Ultra-fast microwave aided synthesis of gold nanocages and structural maneuver studies

Gold nanocages (AuNcgs) are well-studied,hollow,metallic nanostructures that have fascinated researchers in the fields of nanotechnology,materials science,photoelectronics,biotechnology,and medical science for the last decade.However,the time-consuming synthesis of AuNcgs has limited their widespread use in materials science and nano-biotechnology.A novel,ultra-fast,simple,and highly convenient method for the production of AuNcgs using microwave heating is demonstrated herein.This quick method of AuNcg synthesis requires mild laboratory conditions for large-scale production of AuNcgs.The microwave heating technique offers the advantage of precise mechanical control over the temperature and heating power,even for the shortest reaction period (i.e.,seconds).Microwave-synthesized AuNcgs were compared with conventionally synthesized AuNcgs.Structural maneuver studies employing the conventionally produced AuNcgs revealed the formation of screw dislocations and a shift in the lattice plane.Detailed characterization of the microwave-generated AuNcgs was performed using high resolution transmission electron microscopy (HRTEM),scanning electron microscopy (SEM),X-ray powder diffraction (XRD),and spectroscopic techniques.     

Electrical properties of Schottky diodes based on Carbazole

Sandwich structures of Carbazole thin films have been prepared by using vacuum deposition technique. The plot of current density versus voltage (J–V characteristics) shows two distinct regions. In the lower voltage region ohmic conduction and in the higher voltage region space charge limited conduction (SCLC) is observed. Number of states in the valence band (Nv) is calculated from the temperature dependence of J in the ohmic region. From the temperature dependence of J in the SCLC region trap density (Nt) and activation energy are determined. The values of Nv and Nt are in the order 10²³ m⁻³ and 10²⁷ m⁻³ respectively. The value of activation energy is nearly equal to 0.1 eV and that of the effective mobility is 4.5 × 10⁻⁷ cm² V⁻¹ S⁻¹. Schottky diodes are fabricated using Aluminium (Al) as Schottky contact. It is observed that gold (Au) is more suitable for ohmic contact compared to silver (Ag). From a semi logarithmic plot of J versus V, the barrier height (ϕb), diode ideality factor (n) and saturation current density (J₀) are determined. The value of n increases and ϕb decreases on annealing.     

Electrically conducting nylon 6,6–polyaniline short composite fibres synthesised by the solvent coagulation method

Polyaniline (PANI) was blended with nylon 6,6 in concentrated H₂SO₄ and HCl solutions. The solvent coagulation method was utilised to extract short composite fibres of a centimetre in length. A solution of n-butyl acetate, acetone, toluene, 1 μM HCl and chloroform were used as coagulating bath to extract the fibres. The diameters of the fibres ranged from 200 to 300 nm, while the length measured approximately 1 cm, as determined from Scanning Electron Microscopy (SEM). The electrical conductivity varied from 10⁻⁴ to 10⁻² S/cm for different mass fractions of PANI (x_PANI) in the composite fibres. The percolation threshold was reached at x_PANI values between 0.15 and 0.2, and further addition of PANI resulted in saturation of the conductivity of the composite fibre. To observe the effect of MWCNTs on the electrical conductivity of the nylon–PANI fibres, 0.04 g, 0.08 g, 0.4 g and 0.5 g of MWCNTs (1, 2, 10, 12.5 weight percentage, respectively) were added into the nylon–PANI solution and were extracted as fibres in the aforementioned solvents. The electrical conductivity of the short fibres increased by an order of magnitude (0.372 S/cm at 12.5 wt.%) when they were extracted in the presence of the MWCNTs. PANI doped in concentrated HCl exhibited an electrical conductivity of 4.46 S/cm.     

Micellar Growth in Cetylpyridinium Chloride/Alcohol System: Role of Long Chain Alcohol,Electrolyte and Surfactant Head Group

The microstructural transition of aqueous 0.1 M cetylpyridinium chloride (CPC) in the combined presence of salt KBr and long chain alcohol (C₉OH-C₁₂OH) has been studied as a function of alcohol concentration, electrolyte concentration and temperature. The viscosity of the CPC/KBr micellar system showed a peaked behavior with alcohol concentration (C ₀), due to alcohol induced structural transition, which was confirmed by dynamic light scattering (DLS) and rheological analysis. Besides C ₀, the chain length of alcohol (n) was found to show a remarkable effect on the micellization behavior of CPC/KBr system. It was observed that the ability of alcohol to induce micelle growth diminishes with n, which was well supported by viscosity, rheology and DLS measurements. To examine the effect of the electrolyte on the micellar growth, the salt concentration was varied from 0.05 to 0.15 M and it was observed that with increase in [KBr], the peak position shifts towards lower C ₀. The effect of temperature on the micellar system showed interesting phase behavior for CPC/KBr/Decanol. The system exhibited a closed solubility loop with an upper critical solution temperature (UCST) > the lower critical solution temperature (LCST), reminiscence of nicotine-water system. The role of surfactant head group on the structural evolution was revealed by comparing the present results with our previous report for similar micellar system, CTAB/KBr/long chain alcohol.     

