Max Planck Institute for Polymer Research, 10 Ackermannweg, 55128 Mainz, Germany.
J Chem Phys. 2011 Jun 14;134(22):224901. doi: 10.1063/1.3596744.
We examine the thermally induced fracture of an unstrained polymer chain of discrete segments coupled by an anharmonic potential by means of molecular dynamics simulation with a Langevin thermostat. Cases of both under- and over-damped dynamics are investigated, and a comparison with recent studies of bond scission in model polymers with harmonic interactions is performed. We find that the polymer degradation changes qualitatively between the inertial regime and that of heavily damped dynamics. The role of bond healing (recombination) is also studied and probability distributions for the recombination times and overstretched bond lengths are obtained. Our extensive simulations reveal many properties of the scission dynamics in agreement with the notion of random breakdown of independent bonds, e.g., the mean time of chain rupture, <τ> follows an Arrhenian behavior with temperature T, and depends on the number of bonds N in the polymer as <τ> ∝ N(-1). In contrast, the rupture rates of the individual bonds along the polymer backbone indicate clearly the presence of self-induced inhomogeneity resulting from the interplay of thermal noise and nonlinearity. Eventually we examine the fragmentation kinetics during thermolysis. We demonstrate that both the probability distribution function of fragment sizes as well as the mean length of fragments at subsequent times t characterize degradation as predominantly a first order reaction.
我们通过使用 Langevin 热机的分子动力学模拟来研究无应变聚合物链的热诱导断裂，该聚合物链由非谐势连接。我们研究了欠阻尼和过阻尼动力学的情况，并与最近关于具有谐相互作用的模型聚合物中键断裂的研究进行了比较。我们发现，聚合物降解在惯性区和强阻尼动力学区之间发生了定性变化。我们还研究了键愈合（重组）的作用，并获得了重组时间和过度拉伸键长度的概率分布。我们的广泛模拟揭示了许多与独立键随机破坏概念一致的断裂动力学特性，例如，链断裂的平均时间<τ>遵循温度 T 的阿伦尼乌斯行为，并取决于聚合物中的键数 N，即<τ>∝N(-1)。相比之下，聚合物主链上各个键的断裂速率清楚地表明了热噪声和非线性相互作用导致的自诱导非均质性的存在。最终，我们研究了热解过程中的碎片动力学。我们证明，在随后的时间 t 处，碎片大小的概率分布函数以及片段的平均长度都将降解特征化为主要的一级反应。
