Teachers' Notes - Liquid crystals: living cells and flat screen TVs

Make your own liquid crystal thermometer

In this activity your students will be making their own liquid crystal thermometer. This shows some of the unique properties of these materials and how they respond rapidly to temperature. It will save time to have the equipment the students need organised into sets.

It is worth giving the students some background about liquid crystals and have a brief discussion of some of the applications they may be familiar with such as displays for mobile phones, TVs, calculators etc. Read the Science behind the scenes and Why is it important? sections before you start this activity.

For more information about liquid crystals see: http://reynolds.ph.man.ac.uk/lc/

Materials required

Safety glasses
Plain glass slides
Thin glass microscope cover slips
Methanol (Highly flammable, Toxic, see CLEAPSS Hazcard 40B)
Tissues
Double sided sticky tape
Glue (Araldite rapid)
Black PVC tape
Scissors
Scalpels
Cholesteric liquid crystal**
Syringes
Rubber gloves
Cocktail sticks

Note:The choice of glue is very important. If the glue contains a lot of solvent, this will destroy the liquid crystal.

**Available from Hallcrest www.lcrhallcrest.com. The name of the liquid crystal is 'TLC Mixture Bn/R27C6W', and you can request it by emailing the company directly. Contact details are provided on the website.

See students' sheet for full procedure.

Safety: Wear eye protection. This activity requires the use of scalpels and syringes. Methanol is highly flammable. A risk assessment must be done for this activity.

Once your students have made their thermometers, they can develop a scale by recording the colour the thermometer goes at different temperatures. You can ask your students to draw a blank scale in their notebooks before they take any temperature readings.

You could also use an alcohol or mercury thermometer to record the temperature in Celsius along side the different colours. This will give you a more accurate scale for your liquid crystal thermometer.

Curriculum links

Chemical and material behaviour

• 6d: The properties of a material determine its uses.

Energy, electricity and radiations

• 7c: Radiations, including ionising radiations, can transfer energy.
• 7d: Radiations in the form of waves can be used for communication.

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