Rheological Characterization of Polyethylene Oxide (PEO): An Experimental Steady State and Transient Analysis

Poly (ethylene oxide) (PEO) has occupied an important place in the field of polymers for many years because of its intrinsic structure, its solubility in water and its biocompatibility.

Rheological characteristics of fluids are responsible of their behavior during flow. Therefore, it is very important to precisely estimate their values to avoid any errors or uncertainty during their measurement, in order to understand all the physical phenomena and their origin, when analysis the flow behavior. Polyethylene Oxyde (PEO) is used in many industrial applications. In solution with water, it is transparent. This optical characteristics leads to use it as model for optical flow measurement, such us the quantification some instabilities (secondary flow) in viscoelastic fluids flows.

During rheological measurements, some authors have shown a classic shear-thinning behavior for relatively high shear rates. However, at a low shear rate, an erratic behavior (hear thickening and thinning) appears. It is therefore important to understand whether these phenomena are intrinsic to the fluid, or just the result of measurement artifacts. In order to study the effect of the rheological parameters on the flow behavior, and to analyze the origin of some viscoelastic phenomena, such as secondary flow in laminar flow in non-circular ducts, it is important to discriminate effectively the role of the fluids characteristics and errors from the measurement.

In fact, secondary flows appears in flows of highly nonlinear viscoelastic fluids. Their experimental quantification is a real academic and industrial need, as there is a lack of data to validate the numerical calculations and to understand the origin of these flows.  To do so, an exact rheological characterization is necessary.

Solution of PEO are very transparent and exhibits a nonlinear viscoelastic behavior. It constitutes a good candidate for us as model in optical measurement using PIV technics for example.

In this paper, the rheological characteristics of aqueous PEO (Polyethylene oxide) solution having very high molecular weight 4×10⁶ g/mol is analyzed. Shear flow measurements were carried out in steady and transient modes.  As expected, the unique behavior of PEO is found to be heavily dependent on input shear rate and the mechanism of data generation.  Generally, PEO is found to be shear-thinning throughout the experiment, but in the start of experiments from low shear rates, minimum input shear value also affects the shear-thinning behavior. In this study, we analyzed the critical method of applied input shear on the samples within lower shear rate regime. Surprisingly different input methods yield different results. Viscosity curves obtained through shear flow experiments found to be significantly dependent on the input method of shear rate. The experimental measurements were validated by cross and Carreau-Yasuda models.