Figure 6 a TEM picture of the carbon nanocapsule-synthetic mica hybrid, wherein carbon nanocapsules were well dispersed by mica platelets, effectively preventing the carbon nanocapsules from re-aggregation.
Industrial Technology Research Institute (Hsinchu, TW) inventors Gan-Lin Hwang, Shih-Jung Tsai, Jiang-Jen Lin and Yi-Fen Lan developed a carbon nanocapsule-layered silicate hybrid useful in multiple applications. Layered silicates (platelet-shaped) as a dispersant are mixed with carbon nanocapsules (sphere-shaped) by a physical process. The physically mixed hybrid exhibits a homogeneous dispersion phase due to the geometric shape inhomogeneity factor. Aggregation of carbon nanocapsules is thus avoided. The hybrid can be dispersed in a polar or non-polar solvent with a solid content of about 0.01-30 wt %, according to United States Patent 7625952.
The Industrial Technology Research Institute discovery provides a feasible, low-cost approach for dispersing carbon nanocapsule to make the carbon nanocapsule readily for use. In addition, the layered silicate has characteristics of low gas permeability and high resistance to heat, which may be adopted to expand the applications of carbon nanocapsule. Carbon nanocapsules can be utilized in various fields such as biomedical, energy and optoelectronic application. A serious obstacle to the development of these applications is the poor dispersion behavior of carbon nanocapsules.
A carbon nanocapsule (CNC) is a polyhedral carbon cluster composed of an enclosed multilayer graphite structure, whose diameter ranges from 1 to 100 nm but is usually 30-40 nm. As to the graphite layer on the shell of a carbon nanocapsule, the central parts are exclusively six-member rings, the corners are composed of five-member rings, and every carbon atom is sp.sup.2 hybrid orbital. The center of the carbon nanocapsule may be hollow or filled with metal. The carbon nanocapsule is brought about by well-developed graphitic structure, with thermal and electric conductance, high mechanical strength, chemical stability, large superficial content, firm structure and electromagnetic interference shielding.
Pristine carbon nanocapsules have an aggregation configuration and is not readily processible. Owing to the strong van der Waals force between carbon nanocapsule particles, it is not easy to disperse carbon nanocapsules in solvent, which makes it undesirable for use. To improve the dispersion behavior of carbon nanocapsules, attempts have been made by chemical modification and physisorption. Chemical modification (or chemical functionalization) includes strong oxidation, atom transfer radical polymerization, and free radical polymerization. The mechanism of chemical modification involves surface modification with reactive functionality, followed by grafting with organic long chains. Physical adsorption may be carried out by ultrasonication or grinding with solvent, which involves adsorption of small organic molecules, surfactants, polymers, or proteins only through weak intermolecular interactions such as .pi.-.pi. stacking force and electrostatic force.
FIG. 4 is a schematic diagram showing a mechanism for dispersing a carbon nanocapsule by layered silicate;
As shown in FIG. 4, platelet-shaped layered silicate 200 is employed as a dispersant for dispersing spherical-shaped carbon nanocapsule (CNC) 100 by a physical process, thereby forming a CNC-layered silicate hybrid 300. The physically mixed hybrid 300 exhibits a fine, homogeneous dispersion phase due to redistribution of van der Waals attraction force that originally exists in the CNC aggregation. The hybrid 300 can be readily dispersed in a polar or a non-polar solvent and therefore readily processible. Advantages of using layered silicate for dispersing CNC include avoiding structural damage to CNC and preserving desirable properties of CNC. Furthermore, layered silicate has a higher thermal stability than conventional organic dispersants.
The carbon nanocapsule can include hollow carbon nanocapsules, heteroatom-containing carbon nanocapsules, or carbon nanocapsules filled with elementary metals, metal alloys, or metal compounds such as metal oxide, metal carbide, metal sulfide, metal nitride, metal borate, and so on. In addition, the carbon nanocapsule may have a modified surface to carry various functional groups. The layered silicate used as a dispersant comprises nanoscale silicate platelets. The dispersion ability of the layered silicate is related to its aspect ratio. In general, the higher the aspect ratio, the better the dispersion ability, and the less the amount required for dispersion. In one embodiment, the layered silicate has an aspect ratio of at least 30. For example, the layered silicate may have an aspect ratio of about 50-5000. The weight ratio of the carbon nanocapsule to the layered silicate may range from about 10:1 to about 1:10
