Various types of polydiacetylene microcrystals fabricated by reprecipitation technique and some applications

Abstract

The reprecipitation method is a useful technique to fabricate organic microcrystals such as polydiacetylene (PDA), low-molecular-weight aromatic compounds, organic functional dyes, which features are located in a mesoscopic phase between a single molecule and bulk crystals, and organic microcrystals are expected to exhibit peculiar optical and electronic properties. In the present article, the effects of added surfactants and temperature were investigated to develop and establish further the reprecipitation method to control crystal size, shape of PDA microcrystals. Especially, we were much interested in reprecipitation conditions and formation mechanism to form fibrous PDA microcrystals. In addition, as some trial applications, it has been successful to trap an isolated PDA microcrystal and to prepare well-defined PDA microcrystal thin film, using a layer-by-layer procedure. This technique utilized an electrostatic adsorption between microcrystals with highly negative ζ-potential in an aqueous dispersion liquid and polyelectrolyte (polycation) film. As a result, the value of χ(3)(ω) for the resulting layered PDA microcrystal thin film was confirmed to be enhanced by a factor of about 100, owing to concentration effect. Copyright © 2000 John Wiley & Sons, Ltd.