title: Selective droplet coalescence using microfluidic systems.
abstract: We report a microfluidic approach, which allows selective and controlled 1 : 1, 2 : 1 or 3 : 1 droplet fusion. A surfactant-stabilized droplet with an interfacial surfactant coverage, Γ, of >98% will fuse spontaneously with a second droplet when Γ of the latter droplet is <16%. However, when Γ of the second droplet is ~66%, the two droplets will not fuse, unless they have previously been brought into contact for critical time τ. Therefore, controlling the number of droplets in contact for time τ allows precise control over the number of fused droplets. We have demonstrated efficient (proportion of droplets coalesced p(c) = 1.0, n > 1000) and selective 1 : 1, 2 : 1 or 3 : 1 droplet fusion (proportion of correctly fused droplets p(s) > 0.99, n > 1000). Coalescence in this regime is induced by hydrodynamic flow causing interface separation and is efficient at different Ca numbers and using different dispersed phases, continuous phases and surfactants. However, when Γ of the second droplet is ~96% coalescence is no longer observed. Droplet-based microfluidic systems, in which each droplet functions as an independent microreactor, are proving a promising tool for a wide range of ultrahigh-throughput applications in biology and chemistry. The addition of new reagents to pre-formed droplets is critical to many of these applications and we believe the system described here is a simple and flexible method to do so, as well as a new tool to study interfacial stability phenomena.
authors.affiliation: Vilnius University Institute of Biotechnology, Graiciuno 8, Vilnius LT-02241, Lithuania. linas.mazutis@bti.vu.lt
authors.forename: Linas
authors.initials: L
authors.lastname: Mazutis
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Griffiths
mesh_terms: D004655:Emulsions / Q000737:chemistry; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D010316:Particle Size; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D004655:Emulsions; D013501:Surface-Active Agents