Syed Tajammul Hussain

Study of neutron emission in a low-energy plasma focus with β-source-assisted breakdown

The influence of pre-ionization around the insulator sleeve of plasma focus, by a mesh-type ?-source 28Ni63 on neutron emission is investigated. The experiment is conducted on two low-energy (1.15 and 0.58?kJ) Mather-type plasma focus devices. The neutron emission is found to be increased by upto 25%. The results of this experiment suggest that pre-ionization may be helpful in designing a device as a sealed neutron source for different field applications.

Characteristics of x-rays from a plasma focus operated with neon gas

The x-ray emission from a low-energy (2.3 kJ) plasma focus is investigated with neon as the filling gas. Two anode configurations are used in the experiment: the conventional cylindrical anode, and tapered anode slightly toward the open end. The latter geometry enhances soft x-ray emission by an order of magnitude. The emission is pressure dependent and, in both cases, the highest emission is observed at 3–3.5 mbar. For the cylindrical anode, the soft x-ray emission is up to 7 J per shot, which is from a pinched plasma column, 5–6 mm long. For the tapered anode, up to 80 J per shot soft x-ray yield in 4π geometry is recorded, which corresponds to 4% wall plug efficiency. The diameter of the x-ray emission filament is much larger compared with the cylindrical anode. The bulk of emitted radiation is of energy 1.2–1.3 keV, which is thought to arise from recombination of hydrogen-like (Ne X) ions with the low-energy electrons.

New polyaniline/polypyrrole/polythiophene and functionalized multiwalled carbon nanotube-based nanocomposites Layer-by-layer in situ polymerization

In this endeavor, a new type of nanocomposites has been developed from conducting organic polymers (layer-by-layer in situ polymerization of various monomers) and functionalized multiwalled carbon nanotubes (MWCNTs). Initially, functionalization of MWCNTs was achieved by sulfuric acid (H2SO4):nitric acid (HNO3) and HNO3:hydrogen peroxide treatment. A comparative study regarding the synthetic, morphological, and electrical profiles of raw MWCNTs (R-MWCNTs), pure-MWCNTs (P-MWCNTs), functionalized MWCNTs (F-MWCNTs), and polyaniline/polypyrrole/polythiophene-F-MWCNTs (PANI/PPy/PTh/F-MWCNTs) nanocomposites was successfully carried out. Introduction of functional groups on the surface of MWCNTs was confirmed by Fourier transform infrared spectra. Energy dispersive x-ray spectroscopy and Rutherford back scattering were employed for the elemental analyses. Morphology of the obtained hybrid material was studied via scanning electron microscopy and their thermal stability was investigated using thermogravimetric analysis. The dielectric constant and electrical conductivity were also measured. Result exploration revealed that F-MWCNTs were well functionalized ensuing interfacial entrapment between the carbon nanotubes and the matrix. In addition, the layer-by-layer deposition of PPy/PANI/PTh polymers enhanced the electrical conductivity of material relative to the neat ones. Besides, the improved thermal stability of composite was acquired when compared with the homopolymers.

Novel Hybrids Derived from Poly(thiourea-amide)/Epoxy and Carbon Nanotubes

In the present work, nanocomposites of a matrix composed of poly(thiourea-amide) (an aramid)/epoxy (thermoset) and CNTs were fabricated. The hybrids were prepared by in situ polymerization using functionalized and nonfunctionalized CNTs. Amine-terminated poly(thiourea-amide)/epoxy/CNTs hybrids were cured at 120°C with different CNTs content. Chemical linking between amine terminated poly(thiourea-amide) and epoxide group of Bisphenol A diglycidyl ether (DGEBA) formed PTA/DGEBA complex. Hydrogen bonding of PTA with functionalized CNTs was expected to improve the hybrid characteristics. Tensile strength of functional hybrids ranged 57.36–60.68 MPa. 10% gravimetric loss (569–590°C) and Tg of PTA/DGEBA/functional CNTs (235–238°C) showed improvement over PTA/DGEBA/nonfunctional CNTs.

