Low Temperature Synthesis, Surface Modification Of Onion-like Fullerenes And Dispersion In Polymer Matrix

Photonic crystals are a periodical materials which are fabricated by periodically arranging two materials having different dielectric constants. Photonic bandgap is one of the basic characters of photonic crystals, which controls the propagation of light and thus casts the basis for optical devices and communication component. Non-close-packed structured photonic crystals possess a widened bandgap and are easy to form complete photonic bandgap, thus investigating the preparation of non-close-packed structured photonic crystals holds far-reaching meaning. Theoretical calculations showed that C₆₀/AlN, C₆₀/GaN, C₇₀/AlN, C₆₀ films and carbon spheres coated by silica possess photonic bandgap in UV, visible and near-infrared region, which indicates the potential applications of onion-like fullerenes (OLFs) and carbon spheres (CSs) in the field of photonic crystals. Bases on this research background, this thesis has focused on the low-cost preparation, surface modification of onion-like fullerenes carbon materals and the dispersion of these materials in polymer matrix. The conclusions are listed as follows: (1) OLFs were synthesized at low-temperature (400℃) by chemical vapor deposition (CVD) using Fe/Al(OH)₃ and Fe/NaCl as catalysts. Firstly, the influences of reaction temperature were investigated, with respect to the structure and morphology of the product using Fe/Al(OH)₃. as catalyst The results show that low-temperature of 400℃was in favor of the growth of OLFs, the product are composed of OLFs encapsulating Fe₃C. OLFs with high-purity, high degree of graphitization and size of about 15-60nm were obtained after the heat treatment in vacuum. Secondly, the influences of Fe/NaCl with different Fe content were investigated, with respect to the structure and morphology of the product using Fe/NaCl as catalyst. The results show that low Fe content was in favor of the growth of OLFs. OLFs encapsulating Fe₃C with size in the range of 15-50nm were prepared using catalyst containing 0.3wt% Fe. OLFs with high-purity, high degree of graphitization and size of about 15-50nm were obtained after the heat treatment in vacuum. Because the support NaCl could be removed by water washing, high purity OLFs synthesis using Fe/NaCl as catalysts by CVD method is a low-cost efficient route. Based on the experimental results, the growth mechanism of OLFs encapsulating Fe₃C was suggested: gaseous carbon species derived from C2H2 are absorbed and decomposed on the surface of catalyst particles, carbon atom clusters diffuse between crystal lattice of catalyst, precipitate and recombine into graphitic layers. The incomplete precipitation of carbon atoms between crystal lattice of catalyst led to their reaction with Fe and formation of Fe₃C, Fe₃C were encapsulated by graphitic layers, finally OLFs encapsulating Fe3C with the low degree of graphitization were obtained.(2) CSs-silica core-shell structured material was prepared using tetraethyl orthosilicate(TEOS) as precursor of silica by a sol-gel method. Carbon sphere (CSs) cores were prepared by the pyrolysis of acetylene. After CSs cores were removed by calcinations, hollow silica spheres were obtained. Firstly, the influences of the coating medium were investigated. CSs were easy to be coated with silica in basic medium, which produced the compositie spheres with smooth surface and uniform shell thickness. The coating thickness, which is also the shell thickness of the hollow spheres, could be controlled by changing the volumes of TEOS and reaction time. The thermal stability of CSs was improved after silica coating on the surface of CSs. The formation of the core-shell structure was suggested to follow electrostatic interation mechanisam. The surfaces of CSs modified by cationic surfactant cetyltrimethylammonium bromide(CTAB) were characterized by positive charges, and absorbed negatively charged silicon hydroxide species originated from the hydrolysis of TEOS via electrostatic interaction, which provided nucleation sites of silicon hydroxide species on the surface of carbon spheres. And the core-shell structure was formed. The hollow silica spheres were obtained when carbon spheres were removed by calcinating in air.(3) HNO₃/H2O2, HNO₃ and HNO₃/H2SO4 were used as oxidant to modify the carbon spheres surface. The influences of the proportion, concentration and treatment time of the oxidant on the morphology of CSs, the type and amount of the functional groups introduced on the surface of CSs were studied. The dispersion of the oxidized CSs in water was analyzed. When HNO₃/H2O2 was used as oxidant, as HNO₃ and H₂O₂ solution concentration increased, the amount of carboxyl, hydroxyl, carbonyl,and total oxygen-containing functional groups(TOFGs) increased. The amount of carboxyl, hydroxyl, carbonyl, and TOFGs changed with the changing the volume ratio of HNO₃ and H₂O₂. The modification effect was best when CSs were treated by the volume ratio 1:1 of HNO₃ and H2O2, which introduced 0.2614 mmol/g of carboxyl, 1.105mmol/g of hydroxyl, 0.7976mmol/g carbonyl and 2.164 mmol/g of TOFGs onto the surface of CSs. When HNO₃ was used as oxidant, the amount of carboxyl, carbonyl, hydroxyl and TOFGs increased with increasing HNO₃ solution concentration and treatment time, the treatment by concentrated nitric acid for 1h introduced 0.808 mmol/g, 3.021mmol/g of hydroxyl, 1.047mmol/g carboxyl and 4.876mmol/g of TOFGs onto the surface of CSs, which were the maximum value. When HNO₃/H2SO4 was used as oxidant, the amount of the functional groups increased with prolonging treatment time. The treatment by HNO₃/H2SO4 for 1h introduced 0.508mmol/g of carboxyl, 3.51mmol/g of hydroxyl, 0.379mmol/g of carbonyl and 4.379mmol/g of TOFGs onto the surface of CSs. Among the three oxidation systems, the oxidation efficiency of HNO₃/H2SO4 was the highest, followed by HNO₃ and HNO₃/H2O2. The hydrophilicity and dispersion in water of oxidized CSs were improved distinctly. The type and amount of the functional groups introduced on the surface of the carbon spheres were different after different treatment. So the type and amount of the functional groups on the surface of CSs could be controlled by changing oxidation condition.(4) Vinyl groups were introduced on the surface of CSs by carboxyl, hydroxyl functional groups reacting with allylamine or chloromethylstyrene. Vinyl-functional CSs were added directly into methyl methacrylate(MMA) monomer, composite materials containing CSs dispersed uniformly in polymethylmethacrylate(PMMA) matix with good compatibility with polymer were obtained via in-situ polymerization. The oxidized CSs were ionized after the treatment by NaOH. Ionized CSs and polymerizable surfactants octadecyl-p-vinylbenzyl-dimethylammonium chloride (VODAC) were added into MMA. Composite materials containing CSs dispersed uniformly in PMMA matix were obtained. Ionized CSs and VODAC were added into water and dispersed uniformly. And then MMA or styrene(St) was added into the above suspension. Oil phase was taken out after extraction and polymerized. Field emission scanning electron microscopy observation shows that CSs were well dispersed in PMMA matix and had good compatibility with polymer; CSs were well dispersed in polystyrene matix, but the compatibility with polymer was not as good as PMMA.