To enhance the ablation performance and mechanical strength of silicone rubber (SR), pristine multiwalled carbon nanotubes (MWNTs) were dispersed in the polymer matrix using dispersion kneader and two roller mixing mill. Electrical resistivity (100–300°C) was reduced with increasing filler concentration in the host matrix due to the presence and even dispersion of the nanofiller in the rubber matrix. The SR nanocomposite (1 wt % filler contents) has 28% better thermal stability and 100% improvement in the ultimate tensile strength is achieved as compared with the pristine polymer matrix counterpart. Oxy‐acetylene torch was used to evaluate the ablation rates, % char yield, and backface temperature evolution at the back facet of nanoablators during the flame exposure for a specific duration. Ablation performance of the fabricated ablative nanocomposites was enhanced with increasing nanotubes concentration in the polymer matrix. Thermal stability and heat quenching ability of the SR nanocomposites were gradually augmented with increasing filler loadings in the host matrix. Porous silica char, polymer pyrolysis, char composition, and uniform dispersion of MWNTs in the rubber matrix were also analyzed using scanning electron microscopy and energy dispersive spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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Mn 1−x Zn x Fe 2 O 4 nanoparticles (x = 0 to 1) were synthesized by the wet chemical co-precipitation technique. X-ray diffraction and transmission electron microscopy and high resolution transmission electron microscopy were effectively utilized to investigate the different structural parameters. The ac conductivity of nanosized Mn 1−x Zn x Fe 2 O 4 were investigated as a function of frequency, temperature and composition. The frequency dependence of ac conductivity is analysed by the power law σ (ω) ac = Bω n which is typical for charge transport by hopping or tunnelling processes. The temperature dependence of frequency exponent n was investigated to understand the conduction mechanism in different compositions. The conduction mechanisms are mainly based on polaron hopping conduction.

Multiwalled carbon nanotubes (MWCNTs) were modified to covalently attach the carboxylic moiety with their surfaces. Variant concentrations of functionalized multiwalled carbon nanotubes (F-MWCNTs) were introduced into polydimethylsiloxane (PDMS) adopting solution mixing technique. Fourier transform infrared spectroscopy (FTIR) confirms the carboxy functionalization presence on the surface of the nanotubes. X-ray diffraction (XRD) patterns for both MWCNTs and F-MWCNTs illustrate that the crystallinity does not alter with surface modification of the nanotubes. Experimental results simulated that electrical conductivity of the nanocomposites was augmented with increasing filler concentration in the host matrix. Thermal conductivity and thermal impedance of the nanocomposite specimens were evaluated according to developed methodologies and the accumulative data revealed the nanocomposites thermal transport dependence on the F-MWCNTs doping concentration in the host polymer matrix. Thermal stability enhancement with increasing filler incorporation into the polymer matrix was observed in thermogravimetric/differential thermal analyzer (TG/DTA) contours. Crystallization, glass transition, and melting temperatures were examined using differential scanning calorimeter (DSC) and it was observed that phase transition temperatures of the composite specimens can be tuned by varying the nanotubes to matrix ratio. Scanning electron microscopy and energy dispersive x-ray spectroscopy were carried out to analyze the surface morphology/composition of the fabricated nanocomposites and dispersion of functionalized and pristine MWCNTs in the polymer matrix.

Manganites belonging to the series Gd1−xSrxMnO3 (x = 0.3, 0.4 and 0.5) were prepared by wet solid-state reaction and their thermoelectric power was evaluated. Thermoelectric power measurements revealed a peak value at ∼40 K. All the samples exhibited a colossal thermopower at ∼40 K and in that Gd0.5Sr0.5MnO3 exhibited a maximum value of ∼35 mV/K, which is the largest reported for these class of materials at this temperature. Temperaturedependent magnetisation measurements showed that the samples exhibit a phase transition from paramagnetic to spin-glass-like state at these temperatures. Plausible mechanisms responsible for the observed colossal thermoelectric power in Gd-Sr manganites are discussed.

Variant concentrations of ceramic fibers (CerFs) were incorporated into acrylonitrile butadiene rubber (NBR) to fabricate elastomeric ablative composites for ultrahigh temperature applications. The CerFs introduction into the polymer matrix has enhanced the ablation resistance up to 59% and successfully reduced the backface temperature of the polymer composite up to 110 o C during the ultrahigh temperature ablation investigation. Thermal decomposition of the polymer composites was diminished up to 10% with increasing fiber concentration in the rubber matrix. Thermal conductivity was reduced equal to 63% while thermal impedance was enhanced up to 84% with the utmost fiber incorporation into the NBR matrix. The CerFs have adversely affected the mechanical properties of NBR matrix due to their brittle/inert nature and weak interface bonding with the host matrix. Scanning electron microscopy along with the energy dispersive x-ray spectroscopy was used to examine the ablated specimens and the fiber dispersion within the host matrix.

Abstract. Materials belonging to the family of manganites are technologically important since they exhibit colossal magneto resistance. A proper understanding of the transport properties is very vital in tailoring the properties. A heavy rare earth doped manganite like Gd 0·7 Sr 0·3 MnO 3 is purported to be exhibiting unusual properties because of smaller ionic radius of Gd. Gd 0·7 Sr 0·3 MnO 3 is prepared by a wet solid state reaction method. The conduction mechanism in such a compound has been elucidated by subjecting the material to low temperature d.c. conductivity measurement. It has been found that the low band width material follows a variable range hopping (VRH) model followed by a small polaron hopping (SPH) model. The results are presented here.