Controlling laminar flow in microfluidic channels and covalent chemistry of single-walled carbon nanotubes.

摘要

Since their discovery in 1993, single-walled carbon nanotubes (SWNTs) have been one of the most interesting nanomaterials in the past 20 years. Their outstanding electric, optical, thermal, chemical and mechanical properties have opened many new research areas, among which electronic-type based SWNT separation and surface chemical functionalization are of vital importance due to the major challenges for SWNT applications: lacking synthetic approaches for simple electronic-type products and poor dispersion in most solvents. This dissertation describes my work on quadrupole microchannel fabrication for potential dielectrophoresis-based SWNT separation and the covalent chemistry study of SWNTs.;Lab-on-a-chip device with interdigitated electrodes has been reported for SWNT separation. However, quadrupole microchannel would theoretically be more effective than planar interdigitated electrodes with respect to dielectrophoresis-based separation. The first part of this dissertation demonstrates the fabrication of quadrupole microchannel on a lab-on-a-chip device by controlling multiphase laminar flow in microfluidic channels. The n-dodecyl-beta-D-maltoside (DDM)-sheathing phases and bi-layer T-junctions are introduced for the first time to control the electroless plating of silver electrodes on the channel sidewalls three-dimensionally. The method is readily accessible, inexpensive and completely based on planar soft-lithography. The fabricated microchip has the potential applications for high-resolution dielectrophoretic SWNT separation.;The second part of this dissertation focuses on the covalent chemistry of carbon nanotubes. In this study, we discovered a general defluorination mechanism for fluorinated single-walled carbon nanotubes (FSWNTs) in the presence of a wide range of electron donors at room temperature. Depending on the electron donating ability of the donor molecules, spontaneous or photo-induced charge transfer occurs from the electron donors to FSWNTs, which is then followed by the elimination of F- ions. The same mechanism is also applicable when FSWNT obtains electrons electrochemically. Both chemical reaction condition and irreversible electrochemical reduction potential data indicate that the defluorination reactivity of C-F bonds in FSWNT is stronger than those in unstrained compounds but weaker than those in highly strained fullerene derivatives. The reactivity of the electron transfer assisted defluorination originates from not only the strong electron affinity of FSWNTs, but also the strained bonding configuration caused by molecular curvature as it is predicted by related theoretical studies. Cylindrically shaped SWNTs provide a middle point between undistorted molecules and spherical fullerenes in tuning chemical reactivities using molecular curvature effects.;Electron-transfer assisted defluorination of FSWNTs generates reactive carbon radicals on carbon nanotubes. Raman spectra, X-ray photoelectron spectroscopy, transmission electron microscopy and the strengthened mechanical property of defluorinated FSWNT foams indicate that the products are cross-linked SWNTs directly bonding through sp3 C-C bond between adjacent nanotubes. The cross-linked SWNT networks show sensitive Raman response to different laser powers. An intense laser decomposes the cross-linked SWNT networks, making the cross-linked SWNT networks possible to find applications as light, strong and degradable materials.;Besides the chemistry of carbon nanotubes, the covalent chemistry of several other carbon nanostructures including the C60 fullerene, carbon nanobuds (C60- SWNT) and fullerene/nanotube mixtures (C 60/SWNT) is also studied by UV-vis-NIR absorption and NIR fluorescence. Carbon nanobuds synthesized in an aerosol reactor by our collaborators lose the characteristic absorption and fluorescence emission that belongs to SWNTs, indicating that the electronic structure of the tubes in the carbon nanobuds is destroyed. In an attempt to synthesize nanobuds from C60/SWNT mixtures in solution phase through UV-irradiation, it is found that although C60 polymerizes though [2+2] cycloaddition, similar reaction does not occur between C60 and the outer surface of SWNTs, which can be attributed to the lower reactivity of SWNTs due to their reduced surface curvature. The presence of SWNTs in C60 solution slows down the photopolymerization of fullerenes. A quenching effect of SWNTs towards excited C60 probably exists.