Preparation of functional nanostructured particles by spray drying

When particle dimensions are reduced to the order of several nanometers, their physical and chemical properties deviate significantly from the bulk properties of such materials. Because of this, there is abundant potential for their use in future technologies including electronic and optoelectronic, mechanical, chemical, cosmetic, medical, drug, and food technologies. However, due to their extremely small sizes, the particles suffer from many problems related to their surface and thermal stability, shape preservation, handling, assembly in devices, etc. It is therefore an important challenge to solve these problems by developing slightly larger particles (e.g. on the submicrometer scale) in which the properties generated by the nanoscale material are preserved. One approach to this is to trap nanoparticles in a micrometer-sized inert matrix. This approach allows the nanoscale properties to be retained, since nanoparticles are separated from each other in the inert matrix. The inert matrix also serves as a coating medium that inhibits any chemical changes to the surface of the nanoparticles. Their larger size allows easy handling or assembly in devices. A promising method for designing and fabricating these composite structures is a spray method, in which spherical particles can be produced. In this paper, we review the nanostructural processing (synthesis) of submicrometer-sized particles by a spray method, which provides a restricted reaction environment (such as pores or cages) in the matrix for their synthesis and handling. The characterization and potential applications of these composites are also discussed.