Drexel-SDP GK-12 ACTIVITY
Activity: Liquid Crystal Thermometer
Subject Area(s) Metrology, Physics, Chemistry and Engineering
Associated Unit: Meterology, Engineering Concepts
Associated Lesson: Weather around us
Activity Title:
Liquid Crystal Thermometer
Grade Level (_6_-_8)
Time Required:
1 hour
Group Size individual students
Expendable Cost per Group: $5 dollars
Summary: Students will build a liquid crystal thermometer using cholesteric
liquid crystals and transparency film.
Engineering Connection
Engineers frequently design tools to measure physical quantities by taking advantage of physical
properties.
Keywords
Liquid crystals, thermometer, pitch
Educational Standards
 Science: 3.1.7
 Math: 2.3.5, 2.2.8
Pre-Requisite Knowledge
Students should be familiar with change in states of matter and know that materials are made of
atoms and molecules.
Learning Objectives
After this lesson, students should be able to:

Build a liquid crystal thermometer

Describe pitch

Calculate pitch

Convert temperature scales

Describe phase changes in liquid crystals

Model phase changes in liquid crystals with popsicle sticks

Describe light as a wave
Materials List
Each student needs:
 1 self laminating ID Badge
 Transparency with thermometer scale printed on it
 20 popsicle sticks
 pipe cleaner
 ruler
To share with the entire class:
 5 formulations of cholesteric liquid crystals (one for each temperature range)

wood sticks ( wooden cotton swabs work fine…remove the cotton from the end)
Table1. Inventory sheet, part numbers and vendors. Cholesterols can be stored for
future uses)
Cholesteryl benzoate 98%
Cholesteryl Pelargonate
97%
Cholesteryl oleyl carbonate
Aldrich
C75802
$112
100g
Aldrich
Aldrich
C78801
151157
$91.40
$49.40
100g
25g
Clear vials
Swabs
Kimpads
Fisher
Fisher
Fisher
03-339-25C
23-400-107
S47299
Lamenation Strips
Transparency Sheets
Office Depot
Office Depot
920531
753611
Introduction / Motivation
What is the difference between heat and temperature? Heat is the average kinetic energy
of the atoms in a system, whereas temperature the measurement of heat. Typically temperature
is measured with a thermometer and reported as a value a temperature scale. Scientists and
engineers use the Celsius Scale, in the USA weather temperatures are reported in the Fahrenheit
Scale.
To make a thermometer you need a substance that has a measureable linear change in
physical properties over the range of heats you are interested. You can build a thermometer
based on the expansion of a metal or alcohol (mercury and alcohol thermometers), change in
resistance, or in our case color.
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Procedure
Background
Liquid crystals (LC) have two melting temperatures, one representing a phase change
from the solid to liquid crystal and then a phase change from liquid crystal to liquid. The phase
change from solid to liquid crystal is accompanied by a change in optical properties. The LCs
used in this activity were cloudy in the solid and became a translucent pearly color in the LC
temperature range. This change in appearance over a range of temperature close to room
temperature (and body temperature) makes LCs a convenient fun thermometer.
Before the Activity
2 weeks before Activity:
1. Review attached presentation: Liquid Crystal Presentation ( in pdf format)
2. Purchase materials
2 days before Activity
3. Prepare the LCs, follow the synthesis protocol in the Mchale reference below.
4. Print out thermometer templates on transparency film
5. Cut up the transparency film so that the thermometer scales fit in the self laminating
pockets
1 hour before Activity
6. Heat up the LC by heating a water bath and putting the sealed vials in the bath. Direct
heating on a hot plate will burn the LCs.
7. Put together the materials for the students (I gave each student one self laminating
pocket, one thermometer scale transparency) I kept the sticks at each temperature station
to prevent contamination) I put 2 or three vials of the same LC temperature range at each
station so that the students could move from station to station and complete their
thermometers. ( ie Station 1. had LC in the 20-25 C range, Station 2. LC in the 26.5-30.5
C range, Station 3. LC in the 30-33 range, Station 4. LC in the 33-36 C range, and Station
5. LC in the 37-40 C range)
With the Students: Go through the information and activities in the power point presentation
Attachments
Liquid Crystal Presentation
LCThermometer template
Safety Issues
 Students should not eat the LC.
 Recommend using gloves and eye protection because LCs could be an irritant
 Recommend the LC vials be removed from the heat bath and put on tables away from the hot
plate to prevent burns.
Troubleshooting Tips
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If the LC overheats the thermometer will not work.
Have the student remove the tape barrier on the sticky side of the self-laminating pocket and
affix the transparency temperature scale to the sticky side before applying the LC.
Important: the transparency scale must be slightly smaller than the self laminating pocket
or the two sides will not stick together when you are done.
Investigating Questions
1. Why do different LCs have different colors in the LC phase?
2. Can you think of other applications for LCs?
References
McHale, M. Nanotechnology: Ferrofluids and Liquid Crystals, Connexions Web site.
http://cnx.org/content/m15532/1.10/, Nov 6, 2008. Follow the synthesis directions for the liquid
crystals
http://dept.kent.edu/spie/liquidcrystals/
Owner
Drexel University GK-12 Program
Contributors
Anna Fox
Jennifer Atchison
Dorothea Holmes -Stanley
Copyright
Copyright 2008 Drexel University GK-12 Program. Reproduction permission is granted for nonprofit educational use.
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