  Modification and control over the vaporization kinetics of microfluidic
droplets may have strong utilitarian implications in several scientific and
technological applications. The article reports the control over the
vaporization kinetics of pendent droplets under the influence of competing
internal electrohydrodynamic and ferrohydrodynamic advection. Experimental and
theoretical studies are performed and the morphing of vaporization kinetics of
electrically conducting and paramagnetic fluid droplets using orthogonal
electric and magnetic stimuli is established. Analysis of the observations
reveals that the electric field has a domineering influence compared to the
magnetic field. While the magnetic field is noted to aid the vaporization
rates, the electric field is observed to decelerate the same. Neither the
vapour diffusion dominated kinetics nor the field induced modified surface
tension can explain the observed vaporization behaviours. Velocimetry within
the droplet shows largely modified internal ferro and electrohydrodynamic
advection, which is noted to be the crux of the mechanism towards modified
vaporization rates. A mathematical treatment is proposed and takes into account
the roles played by the governing Hartmann, electrohydrodynamic, interaction,
the thermal and solutal Marangoni, and the electro and magneto Prandtl and
Schmidt numbers. It is observed that the morphing of the thermal and solutal
Marangoni numbers by the electromagnetic interaction number plays the dominant
role towards morphing the advection dynamics. The model is able to predict the
internal advection velocities accurately. The findings may hold significant
promise towards smart control and tuning of vaporization kinetics in
microhydrodynamics transport paradigms.
