Hands-on Activity: Silly Semi-Solids

Contributed by: Center for Engineering Educational Outreach, Tufts University

Picture shows lines connecting many red and white dots.
The molecules of a polymer.
copyright
Copyright © Lawrence Berkeley National Laboratory http://www.lbl.gov/Science-Articles/Archive/sabl/2005/February/water-solid.html

Summary

Student teams make polymers using ordinary household supplies (glue, borax, water). They experiment with the semi-solid material when warm and cold to see and feel its elastic and viscous properties. Students will begin to understand how the electrical forces between particles change as temperature or the force applied to the substance changes. Is it a solid, a liquid, or something in between? How might it be used?
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

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 prostheses that they create.It is also important for engineers to understand why various materials display different viscoelastic properties. It is typically the role of a chemical engineer to understand the forces at the molecular level so conclusions can be made as to why certain materials display different properties.

Pre-Req Knowledge

A basic knowledge of the properties of solid and liquid materials.

Learning Objectives

After the activity students should be able to:

  • Understand the properties of polymers and determine whether they are solids, liquids or something in between.
  • Understand how molecular forces change the viscoelastic properties of materials
  • Discuss real-world applications of polymers.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • 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. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Collect information and evaluate its quality. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Use assessment techniques, such as trend analysis and experimentation, to make decisions about the future development of technology. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Biotechnology has applications in such areas as agriculture, pharmaceuticals, food and beverages, medicine, energy, the environment, and genetic engineering. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Chemical technologies provide a means for humans to alter or modify materials and to produce chemical products. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Distinguish among tension, compression, shear, and torsion, and explain how they relate to the selection of materials in structures. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

  • 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

Introduction/Motivation

In everyday life we expect solids to have certain reliable characteristics and liquids to have some very different qualities. Can anyone briefly explain what the difference is between solids and liquids? How are the molecular forces different? 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!

Procedure

  1. Measure 2 tablespoons of water and pour into a small bowl.
  2. Measure 2 tablespoons of white glue and pour into the bowl of water. Stir until well mixed.
  3. 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.
  4. 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.
  5. Knead the putty-like material in your hands until it is completely smooth. This may take 5-10 minutes.
  6. Begin to experiment with the unusual properties of this substance. Ask the Investigating Questions.
  7. Store your semi-solid stuff in a ziploc bag. Wash your hands thoroughly after the activity.
  8. 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.

Investigating Questions

  • 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?
  • Hypothesize what may be happening at the molecular level when you perform the various actions to your substance.
  • Are the molecular forces always the same or do they change when the substance is moved quickly or at a different temperature?
  • Can you imagine any useful applications for a material with these properties?

Assessment

As homework, ask students to conduct some research and write a paper on the "properties of semi solids." Be sure to have the students include properties of the molecular forces 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.

Contributors

Jacqueline Lanfranchi; Mark Bronski; Mike Galecki

Copyright

© 2013 by Regents of the University of Colorado; original © 2005 Worcester Polytechnic Institute

Supporting Program

Center for Engineering Educational Outreach, Tufts University

Last modified: August 28, 2017

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