(227a) Transport Across Spontaneously Generated Interfaces with Ultralow Tension

Simple, scalable, and low cost separation of biomolecules, carbon nanotubes, and other nanoparticles can be achieved by aqueous two-phase extraction, in which incompatible polymers phase separate and nanoparticles partition across the resulting ultralow tension polymer-polymer interface. The method can be readily integrated with microfluidic approaches by generating microscale droplets of initially homogeneous polymer mixtures. Controlled dehydration of the droplets increases the concentration of the polymer phases, inducing phase separation at moderate timescales. Flow can be used to promote coalescence of the individual phases and to drive the more viscous polymer phase toward the tail end of an elongated droplet. Selective partitioning of nanoparticles between the phase-separated compartments in this stage is quantified using inline absorption spectroscopy. At longer timescales, concentration-induced changes in interfacial tension drive wetting transitions in the compound droplet. Observing the evolution of the three-phase contact line allows the interfacial tension of the polymer-polymer interface to be estimated as a function of polymer concentration. Control and observation of these phenomena in microscale droplets offers new tools for characterizing the mechanics of ultralow tension interfaces and the transport and adsorption of nanoparticles onto and across these interfaces.  Microfluidic droplet generation methods can be used to examine these properties over a wide range of compositions of the aqueous polymer mixtures.