Physical Methods

The physical methods for synthesizing the nanocapsules could be separated into two categories: breaking down and building up. The breaking-down process means to mill mechanically the bulk materials to be particles. In general, the breaking-down process could be employed to produce particles of about 1 ^m in size and it is difficult to prepare nanoparticles and nanocapsules with sizes below 100 nm. We shall not discuss this type of the process in detail. The building-up process synthesizes nanoparticles and nano-capsules through the nucleation and growth processes of the elementary particles, like ions and atoms. The building-up process is one of the most effective processes for the formation of nanoparticles as well as nanocapsules, which satisfies the conditions requested for the preparing nano-particles: (1) clean surfaces; (2) controllable sizes and narrow size distribution; (3) easy collections; (4) stability of the particles; (5) high efficiency for production; etc. The basic principles for the building-up process are at first heating metals in gas atmospheres of several hundred to thousands of Pa and then condensing. Depending on the heating procedures, the build-up process could be of several different kinds, such as evaporation, arc discharge/plasma, laser heating, electron beam heating, sputtering, etc. Depending on the gas atmospheres, the final production could be different kinds of nanoparticles/nanocapsules.

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