Effect of coupling agent on the thermal and dielectric properties of PTFE/Sm2Si2O7 composites

The present study investigates the dielectric and thermal properties of PTFE/Sm₂Si₂O₇ composites. The composites were prepared by powder processing technique followed by hot pressing. The variation of the dielectric properties with filler content (0–0.5 V_f) was studied at 1 MHz and 9 GHz. The filler surface was chemically modified using phenyl trimethoxy silane (PTMS) as a coupling agent. The microstructural study using scanning electron microscopy (SEM) showed that the particles were well dispersed in the matrix when coupled with PTMS. The surface modification led to an improvement in the dielectric properties. The PTFE filled with 0.4 V_f silane treated Sm₂Si₂O₇ composite showed a low dielectric loss of 0.0054 and slightly higher relative permittivity of 3.92 when compared with the untreated composite of the same composition. The experimental values of relative permittivities were compared with the theoretical predictions and the Effective Medium Theory was found to agree well even for higher content of silane treated filler. It was found that the addition of silane coupling agent is very effective in improving the thermal properties of the PTFE/Sm₂Si₂O₇ composites.     

Resonant frequencies of circular-sided dual-port microstrip antenna

Simple formulae are presented for calculating the resonant frequencies of a circular sided compact dual-port microstrip antenna. The calculations are in agreement with the experimental observations, with a percentage error of less than two.     

Effect of Filler Content on the Dielectric Properties of PTFE/ZnAl2O4–TiO2 Composites

ZnAl₂O₄–TiO₂ (ZAT)/polytetrafluoroethylene (PTFE) composites were prepared by powder processing method. The structure and microstructure of the composites were analyzed using X-ray diffraction and scanning electron microscopic techniques. The effect of different volume fraction of ZAT (0–0.6) on the dielectric properties of the composites was investigated at 1 MHz and at the microwave frequency of 7 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ZAT content. The samples with 60 vol.% of ZAT filler showed a relative permittivity of 3.9 and dielectric loss of 0.009, respectively, at 7 GHz. The variation of relative permittivity and dielectric loss showed only a very small variation with temperature in the range 25°–70°C for various ZAT/PTFE composites. The relative permittivity obtained experimentally were compared with that of the theoretical values predicted using modified Lichtenecker, Jayasundere—Smith, and Series mixing formulae. They were found to agree well with the predicted values for low filler content.     

Synthesis, characterisation and properties of (Ba1 − xSrx) (Nd1/2Nb1/2) O3 ceramics for application as dielectric resonators in microwave circuits

The (Ba_{1 − x}Sr_x) (Nd_1/2Nb_1/2) O₃ ceramics have been prepared by the conventional ceramic route for different values of x. Addition of a small amount of CeO₂ (1 wt%) as a sintering aid increased the density of the samples. The structure and microstructure of the sintered samples are studied by X-ray diffraction and SEM methods. The dielectric properties of the samples are measured in the microwave frequency region as a function of composition. The dielectric constant decreases as x increases. The coefficient of thermal variation of resonant frequency decreases as the Sr content increases and goes to the negative side. The dielectric properties of (Ba_{1 − x}Sr_x) (Nd_1/2Nb_1/2) O₃ are in the range suitable for application as dielectric resonators in microwave circuits.     

Activity of diastase α-amylase immobilized on polyanilines (PANIs)

Starch hydrolysing enzyme α-amylase (EC 3.2.1.1) was immobilized by physical adsorption and covalent binding onto chemically synthesised polymer, polyanilines (PANIs) in two different forms, emeraldine salt and emeraldine base powder. The immobilization efficiency was affected by the pH of the immobilization medium, contact time and amount of enzyme. The kinetic parameters, reusability and storage stability of the enzyme were studied under free and immobilized condition at optimum pH and temperature. The immobilized enzyme showed enhanced storage stability over a period of 6 months, while free enzyme in solution lost all of its activity within a period of 8 days. Reusability of the enzyme was improved by immobilization. The K_m values for starch hydrolysis were found to be high for the immobilized enzymes.     

Tailoring the microwave dielectric properties of BaRE2Ti4O12 and BaRE2Ti5O14 ceramics by compositional variations

Ceramic dielectric resonators in the BaO-RE₂O₃-TiO₂ (RE=rare earth) system have been prepared by the conventional solid state ceramic route. The dielectric properties have been tailored by substitution of different rare earth oxides and by bismuth oxide addition. The dielectric constants increased with Bi addition whereas the Q decreased. The temperature coefficient of the resonant frequency improved with bismuth addition.     

Lightweight Self-Compacting Concrete Incorporating Industrial Rejects and Mineral Admixtures: Strength and Durability Assessment

By the recent global research developments, a lot of natural and artificial materials that are normally discarded and landfilled, are continually investiga     

Biological evaluation of a new organically modified ceramic-based dental restorative resin

Material tissue interactions of a newly developed organically modified ceramic (ormocer)-based dental restorative composite based on a resin containing mixture of alkoxides of silicone and calcium with polymerizable methacrylate end groups are discussed in this study. Admira, a commercially available ormocer was used as control. A sol–gel process has been used to synthesize organically modified ceramic resins from liquid precursors, which allow one to produce inorganic–organic hybrid polymer materials, which can be functionalized to optimize their physical and chemical properties. Besides, the resulting material properties have been significantly modified by further technological processing such as photochemical curing of the materials by incorporating dimethacrylate groups as organically polymerizable units. Intracutaneous (intradermal) irritation test is found not to elicit any gross signs of tissue reaction. The results of maximization test for delayed hypersensitivity also did not show any adverse skin reaction during the induction or challenge period. Histological analysis after 1, 4, and 12 weeks of subcutaneous implantation of restorative composite resin on the dorsal surface on one side of the spinal column of Wister rats is also found not to reveal any inflammatory response after the implantation. Granuloma and material debris is found to be absent in all three periods of implantation in both test and control. No necrosis was observed around the implanted materials, which were found to be encapsulated by fibrous connective tissue consisting of predominantly fibroblasts and inflammatory cells. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012