Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface

Area of Science:

• Physics
• Materials Science
• Fluid Dynamics

Background:

• Liquid films exhibit complex surface dynamics under external stimuli.
• Dielectrophoresis offers a method to manipulate microscale fluid behavior.
• Understanding micro-wrinkle formation is crucial for microfluidic and soft material applications.

Purpose of the Study:

• To investigate the formation and decay dynamics of dielectrophoresis-induced micro wrinkles on liquid film surfaces.
• To analyze the relationship between electrical forcing, surface tension, and viscous effects in micro-wrinkle dynamics.
• To compare experimental observations with numerical modeling predictions.

Main Methods:

• Generating spatially periodic micro wrinkles using a spatially periodic voltage and dielectrophoresis.
• Characterizing equilibrium wrinkle profiles with high accuracy using Optical Coherence Tomography.
• Analyzing dynamic wrinkle amplitude changes during formation and decay via optical diffraction.
• Measuring decay time constants and relating them to film thickness and viscous levelling.

Main Results:

• Dielectrophoresis successfully induced periodic micro wrinkle deformations on the liquid film surface.
• Optical Coherence Tomography provided submicron accuracy for equilibrium wrinkle profiles.
• Dynamic wrinkle amplitude analysis revealed sub-millisecond formation and decay times.
• The observed decay time constants correlated with surface tension driven viscous levelling, dependent on film thickness.

Conclusions:

• The study successfully demonstrated the creation and characterization of dielectrophoresis-induced micro wrinkles.
• Experimental results for wrinkle decay dynamics align with theoretical expectations for viscous levelling.
• Numerical modeling of Stokes flow with electrostatic forcing supported the observation that wrinkle formation is kinetically faster than decay.