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

The reprecipitation method is a useful technique to fabricate organic micro crystals such as polydiacetylene (PDA), low-molecular-weight aromatic compo unds, organic functional dyes, which features are located in a mesoscopic p hase 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 inv estigated to develop and establish further the reprecipitation method to co ntrol crystal size, shape of PDA microcrystals. Especially, we were much in terested in reprecipitation conditions and formation mechanism to form fibr ous PDA microcrystals. In addition, as some trial applications, it has been successful to trap an isolated PDA microcrystal and to prepare well-define d PDA microcrystal thin film, using a layer-by-layer procedure. This techni que utilized an electrostatic adsorption between microcrystals with highly negative zeta -potential in an aqueous dispersion liquid and polyelectrolyt e (polycation) film. As a result, the value of chi ((3))(omega) for the res ulting layered PDA microcrystal thin film was confirmed to be enhanced by a factor of about 100, owing to concentration effect. Copyright (C) 2000 Joh n Wiley & Sons, Ltd.