BITS Faculty Publications

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Author: search.filters.author.Etika, Krishna ChitanyaSubject: search.filters.subject.Chemical Engineering

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Now showing 1 - 10 of 17
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    Comparison of Covalently and Noncovalently Functionalized Carbon Nanotubes in Epoxy
    (Wiley, 2009-04) Etika, Krishna Chitanya
    Carbon nanotubes typically require the use of a dispersing or stabilizing agent to prevent significant aggregation during incorporation into a polymer matrix. These additives must be strongly associated, either covalently or physically, to achieve their purpose. In this study, multi-walled carbon nanotubes (MWNTs) were dispersed into an epoxy matrix using polyethylenimine (PEI) as a dispersant that was either covalently attached to the nanotubes or physically mixed to result in only noncovalent interaction. Epoxy composites containing covalently modified MWNTs exhibited greater storage modulus and reduced electrical conductivity.
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    The influence of Fe3O4@GNP hybrids on enhancing the EMI shielding effectiveness of epoxy composites in the X-band
    (Elsevier, 2020-07) Etika, Krishna Chitanya
    In this work, the electromagnetic interference (EMI) shielding effectiveness in the X band frequency range of 8–12.4 GHz of epoxy nanocomposites containing Fe3O4 nanoparticles decorated graphene nanoplatelets (i.e., Fe3O4@GNP hybrids) is investigated. The hybrid nanostructures were synthesized in situ by a simple co-precipitation technique and were incorporated into the epoxy matrix by melt blending following a solvent-less approach. Scanning electron microscopy performed on the hybrid nanostructures revealed a good distribution of Fe3O4 nanoparticles on the GNP sheets in the hybrid. A series of epoxy nanocomposites containing varying content of Fe3O4@GNP, GNP and/or Fe3O4 nanoparticles were synthesized and compared for their EMI shielding effectiveness. The SEM of the composite cross-section reveals good filler dispersion in the composites. Overall the nanocomposites containing Fe3O4@GNP hybrids exhibited enhanced EMI shielding performance when compared to samples containing equivalent loading of only GNP and/or Fe3O4. The 1 mm thick composite sample containing 1:3 (wt/wt) Fe3O4: GNP hybrid attenuated 89 % of incident wave power and exhibited an EMI shielding effectiveness value of 9.6 dB in the X-band.
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    Facile One-Pot Hydrothermal Synthesis of Copper Nanowires and Their Impact on the EMI Shielding Capability of Epoxy Composites
    (Wiley, 2021-11) Etika, Krishna Chitanya
    In this work epoxy nanocomposites containing varying content of copper nanowires (CuNW) were produced. The CuNW were synthesized using a facile one-pot hydrothermal synthesis method. The composites were characterized for their electrical conductivity and electromagnetic interference (EMI) shielding effectiveness in the X-band. The electrical conductivity of the epoxy composites was measured, and the composites containing 12 wt % CuNW demonstrated percolated behavior and exhibited a frequency-independent conductivity value of 1.76 × 10−6 S m−1 in the range of 25–200 Hz. The 12 wt % CuNW sample demonstrated an EMI shielding effectiveness value of 6.5 dB, which corresponds to 77.1 % attenuation of the incident electromagnetic wave. Furthermore, an absorption-dominated shielding mechanism was observed in these composites.
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    Environmentally friendly low-cost graphene oxide-cellulose nanocomposite
    (Elsevier, 2022-07) Etika, Krishna Chitanya
    This study primarily aims to develop a simple, cost-effective, eco-friendly nanocomposite filter for dye removal by adsorption. In this work, graphite oxide and graphene oxide were synthesized using a modified Hummers’ process and used to fabricate nanocomposite filters by co-precipitation reactions. Scanning electron microscopy and X-ray diffraction were performed on nanofillers revealing crystallographic and morphological properties of the nanofillers.
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    The influence of hybrid decorated structures on the EMI shielding properties of epoxy composites over the X-Band
    (Elsevier, 2023) Etika, Krishna Chitanya
    This work primarily focuses on electromagnetic interference (EMI) shielding characteristics of copper microparticles (CuMP), Fe3O4@CuMP, and Fe3O4 nanoparticles filled epoxy composites across the X-band. The Fe3O4@CuMP hybrids were synthesized through the water-based coprecipitation technique and analyzed by EDS and SEM. The SEM analysis of the hybrids demonstrated an excellent deposition of Fe3O4 particles on the surface of CuMP. The EDS analysis of the hybrids exhibited Cu, Fe, and O elements present in the hybrid powder sample. A set of epoxy composites containing hybrids, CuMP, and Fe3O4 particles were prepared through a resin blending technique, and its electrical and EMI shielding properties were investigated. The 12 wt% CuMP-filled epoxy composites demonstrate a frequency-dependent electrical conductivity value of 3.8 × 10−9 S/cm at 25 Hz. However, the epoxy composites containing Fe3O4@CuMP hybrids did not show a percolated electrical network and exhibited lower conductivity values than the 12 wt% CuMP-filled epoxy composite. Moreover, the hybrid composites exhibited better EMI shielding effectiveness than CuMP-filled epoxy composites containing equivalent filler loading of CuMP (i.e., 12 wt%). The hybrid composite of 1 mm thick filled with 8:12 (wt%/wt%) Fe3O4:CuMP attenuated 83.4 % of EM wave power and exhibited a SET value of 7.9 dB across X-band of 8–12.4 GHz.
