Controlling the Oligomeric Composition of Carbon‐Fiber Precursors by Dense‐Gas Extraction

Cervo, Eduardo G.; Thies, Mark C.; Fathollahi, Bahram

doi:10.1111/j.1551-2916.2007.02214.x

Cited by 10 publications

(9 citation statements)

References 17 publications

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“…Progress in graphene synthesis has led to increased interest in the assembly of graphene into superstructures, and to the fabrication of novel ordered materials from graphene or engineered graphenic molecular building blocks 1–8. Graphene monolayers typically deposit flat on substrates or associate face‐to‐face to form horizontal stacked papers or multilayer coatings 8–11.…”

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confidence: 99%

Vertically Aligned Graphene Layer Arrays from Chromonic Liquid Crystal Precursors

et al. 2010

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Progress in graphene synthesis has led to increased interest in the assembly of graphene into superstructures, and to the fabrication of novel ordered materials from graphene or engineered graphenic molecular building blocks. [1][2][3][4][5][6][7][8] Graphene monolayers typically deposit fl at on substrates or associate face-to-face to form horizontal stacked papers or multilayer coatings. [8][9][10][11] The opposite structure, vertically aligned graphene layer arrays on substrates ( Figure 1 A ), are more diffi cult to fabricate, but are expected to show a range of unique properties and behaviors. Their high concentration of edge-sites at the top surface would allow functionalization at high density for superhydrophobic/ philic coatings, high-redox-activity electrode surfaces, or chemically patterned surfaces for cell adhesion and guidance. The vertical layer orientation would allow rapid intercalation and deintercalation of lithium in high-discharge-rate thin fi lm batteries, [ 12 ] and would provide high Z -directional thermal/electrical conductivity. If also ordered in a second dimension, such arrays would be anisotropic in the substrate plane and provide unidirectional in-plane heat spreading or optical polarization. If the heights of arrays can be limited to below 50 nm, they may fi nd application as transparent conductive fi lms, [ 10 , 13 ] or as graphene nanoribbons where the ribbon width is set by the array height. Here we use chromonic liquid crystal precursors to fabricate vertically aligned graphene layer arrays (VAGLAs) on substrates and also demonstrate a method to achieve full two-dimensional order, which we defi ne as further control of graphene layer orientational patterns within the substrate plane using local shear-forces. We also demonstrate one example of a unique property of these arrays -the ability to etch Zdirectional nanopores by catalytic hydrogenation, in which cobalt nanoparticles tunnel vertically into and through the arrays as they track vertically receding edge-plane surfaces.A promising route to the desired vertical graphene array structure is one based on polyaromatic precursors, [ 2 ] which can adopt edge-on orientation on substrates. [ 5 , 14 , 15 ] Many polyaromatic compounds, however, do not retain supramolecular alignment upon carbonization, and also their solution or vapor deposition typically gives only short-range order in-plane. [ 2 ] Liquid crystal phases offer long-range order, but most discotic phases are high-temperature viscous liquids that are diffi cult to process and their supramolecular order can also be unstable during carbonization. [ 1 ] A promising solution to these challenges are so-called "chromonic liquid crystals" (CLCs), which combine graphenic disk assembly with water solubility. CLCs are formed from water soluble organic dyes which form massive π -stacks in aqueous solution that act as supramolecular rods. These structures then order into nematic liquid crystal phases through rod self-avoidance at high concentration [ 1 , 16-18 ]

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Vertically Aligned Graphene Layer Arrays from Chromonic Liquid Crystal Precursors

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“…The overall mol wt distribution of the dimer fraction is also approximately Gaussian, and the most prevalent species are consistent with combination of the most common monomer species via condensation, with the accompanying loss of 4-6 hydrogens. In previous work [11], we have shown that mesophase pitches which contain up to 25 mol % dimer can be produced by fractionation of M-50 pitch via DGE. Thus, to our knowledge this study represents the first time that researchers have proposed specific, "nonaverage" molecular structures that are significant constituents in mesophase pitch.…”

Section: Discussionmentioning

confidence: 96%

“…As would be expected, higher operating pressures increase the density of the solvent and increase the average mol wt of the overhead extract. However, column operating temperature has been found to exhibit more complex behavior, with the establishment of a positive temperature gradient from the bottom to the top of the column yielding the best product purities [11]. A liquid-level detector at the bottom of the column operates based on the difference in electrical resistivity between the top and bottom phases and ensures complete separation between the solvent-rich top phase and pitch-rich bottom phase.…”

Section: Dense-gas Extraction Apparatus and Proceduresmentioning

confidence: 99%

“…Thies and co-workers [8][9][10] have recently developed a technique, known as dense-gas extraction (DGE), for separating pitches into fractions of relatively narrow mol wt. Such fractions can serve as standards for additional characterization work; in addition, we are investigating their large-scale production via DGE as "designer" pitches whose molecular compositions are tailored for a given, final carbon product application [11]. In this work, we report on the use of DGE to fractionate a commercially available petroleum pitch, M-50 pitch (Marathon Petroleum Company LLC), into its oligomeric constituents.…”

Section: Introductionmentioning

confidence: 99%

“…Only in recent years have researchers [11][12] developed the ability to monitor the molecular weight distribution (MWD) of a given pitch separation process via MALDI. Thus, DGE conditions were manipulated until monomer-and dimer-rich cuts of the desired purity were obtained.…”

Section: Introductionmentioning

confidence: 99%

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