Stress overshoot of polymer solutions at high rates of shear

✍ Scribed by K. Osaki; T. Inoue; T. Isomura

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 189 KB
• Volume: 38
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/1099-0488(20000715)38:14<1917::aid-polb100>3.0.co;2-6

✦ Synopsis

Overshoot of shear stress, , and the first normal stress difference, N 1 , in shear flow were investigated for polystyrene solutions. The magnitudes of shear corresponding to these stresses, ␥ m and ␥ Nm , for entangled as well as nonentangled solutions were universal functions of ␥ ˙eq , respectively, and ␥ Nm was approximately equal to 2␥ m at any rate of shear, ␥ ˙. Here eq ϭ R for nonentangled systems and eq ϭ 2 R for entangled systems, where R is the longest Rouse relaxation time evaluated from the dynamic viscoelasticity at high frequencies. Only concentrated solutions exhibited stress overshoot at low reduced rates of shear, ␥ ˙eq Ͻ 1. The behavior at very low rates, ␥ ˙eq Ͻ 0.2, was consistent with the Doi-Edwards tube model theory for entangled polymers. At high rates, ␥ ˙eq Ͼ 1, ␥ m and ␥ Nm were approximately proportional to ␥ ˙eq . At very high rates of shear, the peak of is located at t ϭ R , possibly indicating that the polymer chain shrinks with a characteristic time R in dilute solutions.