Browsing by Author "Hameed, N"

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    Dispersing single-walled carbon nanotubes in ionic liquids: a quantitative analysis
    (Royal Society of Chemistry, 2013-08-15) Hameed, N; Church, JS; Salim, NV; Hanley, TL; Amini, A; Fox, BL
    The efficiency of various ionic liquids, specifically the 1-butyl-3-methylimidazolium tetrafluoroborate, hexafluorophosphate, chloride and dicyanamide salts, in dispersing single walled carbon nanotubes has been examined. The SWCNTs were dispersed in the ILs at varying concentrations by grinding. All of the ILs were found to be effective dispersants for nanotubes and quantitative evidences including X-ray scattering, Raman spectroscopy and UV-visible spectroscopy unambiguously showed that BMIM[BF4] is the most efficient IL while BMIM[DCA] is the least effective IL. A quantitative analysis of the interactions between SWCNTs and ionic liquids by analyzing their scattering and spectral features is put forth.© 2013, The Royal Society of Chemistry.
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    Hydrogen bonding interactions, crystallization, and surface hydrophobicity in nanostructured epoxy/block copolymer blends
    (Wiley-Blackwell, 2010-04-01) Hameed, N; Guo, QP; Hanley, TL; Mai, YW
    Hydrogen bonding interactions, phase behavior, crystallization, and surface hydrophobicity in nanostructured blend of bisphenol A-type epoxy resin (ER), for example, diglycidyl ether of bisphenol A (DGEBA) and poly(-caprolactone)-block-poly(dimethyl siloxane)-block-poly(-caprolactone) (PCL-PDMS-PCL) triblock copolymer were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, transmission electron microscopy, small-angle X-ray scattering, and contact angle measurements. The PCL-PDMS-PCL triblock copolymer consisted of two epoxy-miscible PCL blocks and an epoxy-immiscible PDMS block. The cured ER/PCL-PDMS-PCL blends showed composition-dependent nanostructures from spherical and worm-like microdomains to lamellar morphology. FTIR study revealed the existence of hydrogen bonding interactions between the PCL blocks and the cured epoxy, which was responsible for their miscibility. The overall crystallization rate of the PCL blocks in the blend decreased remarkably with increasing ER content, whereas the melting point was slightly depressed in the blends. The surface hydrophobicity of the cured ER increased upon addition of the block copolymer, whereas the surface free energy (γs) values decreased with increasing block copolymer concentration. The hydrophilicity of the epoxy could be reduced through blending with the PCL-PDMS-PCL block copolymer that contained a hydrophobic PDMS block. © 2010, Wiley-Blackwell.
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    Individual dispersion of carbon nanotubes in epoxy via a novel dispersion-curing approach using ionic liquids
    (Royal Society of Chemistry, 2013-01-01) Hameed, N; Salim, NV; Hanley, TL; Sona, M; Fox, BL; Guo, Q
    The effective dispersion of carbon nanotubes (CNTs) in a thermoset was achieved using ionic liquid as the dispersion-curing agent. We preferentially dispersed multiwalled carbon nanotubes (MWCNTs) down to individual tube levels in epoxy resin. Here the dispersion is ruled by the depletion of physical bundles within the MWCNT networks, for which molecular ordering of ionic liquids is considered responsible. The quantitative analyses using ultra small angle X-ray scattering (USAXS) confirmed the dispersion of individual MWCNTs in the matrix. The distance between the dispersed nanotubes was calculated at different nanotube loadings using the power law fitting of the USAXS data. The fine dispersion and subsequent curing, both controlled by ionic liquid, lead to composites with substantially enhanced fracture mechanical and thermomechanical properties with no reduction in thermal properties. Merging processing techniques of nanocomposites with ionic liquid for efficient dispersion of nanotubes and preferential curing of thermosets facilitates the development of new, high performance materials. © 2013, Royal Society of Chemistry
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    Microphase separation induced by competitive hydrogen bonding interactions in semicrystalline triblock copolymer/homopolymer complexes
    (Royal Society of Chemistry, 2013-01-01) Salim, NV; Hameed, N; Hanley, TL; Guo, QP
