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2014, Journal of Applied Physics
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2014, Journal of Applied Physics
J. Appl. Phys. 117, 224903 (2015)
In this paper, the composites of polyvinylidene fluoride (PVDF)/nickel (Ni) prepared through simple blending and hot-molding process have been investigated for dielectric, electromagnetic shielding, and radar absorbing properties. In order to study complex permittivity of the composites in 40 Hz–20MHz frequency range, impedance spectroscopy (IS) technique is used. Besides, the complex permittivity and permeability in addition to shielding effectiveness (SE), reflection coefficient (backed by air), and loss factor are calculated using scattering parameters measured in X-band (8.2–12.4 GHz) by waveguide method. Further, in X-band, a theoretical analysis of single layer absorbing structure backed by perfect electrical conductor is then performed. A flanged coaxial holder has also been designed, fabricated, calibrated, and tested for electromagnetic interference SE measurement in the broad frequency range (50 MHz–18 GHz). The IS results indicate large enhancement in dielectric constant as a function of Ni loading in the polymer-metal composite (PMC) phase. This result has been explained using interfacial polarization and percolation theory. The frequency dependent response of ac conductivity has been analyzed by fitting the experimental data to the “Johnscher’s universal dielectric response law” model. The results obtained for SE (in X-band over broad frequency range) and reflection coefficient indicate that PVDF/Ni composites give better electromagnetic interference shielding and radar absorption properties at filler concentration (fcon)fc in the PMC, whereas at fc<fcon, the charge storage mechanism dominates in the insulator regime of the composite phase. Therefore, the range of PMC compositions below and above percolation threshold has been observed to have different variety of applications.
The analysis of an orthoconic antiferroelectric liquid-crystalline mixture, using dielectric spectroscopy, has revealed a plurality of ferroelectric smectic C* subphases. A great variety of relaxation responses that could indicate the presence of different SmC* subphases has been observed with the differential scanning calorimetry (DSC) technique in partial agreement with other techniques as DSC and optical microscopy. They represent smectic intermediate variants between the ferroelectric phase and the antiferroelectric one, whose study is still open and is collecting a lot of interest in academic field. The results obtained by dielectric spectroscopy were compared with other techniques as differential scanning calorimetry and polarized optical microscopy. The results demonstrate the possibility of using dielectric spectroscopy to highlight subphases that cannot be observed with conventional experimental techniques.
2013, Applied Physics Letters
2014, The Journal of Chemical Physics
2014, Journal of Applied Physics
2014, Applied Physics Letters
Dielectric study was investigated in order to probe the interfacial region fibers/matrix of the polyester composite reinforced with alfa/wool/thermo-binder fibers. Dielectric spectra were measured in the frequency range from 10 1 Hz to 10 6 Hz, and temperature interval from 40 C to 150 C. This study revealed the presence of two dielectric relaxations in the composite. While the first one was attributed to the a mode relaxation associated with the glass transition of the matrix, the second was associated with the conductivity resulting from the carriers’ charges diffusion noted for high temperature above glass transition and low frequencies. As this study did not show the presence of the interfacial polarization effect in the composite, it was accomplished with the vibrational study using the FT-IR and Raman techniques. A great compatibility between fibers and matrix was proven by a less hydrophilic character of the reinforcement giving rise to additional valence vibrations from wool fibers and hydrogen bonds
2015, Journal of Applied Physics
2011
2012, Journal of Applied Physics
2014, Journal of Applied Physics
2015, Journal of Applied Physics
2014, Journal of Molecular Modeling
2014, Applied Physics Letters
2014, Journal of Applied Physics
2012, Applied Physics Letters
2014, Journal of Applied Physics
We present a detailed experimental study on how magnetic and electronic properties of Rb,K-intercalated C60 encapsulated inside carbon nanotubes called peapods can be derived from 13C nuclear magnetic resonance investigations. Ring currents do play a basic role in those systems; in particular, the inner cavities of nanotubes offer an ideal environment to investigate the magnetism at the nanoscale. We report the largest diamagnetic shifts down to −68.3 ppm ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon intercalation. The metallization of intercalated peapods is evidenced from the chemical shift anisotropy and spin-lattice relaxation (T1) measurements. The observed relaxation curves signal a three-component model with two slow and one fast relaxing components. We assigned the fast component to the unpaired electrons charged C60 that show a phase transition near 100 K. The two slow components can be rationalized by the two types of charged C60 at two different positions with a linear regime following Korringa behavior, which is typical for metallic system and allow us to estimate the density of sate at Fermi level n(EF).
