Department of Chemical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
J Chem Phys. 2012 Mar 28;136(12):124907. doi: 10.1063/1.3698473.
There has been much recent debate as to whether mechanical deformation reverses the aging of a material, and returns it to a structure characteristic of the system at a higher temperature. We use molecular dynamics simulation to address this problem by carrying out shear and temperature increase simulation on atactic glassy polystyrene. Our results show explicitly that the structure (as quantified by the torsion population) changes associated with shear and temperature increase are quantitatively--and in some cases qualitatively--different. This is due to the competition between rejuvenation and physical aging, and we show this by carrying out a relaxation simulation. The conclusion agrees with those from previous experiments and simulations, which were suggestive of mechanical deformation moving the system to structures distinct from those reached during thermal treatment.
最近有很多关于机械变形是否会逆转材料老化，使其恢复到高温下系统特征结构的争论。我们使用分子动力学模拟通过对无规玻璃态聚苯乙烯进行剪切和升温模拟来解决这个问题。我们的结果明确表明，与剪切和升温相关的结构（用扭转分布来量化）变化在定量上——在某些情况下在定性上——是不同的。这是由于恢复和物理老化之间的竞争，我们通过进行弛豫模拟来证明这一点。这一结论与之前的实验和模拟结果一致，这些结果表明机械变形使系统移动到与热处理过程中达到的结构不同的结构。
