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

[摘要] Carbon allotropes have taken central stage of nanotechnology in the last twodecades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essentialbuilding blocks for nanotechnology. Their superlative electrical, thermal and mechanicalproperties make them desirable for a number of technological applicationsranging from lightweight strong materials to electrical wires and support for catalysts.However, transferring the exceptional single molecule properties into macroscopic objectshas presented major challenges.This thesis demonstrates that carbon nanotubes and graphite dissolve in superacidsand these solution can processed into macroscopic objects. Chapter 2 reviewsneat CNT fiber literature. Specifically, the two main processing methods —solid–state and solution spinning — are discussed. CNT aspect ratio and fibers structureare identified as the main variables affecting fiber properties. Chapter 3 shows thatgraphite can be exfoliated into single-layer graphene by spontaneous dissolution inchlorosulfonic acid. The dissolution is general and can be applied to various forms ofgraphite, including graphene nanoribbons. Dilute solutions of graphene can be usedto form transparent conductive films. At high concentration, graphene and graphenenanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directlyinto continuous fibers. Chapter 4 describes a solution–based method to form a thinCNT network. This network is an ideal specimen support for electron microscopy.Imaging nanoparticles with atomic resolution and sample preparation from reactivefluids demonstrate the unique feature of solution–based CNT support compared tostate–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase.Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despitenanotube liquid crystals having been reported in various CNT systems, a numberof anomalies such as low order parameter and spaghetti–like, nematic dropletsare reported. However, CNTs in chlorosulfonic acid show elongated, bipolar dropletstypical of other rod–like molecules. Moreover, their large aspect ratio allows capturingthe transition from homogeneous to bipolar transition expected from scalingarguments.The equilibrium shape and merging dynamics demonstrate the liquid natureof CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiberspinning. The influence of starting material, spinning dope concentration, spin drawratio and coagulation on fiber properties is discussed. The linear scaling of fiberstrength with CNT aspect ratio is demonstrated experimentally, once the best propertiesfrom different batches are compared. Moreover, Successful multi–hole spinningdemonstrates the intrinsic scalability of wet spinning to meet the typical productionoutput of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers toother CNTs fibers as well as existing engineered materials. Acid–spun CNT fiberscombine the typical specific strength of high–strength carbon fibers to the thermaland electrical conductivity of metals. These properties are obtained because of ahighly aligned, dense structure. The combined strength and electrical conductivityallow acid-spun fibers to be used as structural as well as conducting wire whilethe combined electrical and thermal properties allow for exceptional field emissionproperties.In conclusion, we demonstrate that multifunctional properties of carbon nanotubesthat have fuelled much of the research in the past 20 years, can be attained on amacroscopic level via rational design of fluid–phase processing.

[发布机构] Rice University

[效力级别] nanotubes