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      Volume 41, Issue 4

      August 2018

    • Effect of pre-annealing on the structural evolution and optical response of Ag films exposed to iodine vapours

      R PRAVEENA V SRAVANI SAMEERA N V PRABHAKARA RAO THIRUMALA C S SUNANDANA M GHANASHYAM KRISHNA

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      Ag thin films of 5nm thickness were deposited on glass substrates by thermal evaporation. The films were divided into two sets, out of which, one set was not annealed and the other set was subjected to pre-annealing at 300$^{\circ}$C for2 h in air. The un-annealed and pre-annealed films were exposed to iodine vapours at room temperature for the durations from 5min to 10 h. The un-annealed films were crystallized into the $\beta$ phase of AgI after exposure for 5 h. In contrast, for the pre-annealed films, crystallization into the $\beta$ phase occurred within the first 5 min. Both sets of films, however, exhibit astrong preferential c-axis orientation in the $\beta$-AgI phase. Optical absorption studies reveal that the un-annealed films exhibit a localized surface plasmon resonance (LSPR) with a peak at 545 nm and a long wavelength shoulder at 620 nm, which shifts to 516nm after iodization for a few minutes. This peak position does not change with further iodization. The LSPR for the pre-annealed films has a single peak at 538 nm. After iodization for a few minutes, this peak shifts to 525 nm. Iodization for 3 h results in a further blue-shift of this resonance to 475 nm. The photoluminescence spectrum reveals two peaks, oneat 368 nm and the other at 712 nm. The first one is assigned to the excitons of AgI, whereas the long wavelength peak is attributed to the presence of disorder in the films. The reasons for the difference in behaviour of the un-annealed andpre-annealed films are discussed.

    • Size and shape dependences of the colloidal silver nanoparticles on the light sources in photo-mediated citrate reduction technique

      S K PANDA S CHAKRABORTI R N BASU

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      Colloidal silver nanoparticles (Ag NPs) with different sizes and shapes were synthesized by photo-mediated citrate reduction of aqueous AgNO$_3$ solution under UV, sun and visible–infrared (VIS–IR) light sources. Pale yellow colourcolloid was obtained under VIS–IR light exposure, whereas reddish yellow colour colloid was yielded under UV light. The colloid prepared under natural sunlight initially appeared as yellow, which turns out to be deep green after 10 h exposure. The colloid prepared under UV light contains fine spherical NPs with diameter ranging from 5 to 10 nm. In addition to spherical NPs, some low-dimensional features like triangles, hexagonal platelets, nanorods were also formed under sunlight. Similar low-dimensional features including spherical particles, long chains of particles and large leaf-like platelets weregrown under VIS–IR light. The colloid prepared under UV light exhibits single plasmonic absorption peak in the violet region of the visible spectra with absorption peak centred at $\sim$405 nm. However, the colloid prepared under sun and VIS–IR light demonstrates multiple plasmonic absorption peaks related to the multi-dimensional nanoparticles. All the NPs were made of pure silver and single crystalline. The colloid prepared under VIS–IR light exhibited significant ageing with time; whereas, the colloids prepared under UV and sunlight seem very stable against ageing even after long time.

    • Metamaterial-based high efficiency portable sensor application for determining branded and unbranded fuel oil

      MEHMET ALI TÜMKAYA MUHARREM KARAASLAN CUMALI SABAH

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      In this study, we have developed an efficient metamaterial (MTM)-based portable fuel oil sensor in order to distinguish branded and unbranded fuel-oil samples. Electromagnetic properties of the fuel-oil samples are experimentallyobtained and these data are defined in numerical analysis to design and test the performance of MTM sensor. Then, simulated MTM-based sensor structure is fabricated and measured to observe the efficiency and agreement to numerical results. Numerical and experimental studies are conducted in the microwave frequencies of 10–11 GHz. The experiment results are in accordance with the simulation ones. It can be seen from the results that the proposed MTM-based sensor can be implemented into the sensor industry for distinguishing the branded and unbranded fuel oil for several frequency regions.

