ULTRASONIC PROPERTIES OF AQUEOUS-SOLUTIONS OF HIGH-MOLECULAR-WEIGHT POLYETHYLENE OXIDE

The concentration dependence of shear viscosity, density, and ultrasonic absorption and velocity in aqueous polyethylene oxide in the hydrodynamic screening and coil contact regions is investigated. Six polymer samples were studied covering the molecular weight range of 1.2 X 10(5)- 2.8 X 10(7). The ultrasonic measurements cover a frequency range of 130-970 kHz. The experiments indicate that ultrasonic absorption and velocity depend on molecular weight of the polymer. The solutions of high molecular weight polymer exhibit transition phenomenon at the critical overlapping concentration, where absorption reaches a maximum, and the viscosity, density, and velocity reach a plateau. These properties are attributed to polymer-polymer interaction. Experimental results suggest that the screening interaction of macromolecules results in strong viscoelastic coupling between macromolecules and a sharp decrease in compressibility, and that direct contact interaction leads to a temporary network structure having a more rigid but looser conformation. Comparison of the observed results with theoretical calculations indicate that dynamic shear viscosity contributes only a small fraction of the absorption actually observed and the polymer-water interaction is an important source of ultrasonic relaxation processes although this cannot describe the molecular weight dependence. The total absorption can be considered as the sum of contributions from polymer-water and polymer-polymer interactions.