Cover image for Highlights in Chemical Technology

Highlights in Chemical Technology

Chemical technology news from across RSC Publishing.

Designer thermometers rise to new levels

25 March 2008

Scientists in Europe and the US have used ionic liquids in liquid-in-glass thermometers as alternatives to mercury and ethanol.

Ionic liquids (ILs) are salts in liquid form and already have a wide range of applications, from use in drug delivery to fuel cells and batteries. Robin Rogers of The Queen's University of Belfast, UK, and his colleagues have now found another role for them. 'We have known the basic properties of ILs and have thought for some time that they should make a great thermometer fluid,' says Rogers. 'We simply had to prove it!'

A thermometer containing an ionic liquid and molecular structures of an ammonium-based and an alkylphosphonium-based liquid

Ionic liquid thermometers can be adapted for a particular temperature range by changing the liquid's make-up

ILs offer several advantages for thermometers: they have a faster temperature response time compared to mercury and operate over a wider range of temperatures compared to many molecular liquids, including ethanol. Non-toxic ILs can be used and their low volatility reduces their ability to escape into the environment, giving an additional environmental advantage over mercury, which needs to be carefully disposed of if a thermometer is broken.

To make its thermometers the US team used normally clear ionic liquids coloured red with an IL-dye. This made the liquid level easily visible without affecting the linear relationship between liquid volume and temperature. The thermometers could be adapted for a particular temperature range by changing the make-up of the liquid. Rogers and colleagues chose an ammonium-based liquid for general applications, as it is economical and non-toxic. They also used an alkylphosphonium-based liquid for a more specialised thermometer with a wider temperature range.

"The work opens up yet another avenue in engineering science, as ILs continue to find relevance in increasingly diverse areas"
- Gary Baker, Oak Ridge National Laboratory, US
Rogers suggests that the thermometers could have uses both in industry and research and development. 'Specialty thermometers with a suitable liquid range could be interesting for operation under extreme environment conditions,' he says, 'for example, Antarctica and deep sea vents.'

Gary Baker, who also works with ILs, at Oak Ridge National Laboratory, US, says that 'using an IL as a filling fluid toward a new class of liquid-in-glass thermometer nicely illustrates the broad potential of ILs as potentially green replacements for conventional solvents.' He adds that 'the work opens up yet another avenue in engineering science, as ILs continue to find relevance in increasingly diverse areas.'

Sylvia Pegg

Link to journal article

Ionic liquids for liquid-in-glass thermometers
Héctor Rodríguez, Margaret Williams, John S. Wilkes and Robin D. Rogers, Green Chem., 2008, 10, 501
DOI: 10.1039/b800366a

Also of interest

Instant insight: Ionic liquids - instantly on site

Natalia Plechkova and Kenneth Seddon examine how ionic liquids are being applied in the real world.

Mild green ionic liquids

Washing with eutectic solvents cleans up biodiesel - and produces glycerol.

Interview: Green-fingered chemistry

Janet Scott tells Nicola Nugent about getting the green message across, the solution to pollution...and edible ionic liquids

The third age of ionic liquids?

Scientists in the US and Poland have shown that ionic liquids could have significant biological applications in drug delivery.

Testing the toxicity of ionic liquids

Ionic liquids have often been touted as the ultimate green solvent, but just how green is green?