Studies On Polymer-Functionalized Single-Walled Carbon Nanotubes In Gas Expanded Liquids

Gas-expanded liquids (GXLs) is a new type of environmentally friendly solvents. The ability of GXLs to readily pressure tune the mole fraction of the gaseous component, and thereby alter the solvating power, fluidity, transport rates and many other properties of these solvents proves advantageous in materials processing and organic reaction. CO2-expanded liquids (CXLs) are the most commonly used class of GXLs. Accordingly, the work in my thesis is described in the following two parts:Non-covalent functionalization of single-walled carbon nanotubes (SWCNTs) with P4VP-b-PS in CXLs:Poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) was prepeared by reversible addition fragmentation chain transfer mediated polymerization (RAFT) method, which is an ideal amphiphilic diblock copolymer for potential applications in emulsion polymerization, colloid stabilization and microreactors, and the self-assembly ability also helps P4VP-b-PS to find wide applications in nanolithography, catalysis, molecular templating, and drug delivery. In this work, the non-covalent functionalization of SWCNTs with P4VP-b-PS in CXLs is studied. It is found that P4VP-b-PS stabilized SWCNTs showed better dispersion in organic solvent. Raman spectra indicated that there exist interactions between SWCNTs and P4VP-b-PS chains. Furthermore, the structure and morphology of P4VP-b-PS/SWCNTs composite were examined, focusing on P4VP-b-PS concentration and the pressure of CXLs. It is found that the P4VP-b-PS wrapping patterns undergo a remarkable morphological evolution from dotted coating crystals to compact kebabs, and then to helical patternings by facile pressure tuning in the high polymer concentration series. In other words, the CXLs method enables superior control of the P4VP-b-PS crystallization patternings on SWCNTs. What is more, the CXL-assisted P4VP-b-PS crystal growth mechanism on SWCNT is investigated.Covalent functionalization of SWCNTs with P4VP-TEMPO by "grafting to" method in CXLs:The covalent modification of SWCNTs with polymer involves either "grafting from" or "grafting to" strategies. This part reports the functionalization of SWCNTs in CXLs with poly(4-vinylpyridine)(P4VP) chains terminated with the2,2,6,6-tetramethylpiperidinyl radical-stabilizing group, that is to say, the "grafting to" method. It is found that P4VP-g-SWCNTs show good dispersion in both organic solvent and aqueous solution (pH=2). Furthermore, the grafting ratio of P4VP to SWCNTs was examined, with the focus on molecular weight of P4VP and the pressure of CXLs. It is amazing that CXLs method could change the grafting ratio of "grafting to" method. The properties of P4VP-g-SWCNTs hybrid were characterized and studied with several methods, including thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) and Raman spectra.