【作者】 李美丽；

【导师】 孙民华；

【作者基本信息】 哈尔滨师范大学 ， 材料物理与化学， 2009， 硕士

【摘要】 本文采用分子动力学模拟的方法,对二元混合液体的相分离和玻璃转变过程进行了研究。探讨了二元混合液体在相分离和玻璃转变过程中的动力学和热力学参数的变化、外压对液体相分离和玻璃转变的影响,以及在玻璃转变过程中的动力学不均匀现象。对于二元Lennard-Jones液体,研究了二元体系中相分离过程、粒子的扩散系数以及相分离域尺寸大小随温度的变化规律。我们发现,相分离域随温度的生长过程可以分为两个阶段,分别是温度比较高的快速生长阶段和低温时的稳定生长阶段;相分离体系中系统的扩散激活能不是常数,而是一个随温度变化的函数。我们还讨论了组元尺寸的变化对相分离过程的影响。结果表明,随两组元中某一组元尺寸σ的减小,系统的扩散性增加,粒子分离程度增强,使系统的相分离域更容易长大,促进系统相分离。研究了二元混合液体在不同外压作用下的相分离与玻璃转变过程,计算了相分离液体在玻璃转变过程中的结构和动力学特征。我们发现,外压会促进液体相分离的产生,并会提高玻璃转变温度,会使β弛豫出现的温度更高、存在的时间更长,导致系统扩散性降低。我们还首次发现,在这个体系中,液体发生相分离后,两相的玻璃转变温度不同,说明相分离液体的玻璃转变过程存在微观不均匀现象。更多还原

【Abstract】 Molecular dynamics (MD) simulation is performed to study the phase separation and the glass transition of a binary liquid mixture. Diffusion active energy, self-diffusion coefficient and microcosmic heterogeneity are discussed in the glass transition.Molecular dynamics (MD) simulation is performed to study the diffusion and phase separation process of binary Lennard-Jones (LJ) liquid. It is found that the growth of phase separation with temperature can be divided into two parts. The first is the fast-growth part at high temperatures and the second is the steady-growth part at low temperatures. Diffusion active energy in the phase separation system isn’t a constant, but a function of temperature and follows the relation of E=a+bTc. The influence of the components size on the phase separation is also discussed. The result shows that the diffusibility increases when the components size decreases. This makes the phase separation more easily.Molecular dynamics (MD) simulation is performed to study the phase separation and the glass transition of a binary liquid mixture when the external pressure is increased from 0Gpa to 2.75Gpa. The structure and dynamics characteristics in the glass transition process are calculated. We find that external pressure will promote the phase separation, and make the glass transition temperature increase. The external pressure will make temperature become high at which theβrelaxation emerge, the time ofβrelaxation become long, and the diffusibility of the system become low. We first find that the phase separation liquid exist microcosmic heterogeneity in the glass transition.更多还原