Impact of high conductivity on particle transport to liquid droplets for liquid marble formation

This study investigates the influence of particle conductivity on the promotion of particle extraction and transport to a pendent liquid droplet in the presence of an electric field by applying a thin metal shell of nickel or gold onto polystyrene core particles. Despite significantly increasing the conductivity of the material, the addition of a metal shell to the core particles did not have a concomitant significant impact on initial particle extraction and transport behaviour. For the same applied potential, gold coated particles were extracted from a smaller separation distance than core polystyrene particles, while nickel coated particles were extracted from a slightly increased separation distance. Small separation distances correspond to a stronger electrostatic force required for extraction, so coating the polystyrene particles with gold made them more difficult to extract. Furthermore, these metal-coated particles were extracted from significantly smaller separation distances when compared to the same polystyrene core particles with conductive polymer shells. This is attributed more to increased inter-particle cohesion than from the increased particle mass as a result of the metal coating. In addition, the nickel and gold metal shell coated particles had differing particle hydrophobicity, impacting the final stability of the resultant liquid marble. Comparison is also made with glass core particles, to observe the impact of constant particle mass and changing conductivity and interparticle cohesion, highlighting that increasing conductivity is less significant than the opposing effect of cohesion. Herein, we conclude that the ability to form liquid marbles using an electrostatic extraction method is dependent on a complex interplay of fundamental particle properties of conductivity, density, and cohesion.