A liquid crystal thermometer, temperature strip or plastic strip thermometer is a type of

thermometer A thermometer is a device that temperature measurement, measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a merc ...

that contains heat-sensitive (

thermochromic Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a differen ...

)

liquid crystals Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. Th ...

in a plastic strip that change colour to indicate different

temperatures Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

. Liquid crystals possess the mechanical properties of a liquid, but have the optical properties of a single crystal. Temperature changes can affect the colour of a liquid crystal, which makes them useful for temperature measurement. The resolution of liquid crystal sensors is in the range. Disposable liquid crystal thermometers have been developed for home and medical use. For example if the thermometer is black and it is put onto someone's forehead it will change colour depending on the temperature of the person. There are two stages in the liquid crystals: #the hot nematic stage is the closest to the liquid phase where the molecules are freely moving around and only partly ordered. #the cold smectic stage is closest to a solid phase where the molecules align themselves into tightly wound chiral matrices. Liquid crystal thermometers portray temperatures as colors and can be used to follow temperature changes caused by heat flow. They can be used to observe that heat flows by

conduction Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble, such as an orchestra. * Conductor (album), ''Conductor'' (album), an album by indie rock band The Comas * Conduction, a type of structured f ...

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

, and

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

. In medical applications, liquid crystal thermometers may be used to read body temperature by placing them against the forehead. These are safer than a

mercury-in-glass thermometer The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714). It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much le ...

, and may be advantageous in some patients, but do not always give an exact result, except for the analytic liquid crystal thermometer which shows the exact temperature between . Liquid crystal thermometers are also commonly used in

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

s in

homebrewing Homebrewing is the brewing of beer or other alcoholic beverages on a small scale for personal, non-commercial purposes. Supplies, such as kits and fermentation tanks, can be purchased locally at specialty stores or online. Beer was brewed dom ...

, and in

mood ring A mood ring is a finger ring that contains a thermochromic element, or "mood stone", that changes colors based on the temperature of the finger of the wearer. Finger temperature, as long as the ambient temperature is relatively constant, is si ...

s. The Liquid crystal thermometer was invented by Bob Parker in California, one of many of the inventor's thermochromic applications patented in the 1970s.

References

Thermometers Thermochromism Liquid crystals {{measurement-stub