Phase separation of parallel laminar flow for aqueous two phase systems in branched microchannel

Aqueous two phase systems (ATPSs) have good biocompatibility and special selectivity. Their phase equilibrium and applications in biological analysis have received much attention. Herein, parallel laminar flow (PLF) in the microchannel can provide an effective platform to enhance mass transfer and preserve separate phases simultaneously. As fundamentals in feasible and convenient sampling of PLF for ATPS, the phase separation methods and rules in branched microchannel were studied in this work, selecting PEG 4000 + Na₂SO₄ + H₂O as a model system. The exploration of flow pattern showed that a stable PFL was easily to form in the shallow microchannel of 200 μm (depth) × 600 μm (width), as long as the velocity of lower phase was higher than 0.51 mm/s. The phase interface of PLF could be easily controlled by the flow ratio of two phases. Single-phase separation could be reliably achieved in T-junction outlets when the flow rate of outlet ascertains to be smaller or larger than that of inlet on the same side. The trifurcate outlets with an extra middle channel could help realize a simultaneous two-phase separation. The flow rate of the extra channel is the key for the phase separation performance, the range of which available for simultaneous two-phase separation is determined by the resistance balance and the flow rates deviation offsetting as well. It is favor for increasing phase separation efficiency to make the products of flow rate, viscosity, and the length of corresponding outlet channel close with each other for the upper phase and the lower phase. The adjustable lengths of three channels can provide flexible choices to enhance simultaneous two-phase separation of diversified ATPSs at various operating flow ratios. A multiport microchip with T-junction inlets and trifurcate outlets designed for adjusting the lengths of branched channels on-chip is a convenient tool for PLF contact and in situ phase separation of ATPSs in varieties of application.