Soft Glassy Dynamics in Polypropylene-Clay Nanocomposites
Soft Glassy Dynamics in Polypropylene-Clay Nanocomposites
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DOI：
10.1021/ma0612374
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发表时间：
2007-01
期刊：
影响因子：
5.5
通讯作者：
Mark A. Treece;J. Oberhauser
中科院分区：
文献类型：
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作者：
Mark A. Treece;J. Oberhauser
采用线性和非线性粘弹性测试方法，研究了含3wt%有机改性蒙脱土、10wt%马来酸酐功能化聚丙烯(马来酸酐含量为1%)和87wt%聚丙烯均聚物的熔融共混聚丙烯-粘土纳米复合材料的动态形态变化。稳态剪切速率扫描表明，粘度随剪切速率单调下降，这是具有屈服应力的机械渗流材料的特征。在长达2小时的退火后的后续扫描显示，在低剪切速率下的粘度仍然显著低于初始扫描，这表明有机粘土的定向缓慢或停滞。在剪切流启动过程中，经过处理的和预剪切的纳米复合材料样品的粘度超调均随退火时间的延长而增加，但预剪切的样品的超调仍然比加工前的小得多。同样，对处理前后的样品进行的小幅度振荡剪切实验也表明，储能模数和复粘度随时间呈对数增长，而损耗角正切则稳步下降。这两组数据都表明，随着时间的推移，流变学越来越像固体，这一现象是在软玻璃动力学的背景下讨论的。
Linear and nonlinear viscoelastic measurements were utilized to probe transient morphological changes in a melt-blended polypropylene-clay nanocomposite containing 3 wt % organically modified montmorillonite clay, 10 wt % maleic anhydride functionalized polypropylene (1% maleic anhydride content), and 87 wt % polypropylene homopolymer. Steady shear rate sweeps show that the viscosity decreases monotonically with shear rate, characteristic of a mechanically percolated material with a yield stress. Subsequent sweeps following annealing of up to 2 h show that the viscosity at low shear rates remains substantially lower than the initial sweep, indicative of slow or arrested organoclay disorientation. In startup of shear flow, as-processed and presheared nanocomposite samples both exhibit increasing viscosity overshoots with annealing time for up to 6 h, although the overshoots for the presheared samples remain uniformly smaller than those of the as-processed material. Similarly, small-amplitude oscillatory shear experiments on as-processed and presheared samples also reveal that the storage modulus and complex viscosity increase logarithmically with time, while the loss tangent declines steadily. Both sets of data point to increasingly solidlike rheology over time, a phenomenon that is discussed in the context of soft glassy dynamics.