TLC is an antonym for Thermochromic Liquid Crystals.
TLC Dot Stickers are first painted black, then coated with a layer of thermochromic liquid crystals (TLCs). Between the temperature range of 25°C to 31.5°C, the Liquid Crystals (LCs) used on dot stickers changes to a state of matter called the Liquid Crystal State. This state of matter has properties of both the solid and liquid states of matter but is not exactly like either. Thus, the name Liquid Crystal State. The liquid crystal temperature range is not the same for all TLC chemicals.
TLCs are transparent to visible light at temperatures below the temperature range of their liquid crystal state as well as above the temperature range of their liquid crystal state. Thus, the TLC dot stickers are black if cooled below 25°C or warmed above 31.5°C. Being transparent to visible light means you can see through the layer of liquid crystals, thus you see the black paint on the sticker. You can think of the transparent TLC layer as being like a layer of transparent tape that you can see through.
Why Liquid Crystals Change Color
TLCs absorb and reflect different parts of the visible light spectrum when in their Liquid Crystal(LC) State. In this state of matter, the LC molecules are grouped much like a winding stair case in that they form a spiraling pattern around an imaginary center axis. As the molecules heat from 25°C to 31.5°C they twist in one direction. The affect of this twisting results in the liquid crystal molecules becoming optically active.
Optical activity refers to a chemical that has more than one 3D shape and each shape affects the absorption of visible light differently. This means that each shape of the molecule has a different color.
The letters, RGB is used to refer to the entire visible light spectrum of colors (red, orange, yellow, green, blue, indigo, and violet). Liquid crystals that reflect the entire visible light color spectrum are called RGB liquid crystals.
Why RGB instead of RGV for violet??? It might have been someone like my local veterinarian who gave this name. I say because I told the dog that the color of my dog was beige. He rolled his eyes and wrote yellow on the dog’s record.
As the liquid crystal molecules are heated, the molecules twist forming a different 3D shape. Note that the chemical make up of the molecules do not change during the twisting, they only change shape. Each shape absorbs and reflects different parts of the visible light spectrum. For RGB liquid crystals, red is seen at the coolest liquid crystal temperature, green at the middle of the temperature range, and blue at the warmest temperature. You can pick out other colors, such as yellow and orange, but generally not indigo and violet.
NOTE: The color indigo was identified by the English scientist Sir. Isaac Newton (25 December 1642 – 20 March 1727), but physicists today have instruments that confirm that indigo is not a separate wave of light energy. Instead, indigo is a blend of blue and violet. I am sad that indigo, like the plant Pluto has been demoted because I still use the mnemonic ROY G. BIV when I need to write the visible light colors in order of their energy. Now I have to visualize the name with a strike through : ROY G. B
When liquid crystals are cooled they twist in the opposite directions.
How to Model the Twisting of TLCs.
1. Cut a sheet of black paper in half. Using transparent tape, secure three sheets of colored paper in the order shown: 1/2 black, 1- blue, 1- green, 1-red, 1/2 black.
2. Starting with the red paper end, roll the connected papers into a tube. Secure the overlapping black paper end with transparent tape.
3. Cutting through all layers of paper making up the tube, cut 4 equally spaced slices about 3 in (7.5 cm) long.
The spiraled paper models the spiraling TLC molecules as they twist when heated. The black is above the LC stage. For the dot stickers, the liquid crystal state begins at 25°C and red, the coolest light energy is reflected. Continued heated, represented by pulling the paper spiral further out of the tube results in the reflection of green light, thus the green spiraling paper. The final color for the RGB model is blue. Last is the black which represents the LC above 31.5°C and the LC are no longer in their LC state, thus they are transparent and the black coating on the dot stickers is visible.
The model only shows the RGB colors, but you could use smaller pieces of paper to represent the full light energy color spectrum, which is red, orange, yellow, green, blue,
indigo and violet.