An insight into structure regulation of uniform polystyrene micro/nano-particles by porogen in premix membrane emulsification process

Manipulation of the shape and size distribution of porous polystyrene (PST) micro/nano-particles by premix membrane emulsification is a big challenge. Here by this technique, we successfully synthesized uniform PST micro/nano-particles with diameters from 700 nm to 7 μm and with pore sizes from 7 nm to 200 nm. The size uniformity of particles was discovered to be affected by 3 key factors: transmembrane pressure, number of emulsification cycles and membrane pore size. The structures of particles were found depend on both porogen system and particle size. Furthermore, the interaction mechanism between porogen and PST particles was analyzed by Quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The addition of porogen reduced the oscillation frequency change (Δƒ) and increased the dissipation change (ΔD) of the tested PST film, which affect the phase separation process between the porogen and PST polymer, and then form different pore size of PST particles. Moreover, the type and dosage of porogen can create various structures of PST micro/nano-particles at different particles size effectively.