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Student teams make polymers using ordinary household supplies (glue, borax, water). They experiment with the semi-soid material when warm and cold to see and feel its elastic and viscous properties. Is it a solid, a liquid, or something in between? How might it be used?

Viscoelastic materials have a wide variety of applications. Many prosthetic implants require materials that have these properties. Biomedical and biomechanical engineers investigate and design these materials to get the best possible combination of elastic and viscous properties in one material to support the functioning of the protheses that they create. chemistry elasticity polymer viscosity viscoelasticity A basic knowledge of the properties of solid and liquid materials. To understand the properties of polymers and determine whether they are solids, liquids or something in between. Discuss real-world applications of polymers. white glue (such as Elmer's) water borax (available in the laundry sections of grocery stores) plastic margarine tub or small mixing bowl, one per team measuring spoons (tablespoon, teaspoon) small ziploc bag, one per team In everyday life we expect solids to have certain reliable characteristics and liquids to have some very different qualities. It can be delightful to play with materials that seem to bridge our expectations of both of these states of matter. Welcome to the world of polymer chemistry! Measure 2 tablespoons of water and pour into a small bowl. Measure 2 tablespoons of white glue and pour into the bowl of water. Stir until well mixed. Measure 2 teaspoons of borax and mix into the same bowl. The mixture begins to congeal immediately. A remarkable film forms on the surface of the water/glue solution. Use your fingers to thoroughly mix ingredients. A large "lump" of a wet semi-solid begins to form between your fingers. Keep mixing ingredients until the lump feels like wet putty. A small amount of fluid remains in the bowl. This is safe to flush down the sink drain. Knead the putty-like material in your hands until it is completely smooth. This may take 5-10 minutes. Begin to experiment with the unusual properties of this substance. Ask the Investigating Questions. Store your semi-solid stuff in a ziploc bag. Wash your hands thoroughly after the activity. After the same material is cold, repeat the process and experiment with it. Ask the Investigting Questions. Discuss how heat and cold affect the properties of the material. What happens when you slowly stretch it? What happens when you pull it abruptly apart? If you roll it into a ball, does it stay in that shape? Is this substance a solid, a fluid, or something in between? Can you imagine any useful applications for a material with these properties? As homework, ask students to conduct some research and write a paper on the "properties of semi solids." Evaluate the paper based on the number of properties they are able to identify and how well they describe them in their own words.