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Non-universal behavior well above the percolation threshold and thermal properties of core-shell-magnetite-polymer fibers
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Image of FIG. 1.
FIG. 1.

(Color online) UV-Vis absorption spectra comparing Fe3O4 (magnetite) nanoparticles before and after grafting PMMA chains (i.e., CSM) compared with pristine PMMA. Inset shows TEM image of core-shell magnetite nanoparticles.

Image of FIG. 2.
FIG. 2.

SEM images of core-shell magnetite filled PMMA electrospun fibers: (a) 10 wt.% at ∼800 rpm, (b) 30 wt.% at ∼1200 rpm, (c) 40 wt.% at 0 rpm, inset at ∼1500 rpm.

Image of FIG. 3.
FIG. 3.

TEM image of nanocomposite electrospun fibers of (a) 10, (b) 20, (c) 30, (d) 40 wt.% of core-shell magnetite loadings in PMMA.

Image of FIG. 4.
FIG. 4.

(Color online) XRD patterns of pure PMMA granuals, PMMA-fiber mat, and nanocomposite fiber mat of filling levels 10-40 wt. %.

Image of FIG. 5.
FIG. 5.

(Color online) (a) Variation of dc conductivity (σdc ) of nanocomposite fibers for various filling levels of core-shell magnetite at RT. (★) conductivity of pristine PMMA,33 (○) dc conductivity for 5 wt.% of magnetite is obtained from literature.10 Inset: grey box at 0wt.% indicates the pristine PMMA, density of magnetite nanoparticles are increasing with wt.%. (b) Nyquist plots for the nanocomposite fibers.

Image of FIG. 6.
FIG. 6.

(Color online) (a) ac conductivity (σac , vertically shifted for clarity) of the nanocomposite fibers against frequency at RT. 0.1 MHz – ω01 Hz → part (i), ω01 ω02 Hz → part (ii), and ω02 – 80 MHz → part (iii). (b) Log-log plot of ac conductivity versus frequency for the nanocomposite fibers of various filling levels.

Image of FIG. 7.
FIG. 7.

(Color online) Dielectric properties of nanocomposite fibers. (a) Log-log plot of dielectric constant (ɛr (ω)) versus frequency (rad/s). Inset is a plot of normalized (independently) capacitance versus frequency (Hz) on log scale, (b) variation of tan δ against frequency at RT. ωc stands for critical frequency at which tan δ is the minimum.

Image of FIG. 8.
FIG. 8.

(Color online) Thermal properties of pristine PMMA fibers and nanocomposite fibers. (a) TGA curves recorded under nitrogen atmosphere. (b) DSC profiles, inset shows decomposition and glass transition temperatures (Td and Tg, respectively) for various filling levels. Connecting lines are only for the guidance to the eye.


Generic image for table
Table I.

Various critical exponents obtained from fittings are tabulated.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Non-universal behavior well above the percolation threshold and thermal properties of core-shell-magnetite-polymer fibers