    • Electrical and magnetic properties of polyvinyl alcohol–cobalt ferrite nanocomposite films

      DHIRAJ KUMAR RANA SURESH KUMAR SINGH SHOVAN KUMAR KUNDU RAM JANAY CHOUDHARY SOUMEN BASU

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      Polyvinyl alcohol (PVA)–cobalt ferrite (CFO) nanocomposite films were synthesized by wet chemical method. The synthesized CFO nanomaterial was characterized by X-ray diffraction (XRD) and transmission electron microscopy(TEM), which confirm the formation of pure phase nanoparticles with cuboid shape. The variation in AC conductivity is measured as a function of frequency (within the range of 100 Hz$^{–1} MHz) and temperature (from 303 to 403 K). It was observed that the frequency exponent, $S$, decreases with increasing temperature, which is explained by correlated barrier hopping (CBH) conduction mechanism. Frequency dependence of real and imaginary parts of the dielectric permittivity of PVA–CFO nanocomposite films for different temperatures is studied on the basis of the modified Cole–Cole model. The dielectric permittivity of the samples reveals an increasing tendency with the concentration of CFO filler in PVA matrix. A high value of 89 emu g$^{−1}$ saturation magnetization and 652 Oe coercivity are observed in CFO nanoparticle.The coercivity increased in PVA–CFO nanocomposite when compared to CFO nanoparticle, which is expected due to inverse magnetostrictive effect. The increasing tendency of dielectric constant and magnetization of the nanocomposites with the increasing CFO concentration enhances the potential of applications in miniaturization of the antenna system and electromagnetic shielding materials.

    • Synthesis and characterization of hydroxyapatite/alumina ceramic nanocomposites for biomedical applications

      S VIGNESH RAJ M RAJKUMAR N MEENAKSHI SUNDARAM A KANDASWAMY

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      In the present work, nanocrystalline hydroxyapatite/alumina (HAp−Al$_2$O$_3$) composite was prepared under specially designed stir-type hydrothermal reactor. The composite was prepared at two different temperatures under autogenous pressure and analysed for crystallinity, size, shape, composition and thermomechanical stability. The electron microscopy study shows the formation of HAp−Al$_2$O$_3$ composite nanorods with uniform distribution. The thermogravimetry analysis reveals better thermomechanical property with minimal weight loss at increased temperature. The effect ofdifferent concentrations of HAp−Al$_2$O$_3$ composite powders against MG63 human osteosarcoma cell lines shows excellent compatibility (80%) at high concentration of 200 $\mu$g ml$^{−1}$. These studies facilitate the formation of biocompatible HAp−Al$_2$O$_3$ composite nanorods for biomedical applications.

    • ZnO nanowire-coated hydrophobic surfaces for various biomedical applications

      AMITENDER SINGH SARAVJEET SINGH

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      Recently, hydrophobic surfaces are finding many applications in the field of biomedical. This study reports the simple and facile method of hydrophobization of various surfaces like glass, semiconductor and polymer, etc. used inbiomedical field by using durable and water-resistant ZnO nanowires coating. The change in contact angle of ethylenediaminetetraacetic acid (EDTA) anticoagulated whole blood (EDTA-WB) on various substrates like; glass, quartz, Si and polydimethylsiloxane (PDMS) before and after ZnO nanowires coating is reported. It was observed that the different type of substrates show great variation in contact angle of EDTA-WB, before and after ZnO nanowires coating. The substrates which are generally hydrophilic for EDTA-WB become hydrophobic after ZnO nanowires coating. This surface-coating technique can be utilized in various biomedical applications, for example, in medical devices and surgical equipments coating, orthopaedic dressings, in-vivo implants and corrosion-resistance surfaces.

    • Fabrication of organic light-emitting diode using molybdenum trioxide interlayer between electrode and organic interface

      DHRUBAJYOTI SAIKIA RANJIT SARMA

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      In this study, high-performance of organic light-emitting diodes (OLEDs) with a buffer layer of MoO$_3$ is demonstrated. With an optimal thickness of MoO$_3$ (12 nm), the luminance efficiency is found to be increased compared to the single layer anode OLED. To study the influence of MoO3 buffer layer on OLED performance, we deposited MoO$_3$ films with different thicknesses on the fluorine-doped tin oxide (FTO) surface and studied J–V and L–V characteristics of the OLED devices. Also, further analysis was carried out by measuring sheet resistance, optical transmittance and surface morphology with the FESEM images. Here, we found that MoO3 (12 nm) buffer layer is a good choice to increase the efficiency of FTO-based OLED devices within the tunnelling region. Here, the maximum value of current efficiency is6.15 cd A$^{−1}$.

