Impact of liquid phase on the electrostatic formation of polymer stabilised liquid marbles and aggregates

Liquid marbles, or small liquid droplets stabilised by hydrophobic particles, have been used in a wide variety of applications including cosmetics, gas sensing and microfluidics. Interest in the commercial and research areas have increased significantly recently to diversify both gas and liquid phases and improve the formation process. Currently, liquid marbles are generally formed by rolling the liquid droplet over a bed of particles, resulting in attachment at the interface. An alternate, non-contact method of liquid marble production, using electrostatic transfer of particles to a pendent drop has been developed within our group. Removing the requirement of direct contact for liquid marble production has allowed for the investigation of a larger range of particles, including polymer latexes with lower contact angles, resulting in the formation of non-spherical shaped liquid aggregates. This study investigates the impact of changing various liquid phase characteristics, including conductivity (NaCl), viscosity (glycerol) and surface tension (ethanol) on the formation of liquid marbles using hydrophobic polystyrene core-shell particles. The observation of the electrostatic transfer of particles at certain applied potentials to the droplet interface is studied as a function of bed-droplet separation. Furthermore, the kinetics and charge transfer were also investigated to assess the impact of the liquids on these mechanisms. Overall surface tension of the ethanol mixture (20 wt%) was too low for consistent liquid marble formation. Increasing viscosity and conductivity did not appear to alter the separation distances at which particles were initially transferred, but charge transfer and kinetic mechanisms were variable between tap water, glycerol and sodium chloride solutions.