Rajdip Bandyopadhyaya

Bio: Rajdip Bandyopadhyaya is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Nanoparticle & Mesoporous silica. The author has an hindex of 28, co-authored 87 publications receiving 2508 citations. Previous affiliations of Rajdip Bandyopadhyaya include Indian Institute of Science & University of Utah.

Stabilization of Individual Carbon Nanotubes in Aqueous Solutions

Abstract: Single-wall carbon nanotubes pack into crystalline ropes that aggregate into tangled networks due to strong van der Waals attraction. Aggregation acts as an obstacle to most applications, and diminishes the special properties of the individual tubes. We describe a simple procedure for dispersing as-produced nanotubes powder in aqueous solutions of Gum Arabic. In a single step, a stable dispersion of full-length, well separated, individual tubes is formed, apparently due to physical adsorption of the polymer.

Molecular Dynamics Study of the Influence of Solid Interfaces on Poly(ethylene oxide) Structure and Dynamics

Abstract: Molecular dynamics (MD) simulation studies of the interface between poly(ethylene oxide) (PEO) and TiO2 have been performed at 423 K using a quantum chemistry-based force field. MD simulations revealed that the PEO density is significantly perturbed by TiO2 surfaces, forming layers of highly dense polymer (compared to the bulk melt) that persisted up to 15 A from the surface. Conformational and structural relaxations of the interfacial PEO were found to be dramatically slower than those of bulk PEO. These effects are attributed to an intrinsic slowing down of PEO dynamics and increased dynamic heterogeneity of the interfacial polymer. The surface structure and electrostatic interactions between PEO and TiO2, rather than the increased polymer density at the TiO2 surface, determine the nature of PEO relaxation at the TiO2 interface.

Improved electrochemical performance of SnO2–mesoporous carbon hybrid as a negative electrode for lithium ion battery applications

Abstract: To utilize the high specific capacity of SnO2 as an anode material in lithium-ion batteries, one has to overcome its poor cycling performance and rate capability, which result from large volume expansion (∼300%) of SnO2 during charging–discharging cycles. Hence, to accommodate the volume change during cycling, SnO2 nanoparticles of 6 nm diameter were synthesized specifically only on the outer surface of the mesopores, present within mesoporous carbon (CMK-5) particles, resulting in an effective buffering layer. To that end, the synthesis process first involves the formation of 3.5 nm SnO2 nanoparticles inside the mesopores of mesoporous silica (SBA-15), the latter being used as a template subsequently to obtain SnO2–CMK-5 hybrid particles. SnO2–CMK-5 exhibits superior rate capabilities, e.g. after 30 cycles, a specific discharge capacity of 598 mA h g−1, at a current density of 178 mA g−1. Electrochemical impedance spectroscopy reveals that the SnO2–CMK-5 electrode undergoes a significant reduction in solid–electrolyte interfacial and charge transfer resistances, with a simultaneous increase in the diffusion coefficient of lithium ions, all these in comparison to an electrode made of only SnO2 nanoparticles. This enhances the potential of using the SnO2–CMK-5 hybrid as a negative electrode, in terms of improved discharge capacity and cycling stability, compared to other electrodes, such as only SnO2 or only CMK-5.

CdS−ZnS Core−Shell Nanoparticle Formation: Experiment, Mechanism, and Simulation

Abstract: CdS−ZnS core−shell nanoparticles are synthesized in a series of water-in-oil microemulsion solutions with increasing microemulsion drop sizes. Shell formation was confirmed by observation of a red shift in the UV−vis absorption spectra. Nanoparticle diameter and shell thickness estimated independently from the spectra and from mass balance approximation are consistent with each other. A new two-stage mechanism of core−shell nanoparticle formation has been developed from the experimental findings that consists of coalescence-exchange of microemulsion drops with nucleation, growth, and coagulation of particles. Quantitative predictions from Monte Carlo simulation of this mechanism compares well with the temporal evolution of experimental mean nanoparticle diameter and shell thickness for most of the cases, except when the nature of water in the microemulsion drops is different from bulk water for very small drop size. An increase in both the core and core−shell nanoparticle diameter with drop size reflects ...

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Chemistry of Carbon Nanotubes

Abstract: Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Band gap fluorescence from individual single-walled carbon nanotubes.

Abstract: Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light.

DNA-assisted dispersion and separation of carbon nanotubes.

Abstract: Carbon nanotubes are man-made one-dimensional carbon crystals with different diameters and chiralities. Owing to their superb mechanical and electrical properties, many potential applications have been proposed for them. However, polydispersity and poor solubility in both aqueous and non-aqueous solution impose a considerable challenge for their separation and assembly, which is required for many applications. Here we report our finding of DNA-assisted dispersion and separation of carbon nanotubes. Bundled single-walled carbon nanotubes are effectively dispersed in water by their sonication in the presence of single-stranded DNA (ssDNA). Optical absorption and fluorescence spectroscopy and atomic force microscopy measurements provide evidence for individually dispersed carbon nanotubes. Molecular modelling suggests that ssDNA can bind to carbon nanotubes through pi-stacking, resulting in helical wrapping to the surface. The binding free energy of ssDNA to carbon nanotubes rivals that of two nanotubes for each other. We also demonstrate that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography. This finding links one of the central molecules in biology to a technologically very important nanomaterial, and opens the door to carbon-nanotube-based applications in biotechnology.