Overview of Janus Particles as Smart Materials

Chapter 24 reviews Janus particles as smart materials. In ancient Roman times, Janus was the god who had two faces (beginnings and endings). In modern science, we have adopted the term to describe particles with two distinct and usually contrasting sides. These particles have the resemblance of the Taijitu symbol in ancient Asian philosophy, where Yin and Yang (dark and bright) were used to describe seemingly opposite forces. It is believed that these two basic elements give rise to complicated change and transition in the whole world. In the same sense, Janus particles are defined by their duality, which can take on a variety of forms and create a wide range of new materials with the simple Janus motif. The possibilities for properties that can be assigned to each half of the Janus particles are vast (for example, hydrophobicity and charge), and are limited only by the fabrication capabilities of their creators. This chapter will provide an overview of the properties and applications of Janus particles as smart materials. To do this effectively, we must first go over some of the common strategies for fabricating Janus materials, since fabrication is still the primary limit for which combinations of properties can be achieved. Then, we will delve into the properties that emerge from these combinations, citing several examples of the self-assembly structures demonstrated by Janus particles. Finally, we will look at some potential applications for Janus systems.