Arup R. Bhattacharyya

Melt mixing of polycarbonate/multi-wall carbon nanotube composites

—Composites of polycarbonate (PC) with multi-wall carbon nanotubes (MWNT) of different concentrations are prepared by diluting a PC based masterbatch containing 15 wt% MWNT using melt mixing in a DACA-Micro Compounder (4 g scale). Electrical resistivity measurements indicate that the percolation of MWNT is reached between 1 and 1.5 wt%. In addition, melt rheology was applied as another sensitive method to detect the percolation of the nanotubes. Atomic Force Microscopy and visual observations of the composite dispersions in a PC-solvent were used to characterise the state of MWNT dispersion. Differential Scanning Calorimetry and Dynamic Mechanical Analysis were applied to detect changes in the glass transition temperature of PC as a result of processing and of MWNT interactions with the PC matrix including the state of dispersion. In addition, DMA confirmed the reinforcement effect of the nanotubes. The results show that the nanotube incorporation also influences the processing behaviour. Due to the enhancement in melt viscosity by adding nanotubes and the enhanced shear forces, the molecular weight of the PC in the composites is reduced as compared to PC extruded under the same conditions. This effect leads to changes in the glass transition temperature and modulus which counteracts the effects originating from the nanotube-polymer interaction.

Reactively compatibilised polymer blends: a case study on PA6/EVA blend system

Reactive compatibilisation of immiscible polymers is becoming increasingly important and a representative study with PA6/EVA system is the focus of this paper. Morphological studies and crystallization behaviour of uncompatibilised and compatibilised blends of PA6/EVA were studied as functions of dispersed phase concentration (EVA or EVA-g-MA) and maleic anhydride (MA) content. Impact properties of the compatibilised PA6/EVA blends were studied as a function of MA content at fixed dispersed phase concentration. SEM studies of cryogenically fractured surfaces showed an increase in average domain size with increase in EVA level. On contrary, the average domain size and the domain size distributions reduced significantly in the presence of EVA-g-MA. This observation is found consistent with increase in EVA-g-MA concentration at a fixed MA level and also at a fixed concentration of dispersed phase with different level of MA in binary and ternary compositions. Morphological observations also revealed that the phenomenon of coalescence is slower in the presence of EVA-g-MA indicating the formation of in situ graft co-polymer at the interface. Impact strength of the compatibilised PA6/EVA blends increased significantly as compared to uncompatibilised PA6/EVA blends. Crystallization studies indicate that PA6 and EVA (or EVA-g-MA) crystallize separately at their bulk crystallization temperature. The degree of crystallinity is reduced marginally with increase in EVA level, whereas, the decrease in crystallinity is more in the presence of EVA-g-MA. SAXS studies indicate the superposition of PA6 and EVA lamellar scattering and the possible mode of insertion is random in nature. In case of reactive systems, SAXS studies also revealed the hindered crystal growth of PA6 and EVA due to the interfacial reaction.

The Role of Microelectronic Integration In Environmental Control: A Perspective

The paper discusses the potential of silicon-based integration of disciplines of microelectronics, microoptics, and micromechanics, ( MEOM ), to achieve sensor -based smart subsystems for pervasive environmental applications. The author proposes a federally-focused initiative to establish an R & D institute to expedite progress and achieve global industrial leadership .

Melt mixed composites of poly(ethylene-co-methacrylic acid) ionomers and multiwall carbon nanotubes: influence of specific interactions.

SnO2 nanoparticles dispersed in Eu3+ doped silica (SnO2-SiO2:Eu3+) were prepared at a low temperature (185 degrees C) in ethylene glycol medium. Transmission electron microscopy studies on as-prepared samples have established that SnO2 nanoparticles having size of 4.6 nm are uniformly covered by the SiO2 matrix. Significant extent of exciton mediated energy transfer between SnO2 and Eu3+ ions in heat treated SnO2-SiO2:Eu3+ samples has been attributed to the diffusion of Eu3+ ions from the SiO2 matrix to the near vicinity of SnO2 nanoparticles and its incorporation in the SnO2 matrix. On the other hand, very weak energy transfer exists for SnO2:Eu3+ nanoparticles heated at different temperatures due to the phase segregation of Eu3+ ions from the matrix.

A supercapacitor based on longitudinal unzipping of multi-walled carbon nanotubes for high temperature application

