Arvind Kumar Saxena

Deagglomeration of multi-walled carbon nanotubes via an organic modifier: structure and mechanism

We have investigated the agglomeration behaviour of two types of multi-walled carbon nanotubes (MWNTs; N-MWNTs and D-MWNTs), which have different chemical functionalities, average diameter, varying extent of agglomeration and agglomerations. The properties were altered by varying the agglomerated structure. The strength of the MWNT agglomerates was estimated via nanoindentation. The work done to indent D-MWNT agglomerates (3910.3 × 10(-8) erg) was higher than for N-MWNTs agglomerates (2316.4 × 10(-8) erg). An organic modifier, the Li salt of 6-aminohexanoic acid (Li-AHA), was used to deagglomerate the MWNTs in an aqueous medium. The stability of the aqueous dispersion of Li-AHA-modified MWNTs was analyzed by UV-vis spectroscopy and zeta potential measurements. An increase in Li-AHA concentration increased the dispersion of MWNTs in the aqueous medium. Furthermore, the mechanism of dispersion of the two types of MWNTs in the aqueous medium in the presence of Li-AHA was determined based on the electrostatic charge repulsion between the negatively charged species. A fluorescence-activated cell sorting technique was used to assess the debundling of MWNT agglomerates in the aqueous medium. We examined the morphology-property relationship in Li-AHA-modified MWNTs.

A novel carbon rich crystalline (C) SiC-Si(n) interface using liquid polycarbosilane as a precursor - a unique Schottky junction

This paper presents a novel rectifying interface material using carbon rich crystalline (C)-SiC and n-type Si by a modified CVD technique, using liquid polycarbosilane as a precursor at 900 °C. The equilibrium band diagram and Fermi level alignment was explained using Poissons model and the depletion approximation. The junction capacitance, depletion width and saturation current were evaluated and further discussed from the perspective of temperature dependency. The junction was found to be Schottky in nature, with a large breakdown voltage of 69 V and low space charge. This type of junction material, having good mechanical strength, is promising for high temperature and high power applications.

Effect of Halloysite Nanotubes as Novel Nanofiller on Peroxide- and Electron Beam Radiation-Initiated Polyphosphazene Elastomer

A tubelike, naturally occurring halloysite clay mineral (HNTs) incorporated polyphosphazene (PPZ) elastomeric nanocomposites had been electron beam radiated and thermally treated for certain applications. To improve the dispersion of raw HNTs (H), an organosilane modifier had been exploited. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) technique were utilized for plausible interaction and intercalation. The efficiency of electron beam radiation over chemical initiation for intra and inter chain network formation within the resin was substantiated through oil and solvent resistance studies. Effective delay in mass transport as compared to the virgin elastomer was observed through thermal analysis. GRAPHICAL ABSTRACT

Immobilization of individual nanotubes in graphitic layers for electrical characterization

A simple route is followed to produce an abundance of individual carbon nanotubes (CNTs) immobilized in graphitic layers to counter the challenge of locating individual CNTs and restrict the lateral displacement of CNTs due to the high electrostatic force exerted by a scanning tunnelling microscope tip for electrical characterization. Graphitic layers are selected for the embedding matrix as graphite and the nanotubes have a similar work function and hence would not perturb the electrical configuration of the nanotube. Solvent mediated exfoliation of graphite layers to insert the nanotubes was preferred over oxidative expansion, as oxidation could perturb the electrical configuration of graphite. During the exfoliation of graphite the optimized amount of nanotubes was introduced into the medium such that an individual nanotube could be immobilized in few-layer graphene followed by precipitation and centrifugation. The dose and the time of sonication were optimized to ensure that damage to the walls of the nanotubes is minimized, although the ultrasonication causes scissoring of the nanotube length. This procedure for immobilizing nanotubes in graphitic layers would be equally applicable for functionalized CNTs as well. The capability of embedding individual nanotubes into a similar work function material in an organic solvent, which could then be transferred onto a substrate by simple drop casting or spin coating methods, has an added advantage in sample preparation for the STM characterization of CNTs.

The Role of Functional Moieties on Carbon Nanotube Surfaces in Solar Energy Conversion

An easily dispersible multiwalled carbon nanotube (MWCNT) derivative is prepared, and provides a platform for the synthesis of the phenyl butyric acid methyl ester (PCBM) analog. The carbene addition reaction of MWCNTs makes derivatives that are less soluble in organic solvents; by exploiting this differential solubility, PCBM analogs can be separated from the unreacted functionalized MWCNTs. Our experimental evidences indicate that it is the unique properties of the butyric acid methyl ester moiety that makes the acceptor material perform better in organic photovoltaics (OPVs). Studying the combination of the butyric acid methyl ester moiety and the deagglomerated functionalized MWCNT structures provides us an insight into nanoscale charge transfer and transportation inside the donor-acceptor domain. It is demonstrated that a strong structure-property relationship exists for the functionalized MWCNTs, which enables us to correlate the functionality on the carbon nanostructures with performance in OPVs.

