Influence of Surface Orientation and Roughness of Stacked Graphene on Thermal Conductivity of Poly(dimethylsiloxane)-Based Composite: A Molecular Dynamics Simulation

The surface structure and distribution of stacked graphene (GE) are irregular and random in the poly(dimethylsiloxane) (PDMS) matrix, whose effect on the heat transfer is unclear. Therefore, a nonequilibrium molecular dynamics simulation is employed to investigate the influence of surface orientation and roughness of stacked GE on the interfacial thermal conductance and thermal conductivity of the GE/PDMS composite. Firstly, the interfacial thermal conductance gradually decreases as the increase of orientation angle of stacked GE. Meanwhile, it rises with increasing amplitude or decreasing wavelength of surface roughness. Interestingly, the interfacial interaction energy is a perfect predictor of the interfacial thermal conductance rather than the commonly believed contact area or roughness degree. Then, the vibrational density of states of interfacial GE along the heat-transfer direction is analyzed, which exhibits a transition of vibrational modes from high frequency to low frequency with decreasing the surface orientation or increasing the roughness of stacked GE. This enhances the interfacial phonon coupling degree, which thus improves the heat energy transfer. Moreover, the effective medium approximation model is utilized to analyze the thermal conductivity of the composite, which decreases by nearly 38% with increasing orientation angle. However, it improves by about 20–70% within the chosen range of roughness structures. The thermal conductivity of the composite from the model and experiments can be comparable. In summary, our results provide a deep and comprehensive understanding of the relationship between surface orientation and roughness of stacked GE and thermal conductivity.