The role of particle-electrode wall interactions in mobility of active Janus particles driven by electric fields

A. M.Boymelgreen*, G. Kunti, P. Garcia-Sanchez, A. Ramos, G. Yossifon, T. Miloh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Hypothesis: The interaction of active particles with walls can explain discrepancies between experiments and theory derived for particles in the bulk. For an electric field driven metallodielectric Janus particle (JP) adjacent to an electrode, interaction between the asymmetric particle and the partially screened electrode yields a net electrostatic force – termed self-dielectrophoresis (sDEP) - that competes with induced-charge electrophoresis (ICEP) to reverse particle direction. Experiments: The potential contribution of hydrodynamic flow to the reversal is evaluated by visualizing flow around a translating particle via micro-particle image velocimetry and chemically suppressing ICEP with poly(L-lysine)-g-poly(ethylene glycol) (PLL-PEG). Mobility of Polystyrene-Gold JPs is measured in KCl electrolytes of varying concentration and with a capacitive SiO2 coating at the metallic JP surface or electrode. Results are compared with theory and numerical simulations accounting for electrode screening. Findings: PLL-PEG predominantly suppresses low-frequency mobility where propulsive electro-hydrodynamic jetting is observed; supporting the hypothesis of an electrostatic driving force at high frequencies. Simulations and theory show the magnitude, direction and frequency dispersion of JP mobility are obtained by superposition of ICEP and sDEP using the JP height and capacitance as fitting parameters. Wall proximity enhances ICEP and sDEP and manifests a secondary ICEP charge relaxation time dominating in the contact limit.

Original languageEnglish
Pages (from-to)465-475
Number of pages11
JournalJournal of Colloid and Interface Science
Volume616
DOIs
StatePublished - 15 Jun 2022

Funding

FundersFunder number
MNFU
Technion Micro-Nano Fabrication Unit
Technion Russel-Berrie Nanotechnology Institute
Iowa Science Foundation
Israel Science Foundation
Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology

    Keywords

    • Active colloids
    • Active matter
    • Electrokinetics
    • Induced-charge electrophoresis
    • Janus particles
    • Particle–wall interactions
    • Soft matter

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