(427g) Flow Microreactor Synthesis of SiO2-Au Patchy Particles

Patchy particles are micro- or nanoparticles with discrete sites (patches) of varying chemical and/or physical properties. Different from isotropic colloidal particles with uniform surface, they are promising for building blocks to fabricate colloidal crystals with novel lattice structures due to their anisotropic interactions. Furthermore, patchy particles with gold or silver patches are attractive because of tunable plasmon resonance wavelengths, which can find biomedical and optical applications. Due to the complexity in the particle geometry, however, synthetic processes typically involve multiple steps or templates, and thus a facile and scalable process is strongly required. In the present study, we establish a flow synthetic process of silica-gold patchy particles by using a non-segmented single phase microreactor. The key concept is selective nucleation and subsequent particle growth on core particle surfaces enabled by high mixing intensity of the microreactor, avoiding the nucleation in the bulk solution phase. In the experiments, we mixed a suspension of surface-modified silica particles containing gold ions with a reducing agent solution in the microreactor, and investigated the effects of the type of reducing agents on size and shape of patches. Our experiments revealed that a strong reducing agent yields silica particles uniformly decorated with gold nanoparticles, while a weaker one produced patchy particles with a dendritic patch on a core silica particle. These results are attributable to the nucleation process at the core surface. A strong reductant produced a lot of small nuclei because of high degree of supersaturation in contrast to dendritic patches yielded by a weaker one which produced smaller number of larger nuclei. The use of a far weaker reducing agent was demonstrated to result in “snowman” shaped patchy particles with a spherical gold particle attaching to a core silica particle. In this manner, we successfully achieved one-step flow synthesis of silica-gold patchy particles with varied size and shape of patches by using a microreactor.