Haley Jeffrey C, Lodge Timothy P
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Chem Phys. 2005 Jun 15;122(23):234914. doi: 10.1063/1.1931656.
The tracer diffusion coefficient of unentangled poly(ethylene oxide) (PEO, M=1000 gmol) in a matrix of poly(methyl methacrylate) (PMMA, M=10 000 gmol) has been measured over a temperature range from 125 to 220 degrees C with forced Rayleigh scattering. The dynamic viscosities of blends of two different high molecular weight PEO tracers (M=440 000 and 900 000 gmol) in the same PMMA matrix were also measured at temperatures ranging from 160 to 220 degrees C; failure of time-temperature superposition was observed for these systems. The monomeric friction factors for the PEO tracers were extracted from the diffusion coefficients and the rheological relaxation times using the Rouse model. The friction factors determined by diffusion and rheology were in good agreement, even though the molecular weights of the tracers differed by about three orders of magnitude. The PEO monomeric friction factors were compared with literature data for PEO segmental relaxation times measured directly with NMR. The monomeric friction factors of the PEO tracer in the PMMA matrix were found to be from two to six orders of magnitude greater than anticipated based on direct measurements of segmental dynamics. Additionally, the PEO tracer terminal dynamics are a much stronger function of temperature than the corresponding PEO segmental dynamics. These results indicate that the fastest PEO Rouse mode, inferred from diffusion and rheology, is completely separated from the bond reorientation of PEO detected by NMR. This result is unlike other blend systems in which global and local motions have been compared.
利用强迫瑞利散射，在125至220摄氏度的温度范围内测量了未缠结的聚环氧乙烷（PEO，M = 1000 g/mol）在聚甲基丙烯酸甲酯（PMMA，M = 10000 g/mol）基质中的示踪剂扩散系数。还在160至220摄氏度的温度范围内测量了两种不同高分子量PEO示踪剂（M = 440000和900000 g/mol）在同一PMMA基质中的共混物的动态粘度；观察到这些体系的时间-温度叠加失效。使用劳斯模型从扩散系数和流变松弛时间中提取PEO示踪剂的单体摩擦因子。尽管示踪剂的分子量相差约三个数量级，但通过扩散和流变学确定的摩擦因子吻合良好。将PEO单体摩擦因子与用核磁共振直接测量的PEO链段松弛时间的文献数据进行了比较。发现PEO示踪剂在PMMA基质中的单体摩擦因子比基于链段动力学直接测量预期的要大两到六个数量级。此外，PEO示踪剂的末端动力学对温度的依赖性比相应的PEO链段动力学要强得多。这些结果表明，从扩散和流变学推断出的最快的PEO劳斯模式与通过核磁共振检测到的PEO的键重排完全分离。这一结果与其他比较了整体和局部运动的共混体系不同。
