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Padekar B.S.,IITB Monash Research Academy | Padekar B.S.,Monash University | Padekar B.S.,Indian Institute of Technology Bombay | Singh Raman R.K.,Monash University | And 2 more authors.
Corrosion Science | Year: 2013

Stress corrosion cracking of the magnesium alloy Elektron 21 (ASTM-EV31A) and AZ91E was studied using constant load test in 0.1M NaCl solution (saturated with Mg(OH)2), and slow strain rate test using glycerol, distilled water and Mg(OH)2 saturated, 0.01M and 0.1M NaCl solutions. Slow strain rate test indicated that EV31A was less susceptible to stress corrosion cracking than AZ91E. Under less intense loading of constant load, EV31A was found to be resistant to stress corrosion cracking. Fractography of EV31A specimens showed little evidence of hydrogen embrittlement. The superior resistance of EV31A is attributed to a more robust oxide/hydroxide layer. © 2013 Elsevier Ltd.

Theivaprakasam S.,IITB Monash Research Academy | Theivaprakasam S.,Monash University | Theivaprakasam S.,Indian Institute of Technology Bombay | MacFarlane D.R.,Monash University | Mitra S.,Indian Institute of Technology Bombay
Electrochimica Acta | Year: 2015

The electrochemistry of the electrolyte plays a significant role in the performance of lithium ion batteries. In order to further investigate the effect of combining an ionic liquid with a conventional electrolyte, a hybrid electrolyte (HE) based on a mixture of 38% N-methyl-N-propyl-pyrrolidinium bis(trifluromethanesulfonyl) imide in an electrolyte consisting of LiPF6 in Ethylene Carbonate: Diethyl Carbonate (1:1) was studied and compared with the properties of a standard organic electrolyte in this work. Thermal measurements reveal that the addition of the ionic liquid improves the thermal stability of the hybrid electrolyte. The interfacial behavior was studied in lithium symmetric cells and it was found that the combined effects of the ionic liquid and the conventional electrolyte results in lower interfacial resistance. The charge-discharge behaviour of LiFePO4 / Li cells was investigated; at the end of 100 cycles, the discharge capacity of the cell with LP30, HE and [C3mpyr][TFSI] was 141 mAh/g, 148 mAh/g and 45mAh/g, respectively. Analysis of the separator recovered from Li/LiFePO4 cells that had been stored for 30 days at 20°C shows iron dissolution from the cathode into the LP30 electrolyte, but not into the hybrid electrolyte. Posthumous studies of the cycled electrodes were carried out using FTIR, XRD, FEG-SEM and HR-TEM analyses, show that the HE forms a permeable interface on the cathode material which prevents metal dissolution from the cathode structure, leading to better cyclic performance. © 2015 Published by Elsevier Ltd.

Wankhede R.G.,IITB Monash Research Academy | Wankhede R.G.,Indian Institute of Technology Bombay | Morey S.,Dow Chemical Company | Khanna A.S.,Indian Institute of Technology Bombay | Birbilis N.,Monash University
Applied Surface Science | Year: 2013

The development of an organic-inorganic sol-gel coating system (thickness ∼ 2 μm) on aluminum is reported. The coating uses glycidoxytrimethoxysilane (GPTMS) and methyltrimethoxysilane (MTMS) as silane precursors, crosslinked with hexamethylmethoxymelamine (HMMM) and followed by hydrophobic modification using a water base short chain per-fluoro emulsion (FE). Such coating resulted in enhanced hydrophobicity with a contact angle of about 120 and sliding angle of 25 for a 20 μL water droplet. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements showed reduced corrosion upon coated substrates than the bare; correlated with both a higher degree of water repellency and formation of low permeable crosslinked sol-gel network. The structure of the coatings deposited was analyzed using Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopy, revealing replacement of hydrophillic surface hydroxyls groups with low energy per-fluoro groups. © 2013 Elsevier B.V. All rights reserved.

Naresh N.,IITB Monash Research Academy | Naresh N.,Monash University | Naresh N.,Indian Institute of Technology Bombay | Wasim F.G.S.,IITB Monash Research Academy | And 4 more authors.
Journal of Materials Chemistry A | Year: 2013

Synthesis of shape-controlled nanoparticles of precious metals with defined size is well-established in the literature and the control over shape and size is achieved using surfactants and capping agents. However, a clean surface without impurities is required for realistic applications. In the present investigation, palladium nanocubes are synthesized using poly(vinylpyrrolidone) and potassium bromide. A novel method for cleaning the nanoparticle surface, i.e., treatment with tert-butylamine is reported. For comparison, a part of the untreated sample is subjected to the commonly used method of heat-treatment in an oxygen atmosphere for surface cleaning. The XPS and FTIR spectra of the heat-treated sample show incomplete removal of PVP and complete removal of Br- and the XRD pattern suggests oxide formation on the Pd surface. Treatment with tert-butylamine provides a clean surface free of PVP and Br -. Cleanliness of the surface is further confirmed by the voltammograms and ORR activities in 0.1 M HClO4. We conclude that tert-butylamine can be an effective solvent for the removal of PVP and a reagent for Br- ions because of its ability to form a quaternary ammonium salt. © 2013 The Royal Society of Chemistry.

