Sudarsan Neogi

IIT Kharagpur, Khargpur, Bengal, India

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Publications (15)19.99 Total impact

  • J Lavanya, N Gomathi, S Neogi
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    ABSTRACT: Tri-layered reduced graphene oxide with better graphitization was synthesized and functioned using radio frequency N2 and O2 plasma. The layer numbers of reduced graphene oxide were determined by atomic force microscopy (AFM) and x-ray diffraction (XRD). The effect of plasma treatment on crystal structure, surface morphology and chemical composition were studied from XRD, transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Fourier transforms infrared spectroscopy (FTIR) and Raman spectroscopy. The chemical species present in N2/O2 plasma during functionalization of tri-layered reduced graphene oxide was analyzed by optical emission spectroscopy. Tri-layered reduced graphene oxide and functioned tri-layered reduced graphene oxide exhibits higher electrochemical performance towards ferrocyanide redox reaction than glassy carbon and platinum electrode with much decrease in overpotential. This indicates that tri-layered reduced graphene oxide and N2/O2 functionalized tri-layered reduced graphene oxide are promising working electrodes in the application of electrochemical based biosensor.
    Materials Research Express. 06/2014; 1(2):025604.
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    ABSTRACT: The effect of temperature pre-exposure on locomotion and chemotaxis of the soil-dwelling nematode Caenorhabditis elegans has been extensively studied. The behavior of C. elegans was quantified using a simple harmonic curvature-based model. Animals showed increased levels of activity, compared to control worms, immediately after pre-exposure to 30°C. This high level of activity in C. elegans translated into frequent turns by making 'complex' shapes, higher velocity of locomotion, and higher chemotaxis index ([Formula: see text]) in presence of a gradient of chemoattractant. The effect of pre-exposure was observed to be persistent for about 20 minutes after which the behavior (including velocity and [Formula: see text]) appeared to be comparable to that of control animals (maintained at 20°C). Surprisingly, after 30 minutes of recovery, the behavior of C. elegans continued to deteriorate further below that of control worms with a drastic reduction in the curvature of the worms' body. A majority of these worms also showed negative chemotaxis index indicating a loss in their chemotaxis ability.
    PLoS ONE 01/2014; 9(10):e111342. · 3.53 Impact Factor
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    ABSTRACT: Surface modification of polypropylene by nitrogen containing plasma was performed in this work in order to improve the wettability which resulted in enhanced biocompatibility and blood compatibility. Various nitrogen containing functional groups as well as oxygen containing functional groups were found to be incorporated to the polymer surface during plasma treatment and post plasma reaction respectively. Wettability of the polymers was evaluated by static contact angle measurement to show the improvement in hydrophilicity of plasma treated polypropylene. Cross linking and surface modification were reported to be dominating in the case of nitrogen plasma treatment compared to degradation. The effect of various process variables namely power, pressure, flow rate and treatment time on surface energy and weight loss was studied at various levels according to the central composite design of response surface methodology (RSM). Except pressure the other variables resulted in increased weight loss due to etching whereas with increasing pressure weight loss was found to increase and then decrease. The effect of process variables on surface morphology of polymers was evaluated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Well spread fibroblast cells on nitrogen plasma treated polypropylene due to the presence of CO, NH2+ and NH+ was observed. Reduced platelet adhesion and increased partial thromboplastin time evidenced the increased blood compatibility.
    Materials Science and Engineering: C. 10/2012; 32(7):1767–1778.
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    ABSTRACT: The Intrauterine Devices (IUDs) are unable to prevent STDs (Sexually Transmitted Diseases) and PIDs (Pelvic Inflammatory Diseases) which seriously restricts their usage. RISUG (Reversible Inhibition of Sperm under Guidance), a potent spermicidal and antimicrobial drug is being coated over copper-T frame (made of polyethylene) by exposing it to vacuum plasma treatment twice to increase the adhesion property of polyethylene. First, the polyethylene alone is exposed to certain process conditions of RF (radiofrequency) plasma which increases the surface roughness by creating micro-and nano-pores (as indicated by scanning electron microscopy and atomic force microscopy). Thereafter RISUG is smeared over the polyethylene of copper-T frame and subjected to the same plasma treatment again. The second plasma treatment causes a "micro-hammering" effect, pushing the drug in the pores and pits formed by the first plasma treatment, resulting in improved bonding. The present study shows that RF plasma treatment alters the surface properties of the copper-T frame without affecting its mechanical properties or primary fabrication.
