Single-Walled Carbon Nanotube DynamicsSimple and Complex Media

[摘要] Understanding the dynamics of single-walled carbon nanotubes (SWNTs) in simpleand complex environments is crucial for establishing potential application of nanotubearchitectures for materials and biosciences. In this thesis we employ the visualizationand analysis tools to image and quantify and the Brownian bending anddiffusion of SWNTs in different media in order to understand and eventually to tailornanotube 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 SWNTis extracted from the variance of the curvature fluctuations. Relaxation times of thebending fluctuations are measured from the autocorrelation of SWNT shapes. Wefind that the bending stiffness scales as the cube of the nanotube diameter, in agreementwith an elastic continuum model. The measured shape relaxation times arein excellent agreement with the semiflexible chain model, showing that SWNTs maytruly be considered as the ideal model semiflexible filaments.The motion of stiff objects in crowded environments has been investigated for morethan three decades in polymer science and biophysics; yet, theory and experimentshave not established whether a minute amount of flexibility affects the mobility ofstiff slender filaments. We image the Brownian motion of SWNTs in a network byNIR fluorescence microscopy. We show direct evidence of SWNTs reptating in thenetwork, and confirm that their small flexibility enhances significantly their rotationaldiffusion. Our results establish the reptation dynamics of stiff filaments and providea framework to tailor SWNTs mobility in confined media.By varying SWNT surface modifications, we can selectively tune the sensitivityof the carbon nanotubes to the different physical properties of the porous media forsensing applications. We introduce a simple procedure for dispersion of SWNTs inaqueous solutions using triblock copolymer, PS-b-P2VP-b-PEO. This process yieldsstable dispersions of individual SWNTs without a need for ultracentrifugation, thusincreasing nanotube yield. We show that the SWNT suspension is stable under awide pH range as well as high salinity environments. These stable suspensions canbe used in a wide range of applications in different media where stability is crucial.

[发布机构] Rice University

[效力级别] engineering