Polymers are ubiquitous in a wide range of applications from structure materials to electronics due to their diverse functionality, light weight, low cost, and chemical stability. The thermal conductivities of the vast majority of amorphous polymers are in a very narrow range, although single polymer chains possess thermal conductivities of orders of magnitude higher. The low thermal conductivity of polymers is a major technological barrier for the reliability and performance of polymer-based electronics due to a limited heating spreading capability. The thermal conductivity of amorphous polymers is universally confined in a very narrow range 0.1-0.5 W/(m\*K). This feature indicates the possible existence of a universal thermal transport mechanism in amorphous polymers regardless of their distinct chemical structures. Researchers have developed and tested several minimum thermal conductivity models for amorphous polymers. All those models use bulk properties as inputs, which lack molecular chain details and thus are not able to describe the dependence of thermal conductivity on temperature, pressure, and orientation, simultaneously. An amorphous polymer is a three-dimensional van der Waals solid formed by entangled, long, one-dimensional molecular chains. Molecular dynamics simulations suggested that a single molecular chain may have a very high thermal conductivity of orders of magnitude higher than its amorphous counterpart. This difference is attributed to the fundamental distinction between the one-dimensional chain and three-dimensional network. A theoretical model for the thermal conductivity of an amorphous polymer considering the microscopic structure of a three-dimensional network is highly desirable. Both intrachain and interchain thermal transport should be incorporated, where the intrachain thermal transport through a covalent bond is more efficient than the interchain thermal transport via van der Waals interactions. We propose a thermal resistance network model for the thermal conductivity in amorphous polymers considering the chemical structure of molecular chains and the interplay of interchain and intrachain thermal transport. Our model elucidates the physical origin of the low thermal conductivity universally observed in amorphous polymers with various chemical structures. The empirical formulas of the pressure and temperature dependence of thermal conductivity can be successfully reproduced from our model not only in solid polymers but also in polymer melts. We further quantitatively explain the anisotropic thermal conductivity in oriented polymers. We will also present our recent progress in identifying a universal formula for thermal conductivity of liquids, polymer, and amorphous solids. The values of thermal conductivity for different materials calculated from our formula are in excellent agreement with the experimental data without using any fitting parameters.


Thermal Resistance Network Model for Heat Conduction of Amorphous Polymers

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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