Charge transport properties, such as the temperature dependent dc conductivity and the frequency dependent conductance, of polymer matrix–metal particles composites, are investigated in the present study. Dc and ac conductivity is examined with varying parameters the filler content, temperature and the frequency in the case of ac field. The examined systems, though they are characterized as dielectrics, exhibit considerable conductivity, which alters by several orders of magnitude with temperature and frequency. The temperature and frequency dependence of conductivity gives evidence for the charge carriers transport mechanism via the occurred agreement of experimental results with the employed hopping models (variable range hopping model and random free-energy barrier model).

Hopping conductivity in polymer matrix–metal particles composites

Molecularly linked gamma-Fe2O3 nanoparticles chains arc produced from superparamagnetic gamma-Fe2O3 nanoparticles under zero applied magnetic field The chains exhibit ferromagnetic interaction between gamma-Fe2O3 nanoparticles that compose them as evidenced by an increase in blocking temperature from similar to 80 K in the case of isolated nanoparticles to similar to 120 K for chains

Chains of Superparamagnetic Nanoparticles

We report on electrical and magnetic properties of polyaniline (PANI) nanotubes (∼150 nm in diameter) and PANI/Fe 3 O 4 nanowires (∼140 nm in diameter) containing Fe 3 O 4 nanoparticles with a typical size of 12 nm. These systems were prepared by a template-free method. The conductivity of the nanostructures is 10 −1 –10 −2  S/cm; and the temperature dependent resistivity follows a ln  ρ∼T −1/2 law. The composites (6 and 20 wt% of Fe 3 O 4 ) show a large negative magnetoresistance compared with that of pure PANI nanotubes and a considerably lower saturated magnetization ( M s =3.45 emu/g at 300 K and 4.21 emu/g at 4 K) compared with the values measured from bulk magnetite ( M s =84 emu/g) and pure Fe 3 O 4 nanoparticles ( M s =65 emu/g). AC magnetic susceptibility was also measured. It is found that the peak position of the AC susceptibility of the nanocomposites shifts to a higher temperature (>245 K) compared with that of pure Fe 3 O 4 nanoparticles (190–200 K). These results suggest that interactions between the polymer matrix and nanoparticles take place in these nanocomposites.

Electrical and magnetic properties of polyaniline/Fe3O4 nanostructures

Effect of ferrofluid concentration on electrical and magnetic properties of the Fe3O4/PANI nanocomposites

Two unique materials were developed, like graphene oxide (GO) sheets covalently grafted on to barium titanate (BT) nanoparticles and cobalt nanowires (Co-NWs), to attenuate the electromagnetic (EM) radiations in poly(vinylidene fluoride) (PVDF)-based composites. The rationale behind using either a ferroelectric or a ferromagnetic material in combination with intrinsically conducting nanoparticles (multiwall carbon nanotubes, CNTs), is to induce both electrical and magnetic dipoles in the system. Two key properties, namely, enhanced dielectric constant and magnetic permeability, were determined. PVDF/BT–GO composites exhibited higher dielectric constant compared to PVDF/BT and PVDF/GO composites. Co-NWs, which were synthesized by electrodeposition, exhibited saturation magnetization (Ms) of 40 emu/g and coercivity (Hc) of 300 G. Three phase hybrid composites were prepared by mixing CNTs with either BT–GO or Co-NWs in PVDF by solution blending. These nanoparticles showed high electrical conductivity and sig...

Poly(vinylidene fluoride)-based flexible and lightweight materials for attenuating microwave radiations.

Ferromagnetic resonance (FMR) and ac conductivity have been applied to study a polymer composite containing as filler a binary mixture of magnetite (Fe3O4) and cementite (Fe3C) nanoparticles (30–50nm) dispersed in a diamagnetic carbon matrix, which was synthesized by the carburization of nanocrystalline iron. Ac conductivity measurements showed thermally activated behavior involving a range of activation energies and power law frequency dependence at high frequencies similar to conducting polymer composites randomly filled with metal particles. Ferromagnetic resonance measurements revealed a relatively narrow FMR line at high temperatures indicating the presence of ferromagnetic nanoparticles, where thermal fluctuations and interparticle interactions determine the FMR temperature variation. An abrupt change of the FMR spectra was observed at T<81K (ΔT⩽1K) coinciding with a sharp anomaly resolved in the temperature derivative of the ac conductivity. This behavior is attributed to the Verwey transition of F...

Ferromagnetic resonance and ac conductivity of a polymer composite of Fe3O4 and Fe3C nanoparticles dispersed in a graphite matrix

The magnetic properties of γ-Fe2O3 ferrimagnetic nanoparticles embedded in a multiblock poly(ether-ester) copolymer have been investigated by static magnetization and ferromagnetic resonance (FMR) measurements at two different dispersion states. Significant variation of the magnetic response is identified below T≈120K, most pronounced in the marked resonance field shift of the FMR spectra, independently of the dispersion state of the nanocomposites. This behavior correlates favorably with the dynamic relaxation of the copolymer, indicating a matrix freezing effect that is attributed to the magnetoelastic coupling of the oxide nanoparticles with the surrounding polymer. At low temperatures, the dc magnetization and FMR measurements vary considerably for the two nanocomposites, indicating essential differences in their ground state, related to the different morphology of the samples and the concomitant variation of interparticle interactions.

Matrix effects on the magnetic properties of γ-Fe2O3 nanoparticles dispersed in a multiblock copolymer

The magnetic properties of gamma-Fe2O3 nanoparticles embedded in a thermoplastic elastomer poly(ether-ester) copolymer by the in situ polycondensation reaction process have been investigated by means of magnetization and ferromagnetic resonance (FMR) measurements at low filler concentrations of 0.1 and 0.3 wt% with the magnetic additive introduced in the polymer matrix in powder and solution form. The magnetic behavior of the magnetopolymeric nanocomposites indicates significant interparticle interaction effects that depend mainly on the dispersion state of the magnetic nanoparticles as well as their concentration, consistent with the variation of the particle microstructure characterized by magnetic aggregates in the nanometer and micron scale for the solution and powder dispersions, respectively. The magnetization and FMR results at different filler concentrations and dispersions show a close correspondence to the relaxation processes of the copolymer, implying the coupling of polymeric and magnetic properties.

M. Maryniak

Papers

Ferromagnetic resonance and ac conductivity of a polymer composite of Fe3O4 and Fe3C nanoparticles dispersed in a graphite matrix

Matrix effects on the magnetic properties of γ-Fe2O3 nanoparticles dispersed in a multiblock copolymer

Magnetic properties of gamma-Fe2O3/poly(ether-ester) nanocomposites.