Experimental study on the capillary thinning of entangled polymer solutions
Experimental study on the capillary thinning of entangled polymer solutions
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DOI：
10.1007/s00397-014-0789-8
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发表时间：
2014-08
期刊：
影响因子：
2.3
通讯作者：
Dirk Sachsenheimer;B. Hochstein;N. Willenbacher
中科院分区：
文献类型：
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作者：
Dirk Sachsenheimer;B. Hochstein;N. Willenbacher
用毛细管破裂拉伸流变仪（CaBER）研究了缠结聚合物和蠕虫状胶束（WLM）溶液的瞬时拉伸行为。瞬态力ratioX= 0.713揭示了存在一个中间牛顿变薄区的聚苯乙烯和WLM解决方案之前的粘弹性变薄。X（t）在第一阶段变薄的指数衰减定义了一个伸长松弛时间λ x，它等于从指数直径衰减D（t）得到的伸长松弛时间λ e，表明初始应力衰减受与在纤维变薄的末端区域观察到的应变硬化相同的分子松弛过程控制。用X（t）讨论了真拉伸粘度和表观拉伸粘度的偏差。观察到最小特劳顿比，其随着聚合物浓度的增加而指数地降低，对于表现出中间牛顿稀化的溶液，在Trmin= 3处趋于平稳，否则在Trmin = 10处趋于平稳。弛豫时间比λe/λs（其中λ是末端剪切弛豫时间）随聚合物浓度的增加呈指数下降，当相对于还原浓度c [η]（其中[η]是特性粘度）作图时，所有研究溶液的数据都塌陷到主曲线上，而与聚合物分子量或溶剂粘度无关。这证实了如前所述，在CaBER实验中非线性变形对缠结聚合物溶液的强烈影响。另一方面，发现所有WLM溶液的λe λsis清楚地表明，这些非线性变形不影响这些活性聚合物体系的毛细管变薄过程。
The transient elongation behavior of entangled polymer and wormlike micelles (WLM) solutions has been investigated using capillary breakup extensional rheometry (CaBER). The transient force ratioX= 0.713 reveals the existence of an intermediate Newtonian thinning region for polystyrene and WLM solutions prior to the viscoelastic thinning. The exponential decay ofX(t) in the first period of thinning defines an elongational relaxation timeλxwhich is equal to elongational relaxation timeλeobtained from exponential diameter decayD(t) indicating that the initial stress decay is controlled by the same molecular relaxation process as the strain hardening observed in the terminal regime of filament thinning. Deviations in true and apparent elongational viscosity are discussed in terms ofX(t). A minimum Trouton ratio is observed which decreases exponentially with increasing polymer concentration leveling off at Trmin= 3 for the solutions exhibiting intermediate Newtonian thinning and Trmin≈ 10 otherwise. The relaxation time ratioλe/λs, whereλsis the terminal shear relaxation time, decreases exponentially with increasing polymer concentration and the data for all investigated solutions collapse onto a master curve irrespective of polymer molecular weight or solvent viscosity when plotted versus the reduced concentrationc[η], with [η] being the intrinsic viscosity. This confirms the strong effect of the nonlinear deformation in CaBER experiments on entangled polymer solutions as suggested earlier. On the other hand,λe≈λsis found for all WLM solutions clearly indicating that these nonlinear deformations do not affect the capillary thinning process of these living polymer systems.