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A color/temperature designator describes the response of a typical liquid crystal chemical make up. This helps in selecting the liquid crystal composition for a particular application. For example, R35C5W designates a formulation which signifies that the event temperature of the liquid crystal (where it turns red) is 35oC. The blue start temperature is 5oC above the red start temperature. This provides an estimate of the bandwidth of liquid crystals as 35-40oC.
The liquid crystals can be either
- narrow band or
- wide band formulation.
The narrow band formulations have bandwidths below 1 or 2oC while wide-band formulations have bandwidths between 5 and 30oC. Micro-encapsulated liquid crystals are commercially available in prefabricated adhesive sheets, sprayable slurries, and in water-resistant micro capsules. Prefabricated LC sheets, which include a black backing material and a protective clear polyester layer for the LCs are most commonly employed. The primary disadvantage of prefabricated sheets is that they have slower temporal response characteristics and increased thermal contact resistance compared with the sprayed liquid crystal. Still, it has been widely in use due to its ease of application. It is worth noting that thin plastic sheets pre-coated with liquid crystals are not only user-friendly, but often exhibit a very clear color display. The typical wide bandwidth encapsulated TLC sheet (Hallcrest, R35C5W) will be of polyester (Mylar), 125 µm thick coated with black paint and an adhesive layer. The total thickness of the sheet is 200 µm.
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