Chapter 6: Light-driven Active Colloids

Active colloids, capable of autonomous motion by harnessing energy available in their surroundings, are of significance for advancing micro/nanoscale technologies. Light, as a ubiquitous external stimulus to propel the motion of colloid particles, offers unique benefits such as remote controllability, flexible tunability, and high temporal and spatial resolution. Light-driven active colloids are defined as the particles at the micro/nanoscale that can swim under light irradiation. They, broadly speaking, include micro/nanomotors composed entirely or partially of inorganic materials, microdroplets and organic matters. Light-driven active colloids are propelled primarily relying on light-initiated transformations involving but not limited to photochemical reaction, molecule isomerism, and pressure and temperature changes. In this chapter, we provide a comprehensive overview of various types of light-initiated transformations associated with propulsion mechanisms related to photochemical reactions, photoelectrochemical phenomena, photothermal effect, and photoisomerisation, as well as optical momentum transfer. Then, we relate them to typical models of light-driven active colloidal systems. Furthermore, we summarise the uniqueness of their motion in terms of motion modulation, phototaxis, and light-induced swarming, while highlighting the important progress towards bionics, cargo capture and transport, environmental remediation, and biomedical engineering.