Tripathi S.,IITB Monash Research Academy | Tabor R.F.,Monash University
Journal of Colloid and Interface Science | Year: 2016

The adsorption kinetics of many systems show apparent two-rate processes, where there appears to be resolved fast and slow adsorption steps. Such non-standard adsorption processes cannot be accounted for by conventional modeling methods, motivating new approaches. In this work, we present four different models that can account for two-rate adsorption and are based upon physically realistic processes - two adsorbing species, two surface sites having different energies, bilayer formation and molecular rearrangement modes. Each model is tested using a range of conditions, and the characteristic behavior is explored and compared. In these models, the effects of mass transport and bulk concentration are also accounted for, making them applicable in systems which are transport-limited or attachment-limited, or intermediate between the two. The applicability of these models is demonstrated by fitting exemplar experimental data for each of the four models, selecting the model on the basis of the known physical behavior of the adsorption kinetics. These models can be applied in a wide range of systems, from stagnant adsorption in large volume water treatment to highly dynamic flow conditions relevant to printing, coating and processing applications. © 2016 Elsevier Inc.

Singh R.,Indian Institute of Technology Bombay | Vishal V.,Indian Institute of Technology Bombay | Vishal V.,IITB Monash Research Academy | Vishal V.,Monash University | Singh T.N.,Indian Institute of Technology Bombay
Scientia Iranica | Year: 2012

The physico-mechanical properties of rocks and rockmass are decisive for the planning of mining and civil engineering projects. The Schmidt hammer Rebound Number (RN), Slake Durability Index (SDI), Uniaxial Compressive Strength (UCS), Impact Strength Index (ISI) and compressive wave velocity (P-wave velocity) are important and pertinent properties to characterize rock mass, and are widely used in geological, geotechnical, geophysical and petroleum engineering. The Schmidt hammer rebound can be easily obtained on site and is a non-destructive test. The P-wave velocity and isotropic properties of rocks characterize rock responses under varying stress conditions. Many statistics based empirical equations have been proposed for the correlation between RN, SDI, UCS, ISI and P-wave velocity. The Artificial Neural Network (ANN), Fuzzy Inference System (FIS) and neuro-fuzzy system are emerging techniques that have been employed in recent years. So, in the present study, soft computing is applied to predict the P-wave velocity. 85 data sets were used for training the network and 17 data sets for the testing and validation of network rules. The network performance indices correlation coefficient, Mean Absolute Percentage Error (MAPE), Root Mean Square Error (RMSE), and Variance Account For (VAF) are 0.9996, 0.744, 25.06 and 99.97, respectively, which demonstrates the high performance of the predictive capability of the neuro-fuzzy system. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.

Ramesh K.V.,IITB Monash Research Academy | Thaokar R.,Indian Institute of Technology Bombay | Prakash J.R.,Monash University | Prabhakar R.,Monash University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

The dynamics of adhesion of a spherical microparticle to a ligand-coated wall, in shear flow, is studied using a Langevin equation that accounts for thermal fluctuations, hydrodynamic interactions, and adhesive interactions. Contrary to the conventional assumption that thermal fluctuations play a negligible role at high Péclet numbers, we find that for particles with low surface densities of receptors, rotational diffusion caused by fluctuations about the flow and gradient directions aids in bond formation, leading to significantly greater adhesion on average, compared to simulations where thermal fluctuations are completely ignored. The role of wall hydrodynamic interactions on the steady-state motion of a particle, when the particle is close to the wall, has also been explored. At high Péclet numbers, the shear induced force that arises due to the stresslet part of the Stokes dipole plays a dominant role, reducing the particle velocity significantly and affecting the states of motion of the particle. The coupling between the translational and rotational degrees of freedom of the particle, brought about by the presence of hydrodynamic interactions, is found to have no influence on the binding dynamics. On the other hand, the drag coefficient, which depends on the distance of the particle from the wall, plays a crucial role at low rates of bond formation. A significant difference in the effect of both the shear force and the position-dependent drag force on the states of motion of the particle is observed when the Péclet number is small. © 2015 American Physical Society.

