气凝胶初级粒子导热系数的分子动力学模拟

Molecular Dynamics Simulation of Thermal Conductivity of Primary Particle of Silica Aerogel

采用分子动力学方法模拟融化-淬火工艺制备非晶态Si O2材料和Si O2气凝胶初级粒子单元。基于非平衡分子动力学（Non-equilibrium molecular dynamics,NEMD）理论计算体态材料和初级粒子单元的导热系数,计算过程考虑了冷热源引起的尺度效应。结果表明,计算得到的体态材料导热系数与文献计算结果吻合良好。对于初级粒子单元,在粒径2-6 nm范围内,粒子直径使得粒子单元导热系数出现了尺度效应,但是影响相对较小。粒子间界面直径对粒子单元导热系数影响很大,当粒子直径为3 nm时,界面直径从0.89 nm增加到2.49 nm,粒子单元导热系数增大了171.61%,粒子界面处的温度阶跃,表明存在明显的界面热阻效应;且界面直径越小,界面热阻越大。

The amorphous Si O2 and primary particle unit（PPU） of Si O2 aerogel are generated using the melting-quenching process based on the molecular dynamics method. Their thermal conductivities（TC） are also calculated by the non-equilibrium molecular dynamics（NEMD）. The size effect on the TC caused by the heat source and heat sink has been taken into account. The predicted TC of the bulk amorphous Si O2 material is in good agreement with the available results in literature. Calculated results also show that the particle diameter has made the TC of the PPU show scale effect in the range of 2-6 nm though the effect is relative small. The diameter of the interface between particles has significant effect on the TC of the PPU which increase 171.61% as the interface diameter increases from 0.89 nm to 2.49 nm when the particle diameter is 3 nm. A temperature drop at the interface showed that there is interfacial thermal resistance between the neighboring particles. It is also shown that, the smaller the interface size, the bigger the interface thermal resistance.