Dissolution, processing and fluid structure of graphene and carbon nanotube in superacids: The route toward high performance multifunctional materials.

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

Engineered polysaccharides: α‐1,3‐glucan acetates showing upper critical solution temperature in organic solvents

Abstract Acetates of α‐1,3‐glucan dissolved in N , N ‐dimethyl acetamide/LiCl are prepared by converting the polysaccharide with acetyl chloride, acetic acid anhydride/pyridine, or with acetic acid/ N,N ′‐carbonyl diimidazole. Values of the degree of substitution for the acetyl groups (DS Ac ) of up to 2.6 are realized. NMR spectroscopic measurements reveal a preferred conversion of the primary hydroxyl group at position 6 followed by positions 2 and 4. Depending on the DS Ac , the samples may be soluble in solvents of different polarity at room temperature or at elevated temperatures showing upper critical solution temperature at DS of about 2.5. This process is found to be reversible

Nanotubes as polymers

AbstractIn this review, we show that the structure and behavior of single-walled nanotubes (SWNTs) are essentially polymeric; in fact, many have referred to SWNTs as “the ultimate polymer”. The classification of SWNTS as polymers is explored by comparing the structure, properties, phase behavior, rheology, processing, and applications of SWNTs with those of rigid-rod polymers. Special attention is given to research efforts focusing on the use of SWNTs as molecular composites (also termed nanocomposites) with SWNTs as the filler and flexible polymer chains as the host. This perspective of “SWNTs as polymers” allows the methods, applications, and theoretical framework of polymer science to be appropriated and applied to nanotubes

High-Solids, Solvent-Free Modification of Engineered Polysaccharides

The nature-identical engineered polysaccharide α-(1,3) glucan, produced by the enzymatic polymerization of sucrose, was chemically modified by acylation with succinic anhydride. This modification reaction was initially performed at the micro scale in a TGA reactor to access a range of reaction conditions and to study the mechanism of the reaction. Subsequently, the best performing conditions were reproduced at the larger laboratory scale. The reaction products were characterized via coupled TGA/DSC analysis, FT-IR spectroscopy, solution viscosity and pH determination. The acylation path resulted in partially modifying the polysaccharide by altering its behavior in terms of thermal properties and solubility. The acylation in a solvent-free approach was found promising for the development of novel, potentially melt-processable and fully bio-based and biodegradable ester compounds

Engineered Polysaccharides: α‐1,3‐Glucan Acetates Showing Upper Critical Solution Temperature in Organic Solvents

Abstract Acetates of α‐1,3‐glucan dissolved in N , N ‐dimethyl acetamide/LiCl are prepared by converting the polysaccharide with acetyl chloride, acetic acid anhydride/pyridine, or with acetic acid/ N,N ′‐carbonyl diimidazole. Values of the degree of substitution for the acetyl groups (DS Ac ) of up to 2.6 are realized. NMR spectroscopic measurements reveal a preferred conversion of the primary hydroxyl group at position 6 followed by positions 2 and 4. Depending on the DS Ac , the samples may be soluble in solvents of different polarity at room temperature or at elevated temperatures showing upper critical solution temperature at DS of about 2.5. This process is found to be reversible

Direct Imaging of Carbon Nanotube Liquid-Crystalline Phase Development in True Solutions

Using direct-imaging cryogenic transmission and scanning electron microscopy, we show different stages of liquid-crystalline phase development in progressively more concentrated solutions of carbon nanotubes in chlorosulfonic acid: a dilute phase of individually dissolved carbon nanotubes; semidilute and concentrated isotropic phases; coexisting concentrated isotropic and nematic phases in local equilibrium with each other; and a fully liquid-crystalline phase. Nanometric resolution of cryogenic electron microscopy reveals carbon nanotube self-assembly into liquid-crystalline domains of several nanometers in width at very early stages. We find significant differences in carbon nanotube liquid-crystalline domain morphology as a function of the carbon nanotube aspect ratio, diameter, and degree of purity

Direct Real-Time Monitoring of Stage Transitions in Graphite Intercalation Compounds

Graphite intercalation compounds (GIC) possess a broad range of unique properties that are not specific to the parent materials. While the stage transition, changing the number of graphene layers sandwiched between the two layers of intercalant, is fundamentally important and has been theoretically addressed, experimental studies revealed only macroscopic parameters. On the microscale, the phenomenon remains elusive up to the present day. Here we monitor directly in real time the stage transitions using a combination of optical microscopy and Raman spectroscopy. These direct observations yield several mechanistic conclusions. While we obtained strong experimental evidence in support of the Daumas–Herold theory, we find that the conventional interpretation of stage transitions as sliding of the existing intercalant domains does not sufficiently capture the actual phenomena. The entire GIC structure transforms considerably during the stage transition. Among other observations, massive wavefront-like perturbations occur on the graphite surface, which we term the tidal wave effect

Direct Real-Time Monitoring of Stage Transitions in Graphite Intercalation Compounds

Graphite intercalation compounds (GIC) possess a broad range of unique properties that are not specific to the parent materials. While the stage transition, changing the number of graphene layers sandwiched between the two layers of intercalant, is fundamentally important and has been theoretically addressed, experimental studies revealed only macroscopic parameters. On the microscale, the phenomenon remains elusive up to the present day. Here we monitor directly in real time the stage transitions using a combination of optical microscopy and Raman spectroscopy. These direct observations yield several mechanistic conclusions. While we obtained strong experimental evidence in support of the Daumas–Herold theory, we find that the conventional interpretation of stage transitions as sliding of the existing intercalant domains does not sufficiently capture the actual phenomena. The entire GIC structure transforms considerably during the stage transition. Among other observations, massive wavefront-like perturbations occur on the graphite surface, which we term the tidal wave effect