Nanotechnologies / Materials
Energy reuse, Organic electronics

Development of thermal switch material using structurechange in organic film including nanostructure
Department of System Innovation, Graduate School of Engineering Science
Professor Yoshiaki Nakamura			

https://researchmap.jp/research_nakamura?lang=en

Assistant Professor Takafumi Ishibe		

https://researchmap.jp/t-ishibe?lang=en

Nanotechnologies / Materials

Abstract
Temperature-triggered thermal switch, which causes thermal
conductivity change in response to the environmental temperature,
is attracting much attention as one of the thermal management
devices. Previous studies have focused on the increase of On/Offswitching ratio. On the other hand, for the social application, it isalso required to tune the switching temperature. However, there
have been no experimental studies about it. In this study, we areaiming at tuning the switching temperature by using the order-ordertransition of liquid crystalline block copolymer film including anisotropic nanostructures. Choosing the different type of mesogens
in the side chain of liquid crystal part modulated the order-ordertransition temperature, resulting in the tuning of switching temperature. This success leads to the social application of thermal switch
under various temperature situations.

▍ Background & Results
Thermal management devices are attracting much attention
for overcoming the issue of heat generation in electronic devices.
Among them, thermal switch allows us to control thermal conductivity. Previous studies have focused on the increase of On/Offswitching ratio. On the other hand, for the social application, it isalso required to tune the switching temperature. However, there
have been no experimental studies about it.
In this study, we focused on the liquid crystalline block copolymer including anisotropic nanostructures. In the blockcopolymer, the order-order transition occurs at the certain temperature:
the morphology of nanostructure is changed from cylinder (lowtemperature phase) to sphere (high temperature phase)(Fig. 1).
Furthermore, the transition temperature depends on the type ofmesogens in the side chain of liquid crystal part. The block copolymer films with the different order-order transition temperatures of
360 and 390 K exhibited thermal conductivity switching behaviors(On/Off switching ratio ~ 2) at the different temperatures of ~360
and ~390 K, respectively(Fig. 2). This result highlights that the control of molecular structure can be a renewed methodology of tuning the switching temperature. Furthermore, we revealed that themagnitude of On/Off switching ratio is attributed to the anisotropyof nanostructures in block copolymer and the heat scattering at thenanostructure interfaces. This gives new insight for heat transportphysics in organic materials.

Fig 1 Tuning the switching temperature in thermal switch using the order-ordertransition in liquid crystalline block copolymer. Choosing the type of mesogens inthe side chain in liquid crystal part modulates the switching temperature.

Fig 2 (a) Atomic force microscope image of the surface of block copolymer including cylinder (low temperature phase).
(b) Thermal conductivites (κ) of block copolymer films as a function of the environment temperature (T). The block copolymer films with the different order-ordertransition temperatures of 360 (the triangles) and 390 K (the circles) exhibit thermal conductivity switching behaviors at the different temperatures of ~360 and~390 K, respectively.

▍ Significance of the research and Future perspective
This study realized the tuning of switching temperature in thermal switch by choosing the different type of mesogens in the side
chain of liquid crystal part, which is related to the order-order transition temperature. This tuning method of switching temperature
has high versatility because this method can be applied to various
material systems only if the switching temperature depends onthe molecular structure. In the future, this success will lead to thedevelopment of thermal management organic material at low cost,
and will contribute to the realization of the society using thermalenergy efficiently.

P a t e n t
Ishibe, Takafumi; Kaneko, Tatsuya; Uematsu, Yuto et al. Tunable thermal switch via order-order transition in liquid crystalline block copolymer. Nano
Letters. 2022, 22 (15), 6105-6111. doi: 10.1021/acs.nanolett.2c01100
UR
L http://www.adv.ee.es.osaka-u.ac.jp/?lang=en
K e y w o r d thermal management, nanotechnology, organic film, structure phase transition
Tr e a t i s e