General Information:
History of the SST Partnership
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Annual Poster Session
Research Areas:
Microsensors
Surface Engineering
Food Pathogens
IR Imaging for Health Monitoring
Thermochromic Pigments
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Thermochromic Pigments for Rapid Visual Assessment of Temperature
The project involves the development of temperature sensitive polymer based pigments that visually and reversibly change colors at a prescribed temperature in the region of –35 to +125 oC. Further, the thermochromic pigments are thermally stable to high temperatures (>200 oC). The temperature of the color change (called the thermochromic transition) can be altered by the structure of polymer based pigment used and can be tailored by chemical modification. In effect, the thermochromic coatings, plastics, or rubbers are thermal sensors that detect a change in temperature with optical or visual transformation. The following picture shows a thermochromic coating at high and low temperature.
The thermochromic polymers can be incorporated into commercially available paints, plastics, and rubbers. Articles containing 0.1 - 1.0% by weight of thermochromic pigments in a host polymer have a visually retrievable, reversible thermochromic transition. The thermochromic paints can be applied in various manners including brush, sponge, roller, and airbrush and adhere strongly to paper, plastic, and metal surfaces. The coatings containing high temperature thermochromic pigments can be used on a variety of surfaces, including radiator caps, fire doors, and engine parts, to prevent serious burns caused by otherwise undetectably hot metals or warn of a potentially dangerous condition. The low temperature thermochromic paints can be used on road-signs to warn of icy conditions on bridges. The thermochromic pigments can also be incorporated into plastics and rubbers via injection molding or extrusion. Plastic articles of interest include food storage containers, frozen food packaging, food service trays, and plastic wrap. The temperature of the thermochromic transition can be adjusted to indicate that the food product is at the proper temperature; cold enough for proper storage, hot enough for serving, or too hot and might result in a burn. Incorporation into rubber materials for tires would provide a visual warning of tire overheating due to improper inflation, one of the primary causes of blowouts. The following video shows a polystyrene chip containing 0.5 % of the thermochromic pigment. The chip is dipped into scalding water to bring about the color change.
Link to a video of the thermochromic transition. (QuickTime Movie)
Thermochromic materials are used in a variety of commercial products including textiles, novelty items, toys, and baby spoons. However, most thermochromic commercial products are derived from liquid crystals or complicated mixtures of organic dyes. Both of these methods require the materials to be microencapsulated. This results in a variety of limitations including poor thermal stability and difficulty in processing. In addition, the materials that are currently available are toxic and easily extracted from most plastics and therefore not approved by the FDA for use in articles that come in contact with food products. Our pigments are not extractable from plastics and have passed FDA standardized tests for food product safety.
The research has been directed by Professors Brett Lucht, Bill Euler, and Otto Gregory. For more information contact Brett Lucht at blucht@chm.uri.edu.
This project has received funding from KM Scientific, the URI Foundation, and the URI Transportation Center/USDOT.