Digestive ripening for self-assembly of thiol-capped gold nanoparticles: the effects of adding dodecanethiol and reflux-heating

Digestive ripening is a unique process to prepare a nearly monodispersed nanoparticle system from a polydispersed particle system. A systematical study is performed to investigate the effects of adding an extra amount of dodecanethiol in a gold colloid at room temperature and reflux-heating in a silicone oil bath at 130 °C on the digestive ripening of thiol-capped gold nanoparticles. The experimental results reveal that adding an extra amount of dodecanethiol at room temperature caused the transition of a polydispersed gold nanoparticle system to a nearly monodispersed gold nanoparticle system. The reflux heating is not necessary for preparing a nearly monodispersed gold nanoparticle system. The reflux heating of the gold colloids with an extra amount of dodecanethiol enhances the transition of the polydisperse gold colloids to nearly monodisperse gold colloids. Prolonged heating causes the nearly monodisperse gold colloids to become bi-disperse. It is the combination effect of the reflux heating and the amount of dodecanethiol that determines the digestive ripening of the thiol-capped gold nanoparticles. The self-assembly of the nearly monodisperse gold nanoparticles is observed. The gold nanoparticles have the tendency to form self-assembled nanostructures with six-fold symmetry, and both monodisperse and bi-disperse nanoparticles would have better ordering.