Browsing by Author "Behabtu, Natnael"

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    Dissolution of graphite, graphite and graphene nanoribbons in superacid solutions and manipulation thereof
    (2017-01-03) Tour, James M.; Pasquali, Matteo; Behabtu, Natnael; Lomeda, Jay R.; Kosynkin, Dmitry V.; Duque, Amanda; Green, Micah J.; Parra-vasquez, A. Nicholas; Young, Colin; Rice University; United States Patent and Trademark Office
    Methods for dissolving carbon materials such as, for example, graphite, graphite oxide, oxidized graphene nanoribbons and reduced graphene nanoribbons in a solvent containing at least one superacid are described herein. Both isotropic and liquid crystalline solutions can be produced, depending on the concentration of the carbon material The superacid solutions can be formed into articles such as, for example, fibers and films, mixed with other materials such as, for example, polymers, or used for functionalization of the carbon material. The superacid results in exfoliation of the carbon material to produce individual particles of the carbon material. In some embodiments, graphite or graphite oxide is dissolved in a solvent containing at least one superacid to form graphene or graphene oxide, which can be subsequently isolated. In some embodiments, liquid crystalline solutions of oxidized graphene nanoribbons in water are also described.
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    Dissolution, processing and fluid structure of graphene and carbon nanotube in superacids: The route toward high performance multifunctional materials.
    (2012-09-05) Behabtu, Natnael; Pasquali, Matteo; Biswal, Sibani Lisa; Thomas, Edwin; Miller, Clarence A.; Adams, Wade
    Carbon allotropes have taken central stage of nanotechnology in the last two decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential building blocks for nanotechnology. Their superlative electrical, thermal and mechanical properties make them desirable for a number of technological applications ranging from lightweight strong materials to electrical wires and support for catalysts. However, transferring the exceptional single molecule properties into macroscopic objects has presented major challenges. This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids and these solution can processed into macroscopic objects. Chapter 2 reviews neat CNT fiber literature. Specifically, the two main processing methods —solid– state and solution spinning — are discussed. CNT aspect ratio and fibers structure are identified as the main variables affecting fiber properties. Chapter 3 shows that graphite can be exfoliated into single-layer graphene by spontaneous dissolution in chlorosulfonic acid. The dissolution is general and can be applied to various forms of graphite, including graphene nanoribbons. Dilute solutions of graphene can be used to form transparent conductive films. At high concentration, graphene and graphene nanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directly into continuous fibers. Chapter 4 describes a solution–based method to form a thin CNT network. This network is an ideal specimen support for electron microscopy. Imaging nanoparticles with atomic resolution and sample preparation from reactive fluids demonstrate the unique feature of solution–based CNT support compared to state–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase. Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despite nanotube liquid crystals having been reported in various CNT systems, a number of anomalies such as low order parameter and spaghetti–like, nematic droplets are reported. However, CNTs in chlorosulfonic acid show elongated, bipolar droplets typical of other rod–like molecules. Moreover, their large aspect ratio allows capturing the transition from homogeneous to bipolar transition expected from scaling arguments.The equilibrium shape and merging dynamics demonstrate the liquid nature of CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiber spinning. The influence of starting material, spinning dope concentration, spin draw ratio and coagulation on fiber properties is discussed. The linear scaling of fiber strength with CNT aspect ratio is demonstrated experimentally, once the best properties from different batches are compared. Moreover, Successful multi–hole spinning demonstrates the intrinsic scalability of wet spinning to meet the typical production output of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers to other CNTs fibers as well as existing engineered materials. Acid–spun CNT fibers combine the typical specific strength of high–strength carbon fibers to the thermal and electrical conductivity of metals. These properties are obtained because of a highly aligned, dense structure. The combined strength and electrical conductivity allow acid-spun fibers to be used as structural as well as conducting wire while the combined electrical and thermal properties allow for exceptional field emission properties. In conclusion, we demonstrate that multifunctional properties of carbon nanotubes that have fuelled much of the research in the past 20 years, can be attained on a macroscopic level via rational design of fluid–phase processing.
