Polymer particles with dimensions in the range of 10-100 um are extensively used in ion-exchange, chromatography columns, and in various biological and medicinal applications, such as coatings, supports for controlled release and so on. A number of methods have been developed to manufacture micrometric polymeric beads with good spherical structure and narrow size distribution. However, many current applications require specific particle structure used as a building block for self-assembled materials, controlling suspension rheology and for engineering colloid composites. Actually, fabrication specific shape of polymer particles is difficult because surface tension likely produces spherical shape in overall length scales.

In this recent study, We fabricate a monodisperse, size-controllable toroidal shape of polymer particles with polysulfone and N,N-dimethylformamide solution, using phase separation technique within a controllable one dimension laminar flow in a capillary microchannel device. As can be seen in figure 1, polymer particle features the average diameter of 40um, thickness of about 20um with a smooth surface. Observation of optical microscopy and SEM indicates a perfect size monodispersion property. Using a high sensitive fast camera, we observed phase separation process directly and found that whole phase separation occurs within the microchannel device, the volume of polymer droplet gradually decreases with the diffusion of N,N-dimethylformamide into PDMS oil, which is used as continue phase to bring polymer particles away. The formation of toroidal structure can be divided into three steps: 1)Velocity profile around polymer droplet in axial flow induces the difference of solvent diffusion from droplet towards continuous oil phase initially, thus resulting in phase separation firstly occurs on the outer edge of the droplet perpendicular to axial flow; 2)polymer chains move from central to the solidified surface; 3)whole droplet solidifies due to solvent diffusion into continue oil phase and forms a toroidal structure.

The method of phase separation in one dimensional axial flow indicates a potential application in fabricating specific shape and size-controllable polymeric particles. Since monodisperse/toroidal structure of polymer particles can be fabricated only one step, this makes it easy to scale-up effectively for mass production in the future.

Key words:  toroidal polymer particle; phase separation; one dimensional flow; capillary microchannel device

Figure 1 Toroidal structure of polymer particle made of polysufone by phase separation process with capillary microchannel device