Wrinkled labyrinths in critical demixing ferrofluid

Area of Science:

• Physics
• Materials Science
• Fluid Dynamics

Background:

• Ferrofluid mixtures exhibit complex phase behavior under external stimuli.
• Understanding thin film dynamics is crucial for microfluidic and material applications.

Purpose of the Study:

• To investigate the sequence of phase transitions in a critical ferrofluid thin film subjected to a magnetic field.
• To elucidate the mechanisms behind droplet formation, pattern transformation, and interface wrinkling.

Main Methods:

• Fabrication of a thin film of a critical ferrofluid mixture.
• Application of a controlled magnetic field to induce transitions.
• Microscopic observation of fluid morphology changes.
• Analysis of wetting phenomena at the liquid-air interface.

Main Results:

• A critical demixing transition forms cylindrical droplets of the minority phase.
• Further increase in magnetic field leads to destabilization of droplets into a labyrinth pattern.
• A wrinkling transition occurs at higher fields specifically at the liquid-air interface, absent with a coverslip.

Conclusions:

• The sequence of transitions is driven by increasing magnetic field strength.
• Wrinkling is attributed to the wetting behavior of the liquid-air interface shifting away from the critical demixing point.
• The presence or absence of a liquid-air interface significantly alters the observed transitions.