Multi-walled carbon nanotubes (MWCNTs) were partially unzipped longitudinally by a chemical method. Unzipped multi-walled carbon nanotubes (UZ-MWCNTs) were characterized by transmission electron microscopic analysis, X-ray diffraction and Raman spectroscopic analyses. UZ-MWCNTs were utilized for electrode preparation and the electrodes were used in the fabrication of a supercapacitor. At room temperature, the UZ-MWCNTs based supercapacitor showed a specific capacitance of ∼41 F g−1, while pristine MWCNTs based supercapacitor exhibited 22 F g−1 at the scan rate of 25 mV s−1. The increase in specific capacitance was attributed to an increase in effective specific surface area of UZ-MWCNTs due to partial unzipping. UZ-MWCNTs based supercapacitor exhibited an increase in specific capacitance with increase in temperature. It showed a specific capacitance of ∼74 F g−1 at 100 °C at the scan rate of 25 mV s−1, while the pristine MWCNTs based supercapacitor did not show any appreciable change in specific capacitance as a function of temperature. UZ-MWCNTs exhibited three-fold increase in specific capacitance as compared to pristine MWCNTs at 100 °C. Impedance spectroscopic analysis of the supercapacitors revealed that the UZ-MWCNTs based supercapacitor exhibited higher internal resistance and lower leakage resistance than pristine MWCNTs based supercapacitor. Continuous ‘charge–discharge’ cycling behaviour indicated that the UZ-MWCNTs based supercapacitor exhibited less stability during initial cycles even though it depicted higher specific capacitance as compared to the pristine MWCNTs based supercapacitor.

High-mobility and low-operating voltage organic thin film transistor with epoxy based siloxane binder as the gate dielectric

This paper reports the fabrication of pentacene-based organic thin-film transistors using a dielectric material, Dynasylan ®SIVO110. The devices exhibit excellent performance characterized by a low threshold voltage of −1.4 V (operating voltage: 0 to −4 V) together with a mobility of 1.9 cm2 V−1s−1. These results are promising because it uses only a single layer of dielectric without performing any intermediate treatment. The reason is attributed to the high charge storage capacity of the dielectric (κ ∼ 20.02), a low interfacial trap density (2.56 × 1011cm−2), and favorable pentacene film morphology consisting of large and interconnected grains having an average size of 234 nm.

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.

Dispersion of non-covalently modified graphene in aqueous medium: a molecular dynamics simulation approach

Molecular dynamics were used to simulate the dispersion of graphene in aqueous medium in the presence of a novel organic modifier, sodium salt of 6-amino hexanoic acid (Na-AHA), which non-covalently modifies the graphene surfaces. The modifier molecule contains an ionizable carboxylate head group and an aliphatic tail. The extent of dispersion was estimated by calculating the potential of mean force (PMF) as a function of increasing concentration of the modifier using the thermodynamic perturbation method in conjunction with molecular dynamics simulations. With increasing concentration of the modifier, the PMF changed from a short-range strong attraction to a long-range repulsion at higher modifier concentrations. The simulation results clearly show the adsorption of modifier molecules at the graphene–water interface, which in turn causes the graphene surfaces to acquire a negative charge. Further, the development of a negative electric potential at the graphene surfaces induces a long-range electrostatic repulsion between the graphene sheets, clearly pointing to an electrostatic stabilization of Na-AHA modified-graphene in aqueous medium.

Fabrication and characterization of flexible films of poly(vinylidene fluoride)/Pb(Fe0.5Ti0.5)O3−δ multi-ferroic nano-composite

Pb(Fe0.5Ti0.5)O3−δ (PTFO) is one of the few multiferroic materials that exhibits coupled co-existence of ferroelectricity and ferromagnetism at room temperature. In this study, phase-pure PTFO multiferroic nanoparticles were dispersed in poly(vinylidene fluoride) (PVDF) matrix via melt-mixing followed by compression molding in order to make flexible film of PVDF/PTFO nanocomposite. Phase pure PTFO nanoparticles with an average particle size of ∼32 nm were synthesized by co-precipitation method. PVDF/PTFO flexible films were prepared, wherein PTFO nanoparticles were varied from 5–25 wt%. The magnetic, ferroelectric, dielectric, magneto-dielectric coupling and morphology, as well as structural properties of these films were systematically investigated. The well saturated magnetic hysteresis loops could confirm the ferromagnetic properties associated with PVDF/PTFO nanocomposite films. The variation of dielectric permittivity and dielectric loss was investigated at frequencies ranging from 10 Hz to 10 MHz for these nanocomposites. The maximum polarization, saturation magnetization and dielectric permittivity were increased with increasing concentration of the PTFO nanoparticles. The ferroelectric, magnetic and magneto-capacitive behaviour at room temperature could suggest the multiferroic nature of the nanocomposite films with significant magnetodielectric coupling.

Electrical Conductivity in Polymer Blends/ Multiwall Carbon Nanotubes

Carbon nanotubes (CNT) based polymer composites have emerged as the future multifunctional materials in view of its exceptional mechanical, thermal and electrical properties. One of the major interests is to develop conductive polymer composites preferably at low concentration of CNT utilizing their high aspect ratio (L/D) for numerous applications, which include antistatic devices, capacitors and materials for EMI shielding. In this context, polymer blends have emerged as a potential candidate in lowering the percolation thresholds further by the utilization of ‘double‐percolation’ which arises from the synergistic improvements in blend properties associated with the co‐continuous morphology. Due to strong inter‐tube van der Waals’ forces, they often tend to aggregate and uniform dispersion remains a challenge. To overcome this challenge, we exploited sodium salt of 6‐aminohexanoic acid (Na‐AHA) which was able to assist in debundlling the multiwall carbon nanotubes (MWNT) through ‘cation‐π’ interactions ...