一个低分子量聚氧化乙烯从亚稳态的折叠链片晶向稳态的伸直链片晶转化增厚过程的研究

THICKENING PROCESS OF LAMELLAR CRYSTALS OF A LOW MOLECULAR WEIGHT POLY(ETHYLENE OXIDE)

报道分子量为5000的聚氧化乙烯(PEO)从熔融态淬火到液氮温度后形成的两次链折叠(2-FC)片晶增厚过程的研究结果.在升温和恒温条件下,采用小角X射线散射(SAXS)在位地跟踪了2-FC片晶增厚成一次链折叠(1-FC)和进一步成为伸直链(EC)片晶的增厚过程.通过对SAXS数据以及它们的一维相关函数的数据的分析,发现在52℃以下,2-FC片晶主要增厚为1-FC片晶;在52℃以上,2-FC片晶则主要增厚为EC片晶;在58℃到EC片晶的熔点的温度区域里,已经形成的1-FC片晶还会熔融,完全转化为EC片晶.利用偏光显微镜(PLM)和扫描电子显微镜(SEM)观察晶体的形貌,比如球晶,获得的研究结果表明,没有发生大范围的晶体破坏后再形成的变化,也就是说片晶的增厚过程是一个发生在球晶内部的薄片晶熔融后转化为厚片晶的过程.

The thickening process of lamellar crystals from two folded-chain（2-FC） lamellae through one folded-chain（1-FC） lamellae finally to extended chain（EC） ones in bulk samples of a poly（ethylene oxide）（PEO） with a molecular weight of 5000 was studied.The samples with 2-FC crystals were prepared by quenching them from their melt to liquid nitrogen.During reheating them or treating them at selected annealing temperatures,we tracked the lamella-thickening process using small-angle X-ray scattering（SAXS）.After analyzing the SAXS data and the corresponding one-dimensional correlation functions,we found that below 52℃ 2-FC crystals primarily thickened into 1-FC crystals;but above 52℃ 2-FC crystals mainly thickened into EC crystals.In the temperature region between 58℃ and melting point of the EC crystals,the newly formed 1-FC crystals will further thicken into EC crystals.Our observations using polarized light microscopy（PLM） and scanning electron microscopy（SEM） show no changes of crystalline superstructures,such as spherulites,formed by these crystals.Therefore,we can conclude that the thickening process,we observed in this crystalline PEO samples,do not cause any destruction of large crystalline superstructures,so it is a process only containing melting of thinner lamella crystals and then recrystallization of the molecules into thicker lamella crystals.More importantly,this process is strictly restricted within some local regions of large crystalline superstructures.