Convective instability in a liquid-liquid system due to complexation with a crown ether

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Fluid Dynamics

Background:

• Complexation reactions involving alkali picrates and crown ethers can induce mass transfer between immiscible phases.
• Convective phenomena in biphasic systems are crucial for understanding reaction kinetics and transport processes.

Purpose of the Study:

• To investigate and visualize periodic convective instability during alkali picrate and dicyclohexano-18-crown-6 complexation.
• To analyze the influence of alkali metal complex stability on the type of hydrodynamic instability observed.
• To explore the role of confinement on fluid motion characteristics.

Main Methods:

• Visualization of convection using precipitated crystals formed during the complexation reaction.
• Optical microscopy for observing fluid motion.
• Particle image velocimetry (PIV) for quantitative analysis of fluid dynamics.
• Radiotracer (137Cs) measurements to track cesium extraction into the organic phase.

Main Results:

• Periodic convective instability was observed in the biphasic system during mass transfer.
• The type of instability (Rayleigh-Taylor or Marangoni) was directly correlated with the stability constants of the formed alkali metal complexes.
• More stable complexes led to higher precipitation and Rayleigh-Taylor instability, while less stable complexes induced pulsating Marangoni cells.
• Confinement effects influenced fluid motion, leading to back-and-forth movements in some cases.

Conclusions:

• The stability of alkali metal complexes dictates the nature of hydrodynamic instability in this biphasic reaction system.
• Marangoni cells exhibit pulsating behavior, and confinement can introduce oscillatory fluid dynamics.
• The study provides insights into the interplay between chemical complexation, mass transfer, and fluid instabilities.