赤藓糖醇微观固液相变及热传导的分子动力学研究

Molecular dynamics study of solid-liquid phase change and heat conduction of erythritol at microscale

采用分子动力学方法对微尺度下赤藓糖醇的固液相变及热传导现象进行了模拟研究。首先选用GROMOS力场计算了赤藓糖醇固液两相的密度并将预测结果与实测值进行对比,验证了该力场的适用性。采用界面/NPT法模拟了赤藓糖醇的微观熔化过程,通过体系的体积突变得到预测熔点约为400 K,和实测值(392±1)K较为吻合。与直接加热纯固态赤藓糖醇的方法相比,该方法由于引入固液界面降低了成核自由能位垒,使得微观熔化过程的模拟更准确。此外,基于非平衡分子动力学方法研究了赤藓糖醇分子间的微观热传导现象。模拟得到液态赤藓糖醇的热导率为0.33~0.35 Wm^(-1)K^(-1),与宏观实测值(0.33±0.02)Wm^(-1)K^(-1)保持一致。因为处于液态时赤藓糖醇的分子分布具有无序性,所以其热导率预测值几乎不随模拟系统的尺寸而变化。

The solid-liquid phase change and heat conduction phenomena of erythritol at the microscale were studied using molecular dynamics（MD） simulation. The GROMOS force field was first utilized to calculate the density of erythritol in both solid and liquid phases. The applicability of this force field was verified by comparing the predicted density with the measured values. The microscale melting process of erythritol was simulated using interface/NPT method. The temperature corresponding to a sudden volume increase of the simulated system was identified as the melting point（400 K）, which is in agreement with the measured value of（392±1） K. Due to lowering of the nucleation free energy barrier by introducing a solid-liquid interface, this method was exhibited to have a better performance in simulating the microscale melting process than the direct heating method on solid erythritol. Moreover, non-equilibrium MD simulation was performed to study the microscale heat conduction between erythritol molecules. The thermal conductivity of liquid erythritol was predicted in the range of 0.33—0.35 Wm（-1）K（-1）, which is consistent with the measured value of（0.33±0.02）Wm（-1）K（-1） on bulk erythritol. The predicted thermal conductivity was found to have a negligible dependence on the size of the simulated system because of the random distribution of erythritol molecules in liquid phase.