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

• Published in: Macromolecules Vol. 49; no. 24; pp. 9647 - 9654
• Main Authors: Liu, Gengxin, Wang, Shi-Qing
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27-12-2016
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.6b02053

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.