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Shape Memory Monsters: They Come Back!
Author: Laura Ruttig
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC- 1542358. This lesson is original, but here are some great lessons that are related to this topic:
In this engaging two-part lab activity, students first make shape memory "monsters," using silicone rubber, stearic acid, and plastic Halloween molds. Then in the second part, students have the chance to try to destroy the monsters, by smashing them with a binder clip into a c-shape. After testing, the control sample won’t change at all. Their shape memory composite will look defeated...until students place it back in the hot water. At that point, the monster will recover to its original scary shape!
As part of the pre-lab reading, students will learn the definitions for key vocabulary such as shape memory, polymers, composites, thermoset and thermoplastic. Students will also learn some of the science behind how shape memory polymers work, and after the lab, they will explore how the types of intramolecular bonding and intermolecular forces contribute to the behaviors they observed in the lab.
What should students know as a result of this lesson?
Students will be able to identify:
- The differences between thermoset and thermoplastic materials
- The definition of a composite material
- Why scientists and engineers work together to develop new customized materials
- Types of careers available in material science, polymer and chemical engineering
What should the students be able to do as a result of this lesson?
Students will be able to do the following:
- Relate crosslinking of polymers to chemical bonding
- Calculate the intramolecular bond types in silicone and stearic acid
- Determine the intermolecular bond types in silicone and stearic acid
- Discuss how the intra- and intermolecular forces relate to the properties of the material
- Safety glasses or goggles
- Safety gloves (non-latex)
- Lab scale
- ~1.0 grams of Stearic acid per lab group - finely ground in a food processor designated for this purpose (power-like consistency works best)
- ~5 grams each Parts A and B (per lab group) of MoldStar20T - Smooth On platinum-cure silicone rubber (any type of silicone rubber will work, but MoldStar20T has the best balance of reaction rate/mold time)
- 4 small cups (2 or 3 oz. size works best) per lab group
- Metal spatula for each lab group
- Paper towels
- 3 small plastic chocolate molds (example: Halloween Molds from Amazon; any mold will work as long as NOT made of silicone, which will bond to the samples)
- 2 large beakers (400 mL or larger) per lab group
- Hot plate per lab group
- Thermometer per lab group
- 3 binder clips per lab group
Optional for demonstration to engage students before lab/explanation:
- Nitinol shape memory wire (available on Amazon and Educational Innovations)
- Poly doh - to demonstrate a thermoplastic material
- Before the demo, prepare a small molded shape using the MoldStar20T to demonstrate a thermoset material, as well as a molded shape using the poly doh to demonstrate a thermoplastic material.
- During the demo, heat water in a beaker on a hot plate to about ~85oC. Ask students to predict what will happen when you place the first shape (the MoldStar20T) material in the hot water. Place in the hot water, and let students observe that no shape change occurs. Exlain what a thermoset material is. Then ask students to predict what will happen to the thermoplastic shape when placed in the hot water (without explaining the term). Demonstrate by placing in the hot water. Discuss the differences between thermoplastics and thermosets.
- Then, ask students to predict what happens when you twist a paper clip and put it in the hot water. Nothing happens, as expected. Then curl or twist up a piece of nitinol wire and place it in the hot water. The wire should immediately straighten, in a discrepant event. Discuss what a shape memory material is, how it works in metals (such as the Nitinol wire) and how scientists and engineers are developing polymer versions of shape memory materials.
- Have students read and answer the pre-lab questions on shape memory, polymers, and composites.
- Have students perform part 1 of the lab.
- The following class period, have students perform part 2 of the lab.
- Have students answer part 2 post-lab questions, and discuss the lab results as a class, clarifying any misconceptions (especially the particulate diagrams).
- Students should be able to distinguish between ionic, polar and nonpolar bonding using the differences in electronegativity.
- Students should be able to determine the intermolecular forces that affect a compound, based on its bond types.
- Students should know the differences between homogeneous and heterogeneous mixtures.
Best Teaching Practices
- Discrepant Event
- Hands on/Minds on Learning
Alignment with Standards
- HS-PS1-1. Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
- HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
- Chemistry / Structure and Properties of Matter / Intramolecular Chemical Bonding / Ionic and Polar/Covalent
- Chemistry / Structure and Properties of Matter / Intermolecular Chemical Bonding / Types and Strengths and Implications for Properties of Substances (Solubility)
- Chemistry / Structure and Properties of Matter / Representing Compounds / Models and Shapes
Students explore how the molecules in a mixture affect the properties of that mixture, incorporating a knowledge of bond types, intermolecular forces, the shape of molecules, and the changes in structure between phases of matter. In addition, students learn about the field of material science, as well as some of the real-world applications for polymers, composites, and shape memory.
- Safety gloves are recommended for handling the stearic acid, as well as the stearic acid composite sample.
- Safety glasses or goggles are recommended, due to the use of heat and glassware, particularly in the second part of the lab.
- Hot plates are used in day 2 of the lab. Use caution, as hot plates may cause burns.
- Students may safely take home the control sample made of silicone in this lab, but should dispose of the stearic acid composite sample.
Shape memory has applications in cutting edge materials for aerospace, such as those used on NASA's Mars Rover. Eyeglasses are sometimes made of a shape memory material with superelasticity. Robotics is another field utilizing shape memory; for example, "muscle wire" that contracts when an electrical field is applied and can be used in artificial limbs.
Pre- and post-lab questions are included to help assess what students learn about polymers, and apply their knowledge of intra-and intermolecular forces.
- Students should work in groups of 2-3.
- This lab requires two days to complete.
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