Particle-covered drops in electric fields: drop deformation and surface particle organization

Abstract

Drops covered by adsorbed particles are a prominent research topic because they hold promise for a variety of practical applications. Unlocking the enormous potential of particle-laden drops in new material fabrication, for instance, requires understanding how surface particles affect the electrical and deformation properties of drops, as well as developing new routes for particle manipulation at the interface of drops. In this study, we utilized electric fields to experimentally investigate the mechanics of particle-covered silicone oil drops suspended in castor oil, as well as particle assembly at drop surfaces. We used particles with electrical conductivities ranging from insulating polystyrene to highly conductive silver. When subjected to electric fields, drops can change shape, rotate, or break apart. In the first part of this work, we demonstrate how the deformation magnitude and shape of drops, as well as their electrical properties, are affected by electric field strength, particle size, conductivity, and coverage. We also discuss the role of electrohydrodynamic flows on drop deformation. In the second part, we present the electric field-directed assembly and organization of particles at drop surfaces. In this regard, we studied various parameters in detail, including electric field strength, particle size, coverage, and electrical conductivity. Finally, we present a novel method for controlling the local particle coverage and packing of particles on drop surfaces by simply tuning the frequency of the applied electric field. This approach is expected to find uses in optical materials and applications.

Multiresponsive Wettability Switching on Polymer Surface: Effect of Surface Chemistry and/or Morphology Tuning

“…Finally, it must be noted that present multistimuli switchable surface is advantageous for its simplicity and flexibility in potential droplet manipulations. In particular, multiswitchable surface properties can be employed at the nano‐ or macro‐scale levels where the application of EF triggering (within 1 V µm −1 range) in combination with temperature and/or pH triggering can solve several key questions in the fields of microfluidic, on‐line drop manipulation, and smart electrophoresis devices …”

Electro-Hydrodynamics of Emulsion Droplets: Physical Insights to Applications

“…A colloidal particle or Pickering droplet is formed when the particle-laden droplet or suspension, for which , is subjected to an electric field [ 21 , 91 , 92 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 ]. Particles can be trapped at the interface more rapidly under a weak electric field (~ 0.1 kV/mm) and once trapped, they remain there.…”

“…Depending on the strength of the electric field, particle concentration, electric conductivity, and size, various particle assemblies can be formed at the interface. Mikkelsen et al [ 134 ] used low to high particle coverage (~0.1 to ~0.8), and analyzed the conductive and non-conductive particle conditions, as shown in Figure 6 A. For high particle concentration of non-conducting particles, such as polystyrene under a weak electric field, the oblate deformation of silicone oil increased as more charges accumulated at the droplet surface and the EHD flows were suppressed.…”

“…For low particle concentrations in a range from ~0.1 to ~0.5 under a weak electric field, the particles at the interface can produce different assemblies, such as “belts” (low-conductivity particles) or “chains” (high-conductivity particles). Belts may form a static or dynamic sinusoid with a change in particle properties and electric field strength [ 91 , 134 ]. High-conductivity particles with regular size, such as spheres, organize into regular chains aligned with the direction of an applied electric field, while random-size particles form random assemblies (See Figure 6 B).…”

“… Self-assembly of particles on the droplet interface by electro-hydrodynamic flows. Under a weak electric field: ( A ) effect of particle electric conductivity and concentration on the particle structure (reproduced from [ 134 ] with permission from The Royal Society of Chemistry). ( B ) Effect of particle electric conductivity and size on the particle structure [ 91 ].…”