摘要
使用小角X光散射（SAXS）方法研究了每臂分子量为5000的四臂聚氧化乙烯在从熔点以上的温度淬火到室温后，在室温到熔点前的温度区域里片晶的增厚过程.采用一维相关函数分析方法分析了SAXS数据，获得了样品的长周期、线性结晶度、结晶层和无定形层厚度随温度的变化.按照这些参数在升温过程中的演变规律，确定了3个特征区域.Ⅰ区约在26-45 ℃内，存在着3种不同厚度的片晶，最厚的片晶层厚度为9.3 nm，线性结晶度、长周期、结晶层和无定形层厚度等参数基本不变，称为不变区.Ⅱ区约在45-52 ℃之间，这些参数都发生变化，SAXS的主峰分化为两个主要的峰，长周期、结晶层和无定形层厚度开始增加，但是，线性结晶度升高后又降低，称为转变区.Ⅲ区约在52-60 ℃之间，体系中只有单一厚度的片晶，其厚度不断增厚，到60 ℃结晶层厚度达15.8 nm，称为增厚区.从分子运动和片晶亚稳定本质分析，可以解释实验上观察到的3个区域发生变化的本质：在不变区里，主要的分子运动几乎被冻结，不可能发生可检测到的片晶结构变化.在转变区里，分子运动开始起作用，未结晶的分子开始结晶.同时，薄片晶会熔融，尔后又重新结晶.在增厚区里，线性结晶度和结晶层厚度增加，也意味着熔融-重结晶过程还在继续，直至达到这个样品可能形成的最厚片晶的熔点.实验观察到的熔融-重结晶过程的本质是聚合物片晶的亚稳态特性，稳定性低的薄片晶向稳定性高的厚片晶转变，即一个典型的奥斯瓦尔德熟化（Ostwald ripening）.
Studies on the lamellar thickening of a 4-arm poly（ethylene oxide） with Mn=5000 for each arm are reported. The samples were prepared by quenching from 70 ℃ to 10 ℃. Small-angle X-ray scattering （SAXS） was used to track the variation of lamellar structure during heating process. Then the SAXS data were further analyzed using one-dimensional correlation function. The following parameters, such as long period, linear crystallinity, crystalline layer thickness and amorphous layer thickness, were determined. Their changes with increasing temperature suggest three temperature regions. Region Ⅰ is in 26-45 ℃. There are three broad scattering peaks with low scattering intensity. They correspond to lamellae with different thicknesses. The crystalline layer thickness of the dominated lamella is about 9.3 nm. Importantly, the parameters mentioned above remain unchanged in Region Ⅰ. Region Ⅱ within 45-52 ℃ is a transition one. The main peak of the SAXS curves turns into two. The long period, linear crystallinity, crystalline layer thickness and amorphous layer thickness began to increase. Region Ⅲ （52-60 ℃） is a thickening region within which the crystalline layer thickness clearly increased with increasing temperature. At 60 ℃ its value is 15.8 nm. These observed results found in the three regions were further explained based on the role of metastable states of polymer lamellae. Within region Ⅰ macromolecules were in a frozen state, thus it was impossible to detect any change related to the lamellar structure. Within region Ⅱ, the temperature is higher enough to let some thin crystalline layers melt and then the melted macromolecules would recrystallize around the thicker ones. In region Ⅲ the continuous melting-recrystallization process proceeds until the melting point of the sample. The observed melting-recrystallization process reflects the metastability of polymer lamellae： Thinner lamellae are in a metastable state with a lower stability, thus will melt to recrystallize to form thicker lamellae with a higher stability. Acctually, the continuous melting-recrystallization process is a typical Ostwald ripening of polymer lamellae.
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2014年第3期415-422,共8页
Acta Polymerica Sinica
基金
国家自然科学基金(基金号20474033和20874053)资助项目
关键词
聚氧化乙烯
小角X光散射
片晶
熔融-重结晶
奥斯瓦尔德熟化
Poly （ethylene oxide ）, Small-angle X-ray scattering, Lamellar thickening, Mething-recrystallization, Ostwald ripening