    Journal of Adhesion Science and Technology 01/2011; 25:151-167. · 0.90 Impact Factor
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    ABSTRACT: Vulcanized ethylene propylene diene polymethylene (EPDM) rubber surface was treated in a radio frequency capacitatively coupled low pressure argon/oxygen plasma to improve adhesion with compounded natural rubber (NR) during co-vulcanization. The plasma modified surfaces were analyzed by means of contact angle measurement, surface energy, attenuated total reflection-infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray sulfur mapping and atomic force microscopy. Several experimental variables such as plasma power, length of exposure time and composition of the argon–oxygen gas mixture were considered. It was delineated that plasma treatment changed both surface composition and roughness, and consequently increased peel strength. The change in surface composition was mainly ascribed to the formation of C–O and –CO functional groups on the vulcanized surfaces. A maximum of 98% improvement in peel strength was observed after plasma treatment.
    Applied Surface Science 01/2011; 257:2891-2904. · 2.54 Impact Factor
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    ABSTRACT: Staphylococcus aureus is one of the most common pathogens responsible for hospital-acquired infections. In this study, S. aureus was exposed to 13.56MHz radiofrequency (RF) plasma generated by two different gases namely nitrogen and nitrogen-oxygen mixture and their sterilization efficacies were compared. Nitrogen plasma had a significant effect on sterilization due to generation of ultraviolet (UV) radiation. However, the addition of 2% oxygen showed enhanced effect on the sterilization of bacteria through nitric oxide (NO) emission and various reactive species. The presence of these reactive species was confirmed by optical emission spectroscopy (OES). Scanning electron microscopy (SEM) analysis was carried out to study the morphological changes of bacteria after plasma treatment. From the SEM results, it was observed that the bacterial cells treated by N(2)-O(2) mixture plasma were severely damaged. As a result, a log(10) reduction factor of 6 was achieved using N(2)-O(2) plasma after 5min treatment with 100W RF power.
    International Journal of Pharmaceutics 08/2010; 396(1-2):17-22. · 3.99 Impact Factor
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    ABSTRACT: Helium-aided sintering of porous unsintered glass is a complex multiscale process, characterised by three different timescales, namely, that of helium diffusion, heat conduction, and radial shrinkage of the glass core. This work presents a multiscale model for quantifying heat and helium diffusion in a shrinking core system by decoupling the timescales based on their orders of magnitude. We obtain analytical solutions of our model, which allow us to quantify the spatio-temporal profiles of temperature and helium concentration in the glass during the sintering process. Our results show that the introduction of helium increases the sintering rate of glass, and we conclude that pre-sintering heating followed by helium-aided sintering is better than simultaneous heating and helium diffusion. We also show that the pre-sintering heating process for a standard glass sample should not be longer than an hour for the sake of heat economy, following which we may switch to the helium-aided sintering process, where the sintering should occur under isothermal conditions for approximately 6 h. We perform dynamic simulations using glass porosity as a parameter, and find the sintering rate to be directly proportional to the initial porosity of the glass sample.La sintérisation assistée à l'hélium du verre poreux non sintérisé est un processus multi-échelle complexe caractérisé par trois échelles de temps différentes, soit celle de la diffusion de l'hélium, celle de la conduction de la chaleur et celle du retrait radial du noyau de verre. Cette étude présente un modèle multi-échelle pour la quantification de la diffusion de la chaleur et de l'hélium dans un système de retrait du noyau en découplant les échelles de temps en se basant sur leur ordre d'amplitude. Nous obtenons des solutions analytiques de notre modèle, ce qui nous permet de quantifier les profils spatio-temporels de la température et de la concentration d'hélium dans le verre durant le processus de sintérisation. Nos résultats montrent que l'introduction d'hélium augmente le taux de sintérisation du verre et nous concluons qu'un chauffage de pré-sintérisation suivi d'une sintérisation assistée à l'hélium est meilleur que la diffusion simultanée de la chaleur et de l'hélium. Nous montrons également que le processus de chauffage de pré-sintérisation pour un échantillon standard de verre ne devrait pas dépasser une heure pour des raisons d'économie de chauffage et qu'après cela nous pouvons passer au processus de sintérisation assistée à l'hélium, processus qui doit se faire dans des conditions isothermiques pendant environ six heures. Nous avons effectué des simulations dynamiques en utilisant la porosité du verre comme paramètre et avons découvert que le taux de sintérisation est directement proportionnel à la porosité initiale de l'échantillon de verre.