Seena V.,Indian Institute of Technology Bombay | Nigam A.,IITB Monash Research Academy | Pant P.,Indian Institute of Technology Bombay | Mukherji S.,Indian Institute of Technology Bombay | Rao V.R.,Indian Institute of Technology Bombay
Journal of Microelectromechanical Systems | Year: 2012

Nanomechanical cantilever based biochemical sensors translate molecular interactions into nanomechanical motions that can be measured by different transduction techniques. Improved sensitivity, reliability, and also cost effectiveness of such sensor platforms have been achieved by the use of polymer materials, along with the employment of smart and compatible transduction techniques. This paper explores an ultrasensitive nanomechanical cantilever sensor platform with a novel transduction technique by integrating a strain-sensitive organic field-effect transistor within a polymer nanomechanical cantilever. This sensor, named as organic CantiFET, has a surface stress sensitivity of 401 ppm\cdot[\hbox{mN/m}] -1 with a low-noise floor. This categorizes the organic CantiFET as an efficient biochemical sensor having a minimum detectable surface stress in the range of 0.18 mN/m. © 2012 IEEE.

Devivaraprasad R.,Indian Institute of Technology Bombay | Ramesh R.,Indian Institute of Technology Bombay | Naresh N.,Indian Institute of Technology Bombay | Naresh N.,IITB Monash Research Academy | And 3 more authors.
Langmuir | Year: 2014

Shape-controlled Pt nanoparticles (cubic, tetrahedral, and cuboctahedral) are synthesized using stabilizers and capping agents. The nanoparticles are cleaned thoroughly and electrochemically characterized in acidic (0.5 M H 2SO4 and 0.1 M HClO4) and alkaline (0.1 M NaOH) electrolytes, and their features are compared to that of polycrystalline Pt. Even with less than 100% shape-selectivity and with the truncation at the edges and corners as shown by the ex-situ TEM analysis, the voltammetric features of the shape-controlled nanoparticles correlate very well with that of the respective single-crystal surfaces, particularly the voltammograms of shape-controlled nanoparticles of relatively larger size. Shape-controlled nanoparticles of smaller size show somewhat higher contributions from the other orientations as well because of the unavoidable contribution from the truncation at the edges and corners. The Cu stripping voltammograms qualitatively correlate with the TEM analysis and the voltammograms. The fractions of low-index crystallographic orientations are estimated through the irreversible adsorption of Ge and Bi. Pt-nanocubes with dominant {100} facets are the most active toward oxygen reduction reaction (ORR) in strongly adsorbing H 2SO4 electrolytes, while Pt-tetrahedral with dominant {111} facets is the most active in 0.1 M HClO4 and 0.1 M NaOH electrolytes. The difference in ORR activity is attributed to both the structure-sensitivity of the catalyst and the inhibiting effect of the anions present in the electrolytes. Moreover, the percentage of peroxide generation is 1.5-5% in weakly adsorbing (0.1 M HClO4) electrolytes and 5-12% in strongly adsorbing (0.5 M H2SO4 and 0.1 M NaOH) electrolytes. © 2014 American Chemical Society.

Nigam S.,Indian Institute of Technology Bombay | Bahadur D.,IITB Monash Research Academy
IEEE Transactions on Magnetics | Year: 2016

Green tea polyphenols have attracted significant interest due to their promising therapeutic potential as antitumor agents. These include catechins that have been explored for various tumors with minimal side effects. This paper demonstrates the fabrication and characterization of dendrimerized magnetic nanoparticles, as delivery vectors for epigallocatechin gallate (EGCG). Glutamic acid-functionalized iron oxide nanoparticles (Glu-Fe3O4) were synthesized and modified with the polyethylene glycol polyamidoamine dendrimers of generations 3, 5, and 6. Nanoparticles were characterized by X-ray diffraction, electron microscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. In aqueous colloidal suspensions, they showed a rapid temperature increase under varying magnetic fields, suggesting their potential in chemothermal therapeutic applications. The loading efficiency of the dendrimerized nanoparticles was calculated to be 32.7%, 51.1%, and 56.4% for generations 3, 5, and 6, respectively. In acidic environments, a sustained drug release profile with an increasing but incomplete release was observed. Importantly, EGCG-loaded nanoparticles induced controlled cell death in human cervical cancer cells, demonstrating a 40% reduction in cell population over 24 h at the highest concentration used, with a linear dose-response. © 1965-2012 IEEE.

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