Department of Physics, University of South Florida, Tampa, FL 33620, USA.
Soft Matter. 2017 Nov 8;13(43):7948-7952. doi: 10.1039/c7sm01442b.
Using molecular dynamics simulations of a tangent-soft-sphere bead-spring polymer model, we examine the degree to which semiflexible polymer melts solidify at isostaticity. Flexible and stiff chains crystallize when they are isostatic as defined by appropriate degree-of-freedom-counting arguments. Semiflexible chains also solidify when isostatic if a generalized isostaticity criterion that accounts for the slow freezing out of configurational freedom as chain stiffness increases is employed. The configurational freedom associated with bond angles (θ) can be associated with the characteristic ratio C = (1 + 〈cos(θ)〉)/(1 - 〈cos(θ)〉). We find that the dependence of the average coordination number at solidification [Z(T)] on chains' characteristic ratio C has the same functional form [Z ≃ a - b ln(C)] as the dependence of the average coordination number at jamming [Z(ϕ)] on C in athermal systems, suggesting that jamming-related phenomena play a significant role in thermal polymer solidification.
使用切线软球珠簧聚合物模型的分子动力学模拟，我们研究了在等静压条件下，半柔性聚合物熔体凝固的程度。根据适当的自由度计数论点，柔性链和刚性链在等静压时结晶。如果采用考虑链刚度增加时构象自由度缓慢冻结的广义等静压准则，半柔性链也会在等静压时凝固。与键角（θ）相关的构象自由度可以与特征比 C =（1 + 〈cos(θ)〉）/（1 - 〈cos(θ)〉）相关联。我们发现，凝固时平均配位数[Z(T)]与链特征比 C 的依赖关系具有与无热系统中平均配位数[Z(ϕ)]与 C 的依赖关系相同的函数形式[Z ≃ a - b ln(C)]，这表明与阻塞相关的现象在热聚合物凝固中起着重要作用。
