Digital, Two-Phase, and Droplet Microfluidics - Microfluidics for Biotechnology - page 156

Figure 4.30 Domain of possible drop division for open EWOD systems obtained by a series of Evolver
calculations. Continuous line: deionized water with contact angles 70° and 115° and surface tension 70
mN/m. Dotted line: ionic liquid with contact angles 60° and 93°, and surface tension 40 mM/m.

pinching region. The pressure inside the liquid is related to the two curvature radi-
uses by

æ 1 1 ö

D = P γ - (4.47)

ç ÷

LG

è R R ø

1 2

where the minus sign takes into account the concavity of the drop surface. The
vertical curvature radius R 1 is

δ

(4.48)

R = -

1

2cos θ

0

and, because the width of the pinching region goes to zero

Figure 4.31 Simulation of splitting a droplet confined between two horizontal plates (the upper
plate has been dematerialized for visualization). The hydrophobic contact angle is 115°, the hydro-
philic contact angle is 75°, and the liquid/gas surface tension is 70 mN/m.