Janus Particles and Janus Droplets

Abstract

This chapter will consider particles with two different hemispheres. Such heterogeneous particles will be referred as “Janus Particles”. The name ‘‘Janus’’ is from the name of a Roman God who has two faces looking into opposite directions. Here the Janus particle is considered as a sphere whose two hemispheres have different properties. For example, a half of the particle is a metal and the other half is a polymer; or a half of the particle’s surface is positively charged, and the other half of its surface is negatively charged. Similar to Janus particles, Janus droplets also have many applications. For example, Janus droplets can be used as carriers for certain molecules or particles, and as micro-reactors with enhanced mixing of the reagents. In this chapter, our interest is to explore the electrokinetic behaviors of Janus particles and Janus droplets in an aqueous electrolyte solution under applied electric field. First, theoretical models and numerical simulations of the electrokinetic motion of Janus particles and Janus droplets are discussed. Then the discussion is focused on electrokinetically induced Janus droplets, from fabrication to experimental investigation. Finally, an application of such a Janus droplet in the operation of an electrically responsive micro-valve is demonstrated.