Colloidal ribbons and rings from Janusmagnetic rods

摘要

Dipolar particles are fundamental building blocks in nature and technology, yet the effect ofparticle anisotropy is seldom explored. Here, we fabricate colloidal silica rods coated with ahemicylindrical magnetic layer to satisfy multiple criteria: nearly monodisperse, easily imagedand magnetic interaction that dominates over gravity. We confirm long-predicted features ofdipolar assembly and stress the microstructural variety brought about by shape and constituentanisotropy, especially by extrapolating knowledge learned from literal molecules. Inthis colloidal system, we describe analogies to liquid crystalline deformations with bend, splayand twist; an analogy to cis/trans isomerism in organic molecules, which in our system can becontrollably and reversibly switched; and a field-switching methodology to direct single ribbonsinto not only single but also multiple rings that can subsequently undergo hierarchicalself-assembly. We highlight subtle material issues of control and design rules for reconfigurabledipolar materials with building blocks of complex shape.