Progress in developing spray-drying methods for the production of controlled morphology particles: From the nanometer to submicrometer size ranges

Control of particle size and morphology has increasingly captured the attention of researchers for decades. The exploration of unique sizes and shapes as they relate to various properties has become a great quest for large field applications. To meet these demands, this review covers recent developments in particle processing. An aerosol-assisted self-assembly technique, with a spray-drying method as a representative of it, to create particles is thoroughly reviewed. Its popularity and its broad use in industry for producing particles are the main reason of this review; thus, elucidation of this method is important for the improvement of particle technology. A practical spray-drying method is described from the step-by-step process to the selection of apparatus types (merits and demerits). Elaboration of particle processing of several morphologies (sphere, doughnut, encapsulated, porous, hollow, and hairy) is discussed in terms of the selection of material types, the addition of supporting materials, and the change of process conditions. Controllable size is also discussed in terms of the adjustment of the droplet size, initial precursor concentration, and the addition of specific techniques. A comparison between a theoretical mechanism and current experimental results (over a 15-year period) are shown to clarify how particles with various sizes and morphologies are designed. This method must be considered an art rather than a science because of its advantages in creating wonderful and unique particle shapes. The performance of various particle morphologies is also demonstrated, which is essential for an understanding of the importance that shape can exert on practical use. Because the method outlined here can be broadly applied to the production of various types of functional materials, we believe that this report contributes new information to the field of chemical, material, environmental, and medical engineering. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.