Greater Thermal Conductivity through Molecular Coupling

Compared to metallic materials, plastics have very low thermal conductivity. In certain application, e.g. insulating foams, this is advantageous

In electronic applications, however, the low thermal conductivity can result in local overheating.

Since polymers usually do not have any freely moving electrons, thermal energy in plastics is transmitted primarily by elastic waves in the solid (so-called phonons). Strong bonds between the individual molecules are needed for heat to be conducted by thermal waves. In amorphous thermoplastics, however, the polymer chains are linked to one another only loosely. For this reason, the vibrations cannot be transmitted from one molecule to the next molecule.

Researchers a the University of Michigan have now succeeded in coupling molecular structures of polyacrylic acid with one another by means of short polymer chains. The coupling is based on hydrogen bonds – these are several times stronger than the forces that normally act between polymer chains.

In the course of experiments, it was noted that the thermal conductivity is raised significantly when polymerized acryloyl piperidine (PAP) is added to the polyacrylic acid. The addition apparently results in numerous thermal conduction paths in the material and heat transport increases to ten times the initial value. The results of the measurements suggest additional principles that can be used to influence the thermal conductivity in amorphous polymers.

Until now, attempts to improve the thermal conductivity of polymers have been based on conductive fillers. This approach, however, also has drawbacks: the additives can change material properties such as the electrical conductivity, light transmission and reflection at the surface. According to the researchers, this newly developed material does not exhibit these drawbacks.