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An Ionic Liquid Thermometer

May 12, 2008 | A version of this story appeared in Volume 86, Issue 19

Credit: Royal Society of Chemistry
Credit: Royal Society of Chemistry

Most commercial liquid-in-glass thermometers are filled with mercury or an alcohol such as ethanol. Both liquids have their limitations: Mercury is volatile and toxic, whereas ethanol has a relatively short range between its freezing and boiling points. Novel thermometers made with ionic liquids, on the other hand, would be inexpensive and nontoxic and would provide a freezing point lower than mercury's, as well as a boiling point higher than ethanol's. That's according to Robin D. Rogers of the University of Alabama, Tuscaloosa, and Queen's University of Belfast, in Northern Ireland, and colleagues, who have constructed ionic liquid thermometers out of narrow Pyrex glass tubes with a reservoir attached at one end (Green Chem. 2008, 10, 501). Ionic liquids are low-melting-point salts with essentially no vapor pressure. Given the large number of possible ionic liquid salts, the wide range of temperatures at which they remain in the liquid state, and their inherent tunability, ionic liquids are ideally suited as thermometer fluids for both general use or specialty applications, Rogers says. For general uses, the team selected tris(2-hydroxyethyl)methylammonium methylsulfate (thermometer shown). They added a red ionic liquid dye to make the colorless ionic liquid visible. The thermometers could be used anywhere a temperature sensor is needed, Rogers notes, but the first applications will probably be in the lab.


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