We developed a W/O miniemulsion reactor system enabling the preparation of biopolymer nanoparticles and control of their morphologies and inner microstructures. First, the W/O miniemulsion was prepared by suspending water nanodroplets containing agarose in oil. Then, we produced agarose hydrogel nanoparticles (AgarH) by the gelation of agarose in nanodroplets. Next, we prepared agarose xerogel nanoparticles (AgarX) by precisely tuning the water evaporation from AgarH. We controlled the morphologies (solid and hollow) and crystal structure of AgarX by changing the pressure and temperature during water evaporation. In fact, AgarX with a hollow structure was generated through rapid evaporation at a low pressure. AgarH was dissolved in Milli-Q water when the temperature was raised to 90 °C. On the other hand, AgarX remained a solid particle under the same conditions, likely because of its high crystallinity. We expect that this technique can be applied to prepare xerogels of diverse biomass-based polymers for the replacement of synthetic polymers.
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