Author: Dr. Katherine Owens
Source: Information on Post-it Notes™ derived from ChemMatters, December 1993 and from Chemecology Vol. 22, March 1993.
In this lesson, students will test the shear strength of different sticky tapes by performing tests in which they will take measurements, record data, and report their findings. They will explain how the usefulness of a manufactured product depends on its function for a particular purpose. Students will learn about how scientists and engineers look to nature to invent products that are useful in our lives. In the video below, graduate student Stephanie Lopez shows how Geckos have inspired polymer scientists at the University of Akron.
What should students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
Tell the following story (note: it might be helpful to have examples of the tapes mentioned in the story to show the class): It's the day before the big middle school dance and the committee is hurrying to finish hanging decorations all over the gym walls. Work is progressing when you notice that you're running out of tape to finish the job. So, you call together your helpers and ask them to look around for more tape and bring back whatever they find as soon as possible while you keep decorating. A few minutes later your helpers return - one has brought a roll of masking tape, another has some clear cellophane tape and some Duct tape, another has clear packaging tape, someone else has a package of Post-it Notes™, and somebody else went to the nurse's office to get medical bandage tape. Quite a selection, you think. There's not much time to waste wondering what tape to use - you're desperate - yet, none of these choices were meant to stick decorations to the gym wall. You wish you knew how "sticky" these tapes are so that the decorations you put up with it won't fall down in the middle of the dance.
How are these tapes alike? How are they different? Some tapes might work OK if the surface is flat and laying down (like a table top), but might fail if you used them on an upright surface (like a wall). Which of these would you choose to finish the decorating job? To hold a bandage in place on a wound? To secure the wrapping on a box you intended to mail? Do all of these tapes have the same function? Are they all made the same? Do they all have the same stickiness? How could you find out?
Well, in this lesson you will be examining the stickiness on various kinds of tape by doing a simple test, the kind of testing that inventors and manufacturers use when they are working with new products. You should be able to determine how well the tape performs if you wanted to use the tape to hang something on a wall.
Assessment: Monitor students' answers to your questions to be sure everyone understands the goals of the lesson. Before proceeding, be sure that students understand the posed problem.
Do a quick demonstration of how to set up the equipment to make the apparatus for testing the stickiness of the materials to be tested.
Every group should test the 0° elevation and an approximately 90° elevation. Note: No books will be needed for these two tests; be sure that the testing track is held upright and steady for the near 90° testing. Decide how many angles of the board (by number of books chosen to lift the board or the actual angle measurement of the incline) you want to test. Be sure that every group uses the same book and performs these same tests. Allow students to make four choices of sticky tape. Note: Marble should be set lightly on the tape - pushing it down firmly will compromise the results. Before beginning the tests, have students predict which tape will be the stickiest and how far they think the marble will roll down the test track. Be sure the students understand that the farther the marble rolls down the test track, the weaker is the sticky tape. Assist students to make their own data chart (sample is given in the worksheet section of this plan). Roll-tests of the marble down the inclined tape-path should be repeated for a total of three tests per tape. Record length that the marble traveled after each test; find the mean distance for each tape.
Assessment: Monitor students' work to check that they are carrying out procedures carefully, making observations, and recording data accurately.
Have students report their findings. Ask students to report what surprised them about the results. Did their data support their predictions? Which one of the tapes chosen was the stickiest in this test? In the discussion of the findings bring out that their tests only examined the stickiness of the tape on a glass surface (the marble) and that manufacturers of the tape would have to test other materials adherence to the tape before marketing the tape as effective on wood, plastic, paper, and other surfaces. To elaborate on this idea, read the label of the tapes chosen for the class tests to see what surfaces the manufacturer has determined that the tape should be used on effectively. Ask students how they think these surfaces were determined.
Explain that there are many tests that products undergo before they come to our stores' shelves. For tape, there are basically two types of tests - one for peel and one for shear (see content knowledge). Ask students how they might design a peel test for the tapes that they tested for shear.
