Applications Activity: Liquid Crystal Sensors

Audience: Middle school class
Time Needed: 50 minutes

Understand how liquid crystals (LCs) relate to other phases of matter (liquid, solid, gas)
Observe that liquid crystals reflect many different colors (wavelengths) of light
Learn that thermally sensitive LCs twist and turn (change pitch & orientation) at different temperatures, which changes the particular color of light that they reflect
Learn that just like some LCs can measure temperature, others can 'sense' particular chemicals and biological agents
Explore how LC sensors can be used to detect changes that cannot be seen with the naked eye
Brainstorm particular applications of LC sensors

One bottle bubbles per group of 2-4 students (see http://www.zurqui.co.cr/crinfocus/bubble/bubble.html)
One sealed vial heat-sensitive liquid crystals per group (see http://mrsec.wisc.edu/edetc/nanolab/LC_prep/index.html)
Liquid crystal thermal sheets for three different temperature ranges, cut into 3" x 6" rectangles (each group should get three sheets total – one sheet of each kind)
Hand warmers (one per group)
Ice packs or ice inside Zip-lock bags (one per group)
Refrigerator magnets in the shape of words and/or other geometric shapes , placed inside opaque envelopes (several per group, but groups could also share)
Overhead transparencies (pdf)
Student worksheets (one worksheet per student):
Brainstorming the Properties of Liquid Crystals (pdf)
Liquid Crystals as Sensors (pdf)
Temperature Sensitive Liquid Crystals (pdf)