    • Synthesis and physico-chemical properties of a new non-centrosymmetric 2-ammoniumbenzamide trioxonitrate crystals [C$_7$H$_9$N$_2$O]NO$_3$

      YAHYA BAHROUNI NEJEH HAMDAOUI LATIFA BENHAMADA

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      2-Ammoniumbenzamide trioxonitrate crystals (2-ABN) were prepared and grown at room temperature. This compound crystallizes in the orthorhombic systemwith non-centrosymmetric P2$1$2$_1$2$_1$ space group. The unit cell dimensions are $a = 4.8900(9)~\AA$, $b = 9.5541(19)~\AA$, $c = 18.961(4)~\AA$ with $V = 885.8(3~{\AA}^3$ and $Z = 4$. The structure refined to a reliability $R$ factor of 4.34%. The 2-ABN structure consists of 2-ammoniumbenzamide cations (C$_7$H$_9$N$_2$O$^+$) and trioxonitrate anions (NO$^−_3$) interconnected by hydrogen bonds originating from amine group donors [$N−H\cdots O$], so as to build a three-dimensional arrangement. The crystal structure, the thermal behaviour and the IR spectroscopic studies were discussed. The optical studies reveal that the 2-ABN crystal could be a good candidate for nonlinear optical devices. The dielectric properties, real and imaginary dielectric permittivities ($\epsilon'$ and $\epsilon''$) and dielectric loss tangent ($\tan (\delta)$), of the crystal at different frequencies of the applied field are reported.

    • Influence of carbon content on the microstructure, mechanical and tribological properties of CrAlCN coatings deposited by DC unbalanced magnetron sputtering

      ELBERT CONTRERAS ROMERO MARYORY GÓMEZ BOTERO WOLFGANG TILLMANN FRANCISCO BOLÍVAR OSORIO GILBERTO BEJARANO GAITÁN

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      The influence of carbon content on the microstructure, mechanical and tribological properties of CrAlCN was systematically investigated. For this purpose, five duplex coatings of CrAlCN deposited on AISI H13 steel by themagnetron-sputtering technique were developed. The carbon content of the coatingswas varied between 10.26 and 80.56 at% by modifying the percentage of methane in the working gas mixture CH$_4$/(Ar $+$ N$_2$). The effect of carbon content on the morphology, microstructure, mechanical and tribological properties of the CrAlCN coatingswas evaluated. Coatings showed a high crystalline structure at lowcarbon contents, consisting mainly of chromium nitrides and aluminium–chromium nitrides. With the increase of carbon content in the coatings, chromium carbides formed at the expense of nitrides, presenting a highly amorphous structure with high carbon content. Initially, the hardness and Young’s modulus of the coatings increased with carbon content, possibly due to hardening of the interstitial solid solution of carbon within the matrix of CrAlN. Then, they were decreased along with the coefficient of friction and wear rate due to the self-lubricating effect of graphite-like carbon. However, above the 54.74 at% carbon, the wear rate of CrAlCN increased again, probably due to the low hardness and adhesion of the coating. The CrAlCN coating with a carbon content of 21.96 at% presented the best balance between mechanical and tribological properties.

    • Precursor-dependent structural properties and antibacterial activity of copper oxide

