Unpredictable Dynamics of Polymeric Reacting Flow by Comparison between Pre- and Post-Reaction Fluid Properties: Hydrodynamics Involving Molecular Diagnosis via ATR–FTIR Spectroscopy

Abstract

In reacting flows, changes in fluid properties induced by the chemical reaction can alter the flow dynamics. Generally, these changes in fluid properties are evaluated by comparison between their pre- and post-reaction properties. If a fluid property such as viscosity decreases between pre- and post-reaction, we expect a decrease in viscosity to occur in the reacting flow. However, this study demonstrates a reacting polymeric liquid flow where a remarkable increase in the viscoelasticity temporally occurs despite the viscosity slightly decreasing after the reaction. We elucidated the underlying reaction mechanism, which involves a structural change in the side functional group (carboxyl) in polyacrylamide at ultrahigh molecular weights (M w > 106) with ultralow concentrations ([polymer] < 1 wt %) by using ATR–FTIR spectroscopy. This study demonstrates the existence of a reacting flow in which examination of microscopic molecular structure is required to understand the macroscopic flow dynamics. The findings will be valuable not only for industrial application such as reactor designs and rheology control but also for opening a new research area: chemically reacting flow involving the diagnosis of molecule structure.

Unpredictable polymeric flow dynamics with reaction between HPAM and Al3+ by comparison between pre- and post-reaction fluid properties

“…Therefore, it will be described in detail below. As previously reported for the Fe 3+ case, 33 the appearance and disappearance of the Weissenberg effect was observed. At that time, the pH immediately decreased.…”

“…Here, the mechanism of the appearance and disappearance of the Weissenberg effect in our previous report 33 is summarized. The idea of the mechanism clarified in the previous report is also applied to the present study.…”

“…To follow the change in the reacting flow between the pH-responsible polymer and metal ion, it is very important to always monitor the pH in the reaction solution. Therefore, the prepared solution was set to the same apparatus as in the previous report 33 (Fig. 1), and we simultaneously measured the torque during the agitation by an impeller using a rheometer (AR-G2, TA instruments) and pH using a pH meter.…”

“…Especially, such unpredictable reacting polymeric liquid flow dynamics by comparison between pre- and post-reaction fluid properties has been hardly reported other than in our previous report. 33 Note that although there is a report by Escala et al 36 about a temporal viscosity change driven by a pH sensitive polymer coupled to a pH-changing chemical reaction, they did not link the temporal viscosity change with reacting flow. In this study, to clarify whether the phenomenon involving temporal change in viscoelasticity during a chemical reaction despite a little change before and after the reaction has a common mechanism or not, we conducted the similar experiment using a typical element, aluminum ion (ferric ion in the previous study 32 ).…”

“…However, we previously demonstrated in 2019 that even when there was a little change in the fluid physical properties pre- and post-reaction, a temporally remarkable increase in viscoelasticity during the chemical reaction was observed. 33 Thanks to the reaction, the Weissenberg effect, 34 a phenomenon that the stirred solution climbs up the stirring shaft when a stirring rod is inserted into a solution, was observed. It occurs when the normal stress of a viscoelastic material overcomes the gravitational force during the rotation of a rod.…”