Sliding-Film Evaporator for Rapid, Morphology-Stable Solvent Removal from Microfluidic Emulsions

Abstract

Droplet microfluidics can generate highly monodisperse PLGA emulsions, but translating this precision to scalable manufacturing is hindered by poorly controlled downstream solvent removal, which broadens size distributions and disrupts core–shell morphology. Here, we develop a sliding-film evaporator (SFE), a microfluidic analogue of industrial falling-film evaporators, that spreads PLGA single and double emulsions into a temperature-controlled thin aqueous film flowing over wafer-etched parallel grooves. After flow on the SFE for approximately 20 s (75 mm in length), more than 80% of the solvent is removed from 90 μm chloroform-in-water single emulsions, and nearly complete removal from water-in-chloroform-in-water double emulsions with outer and inner diameters of 101 and 74 μm, respectively, was achieved. For double emulsions, the SFE preserves the concentric core–shell morphology by eliminating the severe core-rise and coalescence observed in batch drying, yielding microcapsules with an eccentricity (e) of 0.05 compared to an e of 0.21 under static evaporation. Overall, the SFE provides a dynamic, scalable downstream-processing platform that couples microfluidic droplet generation with controlled thin-film evaporation, enabling high-throughput production of PLGA microparticles and microcapsules with preserved morphology and well-defined solvent removal kinetics.