Electrostatic formation of polymer particle stabilised liquid marbles and metastable droplets - Effect of latex shell conductivity.

HYPOTHESIS

Particle cohesion and conductivity affects the electrostatically driven transport of particles to a suspended water droplet. The conditions at which liquid marbles and particle stabilised liquid droplets form are a function of these parameters.

EXPERIMENT

Particle beds placed below an earthed pendent water drop had a negative potential applied, thus inducing an opposing positive charge on the liquid, which results in particle transfer and eventual coating of the liquid drop. Experiments where both the particle bed was constantly moved slowly toward the droplet, and the particle bed remained at a fixed, small separation distance were completed. These enabled the investigation of a number of variables that influence successful aggregate formation, including separation distance between the droplet and particle bed, coating mechanism and kinetics of the transfer process.

FINDINGS

Monodisperse polystyrene core particles with polypyrrole shells of various cohesiveness and conductivity were observed to behave differently in the presence of the applied potential, where the least cohesive and conductive sample (polystyrene) required the smallest separation distance, i.e. the greatest field strength for particle transfer. Increasing conductivity of the particle shell decreases the field strength required for particle transfer, and thus an increase was observed in separation distance at which particles were observed to move to the air-water interface. The transfer kinetics followed the same trend where the least conductive and cohesive sample was the slowest to coat the air-water interface, and vice-versa. Since an increase in cohesion hinders particle transfer, it is concluded that particle conductivity is of greater importance in the electrostatic aggregation process.