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    Large microwave absorption By Fe3O4@CuNW hybrid nanoparticles filled epoxy nanocomposites in the X-Band
    (Elsevier, 2023-03) Etika, Krishna Chitanya
    Microwave absorbing materials (MAM) are in great demand for various applications in both defense and commercial sectors. Polymer composites with tailorable properties have great potential for use as MAM owing to their low density, ease of processing, and low cost. In this work, the microwave absorption by epoxy composites containing, Fe3O4 nanoparticles deposited on the copper nanowires (i.e., Fe3O4@CuNW hybrid), copper nanowires (CuNW), and/or Fe3O4 nanoparticles were investigated for the first time. A set of epoxy composites with different filler loadings were prepared using a solvent-free resin blending method and were characterized for their morphological, surface composition, electrical, dielectric, magnetic, and microwave absorbing properties. The electrical conductivity values of the samples were measured, and the non-hybrid composites demonstrated percolated behavior, whereas hybrid samples exhibited non-percolated behavior. The non-hybrid composite containing 12 wt. % CuNW and 8 wt. % Fe3O4 exhibited the highest electrical conductivity value of 9.8 × 10−5 s/m compared to all other composites. The dielectric and magnetic losses obtained in the hybrid composites are higher than in non-hybrid composites. Furthermore, the hybrid composites containing 12 wt. % CuNW and 8 wt. % Fe3O4 exhibited the highest dielectric loss of 0.9 and magnetic loss of 1.4 as compared to other composites. The hybrid epoxy composites exhibited significantly large absorption with minimal reflections of microwaves as compared to non-hybrid composites containing equal loadings of CuNW or Fe3O4. The hybrid composites containing 12 wt. % CuNW and 2 wt. % Fe3O4 exhibited low reflection power of 26 % and high absorption power of 64 % of the incident microwave as compared to all other composites. The one-millimeter thick hybrid composite filled with 12:8 (wt. %/wt. %) CuNW: Fe3O4 sample demonstrated EMI shielding effectiveness of 19.3 dB and absorbed 60 % of the microwave power over the X-band frequency range of 8–12.4 GHz.
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    Tailoring Properties of Carbon Nanotube Dispersions and Nanocomposites Using Temperature-Responsive Copolymers of Pyrene-Modified Poly(N-cyclopropylacrylamide)
    (ACS, 2010-10-25) Etika, Krishna Chitanya
    Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Stimuli-responsive polymers show conformational changes with an applied external stimulus (pH, temperature, light, etc.). The dispersion of carbon nanotubes by thermoresponsive polymers is shown to enable the macroscopic properties of aqueous suspensions to be tailored as a function of temperature. This work presents the synthesis, characterization, and use of temperature-responsive poly(N-cyclopropylacrylamide) (PNCPA) polymers containing 1, 3, and 5 mol % pyrene-bearing repeat units to tailor the dispersion state of single-walled carbon nanotubes (SWNT) in water. Turbidity measurements show that the lower critical solution temperature (LCST) of PNCPA decreases with increasing pyrene content. Viscosity measurements on aqueous SWNT suspensions stabilized with pyrene-functionalized PNCPA show highly entangled and well-dispersed nanotube microstructure above and below the LCST of the polymer, respectively. UV−vis spectra also confirm that nanotube stabilization by these polymers is dependent upon the pyrene content. Drying of these suspensions produces composites whose microstructure and electrical conductivity vary with drying temperature and pyrene content of the stabilizing polymer. This temperature-dependent dispersion behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems.
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    Tailored dispersion of carbon nanotubes in water with pH-responsive polymers
    (Elsiever, 2010-04-06) Etika, Krishna Chitanya
    In an effort to control the level of carbon nanotube exfoliation in water, pH-responsive polymers (i.e., weak polyelectrolytes) have been used as stabilizers in water. This noncovalent functionalization of single-walled carbon nanotubes (SWNTs) results in suspensions whose dispersion state can be altered by simply changing pH. In this study poly(acrylic acid), poly(methacrylic acid), poly(allylamine) and polyethyleneimine were used to stabilize aqueous SWNT suspensions. The results indicate that SWNTs stabilized with these polymers show a pH tailorable exfoliation and bundling in water, as evidenced by cryo-TEM images and shifts in suspension viscosity. Composite films prepared by drying these aqueous suspensions suggest that nanotube microstructure in the liquid state is largely preserved in the solid composites, with more bundled/networked structures showing higher electrical conductivity. A stabilization mechanism based upon the results obtained is proposed to explain the exfoliation and aggregation behavior of SWNTs. This method of controlling the microstructure of SWNTs in liquid state with pH could have a significant impact on the ability to tailor the microstructure and properties of composites.
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    Temperature Controlled Dispersion of Carbon Nanotubes in Water with Pyrene-Functionalized Poly(N-cyclopropylacrylamide)
    (ACS, 2009) Etika, Krishna Chitanya
    Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Poly(N-cyclopropylacrylamide), containing 5 mol % pyrene-bearing repeat units (p-PNCPA), is shown to vary the dispersion state of single-walled carbon nanotubes (SWNTs) in water. This is a thermo-responsive polymer whose conformation changes with temperature, which in turn leads to changes in the nanotube dispersion state. Cryo-TEM micrographs show that SWNTs stabilized using p-PNCPA transitions from a more exfoliated to a more bundled state as the aqueous suspension temperature is raised above the lower critical solution temperature (LCST) of the polymer (∼30 °C). Viscosity measurements on SWNT/p-PNCPA aqueous suspensions show shear thinning and near Newtonian behavior at 10 and 50 °C, respectively. Drying of these suspensions produces composites whose microstructure and electrical conductivity vary with drying temperature. This behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems.