Superparamagnetic nanocomposites based on superparamagnetic iron oxide nanoparticles and polymethyl methacrylate

V pričujočem delu sem se ukvarjal s sintezo superparamagnetnih nanokompozitov na osnovi nanodelcev γ-Fe2O3 in PMMA. Nanodelce sem sintetiziral s koprecipitacijo Fe2+/Fe3+ ionov v vodni raztopini. Nanodelce prevlečene z oleinsko ali ricinolejsko kislino sem sintetiziral s koprecipitacijo Fe2+/Fe3+ ionov v vodni raztopini v prisotnosti oleinske oz. ricinolejske kisline. Preliminarne raziskave so jasno pokazale, da je nemogoče pripraviti superparamagnetne nanokompozite γ-Fe2O3 v PMMA matrici brez ustrezne funkcionalizacije površine magnetnih nanodelcev. Iz slik s presevnega elektronskega mikroskopa (TEM) sem zaključil, da je vzorec pripravljen z mešanje nanodelcev γ-Fe2O3 s PMMA v acetonu in kasnejšim obarjanjem polimera v vodi, fazno separiran. Vzorec je sestavljen iz aglomeratov nanodelcev γ-Fe2O3, ki niso vgrajeni v polimerno matrico. Nanokompozite sem pripravil z obarjalno polimerizacijo PMMA v prisotnosti nanodelcev prevlečenih z oleinsko kislino. Koloidno stabilni suspenziji nanodelcev prevlečenih z oleinsko kislino v n-dekanu sem dodal monomer metil metakrilat. Polimerizacijo monomera sem izvedel pri povišani temperaturi. Delež nanodelcev v nanokompozitu sem kontroliral preko razmerja nanodelci/monomer. S pomočjo TEM analize sem ugotovil, da so nanodelci homogeno porazdeljeni v polimerni matrici. Z višanjem razmerja prehaja mehanizem nastanka polimernih zrn preko homogene v heterogeno nukleacijo. Nanokompozit ohrani superparamagnetno naravo tudi ob vgradnji relativno velikega deleža vgrajenih nanodelcev, do 48 ut. %. Vgradnja velikega deleža magnetnih nanodelcev je razlog za visoko nasičeno magnetizacijo nanokompozitov, do 31 emu/g. Nanokompozitne delce sem pripravil s polimerizacijo monomera metil metakrilata v prisotnosti nanodelcev v miniemulziji. Koloidno stabilno suspenzijo sestavljeno iz nanodelcev prevlečenih z ricinolejsko kislino, ultrahidrofoba in iniciatorja v monomeru, sem dodal k vodni raztopini surfaktanta. Miniemulzijo sem pripravil s pomočjo ultrazvoka. Polimerizacijo sem izvajala pri povišani temperaturi. S spreminjanjem deleža surfaktanta sem prilagajal povprečni premer nanokompozitnih delcev v razponu med ~25 nm in ~50 nm. Zaradi visokega ζ-potenciala je suspenzija nanokompozitnih delcev v vodi koloidno stabilna. S TEM slik nanokompozitnih delcev sem ugotovil, da so nanokompozitni delci sestavljeni iz nanodelcev, ki tvorijo jedro delca in tankega sloja polimera okrog jedra. V nanokompozitne delce sem uspel vgraditi do 39 ut. % magnetnih nanodelcev, ne glede na velikost nanokompozitnih delcev. Nasičena magnetizacija nanokompozitnih delcev znaša 27 emu/g.Presented work describes synthesis of superparamagnetic nanocomposites, based on superparamagnetic γ-Fe2O3 nanoparticles and PMMA. Nanoparticles were synthesized by the coprecipitation of Fe2+/Fe3+ ions from an aqueous solution. Oleic or ricinoleic acid coated nanoparticles were synthesized by the coprecipitation of Fe2+/Fe3+ ions from an aqueous solution in the presence of oleic or ricinoleic acid. Preliminary study clearly demonstrated that it is impossible to prepare superparamagnetic nanocomposite of the γ-Fe2O3 in the PMMA matrix without nanoparticles functionalization. Sample prepared by the mixing of the γ-Fe2O3 and the PMMA in the acetone and subsequent precipitation of the polymer by water addition, was composed of two separated phases, as observed by transmission electron microscopy (TEM). The phases were identified as agglomerates of the γ-Fe2O3 which were not encapsulated by the PMMA matrix. Nanocomposites were prepared by the precipitation polymerization of the methyl methacrylate in the presence of oleic acid coated nanoparticles. Methyl methacrylate was added to the colloidal suspension of the oleic acid coated nanoparticles in n-decane and in-situ polymerization was carried out at elevated temperatures. The content of nanoparticles was controlled by varying the nanoparticles/monomer ratio. The TEM analysis showed that the nanoparticles were well dispersed in the polymer matrix. The mechanism of formation of the polymer grain changes from homogeneous to heterogeneous nucleation as the ratio is increased. Nanocomposites retained their superparamagnetic nature even when encapsulated by polymer with concentrations up to 48 wt. %. The high loading of magnetic nanoparticles resulted in relatively high saturation magnetizations of the nanocomposites, up to 31 emu/g. Nanocomposite particles were prepared using the mini-emulsion polymerization of a monomer in the presence of the nanoparticles. A colloidal suspension composed of ricinoleic acid coated iron-oxide nanoparticles, the initiator and the ultrahydrophobe in the monomer, methyl methacrylate, was added to an aqueous solution of surfactant and then ultrasonified to promote the formation of the mini-emulsion. The polymerization was initiated by raising the temperature. By changing the content of surfactant, nanocomposite particles with an average diameter ranging from 25 to 50 nm were obtained. Because of the high ζ-potential, the nanocomposite particles formed a stable suspension in water. TEM showed that the core of the prepared nanocomposite particles was composed of iron-oxide nanoparticles homogeneously distributed within a polymer matrix and a thin polymer shell. The content of magnetic nanoparticles dispersed in the polymer was as high as 39 wt. %, resulting in a high saturation magnetization of 27 emu/g