By Josh Perry, Editor
[email protected]

Researchers from each side of the Atlantic collaborated on the development of a new heat sensor with a polymer gels of p-type, in which positively-charged ions carry current, and a highly-conductive n-type polymer gel that carries current with negatively-charged ions.

Research fellow Dan Zhao with the ultra-sensitive printed sensor.
(Peter Holgersson AB/ Linköping University)

According to an article from Linköping University (LIU), scientists from Linköping, Chalmers University of Technology, Stuttgart Media University, and the University of Kentucky combined efforts to design an ultra-sensitive heat sensor from this polymer mix. The sensor is flexible, transparent, and printable.

“The researchers have developed a thermoelectric material that uses ions as charge carriers instead of electrons, and the effect is a hundred times larger,” the article explained. “A thermoelectric material that uses electrons can develop 100 µV/K (microvolt per Kelvin), which is to be compared with 10 mV/K from the new material. The signal is thus 100 times stronger, and a small temperature difference gives a strong signal.”

This is the first printed thermoelectric module that uses ions as charge carriers, according to the article. The module includes linked n- and p-legs and scientists used screen printing to build a sensor with 36 connected legs that produces 0.333 V with a temperature difference of only 1 K.

The research was published in Nature Communications. The abstract stated:

“Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes. Traditional thermopiles can provide accurate and stable temperature reading but they are based on brittle inorganic materials with low Seebeck coefficient and are difficult to manufacture over large areas.

“Recently, polymer electrolytes have been proposed for thermoelectric applications because of their giant ionic Seebeck coefficient, high flexibility and ease of manufacturing. However, the materials reported to date have positive Seebeck coefficients, hampering the design of ultra-sensitive ionic thermopiles.

“Here we report an “ambipolar” ionic polymer gel with giant negative ionic Seebeck coefficient. The latter can be tuned from negative to positive by adjusting the gel composition.

“We show that the ion-polymer matrix interaction is crucial to control the sign and magnitude of the ionic Seebeck coefficient. The ambipolar gel can be easily screen printed, enabling large-area device manufacturing at low cost.”