Liquid Crystal Stickers
Thermochromic Liquid Crystals (TLC) have reversible color changes when heated then cooled. This means they go through the light spectrum of colors as they are heated and as cooled the colors disappear in reverse order.
Shelf life is the length of time that the TLC Stickers will continue to change color with fluctuations of temperature.
All TLC products are sensitive to UV light as well as high temperatures. Exposure to UV light and high temperatures will cause the TLC chemicals to degrade. The first signs that the TLC Stickers are degrading is a loss of brightness in color. Eventually the stickers will not change color at all.
If stored properly, in a cool (room temperature), dark place, the TLC Stickers have a shelf life of at least 6 months. I have TLC stickers that are much older.
Thermochromic Liquid Crystals (LCs) can be highly temperature sensitive, change to many colors, and are more expensive than leuco dyes.
Leuco dyes are the thermochromic dyes used on CAT Stickers and HAT Stickers.
Liquid Crystals are used on the TLC Stickers.
LC’s start black below their temperature range; go through the colors of a rainbow, and then black again above the temperature range. LC’s are reversible in that they can be used over and over again. The picture shows an example of a liquid crystal sheet in response to warming.
Popular liquid crystal applications include medical devices, forehead, aquarium and room thermometers, promotional pieces and advertising applications. Additionally functional devices such as a propane tank gas level indicator are achieving much notoriety. Liquid crystal thermometers are being used for thermal mapping and other industrial applications where custom inexpensive temperature monitoring is warranted. We offer a wide range of LC thermometers as stock products, but also offer literally thousands of products for your label.
LC’s are very similar to the liquid crystal displays used in watches and laptop computers, but our thermochromic LC’s change color with temperature instead of voltage. LC’s can be formulated to change temperature from -22 to +248ºF (-30 to 120ºC), and can be sensitive enough to detect changes as small as 0.2ºF. If kept out of UV light and away from high temperatures and strong solvents, LC products will last for years.
The most prevalent use of liquid crystal is as a self adhesive reversible temperature indicator label that continually monitors temperature offering a visual readout that ranges from traditional numeric displays to custom graphics that can serve as an alert or warning.
What They Are:
These self adhesive labels consist of a series of temperature-sensitive elements containing microencapsulated Thermochromic Liquid Crystal TLC coated on a black backing. Each element changes color distinctly as its rated temperature is reached, passing through the colors of the spectrum in sequence (Tan, Green, and Blue before turning black at a higher temperature. The TLC strips are calibrated so that the indicator that shows green indicates the actual temperature. The color changes are reversible and the reflected colors will be observed in the reverse order upon cooling.
TLCs react to changes in temperature by changing color. They have chiral (twisted) molecular structures and are optically active mixtures of organic chemicals.
The correct scientific name for the materials is CHOLESTERIC or CHIRAL NEMATIC liquid crystals.
The term cholesteric is an historical one, and derives from the first materials to show the characteristic properties and structure of this particular type of liquid crystal were esters of cholesterol. This can be misleading, as many non-sterol derived optically active chemicals (and mixtures containing them) also show the cholesteric liquid crystal structure. It is important to differentiate this sterol and non-sterol derived materials because, although they change color in the same way, they have different properties and can be used in different ways to achieve different effects.
TLC mixtures can be divided into 3 types based on their compositions:
(a) CHOLESTERIC – consist entirely of sterol-derived chemicals;
(b) CHIRAL NEMATIC – composed entirely of non-sterol based chemicals.
(c) COMBINATION – containing both cholesteric and chiral nematic components. Combination mixtures extend the application possibilities and working ranges of TLC formulations by combining the respective advantages of both groups of component chemicals.
All TLCs are CHOLESTERIC LIQUID CRYSTALS, whether sterol-derived, non-sterol-derived or a mixture of the two.
Cholesterics are one of the three major classes of THERMOTROPIC liquid
crystals (produced by the action of heat).
The two others are called smectics and nematics.
LYOTROPIC liquid crystals result from the action of a solvent.