STEM Challenge: Composites

V. STEM Challenge: Designing a Composite. 

Overview

In these series of exploration we have given some effort to understand simple polymers, how to measure the characteristics of the polymer, the nature of chemicals and materials, and different kinds of chemical changes.  Now we give opportunity for our students to use their previous knowledge and skills to design a new chemical composition, a composite.

It might be a good idea to revisit the chemist that started  us on this journey, Stephanie Kwolek:

How can we be like this chemist and use what we have learned to make a new product?  We have polymers, we have chemicals, we have different materials, what would happen if we start combining materials?

Composites

Composites are mixtures, of sorts. They consist of at least two different types of materials, that when combined form something new.  Composites are different than placing two chemical together to bond the atoms and molecules.  The substances continue to have their own characteristics, but when together their characteristics work together. Fiberglass is a good example that most are familiar.  The spun glass is a fabric--one part of the composite. The other part is a resin that hardens into plastic.  When you combine the resin with the spun glass, the composite material becomes a strong construction material.  The substances do not change, however.  The glass is still glass and the resin is not influenced by the mixture.  Together they are a great pair.

Guided Examples

Like Kwolek, we want to use our knowledge to create something new.  As a transition to being totally creative, let's guide learners on how this thinking works.  We know, for example,  how our gelatin polymer works and how to make it stronger by adding borax.  If we add citric acid, on the other hand, we weaken the linking bonds and make it less rigid.

Now let's try a new possibility.  What if we take our gelatin and mix it with  our warm water and then add creme of tartar and baking soda?  Try this:

Procedure

STEP I. Make Mixture A:

1 Part Gelatin

3 parts warm water

Stir until a good consistency

STEP II.  Make Mixture B: 

1 part Creme of Tartar

2 parts Baking Soda

Mix dry

STEP III.  Combine  Mixture A and Mixture B.  Stir.  What have you created? 

The foamy froth we have created can now gel.  Now we have a polymer that has trapped gas bubbles. What sort of practical application could be created with this?  Have students discuss the potential uses.  What kinds of foams are they familiar?  Suppose we combine these with sugar.  Foamy, sweet, and stretchy--have we just created Peeps©?

Sleuthing Possibilities

As we think about ideas for adding to our polymer it is good to do some mind experiments about possibilities.  In the chart below, students can place substances on the y axis and then list their characteristic and how they think that characteristic might work in partnership or with a polymer like gelatin.  

Here are some examples:

Collect a number of possibilities that students can think through.  It may be necessary to review with the groups that are working the nature of the material if they do not remember or if they had not had a chance to review it earlier.

Share-out brainstormed ideas from groups and add your own ideas into the mix.  Help students think about applications and possibilities.

Design

After students have done the min experiment, have them return to their charts and determine which composite might have the most promise.  Have them record their idea as a speculation or hypothesis such as:

"If we add ______(which has a characteristic of ________________) to gelatin, the combination will have the following characteristics:_______________________________.

This kind of composite could be used for:__________________."

Once students have an idea what they want to try, give them access to materials and require that the keep good record of their processes in the STEM/Engineering Notebook.  Students should create several trials to determine what ratio of components have promise.

Testing

Once the material is created, the next step is to measure its performance.  It is here that students will need to measure the parameter by using something that can be counted, measured, timed, or judged.  Designing a way to assess the material will help determine which combination was the best.  For example, if the group makes a sticky polymer that might be used to attach a poster to the wall, then how long does it stick before falling?  

This step will take not only creativity, but an inventive technology that they will need to determine.  This is an important part of engineering.  Measuring the strength, flexibility, elasticity, and many other properties of a substance is key to understanding how materials can be used.  Using numbers to describe behavior of materials is an essential feature of engineering.

It may be that what is produced has a function that does not lend itself to measurement, per se.  For example, a composite might have an aesthetic function or utility.  Let's suppose we make a composite that serves as tool or a material we use to complete some work.  We might ask others how well it performs by doing an evaluation:

___5 Works very well

___4 Works but has some flaws

___3 Sometimes works

___2 Might have possibilities

___1 Not a good invention

Shark Tank

One way to proceed with assessment of their thinking and experimenting is to have the class or an expert panel act as a "shark tank."  In this scenario, the students propose their products by creating a promotion with the following features:

Product Name_____________________

Materials/Ingredients_______________

Description of Product______________

________________________________

Application_______________________

________________________________

Students could write a one page persuasive description, offer an oral argument, create a media piece or poster or some other communication product to "sell" their idea to the panel. The product may be demonstrated or explained. The panel then evaluates the the presentations with a rubric the class might invent:

_____We are ready to fund the start up of this business idea!

_____This product has great promise. Further research should be funded!

_____A good idea, but needs more evidence if we are going to fund the

          project.

_____This doesn't look like it could work.

Some examples of some product proposals created by a group of fifth grade teachers follows: