Journal Articles
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Item Comparison of structural, spectral and magnetic properties of NiO nanofibers obtained by sol-gel electrospinning from two different polymeric binders(Elsevier Ltd, 2015) George, G.; Anandhan, S.NiO is a p-type semiconductor with wide band gap energy. In this study, nickel oxide nanofibers were fabricated by sol-gel electrospinning followed by high temperature calcination, using two sacrificial polymeric binders. Poly(2-ethyl-2-oxazoline) (PEtOx) in water and styrene-acrylonitrile random copolymer (SAN) in N,N- dimethylformamide (DMF) along with nickel (II) acetate tetrahydrate (NATH), as metal oxide precursor, were the two distinct polymeric systems used in this study. The morphological and structural properties of NiO fibers obtained from the aforementioned systems were compared with each other. The degradation behavior of the sacrificial polymeric binder imparted a significant effect on the properties of the obtained NiO fibers. The grain sizes and the activation energies for grain growth of NiO fibers from two systems were different. The non-stoichiometric NiO fibers obtained from the SAN/NATH system had a better ferromagnetic behavior as compared with that produced from the PEtOx/NATH system. This non-stoichiometry made a difference also in the optical band gap energies of the NiO nanofibers. © 2015 Elsevier Ltd.Item Fabrication of styrene-acrylonitrile random copolymer nanofiber membranes from N,N-dimethyl formamide by electrospinning(SAGE Publications Ltd info@sagepub.co.uk, 2015) Senthil, T.; Anandhan, S.Ultrafine styrene-acrylonitrile random copolymer (SAN) nanofiber-based membranes were produced from N,N-dimethyl formamide solution by electrospinning. The purpose of this study was to find the optimum values of the electrospinning parameters and the influence of major significant parameters on the electrospun fiber morphology and the average fiber diameter (Davg) and its standard deviation using design of experiment. A backward elimination model for multiple regression analysis was employed to obtain quantitative interactions among selected electrospinning parameters and the final fiber diameter. The dependence of the Davg and morphology on the critical entanglement concentration was also studied. Morphology of the electrospun nanofiber mats were examined by scanning electron microscopy. Davg of electrospun SAN fibers increased considerably with increasing solution concentration. Fibers with diameters ranging from 40 to 650 nm were obtained. Analysis of variance was utilized to identify the statistically significant parameters (p < 0.05) and error variance. © The Author(s) 2013.Item A comparative study on the physico-chemical properties of sol-gel electrospun cobalt oxide nanofibres from two different polymeric binders(Royal Society of Chemistry, 2015) George, G.; Anandhan, S.In this study, two different sacrificial polymeric binders, namely poly(2-ethyl-2-oxazoline) (PEtOx) and poly(styrene-co-acrylonitrile) (SAN) along with cobalt acetate tetrahydrate (CATH), as the metal oxide precursor, were used for the fabrication of Co3O4 nanofibres through sol-gel electrospinning. It was observed that the degradation behaviour and physical properties of SAN and PEtOx influenced the structure, morphology and spectral properties of Co3O4 nanofibres, as the properties of the nanofibres obtained from the aforementioned systems were compared with each other. The grain size, shape and the activation energies for grain growth of Co3O4 nanofibres obtained from these two polymeric systems were different. This difference in grain size and shape caused a difference in the optical band gap energies and the magnetic properties of the Co3O4 nanofibres. This study reveals that one can tailor the characteristics of cobalt oxide nanofibres by an appropriate selection of polymeric binders for sol-gel electrospinning. © The Royal Society of Chemistry.Item Polyaniline/poly(styrene-co-acrylonitrile) blend nanofibers exhibit enhanced ammonia and nitrogen dioxide sensing characteristics(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Reddy, N.R.; Anandhan, S.Polyaniline (PANI) nanofibers were synthesized by interfacial polymerization method and p-toluene sulfonic acid was used as a dopant to enhance the conductivity of the resultant emeraldine base of PANI. A blend of PANI and poly(styrene-co-acrylonitrile) (SAN) in the form of nanofibers was electrospun on interdigitated copper electrode and was used for sensing of ammonia and nitrogen dioxide. The sensor exhibited excellent sensitivity and responded quickly to those gases at ppm levels as low as 10. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy results revealed that there is a good molecular level interaction between PANI and SAN, which is believed to be the major reason for the excellent gas sensitivity of these blend nanofibers. © 2016, Springer Science+Business Media New York.Item A Mechanistic Study on the Structure Formation of NiCo2O4 Nanofibers Decorated with In Situ Formed Graphene-Like Structures(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Kumar, B.; Gudla, V.C.; Ambat, R.; Kalpathy, S.K.; Anandhan, S.Nickel cobaltite (NCO) nanofibers were synthesized using poly(styrene-co-acrylonitrile) (SAN) as the polymeric binder through sol–gel assisted electrospinning. Defect-free precursor nanofiber mats were pyrolyzed at 773 K at three different pyrolysis soaking times t = 2, 4, and 6 h. The SAN present in the precursor nanofibers caused morphological changes in the NCO nanofibers during their thermochemical degradation. Consequently, fractal aggregates of NCO nanoparticles were formed along the length of the nanofibers. X-ray photoelectron spectroscopy (XPS) revealed both + 2 and + 3 oxidation states for Ni and Co, with spinel crystal defects due to oxygen rich atmosphere. XPS, high-resolution transmission microscopy, and optical analysis showed graphene-like structures embedded within the NCO nanofibers. With increase in pyrolysis soaking time, the morphology of the NCO particles markedly changed from spherical to rod-like. We propose a mechanism for the morphological change of NCO nanoparticles on the basis of crystallite splitting accompanied by particle splitting and reordering. