Centre for Nano Science & Technology
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Browsing Centre for Nano Science & Technology by Author "Dibakar Das"
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ItemPhenomenological and physical modelling of high homologous temperature deformation(University of Hyderabad, 2016-04-01) Sriharsha, Sripathi ; Dibakar DasThe main focus of this study is to critically assess the relevance or otherwise of a mesoscopic grain boundary sliding controlled flow model, which has been proposed as the common basis for explaining superplastic deformation in different classes of materials. The rationale behind this approach is that, as superplasticity is observed to be a near-ubiquitous phenomenon, there could be an underlying physical phenomenon responsible for this. If this were the case, the phenomenology of the superplastic flow process should also be similar for different classes of materials, i.e. there should be a universal curve for superplastic flow in all systems if the experimental variables like stress, strain-rate, strain-rate sensitivity and temperature of deformation are correctly normalized. Starting from these premises, it has been shown that under isothermal conditions the log logσ ε plots of superplastic materials of different classes and the variation of the strain-rate sensitivity with log ε for materials of different classes have near-identical features. The viscosity and the free energy of activation of all the alloy systems at (nearly) the same homologous temperature also vary quite similarly. Thus, the universality in the mechanical response of superplastic alloys is demonstrated. Further, the mesoscopic-grain boundary sliding controlled flow model for superplastic deformation, initially proposed for micron-grained metallic materials, but later extended to include dispersion strengthened alloys, intermetallics, metals with a quasi-crystalline phase, ceramics and ceramic-composites was taken up for consideration. An algorithm was developed to analyze the experimental data in terms of this model, so that many systems could be analyzed successfully. It has been shown that the mesoscopic-grain boundary sliding model satisfactorily describes superplastic deformation in metals and alloys, dispersion strengthened alloysceramics, composites, intermetallics, nanostructured materials and a material containing a quasi-crystalline precipitates and of grain sizes ranging from a few micrometers to a few nanometers. Also, the same approach has been used to satisfactorily explain superplasticity in geological materials and ice. In the present state of its development, in the mesoscopic-grain boundary sliding controlled model, even though theoretical expressions exist, the values of the free energy of activation and the threshold stress needed for the onset of mesoscopic- grain boundary sliding are treated as fitting constants. By way of applying the ideas to an allied, relevant situation, the mesoscopic-grain boundary sliding controlled model was also used to satisfactorily account for the inverse/ reverse Hall- Petch effect observed in materials when the grain size is in the lower ranges of the nanometer scale. Future efforts could be towards a theoretical framework at a mesoscopic level, by estimating the threshold stress necessary for the onset of mesoscopic-grain boundary sliding a priori
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ItemSynthesis and characterization of advanced multifunctional magnetic nanoparticles for biomedical applications(University of Hyderabad, 2017-03-01) Qasim, Mohd. ; Dibakar DasMagnetic nanoparticles (MNPs) have potential applications in the various biomedical fields including anticancer drug delivery, magnetic resonance imaging (MRI), destruction of the tumor via hyperthermia, bio-separation, catalysis, etc. Development of multifunctional magnetic nanoparticles (MFMNPs) could significantly expand the properties of existing magnetic nanoparticles as it combines many different functionalities in a single platform which make them suitable candidates to achieve simultaneous diagnosis and therapy for cancer treatment. Particularly, the design and synthesis of MFMNPs is an extremely focused and dynamic area of present biomedical research because of their potentials applications in targeted drug delivery, multimodal imaging, hyperthermia, photothermal therapy etc. Different combinations of functional materials with different size and shape have been explored to develop MFMNPs based nanocarriers aiming to enhance the effectiveness and safety of anticancer drugs. In this thesis, preparation, characterization and biomedical applications of various advanced multifunctional magnetic nanoparticles have been discussed. First, different types of MNPs have been synthesized and characterized. Then, different multifunctional nanocomposites nanoparticles such as NZF@Alb, Fe3O4@Alb, CF@Alb, mSiO2- CaFe2O4@P(Nipam-Aa), mesoCaCO3@CaFe2O4, NZF@mSiO2, NZF@mSiO2-CuS- PEG, NZF/Zn0.95Ni0.05O, NZF/Zn0.95Ni0.05O-mSiO2, mesoCaFe2O4 NPs, mSiO2@AgNPs and mSiO2@Ag-Fe3O4@P(Nipam) have been prepared. The structural, morphological, thermal, optical, magnetic properties and drug loading/release behaviour as well as biocompatibility/cytotoxicity of prepared multifunctional magnetic nanoparticles have been investigated. Anticancer activities of prepared anticancer drug-loaded multifunctional nano-formulations have been studied against Hela cells. Obtained results show that the present study could be extremely useful for the advancement of multifunctional magnetic nanocarrier’s design and development for biomedical applications.