Flexible temperature modulation devices inspired by traditional Japanese paper crafts

   NIMS has developed a new material processing technique inspired by kirigami—a traditional Japanese paper craft—capable of manipulating and enhancing the local cooling/heating performance of elastocaloric effect at specific areas in response to the application of tensile/compressive force. The performance in plastics, which is known to exhibit only small elastocaloric effects, can also be enhanced in this way. This technique may be used to develop thermal management technologies in flexible electronics.

   Temperature control technologies, such as refrigerators, have been indispensable to our lives. The elastocaloric effect is expected to realize environment-friendly temperature modulation as a promising alternative to vapor compression refrigeration which uses environmentally harmful refrigerants. Active efforts are underway to find materials capable of exhibiting large elastocaloric effects. Although many materials show this effect to varying degrees, only shape-memory alloys had been considered potentially significant elastocaloric materials.

   This research team recently developed a new method of manipulating the magnitude and distribution of the elastocaloric temperature modulation by processing plain elastocaloric materials (Figure (a)) into structures resembling kirigami (Figure (b)). This kirigami processing can focus the internal stress at specific areas of materials with the application of very small tensile forces, resulting in the modification of performance of elastocaloric cooling/heating. The team applied this process to conventional plastic materials—which had been known to exhibit only small elastocaloric effects—and found that their performance of local heat absorption/release in designated areas was greatly improved, far exceeding that of shape-memory alloys which had been known to exhibit the largest elastocaloric effects.

   A diverse array of kirigami processing patterns could provide plastics and many other materials ultrahigh stretchability and flexibility. In future research, the team plans to identify optimum kirigami patterns and materials conducive to temperature modulation induced by the elastocaloric effect, which could develop technologies of precise temperature control for miniaturized electronic devices and realize flexible temperature modulator.

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   This project was carried out by a research team led by Takamasa Hirai (Researcher, Spin Caloritronics Group (SCG), Research Center for Magnetic and Spintronic Materials (CMSM), NIMS), and Ken-ichi Uchida (Group Leader of the SCG, CMSM, NIMS). This work was partly supported by the JST Strategic Basic Research Program CREST (project number: JPMJCR17I1) and the Canon Foundation Research Grant Program under the category, “Creation of Industrial Infrastructure.”

   This research was published in the online version of Advanced Functional Materials, a German scientific journal, on April 19, 2022.