Yüzeyi polimer kaplı magnetit nano taneciklerin yeni bir yöntemle tek basamakta elde edilmesi
A new method for preparing polymer capsulated magnetic nanoparticles in one pot
Yazar: ELİF CAN BELLİKAN
Danışman: PROF. DR. OKAN SİRKECİOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Kimya = Chemistry
Dizin: Emülsiyonlar = Emulsions ; Manyetit = Magnetite ; Nanopartiküller = Nanoparticles ; Polimer kaplama = Polymer coating

Özet:
Magnetit Fe3O4 kimyasal yapısına sahip doğada doğal olarak bulunan bir
demiroksittir. Kendiliğinden mıknatıslanma özelliğine sahip olması ve laboratuvar
ortamında sentezinin oldukça kolay hale gelmesi nedeni ile son yıllarda uygulama
alanları oldukça artmıştır ve araştırıcılar tarafından oldukça ilgi görmeye başlamıştır.
Manyetit nanopartiküller hipertermi tedavisi, hedefli ilaç taşınması, manyetik
rezonans görüntüleme, biyoseparasyon gibi biyomedikal uygulamalar başta olmak
üzere mühendislik alanlarında ve teknolojik sistemlerde kullanılmaktadır. Özellikle
son yıllarda manyetit nanopartiküllerin ıslak kimyasal yöntemlerle sentezlenmeye
başlaması ile bu partiküllerin uygulama alanları giderek artmıştır.
Manyetit       nanopartiküllerin    istenilen      yapıda   ve      boyutta   sentezinin
gerçekleştirilebilmesi bir çok yöntem geliştirilmiştir. Bunlardan ilki Fe(II) ve Fe(III)
tuzlarının yüksek alkoller varlığında muamelesi sayılabilir. Bu yöntemle magnetit
nanopartiküllerin 10-20 nm aralığında sentezlenebileceği söylenmiştir. Ancak bu
yöntem ortamdaki hidroksil iyonlarının ve demir oksitin dengelenmemiş
stokiyometrisine oldukça bağlıdır.
İkinci yöntem olarak yüksek sıcaklıkta Fe(III)?ün Fe(II)?ye indirgenmesi
söylenebilir. Bu yönteminin ortaya koyduğu mekanizma henüz tam olarak
anlaşılamamış olmakla beraber literatürde bu yöntemle yapılmış bir çok manyetit
nanopartikül yer almaktadır.
Bunların yanı sıra magnetit nanopartiküllerin yüzey modifikasyonu ve manyetit
nanopartiküllerin organik maddelerle veya polimerlerle kaplanması halen daha
araştırıcılar tarafından ilgi duyulan ve gelişmeye açık yöntemlerdir. Literatürde bu
yöntemlerle iligili oldukça fazla reçete yer almaktadır.
Bu çalışmada ATRP yöntemiyle sentezlenen P(GMA)?nın , PS-b-P(GMA)?nın asit
ile hidroliz edilmesi incelenmiş ve elde edilen hidroliz ürünleri ile manyetit
nanopartikül sentezi yapılmıştır. Ayrıca PVA ticari polimeri ile de manyetit
nanopartikül sentezi yapılmıştır. P(GMA)?nın hidroliz ürünü PDHPM kaplı manyetit
nanopartikül sentezi organik çözücüde gerçekleştirilmiş ve oluşan manyetit
nanopartikülün suda redispers olduğu görülmüştür. PS-b-P(GMA)?nın hidroliz
ürünü PS-b-PDHPM ile tanecik-kabuk tipinde manyetit nanopartikül sentezi invers
emülsiyon        ortamında (Toluen/Su) gerçekleştirilmiş ve oluşan manyetit
nanopartikülün DMF çözüsünde dispers olabildiği görülmüştür.
Son olarak PVA kaplı manyetit nanopartikül sentezi ise sürfaktan varlığında suda
gerçekleştirilmiş ve oluşan manyetit nanopartikülün suda redispers olduğu
görülmüştür.
FT-IR spektrumları elde edilen manyetit nanopartiküllerin yapısında manyetit
bulunduğunu göstermiştir.
Yapılan ESEM analizi sonucunda manyetit nanopartiküllerin küresel yapıda olduğu
görülmüş ve DLS analizi ile taneciklerin ortalama çapları, polidispersiteleri
belirlenmiştir. Buna gore PDHPM kaplı manyetit nanopartiküllerin ortalama tanecik
çapları 167 nm, polidispersiteleri 0.164, PS- PDHPM içeren tanecik-kabuk tipindeki
manyetit nanopartiküllerin ortalama tanecik çapları polidispersiteleri belirlenmiştir.
