contact; if it gets into eyes, they will become dry and irritated. Be sure to wash hands after use.
What To Do:
Use a pair of scissors to cut off the paper or plastic edge around the entire diaper. Place the padded middle part of the diaper into the zip-closing plastic bag. Reach into the bag with both hands and separate the cotton, paper, and plastic layers of the diaper. Leave all material in the bag. Seal the bag and shake it for about 1 minute. Look at the bottom of the bag as you tilt it to one side. You should notice white granules collecting in the corner of the bag. Now, without opening the bag, move the cotton, plastic, or other large pieces of material toward the top of the bag. Keep the material up there as you shake the bag again. This will allow the granules to fall down to the bottom without getting picked up by the cotton again. After you have about a teaspoon of granules in the corner of the bag, slowly open the bag and remove the large pieces of material. Throw them away. Now, carefully pour the granules into a small cup. Wash you hands.
Place about a cup of water into a small cup. Add two or three drops of food coloring and swirl to mix. Place a small mount (about 1/8 teaspoon) of the powder onto the center of a paper towel. Add one drop of the colored water to the granules on the paper towel. Continue adding one drop at a time to the granules and observe. What do the granules appear to be doing? How many drops can you add to the granules before the water spreads out much on the paper towel?
Take the rest of your granules and pour them into a clear plastic cup. Predict the number of tablespoons of water the granules can gel. Now try it by adding 1 tablespoon of water at a time. Watch what happens. What do you observe? How close was your prediction?
How it works:
The gel particles inside disposable diapers are made of sodium polyacrylate which is a man-made polymer. The sodium ions are the gel's secret weapon for luring water molecules inside its structure at a reasonably low temperature. The polymer gel in a dry diaper only has about one percent water, so the particles are very small. When the diaper gets wet, water molecules
Edible Slime
Have fun playing with (and eating) this slippery, slimy stuff!
Materials:
14 oz. can sweetened condensed milk
1 T. cornstarch
10 to 15 drops green food coloring
What To Do:
Pour the can of condensed milk into a saucepan. Add cornstarch and cook over low heat, stirring constantly. When the mixture thickens, remove from heat and add food coloring. Cool before using.
Soap Slime
Make clean up fun!
Put small scraps of bar soap in a jar. Cover with warm water and seal the jar. Allow to sit for a couple of days until slime forms. You may also want to add some essential oil or lemon juice to make it smell nice.
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