Surface Modification Of Fe₃O₄Nano-particles And Its Effect On The Crystallization Of Poly（Ethylene Glycol）

In this dissertation, magnetic nanoparticles (MNPs) of ferriferous oxide (Fe3O4) wereprepared by means of chemical co-precipitation. The MNPs were grafted with mPEG viacovalent bond. The surface of Fe3O4was first coated with (3-aminopropyl)triethoxysilane(APTES) by a silanization reaction and then linked with mPEG via the amidation reactionbetween-NH2and-COCl to form well-dispersed surface grafted f-Fe3O4. Then they wereblended with PEG to prepare f-Fe3O4/PEG composite by solvent-casting. The obtainedf-Fe3O4were characterized by Fourier transform infrared spectroscopy (FT-IR), X-raypowder diffraction (XRD), thermogravimetric analyzer (TGA), dynamic light scattering(DLS), field emission scanning electron microscopy (FESEM). The crystallization behaviorsof f-Fe3O4/PEG composite were investigated by differential scanning calorimetry (DSC) andpolarized optical microscopy (POM).Compared with unmodified magnetic particles, the aggregation size of f-Fe3O4wassignificantly reduced. They could be uniformly dispersed in acetonitrile, a good solvent ofPEG, and exhibited good compatibility with PEG matrix. With further study ofcrystallization kinetics, PEG crystal structure of f-Fe3O4/PEG composite system was notchanged, but the degree of crystallinity was decreased gradually with increasing f-Fe3O4content. The PEG chains grafted on f-Fe3O4were not able to crystallize. The crystallizationrate of PEG was significantly improved with increasing f-Fe3O4content and the valuereached the maximum with10wt%of f-Fe3O4. These results suggested that f-Fe3O4playedan effective nucleating agent to increase heterogeneous nucleation rate significantly.The crystalline morphology of the f-Fe3O4/PEG composite was observed by POM withhot stage. The results showed that clear and regular banded spherulitic patterns appearedwhich was completely different from common spherulite of pure PEG. Regardless ofnon-isothermal and isothermal crystallization processes of the f-Fe3O4/PEG composites, theband spacing decreased with increasing f-Fe3O4content. Under non-isothermal crystallization, spherulite sizes were reduced to make grains refinement; band spacingincreases with isothermal crystallization temperature increasing. Once crystallizationtemperature was above42oC, banded spherulites were not showed any more.Furthermore, other factors on banded spherulites in f-Fe3O4/PEG composite werediscussed. The results showed that chemical modified Fe3O4as the filler and the PEG as amatrix with molecular weights of2000and4000made more contribution to formation ofclear and regular banded spherulites.