Audience: Middle school class
Time Needed: 50 minutes
Intro to Nano (optional)
Introduce the concept of "nano." For ideas, see "Nanoscale Activities" at http://www.mrsec.wisc.edu/edetc/IPSE/educators/.
Introduction: Liquid Crystal (LC) is a Phase of Matter (5-10 min)
Have students brainstorm the different properties of liquids, solids (crystals), and gases. Note that liquid crystal (LC) is a special phase of matter and have students brainstorm its properties (e.g., liquid-solid hybrid) based on the discussion of liquids and solids.
Optional: Have students arrange the phases of matter based on randomness at the atomic level. Note that atoms in a liquid crystal phase are less random than atoms in a liquid phase and more random than atoms in a solid phase.
Activity: LCs Reflect Different Colors of Light (10 min)
Have students blow bubbles, a particular type (i.e. lyotropic) of LC, and make observations about how their colors change from when they were brand new to right before they pop. (Bubbles will be less colorful as they dry out and get closer to popping.) Note that bubbles reflect all the full spectrum of colors in a rainbow.
Introduce Temperature Sensitive LCs (10 min)
Note that there are many different types of LC including LCs that respond to temperature changes. Have students rub glass vials containing temperature sensitive LCs and make observations, noting that heat is transferred to the LCs from the students hands. Ask students why these LCs might change color at different temperatures.
CAUTION: Do not allow students to open the vials. This type of liquid crystal is toxic.
Experiment: Compare Different LCs at Different Temperatures (15 min)
Give the students liquid crystal thermal sheets that change color in response to different temperature ranges. Have them use their hands with or without hand warmers to order the thermal sheets from low temperature sensitive to high temperature sensitive.
LC Sensor Activity: LC Sensors Can "See" What Our Eyes Can't (15 min)
Use LC sensors to see the invisible thermal print that your hand leaves when
removed from a tabletop. Place a hand warmer over an envelope containing a magnetic
shape/message. Remove the hand warmer and wait a few seconds before placing
on a high temperature sensitive liquid crystal sheet. Note the appearance of
the message on the LC sheet.
Have the students use their thermal sheets to decode other magnetic shapes/messages hidden inside envelopes. They may find the hand warmer and ice pack useful.
Brainstorm Potential Uses for LCs and LC Sensors (optional)
Have students come up with their own ideas for how LC products and sensors might be used in the real world.
Phases of Matter
The atoms of solid are compact with their positions and orientations fixed, whereas those of a liquid can move around, assuming the shape of whatever container the liquid is in. Liquid crystals also have the fluidity of a liquid but their movement is coordinated along the same direction. Therefore, one atom in the liquid crystal phase has an impact on the orientation of another atom close by. Liquid crystals are made by boiling certain kinds of organic compounds and then, subsequently cooling them. For a more in-depth look at the structure of liquid crystals, see the Background for the Teacher transparencies.
Nano is a prefix that means one-billionth of something. For example, nanometer is one-billionth of one meter. The nanoscale is useful in describing the size of atoms, which are subunits of matter. Nanotechnology refers to the design of technology and tools at the nanoscale to manipulate and/or visualize atoms. Phases of matter differ in how much freedom the atoms have in moving around. For example, when atoms have very little freedom, the overall structure is rigid as in a solid.
Light is wave. Different colors of light are characterized by a different wavelength, which is on the order of 400 to 700 hundred nanometers in the visible spectrum. White light consists of all the colors of the rainbow. When white light hits the atoms of a liquid crystal, the orientation of these atoms may allow only certain wavelengths or colors of light to be reflected back to our eyes.
IPSE Interns: Julie He, Jeffrey Maxwell
IPSE Leadership Team: Wendy C. Crone, J. Aura Gimm, Wendy deProphetis, Greta Zenner, and Tom Derenne
The Nanotechnology Activity Guides are a product of the Materials Research Science and Engineering Center and the Internships in Public Science Education Project of the University of Wisconsin - Madison. Funding provided by the National Science Foundation.