Temperature dependence of thermal conductivity in two different liquid crystalline block copolymers (BC-1, BC-2). Image: Yoshiaki Nakamura et al.
Temperature dependence of thermal conductivity in two different liquid crystalline block copolymers (BC-1, BC-2). Image: Yoshiaki Nakamura et al.

Mobile phones from a few decades ago look like antiquated plastic toys today, demonstrating the dramatic miniaturization and increased functionality of modern electronics. Unfortunately, this miniaturization comes with an associated problem – the challenge of dissipating heat – which limits the functionality of ultra-small electronic devices. For practical applications, one neat solution to heat dissipation would be to incorporate a means of modulating the temperature at which a device changes its speed of heat transmission.

Now, in a paper in Nano Letters, researchers from Osaka University in Japan, together with collaborating partners, report experimentally modulating the thermal switching temperature of block copolymers. This study will help researchers cheaply modulate the temperature of organic electronic devices by changing the speed of heat transmission, and thus help solve an important challenge of device miniaturization.

"Liquid-crystalline, nanostructured block copolymers are ideal for our work," explains first author Takafumi Ishibe from Osaka University. "By using changes in temperature to modulate the anisotropy of the nanostructures, one can easily modulate the thermal conductivity of the polymer."

One component of the polymer – known as the mesogen – undergoes a phase transition (from a cylindrical nanostructure to a spherical nanostructure) upon crossing a temperature threshold. This temperature is known as the transition temperature. In other words, the anisotropy—and thus the thermal conductivity—of the polymer depends on the temperature.

The key to the researchers' work is their finding that tuning the chemical composition of the mesogen offers an easy way to change the transition temperature. That is, by straightforward chemical synthesis, the researchers could easily adjust the temperature at which the anisotropy changes occur, and thus change the speed of heat transmission by the polymer.

"We adjusted the transition temperature over the range of 90°C to 147°C by judicious choice of the mesogen," says senior author Yoshiaki Nakamura from Osaka University. "Conductivity-switching was fully reversible, and the difference between the on and off state was approximately two, which is comparable to the conventional values of various thermal switches reported in preceding studies."

Many researchers have changed the on/off ratio of thermal-conductivity-switching materials. However, this study is the first to experimentally focus on modulating the thermal switching temperature by controlling the transition temperature of such materials. By doing so, Nakamura and co-workers have imparted practical functionality to block copolymers that undergo thermal conductivity switching, and at low cost. This innovation holds great promise for sustainable thermal management in upcoming advanced technologies.

This story is adapted from material from Osaka University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.