Buna gore PDHPM kaplı manyetit nanopartiküllerin ortalama tanecik çapları 167
nm, polidispersiteleri 0.164, PS-PDHPM içeren tanecik-kabuk tipindeki manyetit
nanopartiküllerin ortalama tanecik çapları 260,3 nm, polidispersiteleri 0.236, PVA
kaplı manyetit nanopartiküllerin ortalama tanecik çapı 70,8 nm, polidispersiteleri
0.271 bulunmuştur.
Elde edilen manyetit nanopartiküllerin titreşimli örnek manyetometre analizleri
yapılmış ve buradan doyum manyetizasyonları, koersiviteleri ve ağırlıkça Fe3O4
yüzdeleri hesaplanmıştır. PDHPM kaplı manyetit nanopartiküllerin doyum
manyetizasyonu 44.5 emu/g, ağırlıkça Fe3O4 yüzdesi %49.4, PS-PDHPM içeren
tanecik-kabuk tipindeki manyetit nanopartiküllerin doyum manyetizassyonu 3.1
emu/g, ağırlıkça Fe3O4 yüzdesi %3.4 ve PVA kaplı manyetit nanopartiküllerin 12.7
emu/g, ağırlıkça Fe3O4 yüzdesi %14.1 bulunmuştur. PDHPM kaplı manyetit
nanopartikülün koersivitesi 50 Oe bulunmuş, diğer iki manyetit nanopartikülün
koersivitesi ise sıfır (0)?a yakın bulunmuştur.

Abstract:
Magnetite is a naturally occuring mineral having formula, Fe3O4. It shows strong
magnetization abilities comparable with those of superparamagnetic metal alloys
such as ?-Fe2O3 and ?-Fe2O3. Not being oxidable, magnetite is superior to the other
magnetic materials. Since it?s laboratory synthesis from Fe(II) /Fe(III) mixtures by
coprecipitation of their hydroxides, the synthetic magnetite has found great interest
due to it?s widespread application in various fields.
From application point of view, the magnetite powder in nanosize has broader use in
magnetic data memory devices, in loudspeakers, laser printing, magnetic resonance
imaging (MRI), hyperthermia theraphy, targeted drug delivery, bioseparation and
electromagnetic shielding coatings etc.
Preparation of magnetite nanoparticles (MNPs) however, needs special attention
while preparing by wet chemical methods, due to high coalesence tendency of the
preformed nanoparticles. Neverthless, recent developments in the area have shown
that MNPs even with 10-20 nanometers of sizes can readily be attained. Among
those dropwise addition of the solution of Fe(III) /Fe(II) mixtures and reaction of
Fe(III) salt with high boiling alcohols worth to mention. Apparently the first
approach depends on unbalanced stochiometry of hydroxil ion and iron oxides.
In the second approach magnetite formation takes place by partial reduction of
Fe(III) to Fe(II) at the temperatures around 200oC. Although the mechanism has not
been clearly disclosed yet, most probably Fe(II) formation occurs by oxidation of
OH group of the alcohol.
However, why the precipitation of the oxides takes place in a such combination is
not well understood yet. There appears a number of new procedures in the literature
for fabrication of MNPs and their stable in oil and water dispersions. For instance,
excellent and stable dispersions of oleic acid stabilized oil dispersions have been
commercialized in small scales.
Despite those significant developments in nano size magnetite synthesis, covalent
modification of the partical surfaces is still a challenging that needs further
development.
Coating of magnetite nanoparticles with organics especially essential for medical
applications. This is due to biological incompatibility of naked MNPs. In this respect
there are few successfull methods of coating of magnetic nanoparticles. Zhang group
reported coating of MNPs via atom transfer radical polymerization (ATRP) method
using surface bond chloropropionic acid as initiator. Although, a thick polystyrene
layer is formed at the end of this process the resulting nanoparticles are not well
redispersible and suffers from further oxidation of the magnetic core.
In another successfull coating process described by Chu group, MNPs have been
prepared in an inverse micro emulsion system consisting of methacrylic acid /N,N
methylene bis acrylamide and bis (2-ethyl hexyl sulfosuccinate) as emulsifier.
Polymerization of the monomers in this emulsion directly give polymer coated
magnetite nanoparticles.
Emulsion polymerization of styrene in the presence of ironoxide nanoparticles has
been demonstrated by Asher group to give polystyrene nanospheres with magnetic
particles inside. Moreover, precious metal coating has been considered much more
useful and bio-compatible in medical applications. O?Connor and co outhers,
published a method for preparing gold coated magnetic nanoparticles in one step. In
their process FeCl3 solution in N-methyl pyrrolidinone is editted to sodium naftaline
solution at room temperature. Thereafter benzyl pyridine capping agent is edit at
elevated temperature. Gold coating is then created by addition of 4-chloro auric acid
in N-methyl pyrrolidinone. Gold coating of MNPs is of special interest due to easy
reaction of the gold layer with thiol end functional molecules or macromolecules.