    The Canadian Journal of Chemical Engineering 03/2010; 88(2):153 - 160. · 1.00 Impact Factor
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    ABSTRACT: Radiofrequency discharge of helium gas at low pressure was employed to modify surface properties of polycarbonate. The effects of process parameters on wettability and plasma etching were determined by monitoring surface energy and weight loss, respectively. Quadratic equations for surface energy and weight loss, in terms of process variables, namely power, pressure, flowrate and treatment time were developed. Multiple response optimization was performed using central composite design (CCD) of response surface methodology (RSM) to maximize the surface energy and minimize the weight loss. Helium plasma treated polycarbonate resulted in increased hydrophilicity. From optical emission spectroscopic studies helium was identified as excited and metastable atom and ions which caused surface chemistry and morphology changes. Enhanced biocompatibility in terms of increased cell adhesion and proliferation was observed for all plasma treatment conditions. Confluent cell growth was observed with helium plasma treated polycarbonate. Both reduced platelet adhesion and increased partial thromboplastin time (increased to 204 s from 128 s corresponding to untreated polycarbonate) confirm the improved blood compatibility of plasma treated polycarbonate.
    Journal of Adhesion Science and Technology 01/2010; 24:2237-2255. · 0.90 Impact Factor
  • N. Gomathi, C. Eswaraiah, Sudarsan Neogi
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    ABSTRACT: This study deals with the radio-frequency plasma treatment of polycarbonate surfaces with argon. The wettability of polycarbonate was examined by static contact angle measurements with polar solvents (deionized water and formamide) and a nonpolar solvent (diiodomethane). The surface free energy of the polycarbonate obtained from the measured contact angle demonstrated that exposure to argon plasma resulted in an increased surface energy and polarity compared to the untreated polycarbonate. Attenuated total reflection/Fourier transform infrared spectroscopy indicated that argon plasma treatment resulted in surface chemistry changes by hydrogen abstraction from the phenyl ring and methyl group and chain scission at the ether and carbonyl sites. These led to the formation of hydroxyl groups and double bonds. With scanning electron microscopy and atomic force microscopy analysis, changes in the surface morphology and roughness before and after plasma treatment were observed. We followed an experimental matrix with the identified process variables affecting the wettability of the polymer, and optimized the experiments with the response surface methodology of a central composite design. A quadratic model was developed to represent the surface energy in terms of process variables. Optimized process conditions were derived from the predicted model and were confirmed by the experimental data at the predicted optimum conditions. The prediction accuracy of the model was found to be very high. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
    Journal of Applied Polymer Science 06/2009; 114(3):1557 - 1566. · 1.40 Impact Factor
  • N. Gomathi, Sudarsan Neogi
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    ABSTRACT: Surface properties of polycarbonate and polypropylene were modified using low pressure radiofrequency argon–oxygen mixture plasma in order to increase their wettability and make them useful for biomedical applications. The effects of process variables on wettability and weight loss were studied statistically using response surface methodology. Increased surface energies were observed for both argon–oxygen plasma treated polycarbonate and polypropylene. Formation of aldehyde and hydroxyl groups on polycarbonate and hydroxyl group on polypropylene were the surface chemistry changes observed by means of Fourier transform infrared spectroscopy. Qualitative analysis of surface morphology was performed through scanning electron microscopy. A statistical model was developed relating the process variables with the responses: surface energy and percentage weight loss. The obtained statistical models were optimized to maximize the surface energy and minimize the percentage weight loss. Blood compatibility of the polymers was tested for control sample and polymers treated with argon–oxygen plasma at optimized conditions by measuring the partial thromboplastin time. Increased partial thromboplastin time (PTT) was observed for both polycarbonate (144 s) and polypropylene (149 s) after plasma treatment compared to both control samples (128 s).
    Journal of Adhesion Science and Technology 01/2009; 23:1811-1826. · 0.90 Impact Factor
  • N. Gomathi, Venkata K. Prasad, Sudarsan Neogi
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    ABSTRACT: Conjugated polymers have been the subject of many studies because of their widespread applications in electronic and optoelectronic devices. Poly(p-phenylene vinylene) is a leading semiconducting polymer in optical applications. This work is focused on the development of thin films of poly(p-phenylene vinylene) by spin coating and their characterization with Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy to understand their changes. An empirical model has been developed to show the effect of the variables—the spin speed, polymer concentration, and spin time—on the film thickness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
    Journal of Applied Polymer Science 01/2009; 111(4):1917-1922. · 1.40 Impact Factor
  • N. Gomathi, Sudarsan Neogi
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    ABSTRACT: Low pressure plasma treatment using radiofrequency (rf) discharge of argon gas was employed to improve the hydrophilicity of polypropylene. The effects of argon plasma on the wettability, surface chemistry and surface morphology of polypropylene were studied using static contact angle measurements, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Increase in surface energy of polypropylene was observed as a result of argon plasma treatment. SEM and AFM images revealed the increased surface roughness. A set of identified process variables (rf power, pressure, argon flow rate and time) were used in this study and were optimized using central composite design (CCD) of response surface methodology (RSM). A statistical model was developed to represent the surface energy in terms of the process variables mentioned above. Accuracy of the model was verified and found to be high.