      DIPTI V DHARMADHIKARI APARNA S PHIRANGE SUSHMA G SABHARWAL ANJALI A ATHAWALE

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      Inorganic metal oxide nanoparticles of zinc, copper and iron have been widely studied for their use in biomedical research due to their novel physical, chemical and biological properties. Present work involves studies on copper oxide nanoparticles for their antibacterial activity. Copper oxide (CuO) nanoparticles were synthesized by template-free hydrothermal synthesis using different precursors of copper (nitrate, acetate, chloride and sulphate). The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis, ultraviolet–visible (UV–Vis) absorption spectroscopy, scanning electron microscopy (SEM) and zeta potential analysis. The XRD patterns of the synthesized samples show presence of ($−$111) and (111) planes,which can be assigned to the monoclinic phase of CuO with the average crystallite size ranging between 43 and 49 nm. The SEM reveals rod-shaped morphology of the samples with a broad size distribution. The optical band gap calculated by UV–Vis absorption study ranges between 1.35 and 1.38 eV. The highly negative zetapotential values of the CuO synthesized with nitrate ($−23.78\pm 0.95$ mV), acetate ($−11.86\pm 1.06$~mV) and sulphate ($−22.33\pm 0.85$ mV) precursors of copper reveal the good colloidal stability of the synthesized particles. While CuO synthesized with copper (II) chloride shows intermediate stability with the zeta potential as $9.40\pm 1.86$ mV. The antibacterial activityof the synthesized CuO was studied against human pathogens like Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacterial strains, which are proved to be efficient and precursor-dependent. The minimum inhibitory concentrationof CuO against E. coli and S. aureus were found to be 0.15 and 0.1 mg ml$^{−1}$, respectively. CuO nanoparticles exhibit good antibacterial activity, hence, it has potential for biomedical applications in preventing and treating infections.

    • Synthesis, characterization and dielectric properties of TiO$_2$–CeO$_2$ ceramic nanocomposites at low titania concentration

      TOKEER AHMAD MOHD SHAHAZAD MOHD UBAIDULLAH JAHANGEER AHMED

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      TiO$_{2(x)}$–CeO$_{2(1−x)}$ nanocomposites were prepared at low TiO$_2$ composition of 5, 10, 15 and 20%, by using TiO$_2$ and CeO$_2$ nanoparticles obtained by polymeric citrate precursor method. These nanocomposites were characterized by using powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive analysis of X-rays and BET surface area studies. BET studies showed the specific surface area of as-prepared nanocomposites in the range of 239–288 m$^2$ g$^{−1}$. Twenty percent of TiO$_2$-based titania–ceria nanocomposites have smallest average particle size of 30 nm and highest surface area of 288 m$_2$ g$^{−1}$ among all the as-prepared nanocomposites. The dielectric characteristics were measured as a function of frequency and temperature. The dielectric constant of TiO$_{2(x)}$–CeO$_{2(1−x)}$ at room temperature was 35.6 (maximum) at 500 kHz for $x = 0.20$.

    • A first method for preparation of biodegradable fibrous scaffolds containing iodine on the fibre surfaces

      SEMEN I GORENINSKII KSENIA S STANKEVICH ANNA L NEMOYKINA EVGENY N BOLBASOV SERGEI I TVERDOKHLEBOV VICTOR D FILIMONOV

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      Fibrous electrospun scaffolds made of poly(L-lactic acid) (PLLA) and poly($\epsilon$-caprolactone) (PCL) were modified with iodine using ‘solvent/non-solvent’ treatment of the polymer through two-step process. At the first step, the scaffolds were treated with mixture of toluene and ethanol for pre-swelling of the fibre surfaces. Then, treated scaffolds were exposed to iodine vapours to entrap iodine on the polymer surface. Concentration of iodine in obtained materials was measured by means of UV-spectrophotometry. Morphology of the modified scaffolds was characterized by scanning electron microscopy (SEM). Proposed modification had no significant effect on mechanical properties of the scaffolds and their morphologies. Obtained materials demonstrated the E. coli's antimicrobial activity depending on iodine concentration.

    • On the structural and electrical properties of metal–ferroelectric–high k dielectric–silicon structure for non-volatile memory applications

