These laminated sheets of liquid crystal are temperature sensitive. The plastic sheets remain black except for a five-degree temperature range in which they display a series of colors that reflect the actual temperature of the crystal. Using sheets that change colors at different temperatures opens up a world of possibilities for experimentation. Please note that the effects of temperature on each of the liquid crystals depend upon the ambient temperature of the surroundings.LIQUID CRYSTAL SHEET, 20-25oC TRANSITION (68-77oF)
This liquid crystal sheet changes color at a transition point just about equal to room temperature. Depending on the ambient temperature of your room, this liquid crystal will change its color by the heat of your hand, an ice cube or a can of cold soda. The material can be easily cut with scissors. Self-adhesive backing.LIQUID CRYSTAL SHEET, 25-30oC TRANSITION (77-86oF)
This liquid crystal sheet is so sensitive that it can detect the heat print your hand leaves behind! Place your hand on a book for a few seconds, then remove your hand and place the liquid crystal sheet over the spot where your hand was located. Observe as the liquid crystal changes color and makes visible your hand's heat print. Or, simply touch the material and observe the print left by the heat of your hand. The material can be easily cut with scissors. Self-adhesive backing.LIQUID CRYSTAL SHEET, 30-35oC TRANSITION (86-95oF)
This liquid crystal sheet changes color just slightly below body temperature. Placing the sheet near a gentle heat source or warming it with your hands causes the liquid crystal to change color, indicating areas of differing temperature. Try holding a strip against your arm and observe your veins! The material can be easily cut with scissors. Self-adhesive backing.
Sizes are approximate. Order by temperature range.
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Why do liquid crystals change color with temperature?
The long, cigar shaped, molecules of a liquid crystal align themselves into orderly flat planes. The molecules in each flat plane are oriented at a slight angle from the molecules in the plane below it. Eventually, as the stack builds up and each layer is off set by a slight twisting from the one below it, two layers will have the same orientation. The distance between these two aligned layers is called the pitch. When white light is directed at this stack of molecules, the wavelength of light equal to this pitch distance is reflected back. At cold temperatures the pitch is far apart; red light is reflected back. At higher temperatures the molecules move faster and the layers twist more, causing the pitch to become shorter, reflecting blue light. Each liquid crystal has only a few degrees of temperature where the organization is such that light is reflected back. On either side of this temperature range, all light is absorbed and the liquid crystal appears black.