Role of surface wettability in electric-field-induced instability of water droplets

This study experimentally investigates how surface wettability and adhesion influence the deformation and stability of water droplets in a uniform external electric field. Special focus is placed on highly hydrophobic surfaces with strong adhesion (“rose petal effect”), which may arise on functional coatings during operation. Hydrophilic silicon, fluoropolymer, a natural rose petal, and a laser-textured biphilic surface with a controlled seating spot were used as model substrates. Experiments were performed with droplets of different volumes, enabling variation of the balance between capillary and electrostatic forces. The results show that droplet deformation strongly depends on adhesion and surface microstructure. On superhydrophobic and biphilic substrates, droplets exhibit significant elongation along the field direction, leading to Taylor-cone-like deformation and the onset of morphological instability. A threshold-type response is observed at fields around 4 kV/cm. Surfaces with high adhesion can retain larger droplets, which experience possible local field enhancement near the cone-like apex under high electric fields. These findings are relevant for designing hydrophobic coatings for high-voltage insulators and for assessing the risk of discharge initiation on degraded or defective surfaces.