The Study Of Rheological Property Of Poly (Ethylene Oxide) Melts

The behavior of polymer melts is very significant for both rheology theory and industrial processing. Although flow instabilities (melt fracture) are regarded as the intrinsic property of polymers since the 1960s, their molecular mechanisms are still unclear. Besides, these flow instabilities are usually accompanied by wall slip, which makes the phenomenon more complicated. Since 2006, the particle-tracking velocimetry (PTV) observations by Wang's group (Akron University) has revealed shear inhomogeneity in entangled polymers either during startup shear (shear banding) or after large deformation (non-quiescent relaxation), which sheds new light on the subject of polymer rheology. So in 2009, the National Science Foundation (USA) supported five-member team to check the phenomenon.In this work, we combine a home-made high-temperature cone-plate rheometer (the maximum torque is 10 Nm whereas a commercial rheometer typically has 0.2 Nm.) with PTV technique to explore the nonlinear rheological behavior of a high viscosity poly(ethylene oxide) (PEO) melt. Here, the conditions with and without wall slip are both determined and compared.On smooth metal surfaces, the PEO melts exhibited delayed wall slip after shear cessation, when the imposed strain was larger than a critical value. In the absence of wall slip suppressed by gluing technique, the PEO melts exhibited internal macroscopic motions after shear cessation, when the imposed strain was larger than a critical value. Both of the critical strain is around unity, which can be estimated by Wang's theory. The non-quiescent relaxation behavior of entangled melts has only recently been reported once in the literature involving a room temperature melt, and our work is the first PTV observation of non-quiescent relaxation at high temperature.