Activity 7 Polymers GOALS In this activity you will: Make a polymer-based material that has properties different from other states of matter that you have studied. Observe the material s properties and compare them to those of solids and liquids. Describe the process of cross-linking in polymeric materials. Discuss and invent new commercial uses for watersoluble polymers. Compare the viscosities of two non-newtonian fluids. What Do You Think? In ancient times, humans made most of the objects they needed for daily life from natural substances. Relatively little processing was done between harvesting and use. For much of history, people have used metals, cotton, wood, and other natural materials for building, clothing, and tools. In the 1900s things changed dramatically as scientists were able to create new materials. What materials are polyester and rayon made from? How are they manufactured? Record your ideas about these questions in your Active Chemistry log. Be prepared to discuss your responses with your small group and the class. Investigate 1. Measure 50 ml of polyvinyl alcohol (PVA) solution into a beaker. Observe closely the properties of the PVA solution. Refer to the different type of properties you investigated in previous activities to make your observations. 367
Movie Special Effects a) Record your observations in your Active Chemistry log. 2. Measure 10 ml of sodium tetraborate (borax) solution into another beaker. Observe the properties of borax. a) Record your observations in your Active Chemistry log. 3. Add one drop of food coloring to the sodium tetraborate solution. 4. Add the sodium tetraborate solution to the PVA solution while stirring with a wooden stick. Keep stirring until the mixture thickens. When the mixture has thickened, remove the stick. Place a few paper towels on your desktop and use your hands to remove the thickened mixture. Mold and stretch the new material while you observe its characteristics. a) Record your observations in your log. 5. Test your new slime and see if it behaves more like a solid or more like a liquid. Try holding the slime in your fingers and dangling it downward. Wait for a few minutes and record what happens. Place your slime back in the beaker and see what happens as it sits for a few minutes. Try pulling the slime out slowly and see what happens. Now try the same thing but pull quickly. Roll the slime into a ball and try bouncing it gently on the tabletop. a) Record all your observations in your log. 6. It was not difficult to label the PVA solution as a solid or a liquid. Similarly it was easy to label borax. Liquids have very different characteristics from solids. Liquids flow while solids have a rigid shape. Liquids assume the shape of their container and solids have their own shape. Slime blurred the line between the definitions. Liquids spread out when force is applied, but solids break. Liquids splatter when dropped, while solids may bounce. a) In what ways does your slime behave like a liquid? b) In what ways does it behave like a solid? 7. The PVA molecules are relatively long, slender molecules. The sodium tetraborate molecules are shorter and can form bonds on both ends. PVA sodium tetraborate a) Draw a sketch to represent how the substances act in this reaction. Use the model in the diagram to draw PVA molecules alone, and then draw sodium tetraborate molecules alone. Finally, draw the reaction of sodium tetraborate cross-linking the PVA molecules. Remember your drawing is just a representation of the molecules. Active Chemistry 368
POLYMERS In this activity you made slime. This substance is a polymer that has unique characteristics. It is classified as a non-newtonian liquid. Liquids resist flow.this phenomenon is known as viscosity. Newton devised a simple model for fluid flow.you will learn more about this model in later chemistry and physics courses. Liquids like water and gasoline behave according to Newton s model.they are called Newtonian fluids. Ketchup, blood, yogurt, gravy, pie fillings, mud, and slime do not follow the model.they are classified as non-newtonian liquids. Chem Words polymer: a substance that is a macromolecule consisting of many similar small molecules (monomers) linked together in long chains. viscosity: a property related to the resistance of a fluid to flow. polymerization: a chemical reaction that converts small molecules (monomers) into large molecules (polymers). Slime has some characteristics of liquids such as being fluid and taking the shape of its container. On the other hand it bounces and breaks when pulled quickly, as solids do.the unique characteristics of slime are due to the two substances that make it up.the borax solution forms cross-links among the polyvinyl alcohol molecules.these crosslinks make the resulting polymer slower to flow and change shape. The formation of very large molecules from many smaller molecular units is called polymerization. Polymers are materials that are made up of many similar small molecules, called monomers, linked together in long chains.these materials have always existed in nature, but they have only been produced by industrial processes in the 20th century. 369
Movie Special Effects Proteins are natural polymers.they are the basic structural unit of plants and animals.there are more than ten thousand different proteins found in nature, yet they are all made up of combinations of about 20 different amino acids. Starch and cellulose are examples of carbohydrates that are polymers.the human digestive system is able to break apart the bonds that form starch molecules, releasing glucose, which the body uses as a source of energy. Humans cannot digest cellulose. Polyethylene (polyethene) is a polymer made up of many ethane molecules. It is one of many chemicals manufactured from crude oil. It is used to make plastic milk bottles as well as a variety of other objects. Other examples of polymers include polyvinyl chloride, Plexiglas, polystyrene, natural rubber, and Teflon. Checking Up 1. Describe polymers and polymerization in your own words. 2. Name two naturaloccurring polymers. 3. Give examples of five polymers that are manufactured using technological processes. Reflecting on the Activity and the Challenge What monster movie is complete without slime? Now you know how to make slime. Supplies for making slime are relatively expensive. Keep costs in mind as you plan for your special effect. Active Chemistry 370
1. List three ways you could modify the properties of your slime. If the slime you made in this activity is not quite correct for the special effect you have in mind, how might you modify it for use in your movie? 2. List five other uses that might be possible for the slime substance, in addition to its use as a movie special effect. 3. Thin sheets of solid PVA slime have been used in several new commercial products. Since the sheets are soluble in water, they are ideal recyclable containers. Seed manufacturers have made long tapes of PVA sheets with seeds imbedded inside. When the tapes are planted in the ground the PVA dissolves and the seeds are free to grow. Another use is collecting dirty laundry in hospitals. The solid laundry is placed into PVA bags. When it is time to wash the clothing the entire bag is thrown into the washing machine. It is not necessary for workers to handle the dirty clothes again. What two other uses can you think of for PVA sheet material? Inquiring Further 1. Self-siphoning slime Spread your slime on a piece of plastic wrap or waxed paper and let it dry completely. This may take a day or two. Compare the characteristics of the dry slime to the wet slime. PVA slime has been reported to be self-siphoning. To siphon most substances, a tube is placed in a liquid and the siphon is started by sucking the liquid out of the container, over the edge and down the tube. The mass of the water flowing out of the tube creates a pressure difference and draws the remainder of the liquid with it. Slime is supposed to have the same effect, but without the tube! Try demonstrating this self-siphoning effect with your slime. 2. Viscosity of non-newtonian liquids Ketchup is also classified as a non- Newtonian liquid. Determine which non-newtonian liquid is the most viscous (resistance to flow). Set up a retort stand with a ring to hold a long-stem funnel. On the funnel place two marks with a pen at about 2 cm apart. Pour one of the liquids into the funnel and allow it to flow through the stem into a beaker. Let the liquid level come down to your top mark on the side of the funnel and stop the flow with your finger. Using a stopwatch, time how long it takes for the liquid to flow before it reaches the second line after you remove your finger. 371