Magnetowetting dynamics of sessile ferrofluid drops on soft surfaces†
We investigate the magnetowetting behaviour of sessile ferrofluid droplets on elastomeric surfaces with different stiffness. The non-uniform magnetic field engenders deformation and splitting of the ferrofluid droplet, which is greatly influenced by the softness of the substrate. We observe that the decrease in the dynamic contact angle is maximum on the softest substrate, while the contact line remains pinned. Again, for an apparently rigid substrate, the contact radius decreases almost linearly, whereas the decrease in the contact angle appears to be lower than that of soft substrates. The contact line experiences a transition from “stick-slip” on rigid surfaces to “pinned” motion on soft surfaces, which is favoured by the formation of a large wetting ridge and smaller receding contact angle on the latter. We also find that the splitting time and splitting ratio (the ratio of the volume of the daughter droplet to that of the residual droplet) increase with an increase in the softness of the underlying substrate.