Fig. 2. Design of experiments for measuring viscous and elastic moduli and interfacial tension.
a Oscillatory micro-rheology inside a settled droplet. b Time traces of the trap position (Xt; green) and trapping force (Ft; black) on a bead inside a pK:H droplet. A fit of the force trace to a cosine function of time is shown in red. The oscillation frequency (ω/2π) was 1 Hz. c A droplet suspended by two trapped beads at the opposite poles (top: side view; bottom, top view). Trap 2 was fixed in place while trap 1 was pulled toward the left. d Traces of the trap 1 position (Xt1; green) and traps 1 and 2 forces (Ft1 and Ft2; black) measured on a pK:H droplet. The force traces were smoothed by moving average over a 64-ms window; linear fits are overlaid. Trap 1 was pulled at a constant speed of ~0.05 μm/s.