Controllable Preparation And Modification Of Yolk-shell Microspheres Based On Poly(Vinylidene Fluoride)

In this paper,the morphology controllable yolk-shell structure of polymeric microspheres was prepared by the combination of soap-free seeded emulsion polymerization and solvent selective etching.Firstly,the composite microspheres of PVDF@P(St-co-GMA)were prepared by using polyvinylidene fluoride(PVDF)latex particles as the seed,styrene(St),glycidyl methacrylate(GMA)as comonomers and vinylbenzene(DVB)as corss-linking agent.Then,N,N-dimethylformamide(DMF)solvent was used to selectively etch the PVDF cores,and the yolk-shell PVDF@P(St-co-GMA)polymeric microspheres were obtained.And the yolk-shell structure microspheres were used to produce the functional microspheres with fluorescent markers.After grafting FITC,functional microspheres with fluorescent labels were prepared.At the same time,the effect of seed/monomer ratio and polymerization temperature on the morphology of composite particles was investigated systematically.The results show that when the seed/monomer feeding ratio was 0.5 g/1.5 g,the composite particles showed a flower-shaped structure initially,and when the seed/monomer ratio was 0.5 g/2.0 g,the composite particles showed more obvious flower-like shape.Further,addition quantity of the monomer was increased,that is,when the seed/monomer ratio was 0.5 g/4.0 g,the composite particles appeared a variant bowl shape.When the reaction temperature was 75 °C,the composite particle exhibt obvious flower-like morphology,which was helpful to the preparation of yolk-shell structure microspheres during the solvent etching stage.The chemical composition of composite particles was analyzed by Fourier transform infrared spectrometer(FT-IR),and the formation of composite particles was confirmed.The types and contents of surface elements of the composite particles were analyzed by X-ray photoelectron spectroscopy(XPS),and the crystallization behavior of seeds and composite particles was characterized by differential scanning calorimeter(DSC).The DSC results indicated that the composite particles had core-shell structure.The effects of polymerization time,solvent etching time and solvent etching temperature on the yolk-shell micro-spherical morphology were studied in the process of solvent etching.The research results showed that the longer the polymerization time,the thicker the shell layer of the yolk-shell microspheres was.By prolonging etching time,the cavity volume of the particle became larger.By changing the control conditions of polymerization and the order of etching procedures,the functional yolk-shell microspheres with the same or different functional groups on the inside and outside of the shell could be obtained.In this paper,the yolk-shell microspheres were simply prepared by the nucleation method of the polymer surface without using the template.And these functional yolk-shell microspheres have an important application prospect in the fields of chemical catalysis and drug delivery in biological field.