Review: structural diversity in organotin(IV) dithiocarboxylates and carboxylates

Organotin(IV) complexes are known for their outstanding structural diversity and applications. Organotin(IV) carboxylates and dithiocarboxylates form an important class of organotin(IV) compounds. The structural diversity of these compounds emanates from several features including flexibility in coordination geometries, coordination numbers, and versatility of the ligands to engage in different modes of chelation from monodentate to bidentate. Triorganotin(IV) complexes with various ligands mostly demonstrate tetrahedral or trigonal bipyramidal symmetry with some distortions, while diorganotin(IV) and chlorodiorganotin(IV) complexes have variation of geometries and coordination numbers. Some monoorganotin(IV) complexes have also been reported with pentagonal bipyramidal geometries.

Study of the x-ray emission scaling law in a low energy plasma focus

The performance of a low energy (0.6–1.8 kJ) Mather-type plasma focus (PF) device as a Cu–Kα x-ray source is examined. The Cu–Kα and total x-ray emissions are measured for argon and hydrogen filling. It is found that Cu–Kα emission varies as YK [J] ~ [E(kJ)]3.5–4.5 ~ [I(100 kA)]3.5–4.5, whereas the total x-ray emission is found to follow Ytot [J] ~ [E( kJ)]4.5–5.5 ~ [I(100 kA)]4.5–5.5. At optimum conditions, the system with discharge energy of 1.8 kJ is found to generate x-rays with 1.44 ± 0.07% efficiency. About 32% of the emission constitutes the Cu–Kα line radiation. With a cut at the anode tip, the x-ray flux in the side-on direction is increased three times. The modified geometry may help in using the PF as a radiation source for x-ray diffraction.

Synthesis and properties of poly(thiourea-azo-naphthyl)/multi-walled carbon nanotube composites

An aromatic azo-polymer, poly(thiourea-azo-naphthyl), has been synthesized using 1-(5-thiocarbamoylaminonaphthyl)thiourea and diazonium salt solution of 2,6-diaminopyridine. Poly(thiourea-azo-naphthyl) was easily processable using polar solvents and had high molar mass, 57 × 103 g/mol. Electrically conducting and mechanically and thermally stable polymer/multi-walled carbon nanotube nanocomposites were obtained via melt processing technique. Fine distribution of multi-walled carbon nanotubes in a polymer matrix played an essential role in the preparation of polymer/multi-walled carbon nanotube nanocomposites based on interfacial interaction between multi-walled carbon nanotubes and polymer matrix. Field emission-scanning electron microscopy images revealed good dispersion of filler and adhesion of matrix on the surface of multi-walled carbon nanotubes. Accordingly, increasing the amount of multi-walled carbon nanotubes from 1 to 5 wt% increased the electrical conductivity from 2.42 to 4.11 S cm−1. Percolation behavior of the composite was also studied. Tensile modulus for 1 wt% nanocomposite was 4.2 GPa, which increased up to 6.8 GPa on 5 wt% filler addition. A relationship between nanotube loading and thermal stability of the materials was also observed. Ten percent gravimetric loss increased from 502℃ to 538℃ in the presence of 1 wt% multi-walled carbon nanotube. Similarly, glass transition increased from 227℃ to 245℃ in the presence of 5 wt% multi-walled carbon nanotube. Enhancement of the physical properties of multi-walled carbon nanotube-reinforced polymer nanocomposites was accredited to the non-covalent interactions (π–π interactions and secondary bond forces).

CdTiO3 thin films from an octa-nuclear bimetallic single source precursor by aerosol assisted chemical vapor deposition (AACVD)

Mesoporous, crack-free and crystalline CdTiO3 thin films were deposited by aerosol assisted chemical vapour deposition (AACVD) from a single source hetero-bimetallic precursor, [Cd4Ti4(dmae)4(TFA)8(OAc)4O6] 1 [where dmae = N,N-dimethyaminoethanolate, TFA = trifluoroacetate, Oac = acetate]. The precursor 1, prepared by a simple chemical reaction, was characterized by melting point, elemental analysis, thermal analysis (TGA/DTA) and single crystal X-ray analysis. 1 undergoes facile thermal decomposition at 450 °C and has sufficient solubility in common organic solvents to be usable in aerosol assisted chemical vapour deposition of CdTiO3 thin films. The thin films of CdTiO3 deposited on a fluorine doped SnO2 coated conducting glass substrate in one single step were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive (EDX) and Rutherford backscattering spectrometry (RBS). The results indicate that the nanoparticles of grain size ranging from 30–50 nm are homogeneously dispersed with no preferred orientation and both the Cd and Ti atoms are homogeneously distributed in a 1:1 atomic ratio. UV-VIS-NIR and Defuse Reflectance spectroscopies affirm a band gap of 3.4 eV where electrical measurements show that the films possess n-type conductivity.