      PRASHANT SINGH RAJESH KUMAR JHA RAJAT KUMAR SINGH B R SINGH

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      In this article, we report the structural and electrical properties of metal–ferroelectric–high k dielectric–silicon (MFeIS) gate stack for non-volatile memory applications. Thin film of sputtered SrBi$_2$Nb$_2$O$_9$ (SBN) was used as ferroelectric material on 5–15 nm thick high-k dielectric (Al$_2$O$_3$) buffer layer deposited using plasma-enhanced atomic layer deposition (PEALD). The effect of annealing on structural and electrical properties of SBN and Al$_2$O$_3$ films was investigated in the temperature range of 350–1000$^{\circ}$C. X-ray diffraction results of the SBN and Al$_2$O$_3$ show multiple phase changes with an increase in the annealing temperature. Multiple angle ellipsometry data show the change in the refractive index ($n$) of SBNfilm from 2.0941 to 2.1804 for non-annealed to samples annealed at 600$^{\circ}C. For Al$_2$O$_3$ film, $n$ < 1.7 in the case of PEALDand $n$ > 1.7 for sputtered film was observed. The leakage current density in MFeIS structure was observed to two orders of magnitude lower than metal/ferroelectric/silicon (MFeS) structures. Capacitance–voltage (C–V) characteristics for the voltage sweep of $−$10 to 10 V in dual mode show the maximum memory window of 1.977 V in MFeS structure, 2.88 Vwith sputtered Al$_2$O$_3$ and 2.957 V with PEALD Al$_2$O$_3$ in the MFeIS structures at the annealing temperature of 500$^{\circ}$C.

    • Enhanced properties of UPE/ESOA partially bio-nanocomposites reinforced with chitosan functionalized graphene nanoplatelets: an innovative approach

      SHIVKUMARI PANDA DIBAKAR BEHERA PRASANT RATH TAPAN KUMAR BASTIA

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      The current study deals with the successful development of chitosan-functionalized graphene nanoplatelets (CS/GNPs) and their dispersion in the unsaturated polyester (UPE)/epoxidized soybean oil acrylate (ESOA) (80:20 w/w)blend system in different compositions of 0.3, 0.5 and 0.7wt%. The resulting nanocomposite mixturewas achieved by simple sonication method and pressed into a mould for fabrication of nanocomposite. The whole functionalization and nanocomposite preparation procedure were successfully tracked by FTIR, SEM and TEM. Nanocomposite with 0.5wt% of CS/GNPs nanofiller has demonstrated it as the better candidate due to its optimum properties. Again for better comparison, a nanocomposite with 0.5wt% raw GNPs was also fabricated and its properties were studied in detail. This relative study reported lower mechanical, dynamic mechanical, thermal and electrical conductivity values for 0.5wt% raw GNPs than the corresponding CS/GNPs nanofiller-filled nanocomposites. Nanocomposite with 0.5wt% CS/GNPs showed dramatic enhancement inmechanical, dynamic mechanical, thermal and electrical properties as well as reduced corrosion and swelling performance owing to the homogeneous distribution of nanofiller in the blend. Again, the nanocomposite showed the highest thermal and electrical conductivitieswith the best dielectric strength. Thus, the prepared nanocompositeswith optimum nanofiller contentmight serve as partially biodegradable nanomaterial for applications in nanotechnology engineering, thermal applications, such as circuit boards and electrical applications, such as electronic packaging components, electromechanical devices and electric energy storage devices. This nanocomposite can also find their applications in different corrosive- and solvent-based environments.

    • Effect of (meth)acrylates on in situ visible light polymerization of dimethacrylamide

      YULING XU DONG XIE

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      This study reports in situ visible light copolymerization of a synthesized dimethacrylamide with the selected (meth)acrylates. The effects of these selected comonomers with different functional groups on the polymerization rate, degree of conversion, gel time and compressive strength were investigated. The results showed that in situ copolymerization of the dimethacrylamide with the comonomers having an electron-withdrawing and/or acrylate group could significantly increase the polymerization rate, degree of conversion and compressive strength. Contrarily, an electron-donating group on either carbon–carbon double bond or ester linkage could slow down the polymerization. In comparison, its methacrylate counterpart, triethylene glycol dimethacrylate-based system did not show a clear pattern. The formed H-bonds between (meth)acrylamide and organic acid groups may be responsible for higher compressive strengths. Within the limitation of this study, it is concluded that in situ polymerization of dimethacrylamide under visible light can be accelerated by copolymerization with monomers having electron-withdrawing and/or acrylate groups and vice versa.