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.Item Graphene nanoclusters embedded nickel cobaltite nanofibers as multifunctional electrocatalyst for glucose sensing and water-splitting applications(Elsevier Ltd, 2019) Kumar, B.S.; Gudla, V.C.; Ambat, R.; Kalpathy, S.K.; Anandhan, S.Nickel cobaltite (NCO) attains the apex of Sabatier-type volcano plot for electrochemical reaction compared to simple oxides due to synergetic effect of mixed transition metal cations. The combination of high surface area, aspect ratio, and porosity of electrospun NCO nanofibers (NCO-NF) enhance their electrocatalytic performance by improved electron mobility and more active sites. In the present study, NCO-NF fabricated using poly (styrene-co-acrylonitrile) (SAN) as a sacrificial polymer, were embellished with graphene nanoclusters (GNC), which augment the electrocatalytic performance of the NCO-NF. The in situ formed GNC along the NCO-NF are result of the interaction between the polar functional groups of the polymer, and the cations of precursor salts during the calcination of precursor nanofibers. The GNC/NCO-NF with least crystallite size and high aspect ratio having porous NCO nanoparticles and in situ grown GNC were developed using sol-gel electrospinning process assisted by calcination of precursor nanofibers. This simple, eco-friendly, and economical synthesis route with unique structure chemistry of SAN to form GNC and the presence of dual cations (Ni and Co) provides enhanced performance and multifunctionality to GNC/NCO-NF electrodes for electrocatalytic applications, such as biosensors and water-splitting. In the present study, the modified electrodes (GNC/NCO-NF/graphite electrode) exhibited excellent non-enzymatic glucose detection over a wide range of concentration with a lower limit of 1.2 ?M and sensitivity of 1827.5 ?A mM?1 mg?1 in 0.1 M NaOH. Further, the modified electrodes were also tuned for H2O2 detection to aid enzymatic glucose sensing. When examined for bifunctional water-splitting in 1 M NaOH, the electrode reached an onset potential of ?0.537 V and 0.735 V against reversible hydrogen reference electrode and a Tafel slope of 37.6 mV·dec?1 and 67.0 mV·dec?1 for hydrogen and oxygen evolution reactions, respectively. The results prove that GNC/NCO-NF are promising candidates as multifunctional electrocatalyst. © 2019 Elsevier Ltd and Techna Group S.r.l.Item Modelling Behavioural Dynamics for Asymmetric Application Layer DDoS Detection(Institute of Electrical and Electronics Engineers Inc., 2021) Praseed, A.; Santhi Thilagam, P.S.Asymmetric application layer DDoS attacks using computationally intensive HTTP requests are an extremely dangerous class of attacks capable of taking down web servers with relatively few attacking connections. These attacks consume limited network bandwidth and are similar to legitimate traffic, which makes their detection difficult. Existing detection mechanisms for these attacks use indirect representations of actual user behaviour and complex modelling techniques, which leads to a higher false positive rate (FPR) and longer detection time, which makes them unsuitable for real time use. There is a need for simple, efficient and adaptable detection mechanisms for asymmetric DDoS attacks. In this work, an attempt is made to model the actual behavioural dynamics of legitimate users using a simple annotated Probabilistic Timed Automata (PTA) along with a suspicion scoring mechanism for differentiating between legitimate and malicious users. This allows the detection mechanism to be extremely fast and have a low FPR. In addition, the model can incrementally learn from run-time traces, which makes it adaptable and reduces the FPR further. Experiments on public datasets reveal that our proposed approach has a high detection rate and low FPR and adds negligible overhead to the web server, which makes it ideal for real time use. © 2020 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information.Item Enhancing energy absorption in rubber–sand (Ru–San) composite blocks against ballistic impact: a multi-objective optimisation approach(Springer Science and Business Media B.V., 2024) Doddamani, S.; Kulkarni, S.M.; Joladarashi, S.; Mohan Kumar, T.S.; Gurjar, A.K.This study focuses on optimizing process parameters to minimize the thickness of Ru–San composite blocks against high-velocity impact, aiming to enhance projectile energy absorption, particularly in military trench systems. The critical challenge in developing composite blocks as potential sandbag replacements for trench-bunker systems is optimizing their thickness for improved energy absorption during high-velocity impacts. By employing an optimization technique, this study seeks to determine the minimum thickness of the rubber–sand composite block capable of withstanding the full kinetic energy of a projectile without piercing, thereby advancing protective measures in military and security applications. The material used is a rubber–sand composite, consisting of 00 to 20 wt% of sand particles with various sizes ranging from 250 to 750 μm. The optimisation approach employed in this study includes screening design, Vikor and analytic hierarchy process of optimisation techniques. Finite element simulation is used to model the projectile's impact on the rubber–sand composite block and to analyse the energy absorption behaviour of the material under high-velocity impact. The results of this study show that process parameters such as the thickness of the target, wt% of sand, and size of sand particles significantly impact the energy absorption of the rubber–sand composite block. The optimised parameters are determined to be a thickness of 40 mm, 20 wt% of sand, and sand sizes of 750 μm. The findings of this study have important implications for the design and development of materials that can effectively withstand high-velocity impact, particularly in the field of military defence. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.