Effect of modified filler surfaces and filler-tethered polymer chains on morphology and physical properties of poly(azo-pyridyl-urethane)/multi-walled carbon nanotube nanocomposites

Poly(azo-pyridyl-urethane)/multi-walled carbon nanotube (PAPU/MWCNT) nanocomposites were prepared by first synthesizing polyurethane followed by solution dispersing MWCNT in the matrix. We have used two different MWCNTs: the first set of MWCNT contained carboxylic acid group (MWCNT-COOH) and the second set contained acid chloride group (MWCNT-COCl). Afterward, these MWCNT particles were used in the preparation of PAPU/MWCNT nanocomposites. In the first set of nanocomposites, MWCNT-COOH and PAPU were just physically mixed and were designated as PAPU/MWCNT-A. In the second set of nanocomposites, PAPU chains were tethered onto the surfaces of MWCNT-COCl particles and designated as PAPU/MWCNT-AC. Two types of nanocomposites were thus fabricated, including acid functionalized nanotube-based non-tethered PAPU/MWCNT and acid chloride functionalized MWCNT-based tethered system. We have incorporated hydroxyl end-terminated polyurethane via “grafting to” approach to acid chloride functional MWCNT through esterification. Fourier transform infrared spectra confirmed that the matrix was covalently attached to sidewalls of nanotube. Various nanotube loading levels and surface-modified groups were considered to regulate mechanical, thermal and electrical performance of PAPU/MWCNT. The experimental results showed that a moderate loading level of 5 wt. % MWCNT produced the maximum tensile strength (63.1 MPa) in tethered nanocomposites, while the presence of surface carboxylation of MWCNT relatively decreased the tensile strength (49.7 MPa). Comparative studies based on scanning and transmission electron microscopy of the chemically bonded samples revealed unique nano-fibriller morphology. Dynamic mechanical analysis of nanocomposite films showed an increased segmental rigidity with Tg of 144–153℃ in the tethered system relative to pristine PAPU (133℃). Addition of acid chloride functional MWCNT also contributed to an enhancement in the conductivity (2.9–4.7 S cm−1), relative to PAPU/carboxylated MWCNT (2.0–2.7 S cm−1).

Poly(azo-ether-imide) nanocomposite films reinforced with nanofibers electrospun from multi-walled carbon nanotube filled poly(azo-ether-imide)

A high molecular weight (27 × 103 gmol−1) poly(azo-ether-imide) has been fabricated in this study. Well-aligned poly(azo-ether-imide) fibers and poly(azo-ether-imide)/multi-walled carbon nanotube nanofibers-based nanocomposite were then produced by electrospinning via self-reinforcement. Transmission electron microscopy showed that the poly(azo-ether-imide)–multi-walled carbon nanotube electrospun nanofibers were uniform and almost free of defects. Scanning electron microscopy indicated the wrapping of matrix over the bundles of nanofibrs. The as prepared electrospun nanofibers were utilized as homogeneous reinforcement to enhance the tensile strength and toughness of films. The tensile strength and tensile modulus of poly(azo-ether-imide) film reinforced with 3 wt% poly(azo-ether-imide)–multi-walled carbon nanotube nanofibers were 18% and 23% higher as compared to those of the poly(azo-ether-imide) film reinforced with 3 wt% neat poly(azo-ether-imide) nanofibers. The significant enhancement in the overall mechanical properties of the poly(azo-ether-imide)–multi-walled carbon nanotube nanofibers reinforced polyimide films was ascribed to good compatibility between the electrospun nanofibers and the matrix as well as high nanofiber orientation in the matrix. The homogeneous alignment of poly(azo-ether-imide)/multi-walled carbon nanotube nanofibers was also studied using scanning electron microscopy micrographs. Moreover, the thermal stability of poly(azo-ether-imide)/multi-walled carbon nanotube nanofibers reinforced polyimide was superior having 10% gravimetric loss at around 602–617℃ and glass transition temperature in the range of 241–263℃ relative to the neat polymer and poly(azo-ether-imide) nanofiber-based system. This study demonstrated the fabrication of high performance and high toughness polyimide nanocomposites by using this facile self-reinforcement method.