2012, Journal of Applied Physics
2014, Applied Physics Letters
2015, Journal of Applied Physics
2014, Applied Physics Letters
Graphene has recently been shown to possess giant nonlinearity; however, the utility of this nonlinearity is limited due to high losses and small interaction volume. We show that by performing waveguide engineering to graphene's nonlinearity, we are able to dramatically increase the nonlinear parameter and decrease the switching optical power to sub-watt levels. Our design makes use of the hybrid plasmonic waveguide and careful manipulation of graphene's refractive index by tuning its Fermi level. The ability to tailor the nonlinear parameter in graphene based waveguides via the Fermi level provides a paradigm of nonlinear optics devices to be realized.
2014, Applied Physics Letters
2014, Journal of Applied Physics
2014, Journal of Applied Physics
2014, Journal of Applied Physics
2012, Journal of Applied Physics
2010, Journal of Physics and Chemistry of Solids
2014, Applied Physics Letters
We obtain a large third-order optical nonlinearity (v(3)1010esu) of silver nanoparticles dispersed in polyvinyl alcohol/tetraethyl orthosilicate matrix using single beam z-scan technique at 532 nm by Q-switched Nd:YAG laser. We have shown that mechanisms responsible for third-order optical nonlinearity of Ag nanocomposite film are reverse saturable absorption (RSA) and self-defocusing in the purlieu of surface plasmon resonance (SPR). Optical band-gap and width of SPR band of Ag nanocomposite film decrease with increasing silver concentration, which leads to enhancement of local electric field and hence third-order optical nonlinearity. Optical limiting, due to RSA has also been demonstrated at 532 nm
2009, European Polymer Journal
2015, Journal of Applied Physics
2013, Vibrational Spectroscopy
2012, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
2014, The Journal of chemical physics
We provide a general microscopic theory of the scattering cross-section and of the refractive index for a system of interacting colloidal particles, exact at second order in the molecular polarizabilities. In particular: (a) we show that the structural features of the suspension are encoded into the forward scattered field by multiple scattering effects, whose contribution is essential for the so-called "optical theorem" to hold in the presence of interactions; (b) we investigate the role of radiation reaction on light extinction; (c) we discuss our results in the framework of effective medium theories, presenting a general result for the effective refractive index valid, whatever the structural properties of the suspension, in the limit of particles much larger than the wavelength; (d) by discussing strongly-interacting suspensions, we unravel subtle anomalous dispersion effects for the suspension refractive index.
A microbead-assisted planar microwave resonator for organic vapor sensing applications is presented. The core of this sensor is a planar microstrip split-ring resonator, integrated with an active feedback loop to enhance the initial quality factor from 200 to 1M at an operational resonance frequency of 1.42 GHz. Two different types of microbeads, beaded activated carbon (BAC) and polymer based (V503) beads, are investigated in non-contact mode for use as gas adsorbents in the gas sensing device. 2-Butoxyethanol (BE) is used in various concentrations as the target gas, and the transmitted power (S21) of the two port resonator is measured. The two main microwave parameters of resonance frequency and quality factor are extracted from S21 since these parameters are less susceptible to environmental and instrumental noise than the amplitude. Measured results demonstrate a minimum resonance frequency shift of 10kHz for a 35ppm concentration of BE exposure to carbon beads and 160kHz for the polymer based adsorbent at the same concentration. The quality factor of the resonator also changed for different concentrations, but a distinguishable variation is observed for the BAC adsorbents. The high quality factor of the sensor provides the opportunity of real time monitoring of the adsorbent behaviors in remote sensing mode with very high resolution.
2011, Materials & Design