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H J Byrne

Publications and source records attributed to H J Byrne.

4 recordsLinked to original sources
PubMed2006

Bundling and diameter selectivity in HiPco SWNTs poly(p-phenylene vinylene-co-2,5-dioctyloxy-m-phenylene vinylene) composites.

Temperature-dependent (TD) Raman measurements at laser excitation 514.5 nm were performed at different concentrations. The spectral profile of the radial breathing modes were investigated up to a polymer concentration of 1 g/L and were found to be dominated by approximately 1.2-1.4 nm diameter tubes at room temperature. Upon heating above the glass transition of the polymer (60 degrees C) the smaller tubes around approximately 0.9 nm increased significantly in relative intensity. This suggests that below the glass transition of the polymer (60 degrees C) RBMs within the composite are damped and spectral changes cannot be interpreted as diameter selective solubilization. The observed RBM damping at room temperature only occurred up to a concentration of approximately 1.2 x 10(-4) g/L and below this no damping was observed. Photoluminescence intensity (PL) measurements were taken for a range of PmPV concentrations, in which HiPco single walled carbon nanotubes (SWNTs) at 100%, 10%, 1%, 0.1%, 0.01%, and 0% mass fractions were added. Fitting of the concentration dependence to a dynamic absorption/desorption model indicates that the polymer interacts with nanotube bundles until a critical concentration of approximately 1.2 x 10(-4) g/L is reached, below which the nanotubes are isolated. The polymer and or solvent has a significant effect on the debundling and aggregation within these systems. Aggregation and/or interaction with the polymer at higher concentrations can effect the RBM profile in the composite at ambient temperatures, providing an incomplete representation of the selection of diameters present within composites at a particular wavelength.

Journal Article↗
PubMed2005

Temperature-induced nucleation of poly(p-phenylene vinylene-co-2,5-dioctyloxy-m-phenylene vinylene) crystallization by HiPco single-walled carbon nanotubes.

Hybrid systems of the conjugated organic polymer poly(p-phenylene vinylene-co-2,5-dioctyloxy-m-phenylene vinylene)(PmPV) and HiPco single-walled carbon nanotubes (SWNTs) are explored using spectroscopic and thermal techniques to determine specific interactions. Vibrational spectroscopy indicates a weak interaction, and this is further elucidated using differential scanning calorimetry (DSC), confocal laser scanning microscopy, temperature-dependent Raman spectroscopy, and temperature-dependent infrared spectroscopy of the raw materials and the composite. An endothermic transition is observed in the DSC of both the polymer and the 0.1% HiPco composite in the region of 50 degrees C. Also observed in the DSC of the composite is a double-peaked endotherm at -39 and -49 degrees C, which does not appear in the polymer. The Raman spectroscopy of the polymer upon increasing the temperature to 60 degrees C shows a diminished cis-vinylene mode at 1575 cm(-1), with an increase in relative intensity of the trans-vinylene mode at 1630 cm(-1). Partially irreversible change in isomerization suggests increased order in the polymer. This change in the polymer is also manifest in the Raman composite spectrum upon increase of the temperature to 60 degrees C, where the spectrum becomes abruptly dominated by nanotubes. Raman spectroscopy of the composite shows no change at -35 degrees C; however, infrared absorption measurements suggest that the transition at -35 degrees C derives from the polymer side chains. Here the composite at -35 degrees C shows a change in the absorbance of the polymer side chain aryl-oxide linkage at 1250 cm(-1) and alkyl-oxide stretch at 1050 cm(-1). Infrared spectra thus suggest that the transitions in the lower temperature region around -35 degrees C are side chain-induced, while Raman spectra suggest that the transition at 60 degrees C is backbone-induced. Furthermore, temperature cycling induces an irreversible decrease in the mean fluorescence intensity of the polymer, coupled with a further reduction in the mean fluorescence intensity of the composite. This suggests that an increase in crystallization of the composite is supported and enhanced by an increase in ordering of the polymer. Implications are discussed.

Journal Article↗