Fig. 2. Diagram and mechanical analysis of the droplet manipulation.

(A) Phase diagram showing the diverse behaviors of the droplet with the variation of D/d and V. (B) Mechanical analysis explaining the actuating ability of the robot. Three forces, including the adhesion force between the liquid and the beads (F_a), the adhesion force between the liquid and the substrate (f_front), and the resilience force due to the deformation of the droplet (F_e), determine the movement of the TCL at the front end of the droplet (the upper scheme). Two main forces (F_e and f_rear) affect the movement of the TCL at the rear end of the droplet (the lower scheme).