Progress in Polymer Science ( IF 27.1 ) Pub Date : 2021-02-16 , DOI: 10.1016/j.progpolymsci.2021.101376 Leire Sangroniz , Bao Wang , Yunlan Su , Guoming Liu , Dario Cavallo , Dujin Wang , Alejandro J. Müller
The crystallization of heterogeneously nucleated bulk polymers typically occurs in a single exothermic process, within a narrow temperature range, i.e., a single exothermic peak is detected by differential scanning calorimetry when the material is cooled from the melt. However, when a bulk semicrystalline polymer is subdivided or dispersed into a multitude of totally (or partially) isolated microdomains (e.g., droplets or cylinders), in number comparable to that of commonly available nucleating heterogeneities, several separated crystallization events are typically observed, i.e., fractionated crystallization. This situation is often found for the minor crystallizable component in immiscible blends.
When the bulk polymer is dispersed into a number of microdomains that is several orders of magnitude higher than the available number of heterogeneities within it, most microdomains will be heterogeneity-free. In these clean microdomains the nucleation can occur by contact with the interfaces (i.e., surface nucleation) or by homogeneous nucleation inside the microdomain volume. These cases can be easily encountered in cylinders or spheres within strongly segregated block copolymers, or in infiltrated polymers within nanopores of alumina templates.
In this work, a comprehensive review of the known cases of fractionated crystallization is provided. The changes upon decreasing microdomain sizes from a dominant single heterogeneous nucleation, through fractionated crystallization, to surface or homogeneous nucleation are critically reviewed. Emphasis is placed on the common features of the phenomenon across the different systems, and thus on the general conclusions that can be drawn from the analysis of representative semicrystalline polymers. The origin of the fractionated crystallization effects and their dramatic consequences on the nucleation and crystallization kinetics of semicrystalline polymers are also discussed.
中文翻译:
半结晶聚合物的分步结晶
非均相成核的本体聚合物的结晶通常在狭窄的温度范围内在单个放热过程中发生,即,当从熔体中冷却材料时,通过差示扫描量热法检测到单个放热峰。但是,当将块状半结晶聚合物细分或分散为多个完全(或部分)分离的微区(例如,液滴或圆柱体)时,其数量可与常用的成核异质性相比较,通常会观察到几个分离的结晶事件,即,分步结晶。对于不混溶的共混物中的少量可结晶成分,通常会发现这种情况。
当将本体聚合物分散到多个微区中时,该微区比其内部可用的异质性数量高几个数量级,大多数微区将没有异质性。在这些干净的微区中,成核可通过与界面接触(即表面成核)或通过在微区体积内的均相成核而发生。在强分离的嵌段共聚物中的圆柱体或球体中,或者在氧化铝模板的纳米孔内的渗透聚合物中,很容易遇到这些情况。
在这项工作中,对分级结晶的已知情况进行了全面回顾。严格审查了微域尺寸从占主导地位的单一异质成核,通过分步结晶到表面或均相成核的减小的变化。重点放在跨不同系统的现象的共同特征上,因此放在可以从代表性半结晶聚合物的分析中得出的一般结论上。还讨论了分馏结晶效应的起源及其对半结晶聚合物成核和结晶动力学的重大影响。