Single-Walled Carbon Nanotube Dynamics Simple and Complex Media
Doctor of Philosophy
Understanding the dynamics of single-walled carbon nanotubes (SWNTs) in simple and complex environments is crucial for establishing potential application of nanotube architectures for materials and biosciences. In this thesis we employ the visualization and analysis tools to image and quantify and the Brownian bending and diffusion of SWNTs in different media in order to understand and eventually to tailor nanotube mobility in confined environments. We image Brownian bending dynamics of SWNTs in water using Near-infrared (NIR) fluorescence microscopy. The bending stiffness of each chirality-assigned SWNT is extracted from the variance of the curvature fluctuations. Relaxation times of the bending fluctuations are measured from the autocorrelation of SWNT shapes. We find that the bending stiffness scales as the cube of the nanotube diameter, in agreement with an elastic continuum model. The measured shape relaxation times are in excellent agreement with the semiflexible chain model, showing that SWNTs may truly be considered as the ideal model semiflexible filaments. The motion of stiff objects in crowded environments has been investigated for more than three decades in polymer science and biophysics; yet, theory and experiments have not established whether a minute amount of flexibility affects the mobility of stiff slender filaments. We image the Brownian motion of SWNTs in a network by NIR fluorescence microscopy. We show direct evidence of SWNTs reptating in the network, and confirm that their small flexibility enhances significantly their rotational diffusion. Our results establish the reptation dynamics of stiff filaments and provide a framework to tailor SWNTs mobility in confined media. By varying SWNT surface modifications, we can selectively tune the sensitivity of the carbon nanotubes to the different physical properties of the porous media for sensing applications. We introduce a simple procedure for dispersion of SWNTs in aqueous solutions using triblock copolymer, PS-b-P2VP-b-PEO. This process yields stable dispersions of individual SWNTs without a need for ultracentrifugation, thus increasing nanotube yield. We show that the SWNT suspension is stable under a wide pH range as well as high salinity environments. These stable suspensions can be used in a wide range of applications in different media where stability is crucial.