Transcript FMR and DSC study of maghemite nanoparticles in PMMA

FMR and DSC study of
maghemite nanoparticles in
PMMA polymer matrix
J. Typek1 , N. Guskos1,2, A. Szymczyk1, D. Petridis3
1Institute
of Physics, Szczecin University of Technology, Szczecin, Poland
2Department of Physics, University of Athens, Greece
3NCSR Demokritos, Aghia Paraskevi, Athens, Greece
Maghemite – γ-Fe2O3 (iron(III)
oxide)
• inverse spinel cubic structure
• stoichiometric formula
(Fe3+)A O2- (Fe3+ Fe3+2/3[ ]1/3)B O2-3
• 8 Fe3+ ions located in tetrahedral sites
(A-sites) and 16 Fe3+ ions in
octahedral sites (B-sites)
• collinear ferrimagnet
• antiparallel magnetic sublattices A
(4.18 μB) and B (4.41 μB)
• TC=590-675ºC
PMMA (polymethyl methacrylate)
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Polymethyl methacrylate (PMMA)
or poly (methyl 2-methylpropenoate)
is the synthetic polymer of methyl
methacrylate. This thermoplastic and
transparent plastic is sold by the
tradenames Plexiglas, R-Cast,
Perspex, Plazcryl, Limacryl, Acrylex,
Acrylite, Acrylplast, Altuglas,
Polycast and Lucite and is commonly
called acrylic glass or simply acrylic.
The material was developed in 1928
in various laboratories and was
brought to market in 1933.
Temperature of the glass transition
Tg = 85-105ºC
Melting temperatures 130-140ºC
Synthesis of γ-Fe2O3 /PMMA
nanocomposite
•Procedure: preparation of capped magnetic nanoparticles → exchange of the oleate units by
methacrylate units → preparation of γ-Fe2O3/PMMA composite
•γ-Fe2O3 nanocrystalline particles with an average size of 10 nm, chemically bonded to the
chains
•Magnetic nanoparticles capped with oleic acid were prepared by one step method involving
partial oxidation of Fe(II) in alkaline solutions by dilute H2O2. The reaction was conducted in
the presence of oleic acid and under biphase conditions.
•The surface bond oleate groups can be fully exchanged with metacrylate units by refluxing
in ethanol. The exchange reaction ensures the chemical bonding of methacrylate units to the
surface of nanoparticles, which in turn, undergo the polymerization with the vinyl groups of
the methyl mathacrylate.
Incorporation of nanoparticles in the polymer
matrix through chemical bonding
FMR investigated samples – 5 wt% and 10 wt% γ-Fe2O3
DSC study of γ-Fe2O3/PMMA
nanocomposite
0.2
PMMA/5
103.80°C(H)
0.3373J/(g·°C)
0.1
Heat Flow (W/g)
98.19°C
109.55°C
0.0
PMMA/10
Maghemite
content wt%
Tg
[ºC]
Cp
[J/g ºC]
0
99.60
0.349
5
103.80
0.337
10
107.11
0.317
107.11°C(H)
0.3168J/(g·°C)
101.44°C
-0.1
112.76°C
-0.2
-0.3
40
Exo Up
60
80
100
Temperature (°C)
120
140
160
Universal V4.1D TA Instruments
•Tg increases with maghemite content increase →reduced dynamics of polymer
chains, hidering segmental motion
• cp heat capacity decreases with maghemite content → increase of steric hindrance
FMR spectra – temperature dependence
5 wt%
Tblock ~ 40 K ?
Low-temperature range
T=150 K PMMA relaxation?
High-temperature range
FMR parameters – integrated intensity
•FMR integrated intensity Iz ~ (FMR signal amplitude)·(ΔB)2
• Integrated intensity Iz ~ spin susceptibility χ’’
•Iz·T ~(magnetic moment)1/2
5 wt%
FMR spectra: γ-Fe2O3 content
10 wt%
5 wt%
The difference (in intensity) is observed for T>250 K. It could be attributed to the dipoldipol magnetic interaction between nanoparticles.
FMR spectra - decomposition
T=71 K, 5 wt%
Narrow (high-field) component → magnetic easy axis  external magnetic field
Broad (low-field) component → magnetic easy axis || external magnetic field
FMR spectrum decomposition
5 wt%
g-factor
Linewidth [Gs]
Magnetic moment
FMR spectrum decomposition
Narrow component
Broad component
Temperature [K]
Temperature [K]
10 wt%
FMR spectrum decomposition
10 wt%
Integrated intensity [arb. units]
B0
Narrow component
(high field)
B0
Broad component
(low-field)
Temperature [K]
Conclusions
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Increase in maghemite content → Tglass decreases
Blocking temperature ~40 K
Relaxation in PMMA=150 K
Maghemite content differences seen in FMR above 250 K
FMR spectrum reflects magnetic anisotropy of nanoparticles