State Key Laboratory of Polymer Physics and Chemistry and CAS Key Laboratory of Engineering Plastics, Joint Laboratory of Polymer Science and Materials, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
J Chem Phys. 2013 Sep 21;139(11):114904. doi: 10.1063/1.4821175.
The morphology evolution and rheological response of a near-critical composition polybutadiene/polyisoprene blend after the cessation of steady shear was studied with an ARES rheometer and a shear light scattering photometer equipped with an optical microscope in this work. The relationship between the morphology of the blend during the relaxation after the cessation of steady shear with different shear rates and their corresponding rheological properties was successfully established. It was found that the different shear-induced morphologies under steady shear would relax to the equilibrium states via varied mechanisms after the shear cessation. The average size of the dispersed domains in the coarsening process was influenced by the pre-shear history. The results indicated that the pre-shear history could slow down the growth rate of phase domains during the coarsening process. It had effect on the coarsening mechanism on the early stage of relaxation after the cessation of very strong shear when the homogenization effects were strong, but no effect on the late stage. The storage modulus G' increased significantly in the breakup process of the string-like phase. After all the string-like structures were broken up into small ellipsoids, then G' gradually decreased and finally approached to an invariant value. The characteristic rheological behavior can be attributed to the different structure on the relaxation process.
本工作采用 ARES 流变仪和带有光学显微镜的剪切光散射光度计研究了近临界组成聚丁二烯/聚异戊二烯共混物在停止稳态剪切后的形态演变和流变响应。成功建立了不同剪切速率下共混物在停止稳态剪切后的松弛过程中的形态与其相应流变性能之间的关系。研究发现，在停止剪切后，不同的稳态剪切诱导形态会通过不同的机制松弛到平衡状态。在粗化过程中，分散相的平均尺寸受到预剪切历史的影响。结果表明，预剪切历史可以减缓相畴在粗化过程中的生长速率。在强剪切停止后的早期松弛阶段，当均匀化效应较强时，预剪切历史对粗化机制有影响，但在后期没有影响。在串状相的断裂过程中，储能模量 G' 显著增加。当所有的串状结构都断裂成小的椭圆形后，G' 逐渐减小，最终趋于不变的值。这种特征流变行为可归因于松弛过程中不同的结构。
