Editing Liquid Crystal Sheets (section)

== Why This Works ==

The Liquid Crystal Sheets are a form of temperature indicator, utilizing what is known as '''''Thermochromism'''''. Thermochromism is when something will change color because of a temperature change, usually over a small range. Each sheet has tiny micro-crystals in them, and the crystals are arranged in different ways based on what temperature range a scientist will want to use it for. When the sheet is exposed to a heat source, the micro-crystals in the sheet will rotate if it is the right temperature range, causing the sheet to change colors! When the heat source is removed, and as they cool down, the micro-crystals will rotate back, and the sheet will turn black again. They can be used over and over again because of this.

The color change that we are seeing here is a type of ''Iridescence'', where the color you see is due to interference within the material. The Liquid Crystal Sheets are called that because the crystals, in the right temperature range, can move more like a liquid. This is because they are ''Nematic'', meaning that the crystals are all arranged facing in the same direction, and are layered on top of each other. One can think of the crystals as being similar to matches in a box, where the tips are all (or almost all) facing in the same direction, and they are stacked within the box on each other. These layers are put down within a certain temperature range, which allows the crystals, when returned to that range, to move around each other slightly. This movement is what causes the iridescence within the material, and the amount that they move is relative to the temperature of the material. At the low temperature range, the micro-crystals stay spaced out from each other, which allows longer wavelengths to refract and reflect out of the material, resulting in red and yellow colors. As it heats up, the micro-crystals get more excited, and start getting closer to each other. This means that shorter wavelengths will now be reflected instead, which makes it appear more blue and green.