Abstract
Recently, it has been shown numerically that viscosity changes driven by variation in chemical species concentrations due to chemical reaction lead to significant change in miscible viscous fingering pattern. Unfortunately, the predicted change in fingering pattern has not been observed experimentally mainly because miscible viscous fingering experiments are usually performed in Newtonian liquids for which the viscosity hardly changes with concentrations of chemical species. The present study focuses on dependence of viscosity of polyelectrolyte solution on pH (concentration of H+) in order to experimentally study miscible viscous fingering involving viscosity changes induced by variation in concentration of chemical species due to chemical reaction. We selected aqueous sodium polyacrylate (Wako, Molecular weight 2∼7 million) solution (SPA) as polyelectrolyte solution which is expected to show dependence of its viscosity on pH and also selected aqueous polyacrylamide (Polysciences, Inc. Molecular weight 5∼6 million) solution (PAA) as nonionic polymer solution which is expected not to show dependence of its viscosity on pH. Effects of pH, which is varied by the addition of hydrochloric acid (HCl) to the polymer solutions, on the viscosity of SPA and PAA, were examined. The viscosity of SPA significantly decreases with increase in pH, whereas that of PAA hardly changes. Experiments on miscible viscous fingering in a Hele-Shaw cell were performed by using SPA and PAA as the more viscous liquid and HCl and water as the less viscous one. In the case of SPA, fingering pattern formed by HCl significantly changes from that formed by water. In contrast, in the case of PAA, the difference between fingering pattern formed by HCl and that by water is hardly observed. These results show that the change of fingering pattern for SPA is caused by the variation in the viscosity of SPA due to HCl.
