Electrohydrodynamic aggregation with vertically inverted systems.

Area of Science:

• Colloid and Surface Science
• Fluid Dynamics
• Electrochemistry

Background:

• Electric fields induce electrohydrodynamic (EHD) forces in electrolyte solutions containing suspended particles.
• Particle aggregation and stability in EHD flow depend on electrolyte, particle, and field properties.
• Previous studies observed particle aggregation at a bottom electrode.

Purpose of the Study:

• To investigate EHD flow-induced aggregation of sulfonated latex beads in inverted particle-electrode orientations.
• To quantify aggregation behavior, including growth rate, packing density, and order.
• To compare experimental findings with predictions from a scaling model for EHD flow.

Main Methods:

• Utilized 2-μm sulfonated latex beads in NaCl and NaOH electrolyte solutions.
• Employed inverted particle-electrode configurations under an electric field.
• Quantified particle aggregation kinetics and spatial distribution over time.
• Compared experimental data with a scaling model for EHD flow.

Main Results:

• Observed EHD flow-induced aggregation of particles at both top and bottom electrodes.
• Aggregate growth was faster in NaCl solutions compared to NaOH solutions.
• Particles remained stable at the top electrode for over 1 hour.
• A secondary stability location observed in NaOH at the bottom electrode was absent at the top electrode.

Conclusions:

• EHD flow drives particle aggregation, with NaCl electrolytes promoting faster growth than NaOH.
• The scaling model successfully predicts overall aggregation behavior but not all packing differences.
• Further model modifications or reinterpretations are necessary for accurate prediction of particle packing in EHD systems.