    Applied Surface Science 01/2009; 255(17):7590-7600. · 2.54 Impact Factor
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    ABSTRACT: Materials used for biomedical applications are required to have suitable surface properties since they depend more on the surface properties than on the bulk properties. Surface properties greatly influence the cell adhesion and its behavior either directly by guiding cell spreading or indirectly by controlling proteins adsorption and their structural rearrangement on the material. Modulation of physical and chemical properties of polymers by various treatments can render the substrates adhesive for cells in a culture. In the present study, polypropylene surface was modified using helium plasma to enhance cell adhesion to its surface. The experiments were run according to the central composite design of response surface methodology to optimize the process conditions. The effects of the process variables, namely, RF power, pressure, flowrate and treatment time on surface energy and percentage weight loss were studied through central composite design (CCD). A statistical model relating the process variables and the responses was developed. The improved hydrophilicity of polypropylene through helium plasma treatment was observed from its surface energy data. Changes in surface chemistry and surface morphology were studied by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Enhanced cell adhesion to polypropylene treated with helium plasma at the optimum conditions, obtained from the statistical design, was observed from cell adhesion test and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay with L929 mouse fibroblast cells.
    Journal of Adhesion Science and Technology 01/2009; 23:1861-1874. · 0.90 Impact Factor
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    N Gomathi, A Sureshkumar, Sudarsan Neogi
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    ABSTRACT: The choice of polymers for various biomedical applications depends on their surface properties. All polymers do not possess the surface properties required for biomedical applications. Surface prop-erties of the materials like surface free energy, hydrophilicity and surface morphology, which influ-ence the cell–polymer interaction, decide the choice of the polymer. Radio frequency (RF) plasma offers a unique route for surface modification of polymers without affecting their bulk properties. This process results in a smooth, pinhole-free ultrathin film. Plasma treatment of polymers can render the material surface either hydrophilic or hydrophobic through the use of the respective plasma gases. It has found various applications in automobile, electronic, biomedical and chemical industries. In this article the properties and effects of RF plasma treatment of polymers are dis-cussed with reference to their biomedical applications, such as in body implants, bioseparation, sterilization, biosensors, ophthalmology, etc. PLASMA technology is widely used to alter the surface properties of polymers without affecting their bulk prop-erties. The treated polymers have found various applica-tions in automobiles, microelectronics, biomedical and chemical industries. Specific surface properties like hy-drophobicity, chemical structures, roughness, conductiv-ity, etc. can be modified to meet the specific requirements of these applications. The major effects observed in plasma treatment of polymer surfaces are cleaning of organic contamination, micro-etching, cross-linking and surface chemistry modification 1 . Biomaterials that have contact with the human body need an optimal combination of mechanical properties and surface characteristics that re-sults in superior performance in the biological environ-ment. Physico-chemical properties of the surface of the material such as surface free energy, hydrophilicity and surface morphology, which influence the cell–polymer interaction, determine the choice of the polymer. Since in general all polymers do not possess the surface properties needed for biomedical applications, radio frequency (RF) plasma treatment plays a crucial role in incorporating them. Surface modification in a controlled fashion, depo-sition of highly cross-linked films irrespective of the sur-face geometries, formation of multilayer films, eco-friendly nature and the prospect of scaling-up make the RF plasma treatment extremely suitable for biomedical applications. This article provides an overview of recent advances in the biomedical applications of plasma sur-face-modified polymers. The primary focus is on con-temporary literature concerning RF plasma treatment of polymeric biomaterials. Plasma treatment and its effects on the surface of polymers and the results reported on RF plasma treatment in various biomedical applications are summarized.
    01/2008;
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    ABSTRACT: The efficiency of sterilization is reported using radiofrequency (RF) plasma generated by pure Ar and Ar/O 2 mixture on Staphylococcus aureus in terms of germicidal effect (GE). It was observed that Ar/O 2 mixture showed better GE than pure Ar due to the synergetic effect of UV radiation and atomic oxygen species inherent to oxygen plasma as confirmed by optical emission spectroscopy. Scanning electron microscopy revealed the bacterial damage. Optical density values measured at 260 nm were found to be increased confirming the leakage of proteins and cellular contents in the cell.