Dielectric and dynamic mechanical relaxation behavior of exfoliated nano graphite reinforced flouroelastomer composites

Sridhar, V.,Xu, Deng,Pham, Thanh Tu,Mahapatra, S.P.,Kim, Jin Kuk Wiley Subscription Services, Inc., A Wiley Company 2009 Polymer composites Vol.30 No.3

<P>Dynamic mechanical analysis and dielectric relaxation spectra of exfoliated nano graphite reinforced flouroelastomer composites were used to study their relaxation behavior as a function of temperature (−80°C to +40°C) and frequency (0.01 to 10<SUP>5</SUP> Hz). The effect of filler loadings on glass transition temperature was marginal for all the composites and T<SUB>g</SUB> value was in the narrow range of 7.8–8.4°C, which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. Strain-dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.01–10%. The nonlinearity in storage modulus has been explained on the concept of filler-polymer interaction and filler aggregation of the nano graphite platelets. The variation in real and complex part of impedance with frequency has been studied as a function of filler. The percolation of the nano graphite as studied by conductivity measurements is also reported. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.</P>

Microwave synthesis of three dimensional graphene-based shell-plate hybrid nanostructures

Sridhar, V.,Lee, I.,Yoon, H.S.,Chun, H.H.,Park, H. Pergamon Press ; Elsevier Science Ltd 2013 Carbon Vol.61 No.-

Though free standing graphene has excellent physical, chemical and electrical properties, its tendency to restack is a major hurdle in realizing its full potential especially in applications such as lithium ion batteries and super capacitors. In this manuscript, we report synthesis of graphene-based three dimensional (3D) shell-plate nanostructures composed of 'nano-cup arrays' anchored on few-layered graphene (FLG) substrates. The synthesis was carried out by a simple process using eco-friendly ionic liquids and microwave irradiation as the energy source. Morphological studies by scanning electron microscopy and transmission electron microscopy showed vertically anchored graphene nano-cups on graphene substrate. Super capacitor electrodes fabricated with FLG/gCup nano-hybrids and its electrochemical properties are studied by cyclic voltammetry (CV) and galvanostatic charge/discharge (DC) methods. FLG/gCup electrodes showed good electrochemical performance, with a maximum specific capacitance of 421Fg<SUP>-1</SUP> at the charge/discharge current density of 100mAg<SUP>-1</SUP> in 1M KOH electrolyte, which is four times higher than pristine graphene sheets. The utility of our developed technique in synthesis of graphene nano-cup arrays on arbitrary surfaces (glass substrate) is also reported.

Damage evaluation of RC beams strengthened with hybrid fibers

Sridhar, Radhika,Prasad, Ravi Techno-Press 2019 Advances in concrete construction Vol.8 No.1

This paper describes an experimental investigation on hybrid fiber reinforced concrete (HYFRC) beams. And the main aim of this present paper is to examine the dynamic characteristics and damage evaluation of undamaged and damaged HYFRC beams under free-free constraints. In this experimental work, totally four RC beams were cast and analyzed in order to evaluate the dynamic behavior as well as static load behavior of HYFRCs. Hybrid fiber reinforced concrete beams have been cast by incorporating two different fibers such as steel and polypropylene (PP). Damage of HYFRC beams was obtained by cracking of concrete for one of the beams in each set under four-point bending tests with different percentage variation of damage levels as 50%, 70% and 90% of maximum ultimate load. And the main dynamic characteristics such as damping, fundamental natural frequencies, mode shapes and frequency response function at each and every damage level has been assessed by means of non-destructive technique (NDT) with hammer excitation. The fundamental natural frequency and damping values obtained through dynamic tests for HYFRC beams were compared with control (reference) RC beam at each level of damage which has been acquired through static tests. The static experimental test results emphasize that the HYFRC beam has attained higher ultimate load as compared with control reinforced concrete beam.

Electrochemical, Photocatalytic and Photoluminescence properties of BaWO4 and rGO-BaWO4 nano-composites: A Comparative study

Sridhar Ch,Neha,Seo Young-Soo,Rabani Iqra,Turpu G.R.,Tigga Salinta,Padmaja G. 한국물리학회 2024 Current Applied Physics Vol.58 No.-

The rGO-BaWO4 (rGO-BWO) nanocomposites were synthesized by employing the ultrasonic-assisted co-precipitation method. Nanocomposites formed with BWO nanoparticles anchored to layers of reduced graphene oxide through in situ reduction and a homogeneous distribution of BWO nanoparticles were confirmed by SEM images. The rGO-BWO nanocomposite showed improved photocatalytic activity for the visible light degradation of Methylene Blue (MB) dye with a rate constant of 27 × 10 3 min 1 compared to pristine BWO. The band gaps for BWO nanoparticles estimated using UV–Vis DRS are of the order of 3.25 eV–4.25 eV, while they were 2.78 eV–3 eV for rGO BWO nanocomposites. The delocalized surface charges induced by the interactions between the rGO and BWO nanoparticles in the composite material might be responsible for the observed reduction in the band gap. Photoluminescent investigations demonstrate that rGO-BWO nanocomposites have a lower peak intensity compared to pure BWO particles, indicating a reduced recombination rate and better photocatalytic activity. In particular, when used as supercapacitor electrodes, the produced nanocomposites outperform BWO. Because of its larger surface area, the rGO-BWO nanocomposites display two-fold higher outcomes including 586, 571, 406, 375 and 307 F/g compared to BWO 391, 352, 291, 214 and 174 F/g at each current density 1, 2, 3, 5 and 10 A/g and faster charge transfer owing to improved porosity in the surface of rGO-BWO.

