1,720,959 research outputs found
Modifying the Electronic Properties of Single-Walled Carbon Nanotubes using Designed Surfactant Peptides
No full textThe electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino acid sequence of X(Valine) 5(Lysine) 2, where X indicates an aromatic amino acid containing either an electron-donating or electron-withdrawing functional group (i.e. p-amino-phenylalanine or p-cyano-phenylalanine). Circular dichroism spectra showed that the surfactant peptides primarily have random coil structures in an aqueous medium, both alone and in the presence of SWCNTs, simplifying analysis of the peptide/SWCNT interaction. The ability of the surfactant peptides to disperse individual SWCNTs in solution was verified using atomic force microscopy and ultraviolet-visible-near-infrared spectroscopy. The electronic properties of the surfactant peptide/SWCNT composites were examined using the observed nanotube Raman tangential band shifts and the observed additional features near the Fermi level in the scanning tunneling spectroscopy dI/dV spectra. The results revealed that SWCNTs functionalized with surfactant peptides containing electron-donor or electron-acceptor functional groups showed n-doped or p-doped altered electronic properties, respectively. This work unveils a facile and versatile approach to modify the intrinsic electronic properties of SWCNTs using a simple peptide structure, which is easily adaptable to obtain peptide/SWCNT composites for the design of tunable nanoscale electronic devices
A Carbon Nanotube-based Raman-imaging Immunoassay For Evaluating Tumor Targeting Ligands
No full textHerein, we describe a versatile immunoassay that uses biotinylated single-walled carbon nanotubes (SWNTs) as a Raman label, avidin-biotin chemistry to link targeting ligands to the label, and confocal Raman microscopy to image whole cells. Using a breast tumor cell model, we demonstrate the usefulness of the method to assess membrane receptor/ligand systems by evaluating a monoclonal antibody, Her-66, known to target the Her2 receptors that are overexpressed on these cells. We present two-dimensional Raman images of the cellular distribution of the SWNT labels corresponding to the distribution of the Her2 receptors in different focal planes through the cell with validation of the method using immunofluorescence microscopy, demonstrating that the Her-66-SWNT complexes were targeted to Her2 cell receptors.
Fabrication and Characterization of Aging Resistant Carbon Molecular Sieve Membranes for C₃ Separation Using High Molecular Weight Crosslinkable Polyimide, 6FDA-DABA
No full textDue to copyright restrictions full text access from Treasures at UT Dallas is restricted to current UTD affiliates (use the provided Link to Article).Although propylene/propane separation remains a challenge for industrial processes, carbon molecular sieve membranes (CMSMs) have the potential to replace traditional separation methods. A high molecular weight crosslinkable polyimide was utilized to fabricate CMSMs, which showed pure gas permeabilities in excess of 400 barrers with propylene/propane selectivities as high as 25. Mixed gas (C₃H₈:C₃H₆ 50:50) measurements yielded a propylene permeability of 257 barrers and a selectivity of 20. CMSMs from thermally precrosslinked polymer precursors demonstrated a 98% propylene permeability retention after aging for 20 days under vacuum. Active gas flow conditions resulted in slightly lower permeability retention (92.5%) after 15 days of testing. ©2019 Elsevier B.V.NSF (CBET-1403950)School of Natural Sciences and Mathematic
Prevention of Physical Aging within Carbon Molecular Sieve Membranes for Gas Separations
No full textCarbon molecular sieve membranes (CMSMs) are a subclass of porous materials with the ability
to perform molecular sieving. Controlling the jump lengths from one pore to another allows for
enhanced permselectivity of such membranes. This control makes CMS materials extraordinarily
attractive for gas separations, in comparison to state-of-the-art polymeric membranes that separate
molecules based primarily on sorption-diffusion. This work considers the recent progress in the
development of carbon membranes as well as limitations that prevent their commercialization, in
particular the rapid onset of aging that occurs with CMSMs. Various aspects of how properties of
a CMSM may change over time and how important it is to find the optimum starting materials and
process conditions to minimize aging are addressed within. Conditions which affect the
performance of CMSMs and current preparation methods are explored and aligned with future
research needed to achieve commercially viable CMSMs.
Chapter 1 summarizes the history and applicability of CMSMs along with their ability to surpass
commercially used polymeric membranes for gas separations. A focus on their limitations,
primarily physical aging, is addressed along with current endeavors to mitigate it.
Chapter 2 explicates the novel use of metal nanoparticles in CMSMs to scaffold membranes’
inherent pore structure to minimize aging. The in-situ formation of copper nanoparticles within
polymer of intrinsic microporosity-1 (PIM-1) was studied via transmission electron microscopy
and gas permeation.
Chapter 3 describes the synthesis of tailored metal pillars which can be used for various polymeric
precursors, including Matrimid® 5218 and PIM-1. The tunability of the size of the metal
nanoparticles provides a more universal approach to reduce physical aging within CMSMs that
can be monitored by means of gas permeation
Immiscible Polymer Blend Membranes for High Pressure, High Temperature H2/CO2 Separation
No full textHigh pressure and high temperature separation of H2/CO2 is of great interest for clean energy generation in processes such as coal gasification. Flat and tubular membranes of the polybenzimidazole (PBI)/6FDA-DAM immiscible blend containing colloidal ZIF-8 were prepared to test the gas separation performance of single gases and the H2/CO2 gas mixture at various pressures and temperatures. It was found that the amount of colloidal ZIF-8 in the blend has a remarkable effect on membrane morphology and gas separation. An increase of the loading for the colloidal ZIF-8 in the blend leads to a decrease in the size for the dispersed 6FDA-DAM domains. A higher experimental temperature resulted in higher gas permeance through the membrane, while the gas selectivity remained constant. At 30 atm and 300 °C, a 5% colloidal ZIF-8 PBI/6FDA-DAM membrane exhibited a H2 permeance of 29.52 GPU (approximately 472 Barrer), an ideal H2/CO2 selectivity of 17.4, and a H2/CO2 gas mixture selectivity of 12.8. In comparison to other membranes, this polymer blend membrane shows high gas permeance and high gas selectivity, and it surpasses the upper bound of the 2008 Robeson plot for H2/CO2
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Novel Zeolitic Imidazolate Framework/Polymer Membranes for Hydrogen Separations in Coal Processing
Get PDFNanoparticles of zeolitic imidazolate frameworks and other related hybrid materials were prepared by modifying published synthesis procedures by introducing bases, changing stoichiometric ratios, or adjusting reaction conditions. These materials were stable at temperatures >300 °C and were compatible with the polymer matrices used to prepare mixed-matrix membranes (MMMs). MMMs tested at 300 °C exhibited a >30 fold increase in permeability, compared to those measured at 35 °C, while maintaining H{sub 2}/CO{sub 2} selectivity. Measurements at high pressure (up to 30 atm) and high temperature (up to 300 °C) resulted in an increase in gas flux across the membrane with retention of selectivity. No variations in permeability were observed at high pressures at either 35 or 300 °C. CO{sub 2}-induced plasticization was not observed for Matrimid®, VTEC, and PBI polymers or their MMMs at 30 atm and 300 °C. Membrane surface modification by cross-linking with ethylenediamine resulted in an increase in H{sub 2}/CO{sub 2} selectivity at 35 °C. Spectrometric analysis showed that the cross-linking was effective to temperatures <150 °C. At higher temperatures, the cross-linked membranes exhibit a H2/CO2 selectivity similar to the uncrosslinked polymer
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