If you’ve completed the Soaking Up Rays experiment, you might still be a bit baffled as to why there’s a difference between black and white. Here’s a great way to actually “see” radiation by using liquid crystal thermal sheets.
You’ll need to find a liquid crystal sheet that has a temperature range near body temperature (so it changes color when you warm it with your hands.)
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The liquid crystal sheet is temperature-sensitive. When the sheet received heat from the bulb, the temperature goes up and changes color. The plastic sheets remain black except for the temperature range in which they display a series of colors that reflect the actual temperature of the crystal.
Materials:
- hands
- Thermal paper (AKA: Liquid Crystal Sheet)
- Incandescent light bulb (or sunny day)
- Silver highlighter or aluminum foil
1. Color half of the back side of the thermal paper (the side that doesn’t change color) with the highlighter (or cover half of it with foil).
2. Hold it in a position where you can easily see the color-changing side while keeping the light source on the back side.
3. Which side changes color? Is there a difference between the silver and black halves?
You’ll notice that the black half almost immediately changes color, while the silver side stays black. The silver coating reflects the heat, keeping it cool. The black side absorbs the heat and raises its temperature.
Why do liquid crystals change color with temperature? Your liquid crystal sheet is not just one sheet, but a stack of several sheets that are slightly offset from each other. The distance between each layer changes as the sheet warms up – the hotter the temperature, the closer the stacks twist together. The color they emit depends on the distance between the sheets.
The molecules that make up the sheets are long and thin, like hot dogs. When the sheets are cooler, these molecules move around less and don’t twist up as much, which corresponds to reflecting back a redder light. When the temperature rises, the molecules move around more and twist together, and they reflect a bluer light. When the liquid crystal sheet is black, all the light is absorbed (no light gets reflected).
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That paper has special liquid crystals that are not quite solid and not quite a liquid, but they move between smaller phase shifts with the heat of your hand. This is why the paper goes from black to rainbow. And also why you need it as a way to indicate temperature for this experiment.
why that paper.
Did you try Educational Innovations? I think they were the ones listed on the shopping list. You can find them at any scientific store, like Edmund Scientific, American Science & Surplus, and Carolina. You only need a 4″ x 4″ piece.
Where can I buy the liquid crystal sheets? They seem really expensive when I looked on Amazon ($37 for a 12X12), does that sound right?
amazon
70-90 degrees F is a good range for our experiments.
What should the temperature transition be on these sheets?
Thanks!
Where can I buy this?