(250a) Towards Dense Assemblies of Janus Particles through DC Electric Fields

Colloidal crystals are of interest for applications such as structural colors, sensing, and camouflage. The structure and properties of the crystals are greatly influenced by the size and physical properties of the colloidal building blocks. Janus particles, in particular, offer a rich phase diagram that depends on the Janus balance, hydrophobic interactions and charge density. Although some interesting structures have already been found experimentally (e.g., Kagone lattices), according to simulation studies there are still more structures to be found. Nonetheless, exploring the phase diagram of Janus particles is challenging because the system can become kinetically trapped. The purpose of this work is to explore the phase diagram of Janus particles through controlled densification using DC fields. Janus particles are synthesized using physical vapor deposition of gold, whereas their assembly is directly visualized through two-channel confocal laser scanning microscopy. The applied voltage and current density as well as the charge density of particles offer the means to control the assembly process. The experiments make use of the recent finding (Langmuir 30, 15408, 2014) that the strength of Janus particle interactions can be controlled by adjusting the thickness of the hemispheric metallic layer.