Shape Evolution of Precipitate Membranes in Flow Systems.

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Chemical gardens form macroscopic structures via precipitation when a salt seed contacts an alkaline solution.
• Precipitate membranes in chemical gardens regulate reactant interaction and slow the approach to equilibrium.
• Membrane thickening is driven by cross-membrane gradients and selective ion transport.

Purpose of the Study:

• To investigate the growth dynamics and morphology of nickel hydroxide (Ni(OH)2) membranes in chemical gardens.
• To understand the influence of reactant flow rates on membrane development within microfluidic channels.
• To model and quantitatively reproduce the observed growth patterns.

Main Methods:

• Utilized microfluidic channels to control reactant flow and observe chemical garden formation.
• Investigated the growth of Ni(OH)2 precipitate membranes under varying flow conditions.
• Developed and employed a two-variable reaction-diffusion-advection model for quantitative analysis.

Main Results:

• Fast reactant flow resulted in membranes of nearly constant width along the channel.
• Slow reactant flow led to wedge-shaped structures with limited downstream growth.
• Observed membrane shapes and dynamics are governed by the balance between reactant consumption and transport replenishment.

Conclusions:

• The study quantitatively reproduces chemical garden membrane growth using a reaction-diffusion-advection model.
• Flow dynamics critically influence precipitate membrane morphology and growth patterns.
• The findings provide kinetic insights into the formation and evolution of precipitate membranes.