Thermophysical Properties and Morphological Changes of PEEK/LCP Blend System on Combined Effect of Polyphosphazene and HNT-COOH

ABSTRACT This work explored the structural and morphological changes of poly ether ether ketone/liquid crystal polymer blend system, caused due to combined effect of polyphosphazene and acid-modified halloysite nanotubes. Surface modification of halloysite nanotubes gave these the adequate potential to make an effective combination with polyphosphazene. These were became the most promising factor on enhancement of thermophysical properties of blend system. Surface-treated halloysite nanotubes added nanocomposite drastically improves thermal stability than that of the other untreated nanofiller-based nanocomposites and pure blend. The storage modulus, tensile modulus, and tensile strength values increase due to the superior dispersion of the modified halloysite nanotubes in polymer matrix. GRAPHICAL ABSTRACT

Development of insecticide-incorporated knitted fabric having long-lasting efficiency

Insecticide-incorporated knitted fabrics are used to provide long-term efficacy against mosquitoes. This article described the method for making insecticide-incorporated filaments by using bi-component-spinning technique having core-sheath morphology whereas deltamethrin has been incorporated in the sheath-containing high-density polyethylene. The concentration of the deltamethrin is varied from 0.25% to 0.75% to assess its impact on bioassay efficacy. The developed filaments subsequently converted into knitted structure and possess excellent insecticidal efficiency even after 20 wash cycles and therefore can be effectively used for the fabrication of knitted mosquito nets. The residual deltamethrin content was also evaluated after successive wash cycles.

Rheological Behavior of Polycarbosilane Part II: Effect of Heterometal (Al) Content and Nature of Bonding with Si of Polycarbosilane

A few aluminum containing polycarbosilanes named AlOR-PCS and Alac-PCS have been synthesized by the reaction of aluminum isopropoxide (AlOR) and aluminum acetylacetonate (Alac) with polycarbosilane (PCS), respectively. These materials were characterized by Fourier Transform Spectroscopy (FTIR), Thermo gravimetric Analysis (TGA) and Gel Permeation Chromatography (GPC). The rheological properties of these compounds were studied with respect to time, temperature and atmosphere (inert & air). It has been observed that the increase in metal content enhances the crosslinking of the PCS chains. Under similar conditions, the crosslinking of AlOR-PCS derivatives was found slower than Alac-PCS. GPC analysis of the samples showed the increase in molecular weight of these compounds compared to virgin PCS. TGA showed improved ceramic yield with increasing metal content. Alac-PCS gave higher ceramic yield than AlOR-PCS for similar molar ratios of metal complexes.

Wide visible and unique NIR fluorescence from SiC nanocrystals embedded in carbon rich SiC matrix derived from liquid polycarbosilane

A novel epitaxial growth of SiC nanocrystals embedded in carbon rich amorphous SiC films deposited using liquid polycarbosilane as precursor. These films exhibit wide visible and unconventional NIR fluorescence with exceptionally short lifetimes of 146 ps and 138 ps. Fabrication of LEDs is a potential application of these materials.

Study of Electrospun Chitosan Nanofibrous Coated Webs

Fabricated nanowebs are successfully coated with polypropylene spun bonded non-woven fabric with various coating density ranges from 0.25-1.2 gsm. This study describes an electrospinning coating process of pure Chitosan dissolved in TFA and DCM and its detailed characterizations. The optimal solution condition for electrospinning was studied and, thereby, the process was successfully established. The best optimal condition: 11 % Chitosan was successfully electrospun (superlative web structure) in the electric field of 75 KV, distance between spinning electrodes 135 mm and rotation of spinning electrode 5 rpm (throughput). Once it was determined the ideal condition for fabricating web thereafter under identical conditions electro coating process was done by varying collector speed. The resultant nanofibrous web was found to be uniformly coated having mean fiber diameter ranges from 1210-1221 nm. AFM microphotographs indicated the interconnected porous structure of the prepared Chitosan web. Fibrous break down at a solution concentration (2 & 5 %) was revealed by AFM and FESEM images. At higher concentration (14%) web spinability was poor in the form of lumps deposition. Morphology of spun web was greatly influenced by coating density. Thus, these nanofibrous coated membranes have great potential for using as a layer for developing futuristic antimicrobial, biomedical and filtration clothing. Moreover, the developed coated web has a significantly higher production rate (approx 0.25 g/m2min) is potential for commercial viability and could be translated into bulk production.