Blister Packing of Copper Hydroxide and Titania Nanoparticles on Graphene and Its Recycling

Sridhar, Vadahanambi,Gangaraju, Deepa,Chun, Ho-Hwan,Park, Hyun American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.23

3D functional hetero-nanostructures of vertically anchored metal oxide nanowire arrays on porous graphene substrates

Sridhar, V.,Chun, H.H.,Park, H. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.79 No.-

Mesoporous three dimensional hierarchical structure of copper oxide nanowires vertically anchored on graphene substrate was synthesized by a facile and green 'alkali mediated synthesis' under microwave irradiation. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller surface area tests showed highly crystalline nanowires vertically anchored on porous graphene to give a unique mesoporous, hierarchical nanostructures. When applied as anode in lithium ion batteries, our materials exhibit capacity of 770mAhg<SUP>-1</SUP> even after 100 cycles with a Columbic efficiency in excess of 97%, reflecting the ability of the hierarchical network to accommodate the extreme volume changes of metal anodes that occur during the lithiation/delithiation reactions. The utility of our newly developed to synthesize anisotropic titania nano-wires or zinc oxide nano-flowers on graphene substrate is also reported.

Manganese nitride stabilized on reduced graphene oxide substrate for high performance sodium ion batteries, super-capacitors and EMI shielding

Sridhar, Vadahanambi,Park, Hyun Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.808 No.-

<P><B>Abstract</B></P> <P>Though the utility of manganese compounds such as oxides, sulphides has been well researched in energy storage applications such as super-capacitors and lithium-ion batteries, the utility of manganese nitrides hasn't been reported yet, especially as anode in sodium-ion batteries. In this manuscript we report synthesis of manganese nitride decorated reduced graphene oxide (MnN@rGO) prepared by simple microwave nitridation technique and its utility as anode material in sodium-ion batteries, electrodes in super-capacitors and in EMI shielding applications. In energy storage applications such as sodium ion batteries, MnN@rGO electrodes exhibited sodium storage capacity of 716 mAhg<SUP>−1</SUP> whereas when used as electrodes in super-capacitors, a high capacitance value of 639.2 Fg<SUP>-1</SUP> at scan rates of 10 mVs<SUP>−1</SUP> in 1 M Na<SUB>2</SUB>SO<SUB>4</SUB> aqueous electrolyte was achieved. The EMI shielding effectiveness measured in the X-band region of 2–18 GHz was about 30–32 dB which is 300% more than reduced graphene oxide.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report microwave synthesis of manganese nitride nano-particles dispersed on reduced graphene oxide substrate (MnN@rGO). </LI> <LI> The applicability of MnN@rGO in sodium-ion batteries, super-capacitors and EMI shielding applications is reported. </LI> <LI> The versatility of our newly developed technique to synthesize MnN nanoparticles on carbon fibers is also demonstrated. </LI> </UL> </P>

Concomitant endoscopic biliary, duodenal and colonic stent placement for advanced carcinoma of gall bladder

Sridhar Sundaram,Sidharth Harindranath,Praveen Kumar Rao,Nitin Ramani,Aditya Kale,Shraddha Patkar 소화기인터벤션의학회 2021 International journal of gastrointestinal interven Vol.10 No.4

Combined biliary and duodenal stent placement has been reported previously in multiple series. Rarely, colonic obstruction may present simultaneously with duodenal and biliary obstruction in advanced pancreaticobiliary cancers. Biliary, duodenal and colonic obstruction managed simultaneously using endoscopic modalities have been reported in only one case report previously. Here we report outcomes of a case of carcinoma of the gall bladder with biliary, gastric outlet and colonic obstruction managed by endoscopic placement of biliary, gastroduodenal and colonic self-expanding metal stents.

Synthesis of graphene nano-sheets using eco-friendly chemicals and microwave radiation

Sridhar, V.,Jeon, Jin-Han,Oh, Il-Kwon Elsevier 2010 Carbon Vol.48 No.10

<P><B>Abstract</B></P><P>A novel approach to synthesize graphene nano-sheets by combining chemical treatment and microwave radiation is demonstrated using eco-friendly chemicals. Microwave radiation was used to produce strong expansion of the graphite worm in the thickness direction. The graphene nano-sheets obtained in this study were characterized by morphology images, nanoprofilometry, Raman and X-ray photoelectron spectroscopy. Besides being eco-friendly, the proposed method has also the attractive advantage of being rapidly able to produce a lot of graphene nano-sheets.</P>

From rheometry to rheology

Sridhar, T. The Korean Society of Rheology 2000 Korea-Australia rheology journal Vol.12 No.1

Using a variety of examples from the recent literature on extensional flow of polymer solutions, this paper shows that simple constitutive equations are unable to capture the diversity of chain conformations in such flows. Such diversity is a feature of extensional flows and arises because deformation leads to significant chain extension. Substantial local extension appears even at low strains and the behaviour of these stretched out portions influences the dynamics of the chain and makes a dominant contribution to the stress. Both the distribution function and the chain conformation appear to follow different paths during stretching and relaxation. As a result the second moment of the distribution function does not contain enough information to correctly predict the dynamics. Resolution of this deficiency in simple constitutive models is one of the challenges for rheology.