Nonlinear electrokinetic motion of electrically induced Janus droplets in microchannels

The nonlinear electrokinetic motion of electrically induced Janus droplets (EIJDs) in a microchannel is studied in this paper. The EIJDs were fabricated by operating the positively charged aluminum oxide nanoparticles to partially cover the oil droplets with electric field. The nanoparticle coverage of the EIJDs changes with the electric field strength, which leads to the variation of the electrophoretic mobility of the EIJDs. Therefore, the electrokinetic velocity of the EIJDs in a microchannel changes nonlinearly with the electric field strength. In this research, the variations of the nanoparticle coverage under both constant and time-varying electric fields were studied first. The results indicate that the nanoparticle coverage of the EIJDs decreases with the increase of the electric field strength, and an empirical equation for calculating nanoparticle coverage as a function of the electric field was derived. Under time-varying electric field, the variation of nanoparticle coverage lags behind the change of electric field, and the nanoparticle coverage changes differently under different time-varying electric fields. The experimental results of the electrokinetic motion of the EIJDs in a microchannel confirm that the electrokinetic velocity increases nonlinearly with the electric field. Due to the lag of the nanoparticle coverage change, the variation of the electrokinetic velocity in a microchannel is different between the increasing and decreasing periods of the time-varying electric field.