    • Thermal and curl properties of PET/PP blend fibres compatibilized with EAG ternary copolymer

      YONG WAN PARK MIRA PARK HAK YONG KIM HWAN CHUL KIM JONG CHEOL LIM FAN-LONG JIN SOO-JIN PARK

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      Blends of polyethylene terephthalate (PET)/polypropylene (PP) and the ternary copolymer ethylene–acrylic ester–glycidyl methacrylate (EAG) as the compatibilizer were prepared using a twin-screw extruder. The thermal properties,densities and morphologies of the blends were determined using various techniques. Next, PET/PP blend fibres were prepared using a melt–spinning system, and their curl properties were investigated. Scanning electron microscopy (SEM) results showed that the number of PP particles in the PET matrix and size of the PP phase decreased as the EAG content increased. The melting temperature ($T_{\rm m}$) and cooling crystallization ($T_{\rm cc}$) values of PP in the PET/PP blends decreased significantly after the addition of 1% EAG. The density of the PET/PP blend fibres decreased significantly with increase in the EAG and PP contents. After curl formation, the curl length of PP in the fibres was shorter than that of PET.

    • Effect of annealing on tungsten oxide thin films for acetone gas detection

      SMITI SACHDEVA RAVINDER AGARWAL AJAY AGARWAL

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      The gas-sensing properties and topology of tungsten oxide thin films deposited by reactive-ion radiofrequency magnetron sputtering were investigated at room temperature. The abnormalities in sensing film behaviour were observedwhen acetone gas is flowed over surface. The reduction reaction of surface and oxidation reaction of acetone gas were studied. As the gas comes in contact with the surface, the molecules tend to reduce the surface, hence, decreasing theresistance. The sensing film was annealed at different temperatures, viz., 300, 400, 500, 600 and 700◦C for 1 h each for the purpose of finding the optimum annealing temperature to detect acetone gas. Various characterizations, viz., XRD, AFM, FESEM, thickness measurement through surface profiler, gas-sensing characterization for recording resistance changes were performed. The optimum annealing temperature at which the sensing film gives maximum response when it comes in contact with acetone gas was computed to be 50$^{\circ}$C. Also, operational optimum temperature for sensing film annealed at 500$^{\circ}$C was computed to be 260$^{\circ}$C. A grain size of 7.3 nanometres was computed through analysis of AFM image and a film thickness of 100 nm was calculated through surface profiler. The SEM image of the film demonstrates that the grains developed on the surface, which increase in size with increase in the annealing temperature. The XRD patterns reveal thatthe oxide showed up was WO$_2$. It was observed that the response percentage is $\sim$31% for acetone vapour concentration of 20 ppm, $\sim$19% for the concentration of 15 ppm and $\sim$15% for the concentration of 10 ppm. The response time of the sensor is $\sim$5 min and the recovery time is 4 min.

    • Effect of deposition times of Al$_2$O$_3$ buffer layer on the structural and optical properties of AZO film on the polyethylene terephthalate substrates

      YAODONG LIU XINYUE WANG YING HAN HUA CHEN

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      The aluminium-doped zinc oxide with Al$_2$O$_3$ buffer layer (AZO/Al$_2$O$_3$) films were deposited on the polyethyleneterephthalate substrates by radiofrequency magnetron sputtering. Compared with the AZO films without Al2O3 buffer layer, the crystallite size and (002) peak of the AZO/Al$_2$O$_3$ films changed with the deposition times; the full-width at halfmaximum (FWHM) of (002) peak decreases from 0 to 25 min. The effects of Al2O3 buffer layer on the surface morphology of AZO/Al$_2$O$_3$ and optical properties of films were investigated by SEM and UV–Vis–NIR spectrophotometer, respectively. The results reveal that the average transmittance of the AZO films in the visible wavelength region is $\sim$90%, stronger deep level emissions centred on 550 nm is attributed to intrinsic defects in the AZO films on the organic polymer PET substrates.