Benign route for the modification and characterization of poly(lactic acid) (PLA) scaffolds for medicinal application

Scaffolds fabricated from polymers have imprinted its wide applicability in the field of tissue engineering. The surface of electrospun poly(lactic acid) (PLA) nanofibers was modified to improve their compatibility with living medium. PLA film were treated with alkali solution to introduce carboxyl groups on the surface followed by covalent grafting of gelatin using Xtal Fluoro‐E as coupling agent. The gelatin g‐PLA polymer synthesized via ‘graft‐onto’ method exhibit fascinating properties as studied by contact angle measurement, fourier transformed infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, water vapor transmission rate(WVTR), swelling studies and differential scanning calorimetry. The fabricated gelatin g‐PLA scaffolds were further characterized to conduct the study on hydrolytic degradation, and extent of biodegradation at ambient temperature. It was observed from the in‐vitro analysis that the gelatin g‐PLA nanofiber (with hemolytic percentage, 0.56 ± 0.13%) was cytocompatible with fibroblast cell and does not impair cell growth. The WVTR obtained for the electrospun mat around 2900 ± 100 g/m². 24 h signifies the optimal moist environment required for tissue engineering especially wound healing. Notably, many of these strategies resulted in porous hydrophilic scaffolds with human cell growth and proliferation for medical applications of various types. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46056.     

Electrical and Thermal Properties of Twin-Screw Extruded Multiwalled Carbon Nanotube/Epoxy Composites

This paper presents the experimental results of dispersing multiwalled carbon nanotubes (MWNTs) into epoxy (space grade structural adhesive) nanocomposites using co-rotating twin screw extrusion process. Two sets of specimens were prepared; set 1 with ultrasonication for predispersing MWNT before extrusion and set 2 direct dispersion of MWNT in the extruder. MWNT was loaded up to 8 vol.% in both the sets. The specimens were characterized for room temperature volume and surface resistivities as per ASTM D257 using Keithley Model 6517 and for thermal conductivity in the temperature range ?50 to 150 °C as per ASTM E 1530 using Thermal Conductivity Instrument (TCI) 2022 SX211. The volume resistivity of sets 1 and 2 decreased to an extent of 10¹¹ and 10⁹ respectively. The surface resistivity drop was of the order of 10⁹ for both the sets. These drops corresponded to the maximum MWNT loading of 8 vol.%. Electrical conductivity values of the specimens were fitted into the Power Law Model to evaluate the critical exponent. Both sets 1 and 2 showed increase in thermal conductivity with increase in temperature in the testing range. Thermal conductivity increased with increase in filler loading and the maximum increase was 60% at 150 °C in case of 8 vol.% MWNT nanocomposites for set 1. The corresponding value for the set 2 was 25%. Thermal conductivity values were predicted using Lewis Nielson model. DSC of the specimens showed increase in glass transition temperature with increase in filler loading. The dispersion of the nanofillers was studied using SEM and the surface morphology using AFM.     

Silicon carbide wires of nano to sub-micron size from phenol-furfuraldehyde resin

Phenol-furfuraldehyde (PFu) resin synthesized in our laboratory was characterized for its thermal properties and mixed with elemental silicon and the mixture was evaluated as precursor for SiC ceramics. The mix on sintering at 1,500 °C gave nano-SiC powder. The sintering experiment carried out in flowing argon has also resulted in the formation of SiC wires/fibers having diameter in nano to sub-micron range.     

Hybrid area exploration–based mobility‐assisted localization with sectored antenna in wireless sensor networks

In common practice, sensor nodes are randomly deployed in wireless sensor network (WSN); hence, location information of sensor node is crucial in WSN applications. Localization of sensor nodes performed using a fast area exploration mechanism facilitates precise location‐based sensing and communication. In the proposed localization scheme, the mobile anchor (MA) nodes integrated with localization and directional antenna modules are employed to assist in localizing the static nodes. The use of directional antennas evades trilateration or multilateration techniques for localizing static nodes thereby resulting in lower communication and computational overhead. To facilitate faster area coverage, in this paper, we propose a hybrid of max‐gain and cost‐utility–based frontier (HMF) area exploration method for MA node's mobility. The simulations for the proposed HMF area exploration–based localization scheme are carried out in the Cooja simulator. The paper also proposes additional enhancements to the Cooja simulator to provide directional and sectored antenna support. This additional support allows the user with the flexibility to feed radiation pattern of any antenna obtained either from simulated data of the antenna design simulator, ie, high frequency structure simulator (HFSS) or measured data of the vector network analyzer (VNA). The simulation results show that the proposed localization scheme exhibits minimal delay, energy consumption, and communication overhead compared with other area exploration–based localization schemes. The proof of concept for the proposed localization scheme is implemented using Berkeley motes and customized MA nodes mounted with indigenously designed radio frequency (RF) switch feed network and sectored antenna.     

“String and bead” model of copper modified polycarbosilane: synthesis and applications

Journal of Materials Science - The synthesis of metal modified polycarbosilanes is currently an area of significant activity. These polymers can be processed to advanced materials such as ceramic...