The researches find that the In reacting flows, changes in fluid properties induced by the chemical reaction can alter the flow dynamics. Generally, these changes in fluid properties are evaluate 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.
Changes in fluid properties
We elucidated the underlying reaction mechanism; which involves a structural change in the side functional group (carboxyl) in polyacrylamide at ultra-high molecular weights (Mw > 106 ) with ultra-low 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 require 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. Reacting flows; wherein chemical reactions occur in flowing fluid; are ubiquitous phenomena appearing across the industrial, environmental, and biological fields.
The chemical reactions
Thus far, numerous experimental and theoretical reacting flow studies have been performed on the chemical reaction-induced modification of flow dynamics in the liquid phase via changes in density, viscosity, interfacial tension; and viscoelasticity. These fluid property changes are generally evaluate by comparison between the observe properties before and after the reaction. In other words; if a fluid property such as the viscosity of the solution is higher after the reaction
than before, we would expect that an increase in viscosity occurs from the reaction during flow.
Generally in such cases, the ratio between the reaction rate and flow rate, which is know as the Damköhler number; plays a crucial role in the reactive hydrodynamics. Therefore, if there is no change between these values, we consider the reaction to no influence on the flow dynamics. However; in the present study, we show what is, to the best of our knowledge; the first observation of a remarkable change in flow dynamics induce by the reaction that occurs temporally, which is contrary to what is expect based on the pre- and post-reaction fluid properties.
The reactive hydrodynamics
The temporal behavior of the reacting flow is shown in and Supplementary Movie 1. Here, a Weissenberg effect occurs where the stirred solution climbs up the stirring shaft, which is caused by viscoelasticity 30 . The occurrence of the Weissenberg effect is considered to be caused by an increase in the viscoelasticity driven by the chemical reaction between partially hydrolyzed polyacrylamide (HPAM) and Fe3+ aq.