8 I Physics
How do mood rings really work? Physics, chemistry, and physiology rule out psychic forces BY CATRYN ZHARYY, BEHAVIORAL NEUROSCIENCE, 2023 DESIGN BY IAN PROULX, BIOENGINEERING, 2022
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he smallest piece of magic you can hold in your hand, a mood ring and its power to channel one’s innermost emotions into trippy blends of color has charmed children and adults alike for close to 50 years. Since reaching peak popularity in the 1970s, the mood ring’s selling point has always been that it mystically changes color depending on the temperament of the wearer. It might be easy to pass off the mood rings and necklaces that crowd out gift shops as just another kiddish gimmick; but, in fact, they are rooted in more science than crookery. At the heart of mood ring “technology” is the unique chemistry and physics of liquid crystals. These naturally exist in a molecular state neither completely solid nor liquid. The components of liquid crystals tend to maintain their order similarly to the atoms of a solid, but can shift their orientation with a fluidity more like a liquid.
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direction of lightwaves minimizes wave interference and enables reflection and absorption of a diversity of light wavelengths, AKA colors. So how can all this be manipulated to reflect something as abstract as a human emotion? Changes in emotion manifest themselves in changes in one’s external body temperature. The base of the ring conducts heat to the cholesteric thermotropic liquid crystals, whose molecular helical organization twists in response. The resulting elongation or compression of the crystal “spring” structure enables the absorption of varying wavelengths of light.
In a neutral emotional state, the crystals hardly twist and naturally reflect blue/green light. In a more passionate state, the body directs more blood to the surface of the skin, heating up the crystals and compressing the molecular helix, which in turn reflects shorter wavelengths of light like indigo and violet. passionate state, the
Materials which exist flexibly between normal states of In a more matter are called mesogens. body directs more blood to the For each liquid crystal In more alert states, ranging mesogen—the major types are from excitement to anxiety, surface of the skin, heating up thermotropics, polymerics, the body’s physiological the crystals and compressing and lyotropics (used in response is to direct soaps)—the particular blood away from the skin the molecular helix, which in turn chemical compounds that and toward the internal reflects shorter wavelengths of make up its molecules dictate organs. The skin becomes the mesogen’s physical, colder, the “spring” in the light like indigo and violet.” electronic, and optical crystals elongates, and the properties. Furthermore, mood ring reflects longer liquid crystal mesogens can exist in different molecular wavelengths of light like yellow, red, and brown. Effectively, organizations called mesophases: the most common liquid the mood ring-wearer is changing the color of liquid crystals crystal mesophases are nematic, cholesteric, and smectic. The with her brain (more specifically, the brain’s awesome body“stone” in a mood ring is actually a hollow piece of glass or regulating abilities). quartz filled with cholesteric thermotropic liquid crystals. Of course, sometimes the body’s temperature can change as Nematic and cholesteric liquid crystals have similar a result of factors unrelated to emotion (simply being in a formations; their molecules, characterized as “rigid rods,” cold environment or releasing heat during exercise can tip are randomly positioned but all point in the same direction. off the crystals). But the mood ring’s marketing is not so In a nematic crystal, the molecules in each layer point in the deceptive—to some extent, there is a real connection between same direction as those in the adjacent layer. But as one moves one’s mood and the colors that appear. through a cholesteric crystal, the direction of the molecules changes slightly—when all the layers are seen together, the A child will explore and test out a mood ring to no end; it’s molecules appear to organize in a helical manner. only as age creeps in that a person abandons more and more of his curiosity for cynicism and exhaustion. Fortunately, it The unique organization of a cholesteric crystal enables the only takes some research and experimenting to come closer circular polarization of light, giving mood rings their color. to the truth: that magic exists. Maybe not in a mood ring Light polarization occurs when a beam of light that contains itself, but in the laws that dictate the natural world. And lightwaves lying in different planes interacts with a medium that thing a kid would call a magic trick is really what we which leaves it yielding lightwaves lying in only one plane. call science. As light enters a cholesteric thermotropic liquid crystal, it is sequentially refracted through differently oriented layers Liquid Crystals (2007). DOI:10.1002/0470084030 of molecules, causing it to exit the crystal at different angles Molecular Crystals (1969). DOI: 10.1080/15421406908084865 Optical Materials (2015). DOI: 10.1016/j.optmat.2015.07.010 (this is the circular part of circular polarization). The varied
