Preparation And Self-assmbly Of Anisotropic Composite Particles Based On Poly(Vinylidene Fluoride)

Poly(vinylidene fluoride)(PVDF)was used as seeds and 4-vinyl pyridine(4VP)was used as monomers.Nonspherical poly(vinylidene fluoride)/poly(4-vinyl pyridine)(PVDF/P4VP)composite particles were prepared via a facile one-step soap-free seeded emulsion polymerization.The influence of polymerization time,addition of ammonia solution,stirring speed and monomer/seed feed ratio on the micromorphology of PVDF/P4 VP composite particles was investigated.According to the experimental results and the incompatibility of 4VP and PVDF,the formation mechanism of composite particles based on surface nucleation was proposed.In addition,PVDF/P4VP@P(St-co-AA)raspberry-like particle clusters were prepared by self-assembly of snowman-like PVDF/P4 VP composite particles with poly(styrene-co-acrylic acid)[P(St-co-AA)] particles.The micromorphology of the composite particles was characterized by scanning electron microscopy(SEM).The average particle size and particle size distribution of the composite particles were determined by dynamic light scattering(DLS).The chemical composition of the composite particles was analyzed by Fourier transform infrared spectroscopy(FT-IR).The confined crystallization of PVDF was studied by differential scanning calorimetry(DSC).The hydrophilicity of the composite particles was measured by contact angle tester.The surface element kinds and contents of particle clusters were analyzed by X-ray photoelectron spectroscopy(XPS).The study results showed that ammonia solution could prevent the nucleation of P4 VP prepolymer in the aqueous phase,which played an important role in maintaining the stability of PVDF/P4 VP polymerization system and the uniformity of composite particles.The stirring speed of the system could influence the mobility of 4VP-swollen P4 VP on the surface of PVDF seeds,which played an important role in controlling the morphology of PVDF/P4 VP composite particles.When the stirring speed was low,the composite particles mainly presented a dumbbell-like shape;when the stirring speed was high,the composite particles mainly presented a snow-like shape.The size of the P4 VP bulges on the composite particles could be easily tailored by changing the 4VP/PVDF feed ratio without destroying the snowman-like shape of the composite particles.The formation of PVDF/P4 VP composite particles consisted of two steps: one morphology control step appeared at the initial polymerization stage;the other P4 VP growth step appeared at the middle and later polymerization stage.In addition,raspberry-like particle clusters with hierarchical structure and PVDF bulges protruding outward could be obtained through the self-assembly of snowman-like PVDF/P4 VP composite particles with P(St-co-AA)particles via strong interaction between pyridine groups of 4VP and carboxyl groups of AA.