亚稳态的相尺寸对部分结晶聚合物结构与形态的影响

Size Effect of Metastable States on Semicrystalline Polymer Structures and Morphologies

在经典概念中，亚稳态相应于一个局部的自由能极小值，它最终会通过一个活化过程弛豫到稳定的平衡态，一个整体上的自由能极小值。这一过程不同于非稳态的无位垒弛豫，后者是自发进行的。作为一个亚稳态，它的寿命应长于测量的时间尺度。这在实际上取决于实验设备和测量者的耐性。在亚稳态的经典概念中假设体系都是足够大的，因此不须考虑相尺寸或其它动力学效应对体系的影响。一般来说，与小分子相比，高分子进入亚稳态要容易得多。具有多重微结构层次的聚合物体系可因小的相尺寸、组成、外场或其它因素而呈现亚稳态。本文将着重于亚稳态的概念和具有两个有序结构时聚合物相转变过程中亚稳态观测，这些结构间的相稳定性关系是通过相尺寸，也就是片晶厚度来讨论的。有关亚稳态和亚稳性的概念不只对科学地理解高分子凝聚态物理是重要的。

Abstract A classical concept of a metastable state is a local free energy minimum that may ultimately relax to the stable equilibrium state of a global free energy minimum via an activation process. This process is different from the barrierfreerelaxationthatspontaneouslytakesplace when an unstable state relaxes.In order to be classified as metastable,the lifetime of a metastable state must be longer than the time scale of observation,which in turn is practically limited by experimental equipment and the patience of the observer.In the classical concept of metastable states there is an assumption that the systems are large enough so that there is no need for consideration of size or other kinetic effects on the system.In general,polymers are much more prone to access the metastable region than small molecules.Polymeric materials,with their various hierarchies of microstructure,may have metastable states present due to small phase size,composition,external fields and other causes.In this review,our focus will be on concepts and experimental observations of metastable states in polymer phase transformations where two ordered structures exist.The phase stability relationships of these structures will be discussed with respect to the phase size,namely,the lamellar thickness.The concepts involved in metastable states and metastability are not only important in the scientific understanding of condensed polymer physics,but are also useful for practical materials development and applications.