关键词: 热传导, 微尺度, 分子模拟, 尺度效应, 十八烷酸

Abstract:

The thermophysical properties of steaic acid (SA) has a significant size dependence. However, only the macroscopic heat transport properties have been fully studied, which limits the further improvement of the thermal properties of composites phase change materials (PCMs) with microscale structure features, such as nanocapsule, aerogel materials and porous material. Therefore, in order to meet the research needs of materials design of the high-performance composite PCMs, the nanoscale heat transport properties of SA need to be discovered urgently. In this work, based on molecular dynamics simulation, the difference of thermal conductivity and the thermal transport mechanisms of SA in three forms of bulk, nanowire and nanochain were systematically studied. The thermal conductivity of three forms simulated by equilibrium method dynamics was 0.4546, 0.2213 and 0.0085 W·m^-1·K^-1, respectively. And the vibration density of states and overlap energy were used for the further exploration of the heat transport mechanism. The results show that the thermal conductivity of bulk is the largest, followed by the nanowire, and the nanochain has the lowest thermal conductivity. Due to the size effect, which results in the more boundary scattering events, the attenuation of phonon vibration at lower frequencies causes the nanowire thermal conductivity to be lower than that of the bulk. Besides the boundary scattering, the curled SA molecules in the nanochain cause the serious decrease of phono overlap energy between bonding atoms on the end of molecules. The high mismatch level of atoms increases the phonon scattering events happen in the molecule and hinders the heat transport between two molecules, and results in the lowest thermal conductivity in the SA nanochain.

Key words: heat conduction, microscale, molecular simulation, size effect, stearic acid