İnverse micro emulsion method reported is based on the reduction of FeSO4 by
NaBH4 in oil in water system using cetyltrimethyl ammonium bromide (CTAB) as
surfactant and butanol as co-surfactant. In the presence of octane as continuous phase
addition of tetra-chloro auric acid has been demonstrated to give gold coated iron
nanoparticles.
Coating of magnetic with a silica shell has been studied by few groups. One common
approach for the silica coating is formation of silica nanoparticles by Stöbers sol-gel
process in the presence of MNPs using TEOS (Tetraethoxysilane) and water.
Hydrophilic surfaces of resulting particles allows further modification. As mentioned
above, despite those significant developments coating of magnetic nanoparticles is
still in it?s infancy and needs further investigations.
In this work, we have studied preparing of polymer coated MNPs in one pot. The
method investigated is aimed at concommittant formation and coating of MNPs.
Our new methodology is simply based on instanteneous crosslinking of polyvinyl
alcohol (PVA) with Fenton reagent in aqueous solution at room temperature. In this
reaction Fe(II) is oxidized to Fe(III) while an OH radical is forming from hydrogen
peroxide. Proton abstraction of the OH radical from PVA backbone yields
macroradicals combination of which results in instanteneous crosslinking, so that
Fe(III) salt formed remaines entrapped within the crosslinked polymer matrix. It was
shown that a proper choice of Fe(II) / H2O2 molar ratio gives PVA coated iron salt
mixture in 2 / 1 Fe(III) / Fe(II) molar ratio. Final treatment of this heteregenous
mixture with ammonia gives PVA coated magnetite particles in submicron sizes,
mostly being in 300-550 nm size.
In our ongoing works this chemistry was exploited for preparing nanosizes magnetite
nanoparticles tightly coated with PVA glycidol functional acrylic polymer.
For preparing polymer coated MNPs, in this work commercial PVA, poly(2,3-di
hydroxy propyl methacrylate) P(DHPM) and polystyrene-b-P(DHPM) were used.
PHPM and the block copolymers were prepared in well defined structures using
ATRP technique.
Magnetite formation was carried out in homogeneous solution for the case with
PDHPM, whereas mini-emulsion system was used for the case with PVA. We have
obtained stable solution/dispersions in each case. To isolate MNPs from the
mixtures, we have used thermal aging or magnetic separation techniques.
Inverse emulsion system (water in oil) was employed for the case of the block
copolymers using Span 80 as emulsifying agent. This process yielded core-shell
MNPs containing 3,1 percent of magnetite.
Among those the material obtained using PVA coating material has shown to be only
partially hydrophilic, but not redispersible in any organic solvent or their mixtures.
ESEM pictures shows that the particle sizes are in 17-19 nm size range. It?s
magnetization behavior examined by VSM (Vibration Sample Magnetometer)
technique revealed that, the sample containing 14.1 % magnetite shows no detectible
coercivity, which is agreement with their sizes.
The magnetite material prepared in the presence of PDHPM has a partical size range
of 19-29 nm as inferred from ESEM pictures. This material was found to be easily
redispersible in water although it has the highest magnetite content (49.1%).
Although it has showed a reversible magnetization curve it represented a slight
coercivity around 50 Oe.
The material obtained from the block copolymer (PS-b-PDHPM) showed a low but
reversible saturation magnetization around 3,4 emu/g, but no detectable coercivity.
This result is in agreement with their sizes inferred from ESEM pictures (24-38 nm).
As a result Fenton reaction can be applicable in preparing both hydrophilic and
hdrophobic magnetite nanoparticles entrapped within polymer matrixes in one
reaction flask which has not been reported so far.
The simple strategy presented in this work can easily be employed for preparing
polymer compatible or bio-compatible magnetite nanoparticles. Although magnetite
nanoparticles derived from PVA is not easily redispersible, its further surface
modification with suitable monomers or low moleculer weight organics may be used
to impart redispersibility and bio-compatibility. The resulting material might be used
in medicine for hyperthermia theraphy or so on.
As a result Fenton reagent is a vesatile tool for preparing magnetite nanoparticles
entrapped in suitable polymers or block copolymers having hyroxil side groups. The
procedure is attractive due to its starting from commercially available or readily
attainable polymer materials and its simplicity of process.