    • Morphology-controlled ultrafine BaTiO$_3$-based PVDF–HFP nanocomposite: synergistic effect on dielectric and electro-mechanical properties

      VAIBHAV KHIRATKAR RADHAMANOHAR AEPURU H S PANDA

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      Perovskite-based flexible nanocomposites were realized by dispersing BaTiO$_3$ and modified monodisperse BaTiO$_3$ in PVDF–HFP matrix. BaTiO$_3$ was modified in situ by the addition of carbon solution, which was prepared electrochemically by using graphite rod. Structural characterization revealed that the decrease in tetragonality due to reductionin particle size of modified BaTiO$_3$ than unmodified BaTiO$_3$. The controlled morphology of treated-BaTiO$_3$ nanoparticles was well dispersed in polymer matrix and exhibited effective dielectric constant.High active surface area of modified BaTiO$_3$ suggested strong interfacial polarization, reduced dielectric loss and induced relaxation as compared to PVDF–HFP/BTnanocomposite. The experimental dielectric behaviour was fitted with theoretical Maxwell–Garnet model and composites followed up to 20 wt.% filler. The polarization effect was further proven by electric modulus studies of nanocomposites in broad frequency (0.1 Hz–1 MHz) and temperature ($−$40 to 130$^{\circ}$C). The results suggested that the shift in relaxation peakstowards higher frequencies with increase in filler content in polymer matrix. Further, a flexible-pressure sensing device was fabricated and evaluated for real applications.

    • A facile route for graded conversion of carbon fabric to silicon carbide fabric and its oxidation kinetics study in atmospheric high-temperature environment

      JYOTI PRAKASH MANASI GADE BHASKAR PAUL KINSHUK DASGUPTA

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      Silicon carbide fabric converted from carbon fabric was prepared by a facile halide-activated pack cementation method. The XRD, SEM and EDS analyses confirm the formation of SiC fibres with graded conversion of carbon toSiC from surface to core of individual carbon fibres of carbon fabric. The graded conversion of carbon fibre to SiC was uniform and homogeneous throughout the fabric dimension. The thermokinetics of oxidation in atmospheric environmentwas studied by TGA analysis. The reaction kinetics and governing mechanism for oxidation of bare carbon fabric and silicon carbide fabric were calculated using Kissinger and Ozawa methods. It was observed that the activation energy forbare carbon fabric and silicon carbide fabric converted from carbon fabric are 62 and 174 kJ mol$^{−1}$, respectively. Further, it was observed that the silicon carbide fabric converted from carbon fabric follows the second-order surface reaction oxidation mechanism.

    • Thioglycolic acid-capped CdS quantum dots modified with Co$^{2+}$ as a fluorescent sensor for dopamine

      TUANJAI NOIPA WITTAYA NGEONTAE

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      A new selective fluorescent sensor for detection of dopamine (DA) using Co$^{2+}$ -decorated thioglycolic acidcapped CdS QDs (Co$^{2+}$@TGA–CdS QDs) was proposed. Basically, the fluorescent intensity of TGA–CdS QDs can bequenched by Co$^{2+}$. However, with the addition of dopamine into the solution of Co$^{2+}@TGA–CdS QDs, the fluorescent intensity was efficiently quenched due to the formation of the efficient quencher (Co$^{2+}$–dopamine complex). Thus, the concentration of dopamine can be determined by tracking the decrease in the fluorescent intensity of the Co$^{2+}$@TGA–CdSQDs. The proposed sensor showed high selectivity towards the detection of dopamine over other catecholamine derivatives and related compounds. Under optimal conditions, the quenching efficiency of dopamine on the Co$^{2+}$@TGA–CdS QDs system was linearly proportional to the concentration of dopamine in the range of 20−100 $\mu$mol l$^{−1}$. The limits of detectionand quantification were 1.8 and 12.7 $\mu$mol l$^{−1}$, respectively. This sensor system was demonstrated to detect dopamine in real urine samples with satisfactory results.

    • Synthesis and luminescence properties of TiO$_2$ :Yb–Er mesoporous nanoparticles