    Microphase separation through competitive hydrogen bonding interactions in ABC/D triblock copolymer/homopolymer complexes is studied for the first time. This study investigated self-assembled nanostructures that are obtained in the bulk, by the complexation of a semicrystalline polystyrene-block-poly(4-vinylpyridine)-block-poly(ethylene oxide) (SVPEO) triblock copolymer with a poly(4-vinyl phenol) (PVPh) homopolymer in tetrahydrofuran (THF). In these complexes, microphase separation takes place due to the disparity in intermolecular interactions among PVPh/P4VP and PVPh/PEO pairs. At low PVPh concentrations, PEO interacts relatively weakly with PVPh, whereas in the complexes containing more than 30 wt% PVPh, the PEO block interacts considerably with PVPh, leading to the formation of composition-dependent nanostructures. SAXS and TEM results indicate that the cylindrical morphology of a neat SVPEO triblock copolymer changes into lamellae structures at 20 wt% of PVPh then to disordered lamellae with 40 wt% PVPh. Wormlike structures are obtained in the complex with 50 wt% PVPh, followed by disordered spherical microdomains with size in the order of 40-50 nm in the complexes with 60-80 wt% PVPh. Moreover, when the content of PVPh increases to 80 wt%, the complexes show a completely homogenous phase of PVPh/P4VP and PVPh/PEO with phase separated spherical PS domains. The fractional crystallization behavior in SVPEO and complexes at lower PVPh content was also examined. A structural model was proposed to explain the microphase separation and self-assembled morphologies of these complexes based on the experimental results obtained. The formation of nanostructures and changes in morphologies depend on the relative strength of hydrogen bonding interactions between each component block of the copolymer and the homopolymer. © 2013, Royal Society of Chemistry
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    Nanofibrillar micelles and entrapped vesicles from biodegradable block copolymer/polyelectrolyte complexes in aqueous media
    (ACS Publications, 2013-07-09) Salim, NV; Hameed, N; Hanley, TL; Waddington, LJ; Hartley, PG; Guo, Q
    Here we report a viable route to fibrillar micelles and entrapped vesicles in aqueous solutions. Nanofibrillar micelles and entrapped vesicles were prepared from complexes of a biodegradable block copolymer poly(ethylene oxide)-block-poly(lactide) (PEO-b-PLA) and a polyelectrolyte poly(acrylic acid) (PAA) in aqueous media and directly visualized using cryogenic transmission electron microscopy (cryo-TEM). The self-assembly and the morphological changes in the complexes were induced by the addition of PAA/water solution into the PEO-b-PLA in tetrahydrofuran followed by dialysis against water. A variety of morphologies including spherical wormlike and fibrillar micelles, and both unilamellar and entrapped vesicles, were observed, depending on the composition, complementary binding sites of PAA and PEO, and the change in the interfacial energy. Increasing the water content in each [AA]/[EO] ratio led to a morphological transition from spheres to vesicles, displaying both the composition- and dilution-dependent micellar-to-vesicular morphological transitions. © 2013, American Chemical Society.
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    Reactive block copolymer modified thermosets: highly ordered nanostructures and improved properties
    (Royal Society of Chemistry, 2010-12-21) Hameed, N; Guo, Q; Xu, ZG; Hanley, TL; Mai, YW
    A highly ordered poly(dimethyl siloxane)-poly(glycidyl methacrylate) (PDMS-PGMA) reactive diblock copolymer was synthesized and used to modify bisphenol A-type epoxy resin (ER). The PDMS-PGMA block copolymer consisted of epoxy-miscible PGMA blocks and an epoxy-immiscible PDMS block. The PGMA reactive block of the block copolymer formed covalent bonds with cured epoxy and was involved in the network formation, and the PDMS block phase separated to give different ordered and disordered nanostructures at different blend compositions. The solvent cast PDMS-PGMA diblock copolymer showed ordered hexagonal cylindrical morphology. A highly ordered morphology consisting of hexagonal cylinders inside the lamellar morphology was observed in the cured PDMS-PGMA block copolymer. In the cured ER/PDMS-PGMA blends, a variety of morphologies including lamellar, cubic and worm-like and spherical nanostructures were detected depending on the blend composition. Moreover, the addition of this reactive diblock copolymer significantly increases the hydrophobicity and the glass transition temperature. It also improves the tensile strength and tensile ductility of the nanostructured thermosets at low diblock copolymer contents. © 2010, Royal Society of Chemistry