Thermal conduction in an electrical insulating polymer

The drive of many electronic technologies towards miniaturisation, weight reduction and integration has increased the need for smart materials that can cope with new arising issues, such as the need for fast heat dissipation. The same issue is faced in electric motors and generators, automotive, solar panels, batteries, and heat exchangers in power generation. Metals can be used due to their high thermal and electrical conductivity, but they are expensive and rather heavy: for this reason, research is trying to replace metals with cheaper and lighter materials. An obvious choice is to use polymeric materials (plastic) that, in addition to the lower cost and weight, also have the advantage of being easily processable in a variety of shapes and sizes. However, polymers usually have very low thermal conductivities and suitable fillers (metal or ceramic particles being the most common ones) are added to increase the conductivity to the desired levels. The use of composites has drawbacks related to the need of further processing of the material, the change in mechanical properties due to the addition of fillers and the problems related to the end-of-life disposal. Moreover, the amount of fillers should be carefully controlled if the target is to get a material that is both thermally conductive and electrically insulating.
In principle, heat conduction could happen in polymers through the mechanism of lattice vibrations: the reason for the very low conductivity observed for these materials is mainly related to the random orientation and entanglement of polymer chains. It has been recently demonstrated that, if the polymer chains of a simple polymers such as polyethylene can be aligned, high thermal conductivity can be achieved in the direction of alignment. In order to achieve high conductivities, it is also desirable to have very long polymer chains, to minimise lattice defects brought by the chain ends. This is the case for Ultra High Molecular Weight Polyethylene (UHMWPE): however, the chain alignment process for this material is rather cumbersome and demands the use of large amounts of solvent to 'disentangle' the very long chains.
The proposed research aims to overcome these issues, building on our success at fine tuning the molecular characteristics and improving the processability of UHMWPE. We have devised a synthetic strategy that enables us to directly obtain UHMWPE with a reduced number of entanglements. We have demonstrated that this material can be easily processed, without the need for any solvent, to give tapes and filaments with high chain alignment. Moreover, our method offers the unprecedented possibility to tailor the molecular weight of the polymer as well as the chain alignment, by simply changing the reaction or processing conditions. In this project, we wish to apply the knowledge that we have developed on "disentangled UHMWPE" to study the effects that molecular structure and orientation have on the thermal conductivity of this material. The results coming from this project will enable us to realise a light-weight, cheap, easy to process and to recycle material where the thermal conductivity can be tuned in a range of useful values by suitable modifications of the synthetic and processing steps.

The target of the proposed project is to realise a polymeric material that while being electrically insulating has a thermal conductivity in a range close to those of metals. From a technological point of view, this material could represent an alternative to those nowadays used in heat dissipation applications, mainly metals and plastic composites.
In many cases, metals are not a suitable option for heat-dissipating components, due to their higher density, lower formability and the fact that they are also electrically conductive. For example, the rapid development of integrated electronic circuits used in the electronic and communication industry has brought a higher demand for plastic wiring boards and packages that efficiently dissipate generated heat. For the next generation of portable information devices, high-thermal-conductivity films are required. Products using LED technology need very powerful LEDs for higher brightness, but conventional plastic cannot dissipate the resulting heat efficiently. In the automotive industry, thermally conductive plastic composites are used in diesel fuel pumps, headlamp reflectors and radiators.
The main issues related to the plastic composites are their cost, which increase with the range of conductivity required, their processing, usually requiring the use of harsh chemicals, and their end-of-life disposal.
With respect to polymer composites, the material that this project aims to develop offers easier processing, not needing harsh temperatures and harmful solvents, less recycling issues, due to the absence of any filler, and ultimately a lower cost alternative. These characteristics meet the societal requirements for cheaper, lightweight products that have less impact on the environment. The material could be used to build components used in different fields such as electronic, automotive, energy, communication, and food industries. The application of our material in any of these fields would represent both a direct benefit (for example, electronic components of everyday use would be cheaper and perform better) and an indirect benefit (for example, the use of this material in the industrial environment could help in reducing the carbon footprint of the industry) to society. The involvement of a partner company having expertise in polymer processing will ensure the adequate support to the PI to transfer the successful findings into a product that can be launched on the market.
The related research on the relationship between molecular structure, material processing and thermal properties will bring significant advances also to the fundamental understanding of soft matter. We believe that the know-how acquired on thermal conduction through lattice vibrations in simple polymers made of just carbon and hydrogen could be extended to more complex systems, broadening the impact of the findings.
Lastly, the proposed research will have a significant impact on the persons directly involved in the research. The PI will expand her field of scientific expertise and develop the necessary managerial and communication skills to increase her chances to become a research leader in her field. The Research Associate and the technician will participate in shaping the research, thus expanding their range of expertise and responsibility. Other persons involved, such as the academic mentors, the modelling advisor and the industrial contacts will have the chance to build new links that could last beyond the duration of the project.