当前位置: X-MOL 学术ACS Macro Lett. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Mechanisms of Directional Polymer Crystallization.
ACS Macro Letters ( IF 5.1 ) Pub Date : 2020-06-23 , DOI: 10.1021/acsmacrolett.0c00346
Alejandro A Krauskopf 1 , Andrew M Jimenez 1 , Elizabeth A Lewis 2 , Bryan D Vogt 3 , Alejandro J Müller 4, 5 , Sanat K Kumar 1
Affiliation  

Zone annealing, a directional crystallization technique originally used for the purification of semiconductors, is applied here to crystalline polymers. Tight control over the final lamellar orientation and thickness of semicrystalline polymers can be obtained by directionally solidifying the material under optimal conditions. It has previously been postulated by Lovinger and Gryte that, at steady state, the crystal growth rate of a polymer undergoing zone annealing is equal to the velocity at which the sample is drawn through the temperature gradient. These researchers further implied that directional crystallization only occurs below a critical velocity, when crystal growth rate dominates over nucleation. Here, we perform an analysis of small-angle X-ray scattering, differential scanning calorimetry, and cross-polarized optical microscopy of zone-annealed poly(ethylene oxide) to examine these conjectures. Our long period data validate the steady-state ansatz, while an analysis of Herman’s orientation function confirms the existence of a transitional region around a critical velocity, vcrit, where there is a coexistence of oriented and isotropic domains. Below vcrit, directional crystallization is achieved, while above vcrit, the mechanism more closely resembles that of conventional isotropic isothermal crystallization.

中文翻译:

定向聚合物结晶的机理。

区域退火是一种最初用于纯化半导体的定向结晶技术,在此应用于结晶聚合物。通过在最佳条件下定向固化材料,可以严格控制半结晶聚合物的最终层状取向和厚度。Lovinger和Gryte先前已假定,在稳定状态下,经历区域退火的聚合物的晶体生长速率等于通过温度梯度抽取样品的速度。这些研究人员进一步暗示,当晶体生长速率在成核过程中占主导地位时,定向结晶仅在临界速度以下发生。在这里,我们对小角度X射线散射,差示扫描量热法,区域退火的聚环氧乙烷的交叉偏振光学显微镜检查这些猜想。我们的长期数据验证了稳态ansatz,而对Herman方向函数的分析证实了临界速度附近存在过渡区域,v crit,其中存在定向域和各向同性域。低于v crit时,可实现定向结晶,而高于v crit时,其机理与常规的各向同性等温结晶更为相似。
更新日期:2020-07-21
down
wechat
bug