Tell the students the story of the invention of Post-it Notes™ (see content knowledge) as an example of a product that has a particular use for a particular purpose.
Assessment: Have students explain how the usefulness of a manufactured product depends on its function for a particular purpose. As an example, show the students various kinds of pens - highlighter, washable marker, permanent ink chart marker, ballpoint pen, etc. and ask students to describe the uses of each. If they needed to mark important sentences in a reading passage, which pen would they choose and why would they find the other pens to be not useful.
Tell students about how scientists and engineers look to nature to invent products that are useful in our lives. They call their work biologically-inspired design. Geckos can stick to surfaces without any liquid and the bond is strong between their feet and the surface. The microscopic hairs (setae) on its feet can bend to fill in the uneven spaces on a surface (see diagram below), resulting in a very strong adhesive force.
But, this adhesive force releases easily when the gecko lifts its foot. Generally, the stronger the adhesive, the harder it is to keep clean (have you ever used a piece of packing tape to take lint or pet hairs off of your clothing?). The gecko's setae are self-cleaning so they cling over and over again (reusable). Gecko-inspired adhesive tapes, for example, have great functionality. They are dry, reusable (unlike most commonly available tapes), not time-sensitive (they will stick indefinitely, unlike cellophane tape which gets brittle over time), and work in a vacuum (applications for use in the space program).
Student research project - searching for information on adhesives. See rubric for further detail. Suggested topics include the following:
Assessment: See Rubric
Complete a data table; make graph using collected data; use the Internet to search for information.
Common Core Standards:
There are two kinds of forces that tend to break the bond between an adhesive and a surface. Shear force pulls parallel to the surface while peel force pulls in a direction perpendicular to the surface (see diagram below). If you want to tape an item to a wall, you would choose a tape with a strong shear force. If you choose painters' tape in your home decorating job, you would want to easily remove the tape after painting, so the tape should have low peel strength. Post-it Notes™ should have moderate shear strength so they won't fall off your bulletin board and low peel strength so that they can be easily removed.
Two researchers at the 3M Company are responsible for the product we know as Post-it Notes™. In 1968 Dr. Spencer Silver, an organic chemist, was studying the modification of an existing polymer-based adhesive, hoping to come up with a new, strong adhesive product. What he got in his lab was an adhesive that when applied between surfaces to be bonded together exhibited moderate shear strength and low peel strength. The adhesive could bond with one surface and be easily removed from another. At the same time, a chemical engineer, Arthur Fry, had an annoying problem. Fry sang in his church's choir and used small pieces of paper to keep track of the hymns to be sung at the church service. To his frustration, as he turned the pages in his hymnal, the bits of paper would often fall out and he'd lose his place. At work his job was to find uses for the new chemicals that the scientists made in the labs. Eventually, Silver's adhesive and Fry's suggestion to use this "weak" adhesive on the pages of a note pad resulted in the Post-it Notes™ we find so useful. To make this product work well took much more effort both in the chemist's lab and in the development of new engineering techniques - note the essential collaboration of science and engineering. The full story of getting Post-it Notes™ to market is a fascinating one and would make a very interesting research project.
Remind students to use all substances for their intended purpose. Dispose of all testing tapes in the wastebasket.
Adhesive tapes are a commonly used product around the home, in school, at work, in hospitals, and in industry. Tapes are made for various purposes so their stickiness varies. See Content Knowledge section.
Have students explain how the usefulness of a manufactured product depends on its function for a particular purpose. As an example, show the students various kinds of pens - highlighter, washable marker, permanent ink chart marker, ballpoint pen, etc. and ask students to describe the uses of each. If they needed to mark important sentences in a reading passage, which pen would they choose and why would they find the other pens to be not useful.
Grouping Suggestions: Groups of four recommended: materials manager/waste disposer, product tester, data recorder, and results reporter. Take care to group students to ensure a diverse mix of ability and talent.
Pacing/Suggested Time: Introduction, testing, reporting, discussion, and assessment - 4 days