| 簡(jiǎn) 介： |
Polymer solutions forming transient networks show unique rheological properties.Specifically, most of the systems undergo shear thickening at high shear rates. The transient network systems might be divided into two ategories. One is the systems composed of polymer chains and small-sized crosslinkers, and the other is so-called
associative polymer systems. Aqueous solutions of poly(vinyl alcohol) (PVA) and sodium borate belong to the former, and hydrophobic ethoxylated urethanes (HEURs)
are typical of the latter, both of which show shear thickening. Until now much work, in
experimental and theoretical approaches, has been made to clarify the origin of the shear thickening in a microscopic level. The results provide several possibilities for the shear thickening (for example, non-Gaussian elasticity of polymer chains), but they are
still in controversy. The origin of the shear thickening in the microscopic level may be different if the category differs, but causes in phenomenological rheology must be
common for both categories. The aim of this study is to examine the origin of the shear thickening of an associative polymer system belonging to the latter category: more directly, to survey experimental evidences for long time relaxations causing the shear thickening under flow. |
