Based on the experimental data for turbulent flow, these junction loss coefficients can be found in the literature in the form of analytical or empirical expressions characterized by branch angle, area ratio, and flow ratio[9, 10], which are not appropriate to use for laminar flow conditions.
Primary emulsion droplets were formed in a fluorocarbon-coated chip in which a surfactant-containing fluorous oil carrier phase meets an aqueous stream at a flow-focusing junction.
Channels downstream of the flow-focusing junction were rendered hydrophilic by a treatment with a 5% (wt/vol) polyvinyl alcohol (PVA) solution16, which was flowed in the inlet for the outer aqueous solution for 5 min while blowing air into the other inlets to avoid contact of the PVA-solution with device regions upstream of the flow-focusing junction.
Design of the flow-focusing junction was adapted from Desphande et al.16 (Supplementary Figure 1).
The critical condition for bubble breakup in a microfluidic flow-focusing junction was studied in this work.
On the basis of these two expressions, the critical condition for the bubble breakup in a microfluidic flow-focusing junction was deduced: l0wc= 1.5u1u20.75Ca2-0.13, where wc is the width of microchannel, Ca2 = u2μ/γ, and γ is the surface tension.
The critical condition for bubble breakup was investigated by varying the bubble length l0, liquid viscosity μ, velocity of the liquid from the main channel of the flow-focusing junction u1, and velocity of the liquid from the side channels of the junction u2.
As shown in Figure 4B,C, in the presence of 1.0 wt% K, 1A will begin to diffuse (aided by chaotic advection) to the oil water boundary upon droplet formation at the flow-focusing junction (B1).
By application of vacuum to the outlet wells, sample and oil are drawn through a flow-focusing junction where monodisperse droplets are generated at a rate of ∼1 000 per second.
