Evolution of the pressure for the breakup with tunnels (Ca = 0.004, l/w = 0.70). (a) The inlet pressure of the main channel, P_inlet, and the outlet pressures of the splitting channel, P_{outlet i} and P_{outlet ii}. (b) The neck thickness δ^*, the Laplace pressure of rear droplet interface P_δ, and the inlet and the outlet pressures in A-A stage (t^* = 0–3.5 ms).