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43672-AC10
Thermal Transport across Organic/Inorganic Interfaces
Thermal Transport Across Organic/Inorganic Interfaces.
The primary goal of this project is to understand the transport of energy through the interface between two structurally and thermally mismatched materials. A pre-requisite for developing this understanding is to predict the thermal properties of polymers at nanoscale level.
In order to do this, our molecular dynamics program with implementation of Reactive Empirical Bond Order (REBO) model was modified to simulate thermal transport in carbon-based materials. The REBO potential had previously been used only for characterization of structural and energetic properties of hydrocarbons.
Simulations of thermal conductivity of diamond have been carried out with REBO potential at 300K to verify the relevance of selected method. The results, obtained with systems of various sizes, demonstrated good agreement with experimental data and simulations utilizing different interatomic potential. The same technique was applied to model thermal conductivity of crystal polyethylene. We have found that conductivity of polyethylene slabs with different sizes up to ~100nm reached the value of ~51W/mK nicely in accord with literature data for drawn polymers. However the value that was obtained by extrapolation to infinite length chains was an order of magnitude larger than predicted by experiment. These results imply that the structure of polyethylene in the simulation is a severe idealization of the experimental structure, leading to much more efficient thermal transport than experimentally. During the next year we plan to continue modeling of thermal conductivity of polymers at different temperatures, including polymers containing structural defects, polymers with various functional groups, polymers with cross-linked chains and amorphous polymers.
The interfacial (Kapitza) conductance at the interface between diamond and polyethylene was measured by simulation of direct heating of one end of the sample and cooling of another. The best bond matching between two materials was provided by placing (011) oriented diamond along the chain direction of polyethylene. The value of thermal conductance for ideal diamond/polyethylene interface was found ~620MW/m2K which is surprisingly high and close to the value measured for solid TiN/MgO interface. This is significantly larger than the value obtained experimentally for the seemingly analogous polymethyl methacrylate/alumina interface. Therefore, for the next year we plan to investigate how diamond/polyethylene conductance is impacted by variation of size and orientation of the systems, bond connectivity, temperature and polymers cross linking.
