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  1. Abstract

    Cross‐linking polymethylhydrosiloxane (PMHS) with divinylthiophene (DVT) via hydrosilylation in highly dilute conditions and subsequent supercritical drying in CO2yield a polymeric aerogel containing aromatic sulfur integrally and uniformly distributed throughout the monolith. Fourier‐transform infrared (FT‐IR) spectroscopy indicates almost complete consumption of vinyl groups and SiH bonds in the product. Both FT‐IR and Raman spectroscopic analyses support loss of conjugation of vinyl groups with the retained double bonds of the thiophene ring. Scanning electron microscopy (SEM) indicates a condensed colloidal structure with characteristic particulate diameters of about 165 nm. SEM coupled with energy dispersive X‐ray spectroscopy elemental mapping shows that sulfur is distributed homogeneously in the polymeric aerogel. Porosimetry of the mesoporous aerogel indicates the effective average pore diameters are about 12 nm. Thermogravimetric analysis (TGA) establishes greater thermal stability of the PMHS‐DVT product than either of the pure unreacted components. TGA coupled with mass spectrometric (TG‐MS) identification of the volatiles released during pyrolysis shows that sulfur is driven from the cross‐linked polymer as thiophene and its derivatives. Recorded mass spectra support the hypothesis that cross‐linking DVT bridges between PMHS chains in the polymeric aerogel, and that this results in a more thermally stable monolith.

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  2. The advent of a new vacuum ultraviolet (VUV) spectroscopic absorption detector for gas chromatography has enabled applications in many areas. Theoretical simulations of VUV spectra using computational chemistry can aid the new technique in situations where experimental spectra are unavailable. In this study, VUV spectral simulations of paraffin, isoparaffin, olefin, naphthene, and aromatic (PIONA) compounds using time-dependent density functional theory (TDDFT) methods were investigated. Important factors for the simulations, such as functionals/basis sets and formalism of oscillator strength calculations, were examined and parameters for future PIONA compound simulations were obtained by fitting computational results to experimental spectra. The simulations produced satisfactory correlations between experimental observations and theoretical calculations, and enabled potential analysis applications for complex higher distillate fuels, such as diesel fuel. Further improvement of the methods was proposed. 
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  3. The present study introduces a facile single-source precursor preparative access to bamboo-like multiwalled carbon nanotubes (MWCNTs) highly dispersed within a mesoporous silica-rich matrix. The metal-free single-source precursor was synthesized via a one-pot sol–gel process using tetramethyl orthosilicate (TMOS) and 4,4′-dihydroxybiphenyl (DHBP) and converted subsequently via pyrolysis under an argon atmosphere into MWCNT/silica nanocomposites. The in situ segregation of the highly defective bamboo-like MWCNTs was carefully investigated and has been shown to occur within the mesopores of the silica-rich matrix at relatively low temperatures and without the use of a metal catalyst. The experimental results have been supported by extensive computational simulations, which correlate the molecular architecture of the single-source precursor with the structural features of the carbon phase segregating from the silica matrix. Furthermore, the role of hydrogen in the stability of the prepared nanocomposites as well as in the high-temperature evolution and morphology of the segregated MWCNTs has been discussed based on vibrational spectroscopy, calorimetric studies and empirical potential calculations. The results obtained within the present study may allow for designing highly-defined nanocarbon-containing composites with tailored structural features and property profiles. 
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  4. We investigate the impact of solvents on the microstructure of poly(methylhydrosiloxane)/divinylbenzene (PMHS/DVB) aerogels. The gels are obtained in highly diluted conditions via hydrosilylation reaction of PMHS bearing Si-H groups and cross-linking it with C=C groups of DVB. Polymer aerogels are obtained after solvent exchange with liquid CO2 and subsequent supercritical drying. Samples are characterized using microscopy and porosimetry. Common pore-formation concepts do not provide a solid rationale for the observed data. We postulate that solubility and swelling of the cross-linked polymer in various solvents are major factors governing pore formation of these PMHS/DVB polymer aerogels. 
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