Electric field induced reversible spreading of droplets into films on lubricant impregnated surfaces

Electric fields can be used to force a droplet to wet a solid surface using an applied voltage. However, significant hysteresis usually occurs associated with pinning forces at the contact line. Here we report the forced spreading and subsequent retraction of droplets into liquid films in air on lubricant impregnated surfaces (also known as slippery liquid infused porous surfaces, SLIPS) where the contact line is completely mobile. We first confirm that we achieve a complete removal of hysteresis for the electrowetting of droplets above the saturation voltage. We then show that contact angle hysteresis can be reduced to less than 4° whilst retaining the ability to fully spread a droplet into a liquid film using an interface localized from of liquid dielectrophoresis (dielectrowetting). In both cases, we find that the cosine of the contact angle has a quadratic dependence on applied voltage, consistent with previous theoretical expectations. Thus, our work demonstrates that fully reversible spreading encompassing a wide range of partial wetting droplet states and a film state can be achieved in air in a controllable manner with very low levels of hysteresis.