      I L VERA ESTRADA R NARRO-GARCÍA T LÓPEZ-LUKE V H ROMERO J A CHRISTEN E DE LA ROSA

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      Mesoporous spherical Yb–Er-doped TiO$_2$ nanoparticles were prepared by sol–gel method. The structure and morphology of the nanoparticles were characterized using Raman, Fourier transform infrared spectroscopies, transmission electron microscopy and by low-temperature N$_2$ adsorption. It is shown that both anatase (tetragonal) and brookite (orthorhombical) phases are present in the titania nanoparticles. Their diameter size is between 12 and 15 nm and an average surface area of 136 m$^2$ g$^{−1}$. Under infrared irradiation, the nanoparticles show luminescence by an upconversion process of the ytterbium and erbium ions, the green emission corresponds to ${}^2$H$_{11/2}$ $+$ ${}^4$S$_{3/2} \to {}^{4}$I$_{15/2}$ transition and for the redemission, the transition energy is: ${}^4$F$_{7/2} – {}^4$I$_{15/2}$. The green and red photoluminescence intensities are highly dependent on the OH amount, which is produced during the hydrolysis and condensation processes and depends on the reaction time, nanoparticles wash and annealing temperature. The influence of synthesis parameters on the properties of porosity andluminescence was studied by the Plackett–Burman experimental design.

    • Effect of solvent–vapour annealing on morphology, structure of copper(II) phthalocyanine thin films and device performance

      JING XU XUEQIANG LIU WENLONG HOU HUIYUN GUO LAN YU HAIQUAN ZHANG

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      We investigate the molecular orientation transition and resulting morphology of copper phthalocyanine (CuPc) thin films induced by solvent–vapour annealing (SVA) in detail. Seven solvents are utilized to tune the morphology of CuPcthin films. The morphology, crystalline structure and optical properties of the CuPc active layer were investigated through field emission scanning electronmicroscopy (FESEM),X-ray diffraction (XRD) and ultraviolet–visible (UV–Vis) absorption spectrum, respectively. The result demonstrates that morphology and structure are depended on the type of solvents. Thehigh crystallinity of the CuPc films with a larger grain size and less grain boundaries can be observed. As a result, the resistance of the conducting channel is decreased, leading to an improved performance of the organic field-effect transistor (OFET).

    • Rheological behaviours of silica/water, silica/PEG systems and mechanical properties of shear thickening fluid impregnated Kevlar composites

      EBRU SARALOGLU GÜLER

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      Evolution in armour materials is critical to improve the protection abilities together with the properties of flexibility and lightness. Silica colloidal suspensions are important candidates to improve strength of the armour materials.The dispersing medium of the silica particles acts as an important role in the formation of shear thickening fluids (STF). STF has the ability to have increased viscosity by increasing the shear rate. Rheological, impact, flexibility and yarn pull-out tests were performed during the study. This study demonstrated that STF did not occur in the case of dispersing silica in water, but increased the impact resistance when Kevlar treated by the silica dispersed in water as compared to neat Kevlar. Fumed silica distribution in polyethylene glycol (PEG) led to STF creation confirmed by the rheological tests. The impact resistance of STF-treated Kevlar was found to be improved when compared to silica-dispersed water-impregnated Kevlar. It was observed that the pull-out force values of STF-fertilized Kevlar were increased compared to neat Kevlar.

    • Sn$^{4+}$-doped TiO$_2$ nanorod array film with enhanced visible light photocatalytic activity

      SHINING NI TIANTIAN ZHOU YUANNA ZHU YONGQIANG CAO PING YANG

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      Sn$^{4+}$-doped TiO$_2$ nanorod array film (NAF) on the fluorine-doped tin oxide (FTO) conducting glass was successfully synthesized using the facile hydrothermal method. The NAF photocatalysts were characterized by the scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–Vis diffuse reflectance spectra (DRS). The SEM images showed that both doped and pure TiO2 NAFs exhibited a good nanorod array structure. Sn$^{4+}$-doped TiO$_2$ NAF still maintains rutile crystal structure, which was identical to that of pure TiO$_2$ sample. By means of the DRS measurement, it was found thatthe Sn$^{4+}$ doping in TiO$_2$ nanorod could induce an obvious enhancement of visible light absorption owing to the introduction of doping energy level in the band gap of TiO$_2$. The degradation of methyl orange (MO) demonstrated that the Sn$^{4+}$-doped TiO$_2$ NAF exhibited an enhanced photocatalytic activity than pure TiO$_2$ NAF under the visible light ($\lambda > 400$ nm) irradiation,which should be attributed to the enhanced visible light response and improved separation efficiency of photogenerated carriers of Sn$^{4+}$-doped TiO$_2$.

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