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Polymer Modification Of Carbon Nanotubes And Its Properties

Posted on:2006-12-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:X F LiFull Text:PDF
GTID:1101360182969214Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Carbon nanotubes (CNTs) have been one of the hottest research topics since the discovery because of their unique architecture, mechanical properties and wide potential applications. However, the CNTs have very high thermo stability and until now it cannot dissolve in any solvent, which limits the further development and application of CNTs remarkably. The CNTs is made of sp~2 carbon atoms, each of them contributes a p-electron to construct a highly delocalized πelectron cloud along the wall, which can combine with other molecules containing πelectrons through π-πinteraction, and get chemically modified CNTs. In this paper, seven CNTs derivatives were prepared including poly(ethylene glycol)/carbon nanotubes (PEG/CNTs) and epoxy acrylate/carbon nanotubes (EA/CNTs) by means of polymer groups reaction, polyacrylamide/carbon nanotubes (PAM/CNTs) derivative by an in-situ ultraviolet (UV) radiation initiated polymerization, acrylonitrile–butadiene–styrene/carbon nanotubes (ABS/CNTs) and trans-polyisoprene/carbon nanotubes (TPI/CNTs) by an UV radiation grafted reaction, poly(vinyl alcohol)/carbon nanotubes (PVA/CNTs) and polystyrene/carbon nanotubes (PSt/CNTs) by in-situ free radical polymerization. The microcosmic structures and morphology of the derivatives were characterized by the instruments of Fourier transform infrared spectroscopy (FTIR), UV-visible absorbance spectra (UV-vis), Fluorescence spectra (FS) and Transmission electron microscope (TEM). The results show that CNTs can be modified by polymer in-situ polymerization. And TEM shows that the PSt/CNTs colloid is tubes with tiny balls in nanometer scale, but in the images of other derivatives of CNTs, polymer is coated on the surface of CNTs and much more chains are assembled at the ends of CNTs. PEG/CNTs, PAM/CNTs, PVA/CNTs and colloidal PSt/CNTs that were synthesized can be resolved in water, which can open a convenient door for other chemists in further research. At same time special functional materials with CNTs can be made by this way, which makes CNTs becoming the most promising materials be worthy of the name. The tribology of behavior of CNTs derivatives and their complexes with OPZ (a type of water-soluble zinc alkoxyphosphate) as lubricant additives of water base stock was studied by four-ball tribotester. When the PEG/CNTs and PAM/CNTs content reach 0.5 wt.% and 0.3 wt.% respectively, the wear scar diameter (WSD) is minimum to 0.68 mm and 0.62 mm. When the PVA/CNTs and colloidal PSt/CNTs content reach 0.25 wt.% and 1.0 wt.% complexes with OPZ respectively, the WSD are minimum to 0.38 mm and 0.36 mm, and the maximum non-seized load (PB) are maximum to 610 N and 680 N. This infers that derivatives of CNTs have pretty good load carrying and anti-wear performance in water fluid. Their properties of lubrication are not proportional to its content, and excessive adding may lead descending of the lubrication properties. The worn surface in four-ball machine testing was observed by scanning electron microscope (SEM). The images demonstrated that the wear scar obviously became smaller and relatively smoother when adding the derivatives of CNTs as additive, which intuitionistically showed us their good lubrication properties. The friction signals of PEG/CNTs, PAM/CNTs and PVA/CNTs spin casting thin films could be measured at different applied loads for the same area in the friction force microcopy (FFM) map. Three derivatives have same characterization: derivative and homopolymer films exhibit stable and lower friction signals below the 100 nN load due to polymer soft chains and flat surface. However, after load of 100~140 nN, the difference in friction signals between the two films is larger. The friction coefficient decreased significantly as the CNTs addition. The results can be attributed to the additional load-bearing ability afforded by CNTs chemically bonded on the derivative chains which molecules are reasonable to consider anti-wear for its flexibilities. Based on the experimental study on water-soluble core-and-shell derivatives including CNTs additives made by our group, its lubrication mechanism was speculated preliminarily. It is supposed that derivative can penetrate into the interface and deposit there to support and isolate two relative motion surfaces during friction process, and has the possibility to cause microcosmic rolling effect between two rubbing surface. And therefore, the anti-wear performance of the base stock was improved. Further more, there are rolling effect with boundary lubrication in the complexes with the OPZ solution. UV curing coating of EA/CNTs was prepared by the molecule group reaction of CNTs with EA. The anti-infrared/ultraviolet property was characterized by UV-vis and FTIR preliminarily. The results demonstrated that, its transmittance was greater than 85%in visible spectrum, the transmittance was 42.3% in near infrared wave range (4000cm-1~14000 cm-1) and it shielded most of wave in ultraviolet region (< 300 nm). At same time the mechanical property of composite coating was improved. So this new nano-composite materials would be expected to be an anti-infrared/ultraviolet thin coating in functional applications. TPI/CNTs and ABS/CNTs composites were prepared by UV irradiated at room temperature. The resistivity of composites decreases 107 times with adding 5 wt.% CNTs. In the 20~100℃temperature range, the resistivity of UV irradiated composites almost keeps stability. In the 2~10GHz microwave range, the ε′′of composites are from 21 to 50. So the new composites would be potential electromagnetic shielding materials. In conclusion, the study on CNTs as functional materials is in the ascendant. Our works are based on the polymer chemically-modified CNTs, and to evaluate the tribology, optical, electrical and magnetism properties of polymer/CNTs, which will provide new ideologies and methods for tribology of CNTs.
Keywords/Search Tags:Carbon nanotubes, Polymer modification, Lubrication additive, Microtribology, Wave shielding, Electromagnetic property
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