Interfacial deformation under electric fields is a common phenomenon in many industrial processes. Particularly, we are interested in the dynamics of sessile soap bubbles in a parallel-plate electric field which exhibits a stable deformation regime followed by conical instability. Using side-view imaging, we track the equilibrium shapes, the transition to the unstable regime, and the pre-jet apex dynamics within one experimental system. In the stable regime, the meridional profile is well described by an ellipsoid-of-revolution fit, and the aspect ratio collapses across initial bubble sizes onto a single steady-state branch when plotted against the dimensionless field $E^{*}=\sqrt{{\mathrm{Bo}}_e}$ for data acquired within a fixed ambient session where the electric Bond number ${\mathrm{Bo}}_e$ is defined as ${\varepsilon }_0{E}_0^2{R}_0/\left(2\gamma \right)$. The end point of this branch marks the transition to the unstable regime. Above the onset of instability, the apex sharpens into a cone with half-angle $30.0^{\circ } \pm 0.6^{\circ }$, below the classical Taylor value. We interpret this smaller angle as a dynamic pre-jet angle rather than as a modified static Taylor-cone angle. To quantify the late pre-jet stage, we define the axial distance $\ell \left(t\right)$ from the instantaneous apex to a fixed reference vertex determined from the terminal cone geometry and measure its evolution. The corresponding rate grows as jetting is approached, and a near-tip inertia-capillary model captures the observed logarithmic trend as an approximation. Together, these measurements establish a single-system experimental benchmark in which stable electrocapillary deformation is organized by a single steady-state branch that leads into conical instability and pre-jet dynamics.

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• Drop & bubble phenomena
• Electric field effects
• Surface & interfacial phenomena