Lifelong Learning Programme

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TEACHERS EXPERIENCES FORM

Title of the Experience
About polymers
Name of the teacher
P.M.
Country where it took place
Romania
School typology
High Secondary School
Thematic Area
Chemistry
Experience typology
Laboratory
Type of contact
Direct
Description of the Experience
When we talked about polymers, their long molecules and the necessary forces to keep them in one piece we carried out the following experiment. We needed balloons and long nails.
We blew up a balloon – not too full – and tied it shut. We took a long nail, dipped it in Vaseline. Then carefully we pushed the nail all the way through the balloon without breaking it. On the contrary when we stuck the nail into the side of the balloon the balloon broke. The explanation is simple: the rubber in the balloon consists of many long molecules that are linked together (like the noodles in a plate of spaghetti stick together). These long molecules are called polymers; when molecules of a polymer are chemically attached to each other, it is called cross-linking. These links hold the polymer molecules together and allow them to stretch…up to a point. When the force or tension pulling on the cross-links is too great, they will break, and the polymer will pull apart. The rubber at the ends of the balloon is stretched out less than in the middle of the balloon. Therefore, there is less force pulling on it. This allows the tip of the nail to break some polymer cross-links, push aside the molecules of rubber, and slide into the balloon.
In the side of the balloon, there are fewer polymer molecules. When you push the tip of the nail through the rubber in the side of the balloon and the nail breaks a few of the cross-links, the tension on the remaining cross-links is too great, and the balloon breaks.

Comments on this Teachers Experience

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Date: 2014.10.16

Posted by Silviana Ivanova (Bulgaria)

This is definitely a practice I will use in my teaching. It is very good experiment and it will be very interesting for students. I think all teachers can agree that students learn better, when the learning material is presented in an attractive way. I think this example is excellent to make students interested and more engaged in the education process.

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