Termination of crystallization or ordering of flexible, linear macromolecules
Termination of crystallization or ordering of flexible, linear macromolecules
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柔性线性大分子的结晶或排序终止
DOI：
10.1007/s10973-012-2326-2
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发表时间：
2012
影响因子：
4.4
通讯作者：
B. Wunderlich
中科院分区：
文献类型：
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作者：
B. Wunderlich
这篇综述涉及在从非晶相过渡到热力学平衡之前“柔性线性大分子的结晶或有序终止”。它利用后见之明的精确解释旧实验，并将最近的实验与从著名的旧实验中获得的知识进行反向整合，这些实验导致了这个悖论：半有序样品一旦产生，其无序性往往遵循零熵产生路径，即其潜热与非平衡相的自由焓有关，而在有序时，聚合物熔体存在一个亚稳温区，该亚稳温区不能被有序相的核破坏。通过成核和生长的经典结晶方案被用来为讨论奠定基础。这个方案已经被用来描述单个基序的运动，以结晶小的，刚性分子和它的慢速，当接近玻璃化转变。对于柔性大分子，排序机制需要扩展到描述分子片段的多个基序的合作排序方案，并且在接近更宽的玻璃过渡区时需要更复杂的多步减速。导致柔性大分子不完全有序的结构特征是在有序相和无序相之间的相界处产生的三维缺陷，最初称为非晶态缺陷。这些非晶缺陷中的物质具有更广泛的玻璃化转变。如果这种玻璃化转变位于不受约束的非晶相的玻璃化转变之上，则非晶缺陷代表一个单独的纳米相，称为刚性非晶部分。现代差示扫描量热法（DSC），温度调制DSC和差示快速扫描量热法允许研究涉及非晶相，晶体和中间相的液固转变的潜热和热容变化。在这个更复杂的框架中，“柔性线性大分子结晶的终止”与摩尔质量分离的可能性一起被描述为远程和局部扩散，而不是热力学机制。
This review concerns the “termination of crystallization or ordering of flexible, linear macromolecules” before the transition from the amorphous phase reaches thermodynamic equilibrium. It makes use of the precision of hindsight in interpretation of old experiments and the back-integration of more recent experiments into the knowledge gained from the well-known older experiments which had led to the paradox: Once the semi-ordered sample is produced, its disordering frequently follows a zero-entropy-production path, i.e., its latent heat is linked to the free enthalpy of the non-equilibrium phase, while on ordering, there exists a metastable temperature region of the polymer melt which cannot be broken by nuclei of the ordered phase. The classic scheme of crystallization via nucleation and growth is used to set the stage for the discussion. This scheme has been used for many years to describe the motion of single motifs to crystallize small, rigid molecules and its slow-down when approaching the glass transition. For flexible macromolecules, the ordering mechanism needs to be expanded to the description of cooperative ordering schemes of more than one motif of the molecular segments and a more complicated, multiple-step slow down when approaching the much wider glass transition region. The structural features causing the incomplete ordering of flexible macromolecules are the three-dimensional defects created at the phase boundaries between ordered and disordered phases, initially called the amorphous defects. The matter contained in these amorphous defects possesses a much broader glass transition. If this glass transition lies above the glass transition of the unrestrained, amorphous phase, the amorphous defects represent a separate nanophase, called a rigid-amorphous fraction. Modern differential scanning calorimetry (DSC), temperature-modulated DSC, and differential fast scanning calorimetry permit the study of latent heats and heat-capacity changes involved in the liquid–solid transitions of amorphous phases, crystals, and mesophases. In this more complex framework, the “termination of crystallization of flexible, linear macromolecules” is described together with the possibility of molar mass segregation by long-range and local diffusion instead of a thermodynamic mechanism.