The dielectric constant of fluorinated polymides, their blends, and composites is known to decrease with the increase in free volume due to a decrease in the number of polarizable groups per unit volume. Herein, we report an interesting finding on the origin of dielectric constant in a polymer blend prepared using a fluorine-containing polymer and a polyimide probed in terms of its available free volume, which is distinct from the generally observed behavior in fluorinated polyimides. For this study, a blend of poly(vinylidene fluoride-co-hexafluoro propylene) and poly(ether imide) was chosen and the interaction between them was studied using FTIR, XRD, TGA, and SEM. The blend was investigated by positron annihilation lifetime spectroscopy (PALS), Doppler broadening (DB), and dielectric analysis (DEA). With the increase in the free volume content in the blend, surprisingly, the dielectric constant also increases and is attributed to additional space available for the polarizable groups to orient themselves to the applied electric field. The results obtained would pave the way for more effective design of polymeric electrical charge storage devices.

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Barium titanate nanoparticles with an average size of <100 nm were added to poly(vinylidene fluoride‐trifluoroethylene) copolymer in varying concentrations (0.2, 0.4, 0.6, and 0.8 wt%) in liquid phase under bath sonication and annealed at 120°C for 2 h. The Fourier transform infrared spectroscopy, X‐ray diffraction, Raman spectroscopy, and Differential scanning calorimetry studies reveals an increase in the β‐phase content of the nanocomposite, which is a promising inference for the increased ferroelectric property of the material. Scanning electron microscopy and Atomic force microscopy was used to study the surface topography of the spin coated thin films. Polarization–electric field studies clearly indicating the enhanced ferroelectric nature of optimized concentration with highest remnant polarization. All these results nominate this polymer nanocomposite as a promising material for ferroelectric applications like nonvolatile memory devices. POLYM. COMPOS., 38:1655–1661, 2017. © 2015 Society of Plastics Engineers

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The long period fiber grating (LPFG) is widely used as a sensor due to its high sensitivity and resolution. However, the broad bandwidth of the attenuation bands formed by the mode coupling between the fundamental core mode and the cladding modes constitutes a difficulty when the device is used as a conventional sensor. To overcome this limitation, a Michelson interferometer-type sensor configuration has been developed, using an LPFG grating pair formed by coating a mirror at the distal end of the LPFG. This sensor configuration is more convenient to use and is able to overcome the limitations of the single LPFG based sensor as the shifts in the attenuation bands being more easily detectable due to the formation of the sharp spectral fringe pattern in the LPFG based Michelson interferometer. In this work, I studied the LPFG based Michelson interferometer as the refractive index sensor and discussed the sensitivity enhancement of the LPFG based Michelson interferometer as a refractive index sensor by employing higher order cladding modes and by reducing the cladding radius. The results demonstrated the HE 17 mode with a cladding radius of 62.5 µm, in the range of surrounding refractive index (SRI) of 1-1.45, and its resonant peak showed a wavelength shift of 26.99 nm/RIU. When the cladding region was further reduced to 24 µm, the resonant peak showed a wavelength shift of 569.88 nm/RIU, resulting in a sensitivity enhancement of nearly 21 times. However, as the cladding region was etched further, then the HE 17 order cladding mode and higher mode would be cut off. Therefore, the implementation of high sensitivity for SRI sensing with the reduced cladding in the LPFG based Michelson interferometer is dependent on the proper combination of the cladding radius and cladding mode order.

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