Preparation and Application of Aligned Carbon Nanotube/Polymer Composite Material

Carbon nanotube (CNT)/polymer composite materials have been widely studied for two decades. However, there remains a common and critical challenge, i.e., random dispersion of CNTs in polymer matrices, which has largely lowered their properties and limited their applications. Herein, we have developed a general method to prepare highly aligned CNT/polymer composite materials in formats of array, film, and fiber. The key procedure is to synthesize spinnable CNT arrays with high quality by a chemical vapor deposition process. Fe/Al2O3 was used as catalyst, ethylene was used as carbon source, a mixture gas of argon and hydrogen was used as carrying gas. The optimal growth conditions were summarized as below: thickness of 1.2 nm for Fe, thickness of 3 nm for Al2O3, flow rate of 400 standard cm(3)/min for argon, flow rate of 90 standard cm(3)/min for ethylene, flow rate of 30 standard cm(3)/min for hydrogen, growth temperature of 740 degrees C, and growth time of 10 min. Here the catalyst system was coated on silicon substrate by electron beam evaporation with rates of 0.5 and 2 angstrom/s for Fe and Al2O3, respectively. To prepare CNT sheets or fibers, the spinnable array was first stabilized in a stage. A blade was then used to draw a ribbon out of the array. A CNT sheet would be obtained if the ribbon was directly pulled out without rotation, while a fiber should be produced if a rotary spinning was used. The spinning speed was about 15 cm/min. Monomer/polymer solutions or melts were directly coated onto the aligned CNT sheet or fiber to produce the aligned CNT/polymer film or fiber. Due to the high alignment of CNTs in polymer matrices, the resulting composite materials exhibited remarkable physical properties, e.g., the mechanical strength and electrical conductivity can be improved for one and three orders compared with the conventional solution blending method, respectively. These novel composite materials are promising for a wide variety of applications. The use of them as novel counter electrodes to fabricate dye-sensitized solar cells has been investigated as a demonstration. In a typical fabrication, an aligned CNT/polymer film (typical thickness of 5 mu m) was first transferred onto fluorine doped tin oxide as counter electrode. A layer of TiO2 was coated onto fluorine doped tin oxide as working electrode, followed by immersion into 0.5 mmol/L cis-diisothiocyanato-bis(2,2'-bipyridy1-4,4'-dicarboxylato) ruthenium(II) bis(tetrabutylammonium) (also called N719) solution in a mixture solvent of acetonitrile/tert-butanol (volume ratio of 1/1) for 16 h. After being further rinsed with acetonitrile and dried, the N719-incorporated TiO2 electrode was assembled with the counter electrode. An electrolyte which consisted of Lil, I-2, 2-2-3-with propyl methyl 5-membered imidazole iodine, GuSCN, and tri-butyl-phosphate in dehydrated acetonitrile was injected into the cell through a hole on the counter electrode. The hole was finally sealed with surlyn and a piece of glass.