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    Experimental realization of crossover in shape and director field of nematic tactoids
    (American Physical Society, 2015) Jamali, Vida; Behabtu, Natnael; Senyuk, Bohdan; Lee, J. Alex; Smalyukh, Ivan I.; van der Schoot, Paul; Pasquali, Matteo; Smalley Institute for Nanoscale Science and Technology
    Spindle-shaped nematic droplets (tactoids) form in solutions of rod-like molecules at the onset of the liquid crystalline phase. Their unique shape and internal structure result from the interplay of the elastic deformation of the nematic and anisotropic surface forces. The balance of these forces dictates that tactoids must display a continuous variation in aspect ratio and director-field configuration. Yet, such continuous transition has eluded observation for decades: tactoids have displayed either a bipolar configuration with particles aligned parallel to the droplet interface or a homogeneous configuration with particles aligned parallel to the long axis of the tactoid. Here, we report the first observation of the continuous transition in shape and director-field configuration of tactoids in true solutions of carbon nanotubes in chlorosulfonic acid. This observation is possible because the exceptional length of carbon nanotubes shifts the transition to a size range that can be visualized by optical microscopy. Polarization micrographs yield the interfacial and elastic properties of the system. Absorbance anisotropy measurements provide the highest nematic order parameter (S=0.79) measured to date for a nematic phase of carbon nanotubes at coexistence with its isotropic phase.
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    High-Ampacity Power Cables of Tightly-Packed and Aligned Carbon Nanotubes
    (Wiley, 2014) Wang, Xuan; Behabtu, Natnael; Young, Colin C.; Tsentalovich, Dmitri E.; Pasquali, Matteo; Kono, Junichiro; Richard E. Smalley Institute for Nanoscale Science and Technology
    The current-carrying capacity (CCC), or ampacity, of highly-conductive, light, and strong carbon nanotube (CNT) fibers is characterized by measuring their failure current density (FCD) and continuous current rating (CCR) values. It is shown, both experimentally and theoretically, that the CCC of these fibers is determined by the balance between current-induced Joule heating and heat exchange with the surroundings. The measured FCD values of the fibers range from 107 to 109 A m−2 and are generally higher than the previously reported values for aligned buckypapers, carbon fibers, and CNT fibers. To the authors’ knowledge, this is the first time the CCR for a CNT fiber has been reported. The specific CCC value (i.e., normalized by the linear mass density) of these CNT fibers are demonstrated to be higher than those of copper.
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    Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity
    (AAAS, 2013) Behabtu, Natnael; Young, Colin C.; Tsentalovich, Dmitri E.; Kleinerman, Olga; Wang, Xuan; Ma, Anson W.K.; Bengio, E. Amram; ter Waarbeek, Ron F.; de Jong, Jorrit J.; Hoogerwerf, Ron E.; Fairchild, Steven B.; Ferguson, John B.; Maruyama, Benji; Kono, Junichiro; Talmon, Yeshayahu; Cohen, Yachin; Otto, Marcin J.; Pasquali, Matteo; Richard E. Smalley Institute for Nanoscale Science and Technology
    Broader applications of carbon nanotubes to real-world problems have largely gone unfulfilled because of difficult material synthesis and laborious processing. We report high-performance multifunctional carbon nanotube (CNT) fibers that combine the specific strength, stiffness, and thermal conductivity of carbon fibers with the specific electrical conductivity of metals. These fibers consist of bulk-grown CNTs and are produced by high-throughput wet spinning, the same process used to produce high-performance industrial fibers. These scalable CNT fibers are positioned for high-value applications, such as aerospace electronics and field emission, and can evolve into engineered materials with broad long-term impact, from consumer electronics to long-range power transmission.