Entangled Linear Polymer Solutions at High Shear: From Strain Softening to Hardening

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• 作者：Gengxin LiuShi-Qing Wang
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：December 27, 2016
• 年：2016
• 卷：49
• 期：24
• 页码：9647-9654
• 全文大小：631K
• ISSN：1520-5835

文摘

The present rheological study reveals for the first time that entangled polymer solutions made of linear polystyrene or poly(methyl methacrylate) can exhibit strain hardening due to non-Gaussian stretching during startup shear at sufficiently high rates and temperatures well above their overall glass transition temperatures: T_g,solute > T_exp > T_g,solution. The solutions made of high-T_g polymers only show partial yielding in the sense that both shear and normal stresses grow monotonically in time until a point of rupture, signified by an emergent cusp in the stress vs strain curve and macroscopic breakup along a shear plane. The shear softening-to-hardening transition, which occurs as a function of the applied shear rate, happens at lower equivalent rate with decreasing temperature, violating the time–temperature superposition principle.