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Design, manufacturing and control of INterfaces in THERMally conductive polymer nanocomposites

Periodic Reporting for period 4 - INTHERM (Design, manufacturing and control of INterfaces in THERMally conductive polymer nanocomposites)

Reporting period: 2019-09-01 to 2020-11-30

INTHERM project addressed the design, manufacturing and control of interfaces in thermally conductive polymer/graphene nanocomposites. In particular, the reduction of thermal resistance associated to the contacts between conductive particles in a percolating network throughout the polymer matrix was targeted, to overcome the main bottleneck for heat transfer in nanocomposites and obtain lightweight materials with higher efficiency in heat transfer, with potential application is a number of heat exchanger devices, eventually contributing to the research and development efforts in energy saving, energy recovery an emission reductions.
The project included the investigation of novel chemical modifications of nanoparticles to build thermal molecular junctions, behaving as thermal bridges between adjacent particles as well as the research for advanced characterization methods for particle/particle interfaces and controlled processing methods for the preparations of nanocomposites with superior thermal conductivity.
The manufacturing of molecular junctions was successfully obtained, leading to significant enhancements in both in-plane e and cross-plane thermal conductivity of the networks of nanoparticles, thus validating the fundamental concept of INTHERM. Beside molecular junctions, the effect of local crystallization of polymers on the surface of graphene related materials was also demonstrated to enhance remarkably the quality of thermal contacts, thus providing an additional route for the design and obtainment of efficient heat transfer in nanocomposites.
The implementation of INTHERM principles in different polymer, preparation methods and nanostructured materials formulation lead to the development of a range of lightweight, tough and flexible materials, with thermal conductivity up to 200 W/mK, effectively bridging properties domains of conventional polymers and thermally conductive inorganics.
Phenomena controlling thermal transfer between conductive particles were investigated both experimentally and computationally. Both the extent of contact area and quality of the contacts were confirmed to control the overall thermal conductance at the particle-particle contacts. Different types of molecular junctions were screened computationally via novel molecular dynamics and DFT methods to select the most promising chemical structures for the functionalization of graphene and graphite nanoplates. The covalent functionalization with molecular junctions was obtained with suitable bifunctional molecules, able to build thermal bridges between conductive nanoflakes. Alternatively, non-covalent functionalization with ad-hoc synthesized polyaromatic molecules able to interact on the surface of graphene and related materials. Both covalent and non-covalent molecular junctions were experimentally proven to enhance the thermal conductivity at the macroscale, leading to thermally efficient graphene-based nanopapers able to outperform conventional metal foils, while granting for dramatic weight reduction. Concerning polymer nanocomposites, methods for dispersion of graphene were developed via melt extrusion polymerizations. Solution processing and post impregnation of preformed networks of conductive particles were also successfully developed. By these methods, a range of highly conductive and flexible nanocomposite materials were found, ranging from a few W/mK for conventional nanocomposites prepared via melt blending to above 150W/mK for polymer bound nanopapers deposited from solution.
INTHERM proved the possibility of exploiting complex chemical functionalization to the enhancement of thermal contacts. By the screening of different molecular junctions and correlation with their phonon transfer efficiency we also contributed to the determination of the best performing class of junctions, which efficiency was found to depend on both length and conformational stiffness. The validation of the concept of molecular juctions for the enhancement of thermal contacts between nanoparticles represent a significant progress in the state of the art of nanostructured conductive materials, paving the way for further research work towards more efficient materials and heat exchange devices.
INTHERM project concept