Structural characterization of macroscopic single -walled carbon nanotube materials

Wei Zhou, University of Pennsylvania

Abstract

In this thesis, we studied the structural properties of macroscopic materials of single-walled carbon nanotubes (SWNTs) in the form of fibers, films and suspensions. We characterized the preferred orientations in partially aligned SWNT fibers and films, combining x-ray fiber diagram and polarized Raman scattering. Our texture model consists of an aligned fraction, characterized by the angular distribution width of tube axes, plus a completely unaligned fraction. For neat fibers extruded from SWNT/superacid suspensions through a small orifice, the distribution width and the aligned fraction both improve with decreasing orifice diameter. For magnetic field-aligned SWNT films deposited from surfactant suspensions, the aligning effects of deposition and external magnetic field force in the film plane are additive, the out-of-plane mosaic being narrower than the in-plane one. SWNTs dispersed in superacid or aqueous surfactant solutions are precursors for many applications. In oleum, SWNTs can be charged and protonated by H 2SO4 molecules. X-ray scattering indicates that H2SO 4 molecules align along nanotube axes to form cylindrical shells wrapped around nanotubes. This finding establishes the validity of a long-standing important but still debated physical chemistry concept, “structured solvent shells surrounding dissolved ions”. Differential scanning calorimetry confirms that the partly ordered H2SO4 molecules are a new phase, with distinct freezing/melting behavior. X-ray scattering at low temperature further shows that crystallization of the bulk-like acid surrounding the structured shells is templated by the SWNTs. The specific orientation of the acid crystallites provides solid evidence for direct protonation of SWNT. We studied the morphologies of SWNT suspensions using small-angle neutron scattering. We observed rigid rod behavior from SWNTs dispersed in water using sodium dodecylbenzene sulfonate surfactant, suggesting that SWNTs exist mainly as individual tube and small ropes in the suspension. In many other surfactants and organic solvents, SWNTs form aggregates. In superacid, SWNTs dissolve as isolated individual tubes and small ropes at low concentration (∼00.01 wt%) while at high concentration, the tubes and ropes self-assemble into liquid crystalline strands of mobile solvated nanotube spaghettis, which exhibit a self-similar fractal-like structure.

Subject Area

Materials science

Recommended Citation

Zhou, Wei, "Structural characterization of macroscopic single -walled carbon nanotube materials" (2005). Dissertations available from ProQuest. AAI3179848.
https://repository.upenn.edu/dissertations/AAI3179848

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