Preparation of Poly(vinylidene fluoride)/Poly(4-vinyl pyridine) Janus Particles

Snowman-like Janus particles of PVDF/P4VP were prepared via a soap-free seeded emulsion polymerization using poly(vinylidene fluoride) (PVDF) latex particles as seeds and 4-vinyl pyridine (4VP) as functional monomer. All seeded emulsion polymerization was carried out in a four-necked round-bottom flask of 100 mL capacity. First, dialyzed PVDF latex (4.0 g) with a solid content of 12.5 wt% was dispersed in deionized water (40.0 g), and the dispersion was further ultrasonicated for 40 min to avoid any particle agglomeration. The flask was placed in a water bath preset at 30 degrees C and nitrogen-purged for 15 min to remove O-2 before additions of ammonia solution (1.0 g) and 4VP (0.5 g). Nitrogen-purge was maintained during the entire reaction process. The mixture was stirred at 250 r/min for 1 h to allow the monomers to swell the PVDF seed particles, followed by heating to 60 degrees C. Subsequently, 1.5 mg of K2S2O8 were added to trigger the polymerization, and the reaction lasted for 4 h. The average particle diameter and particle size distribution (PDI) of the composite particles were determined by dynamic light scattering. The micromorphology of the composite particles was characterized by scanning electron microscopy. The chemical composition of the composite particles was confirmed by Fourier transform infrared spectroscopy. The confined crystallization of PVDF in the composite particles was studied by differential scanning calorimetry. In this study, the introduction of an appropriate amount of ammonia solution into the polymerization system played a vital role in maitaining the stability of the reaction system and the uniformity of the composite particles, possibly due to the prevention of P4VP nucleation in the aqueous phase. One side of the compsite particles obtained was PVDF and the other side was P4VP with pyridine groups, which could be used for further modification and assembly.